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39. Disasters, Natural and Technological

Chapter Editor: Pier Alberto Bertazzi

Table of Contents

Tables and Figures

Disasters and Major Accidents
Pier Alberto Bertazzi

     ILO Convention concerning the Prevention of Major Industrial Accidents, 1993 (No. 174)

Disaster Preparedness
Peter J. Baxter

Post-Disaster Activities
Benedetto Terracini and Ursula Ackermann-Liebrich

Weather-Related Problems
Jean French

Avalanches: Hazards and Protective Measures
Gustav Poinstingl

Transportation of Hazardous Material: Chemical and Radioactive
Donald M. Campbell

Radiation Accidents
Pierre Verger and Denis Winter

     Case Study: What does dose mean?

Occupational Health and Safety Measures in Agricultural Areas Contaminated by Radionuclides: The Chernobyl Experience
Yuri Kundiev, Leonard Dobrovolsky and V.I. Chernyuk

Case Study: The Kader Toy Factory Fire
Casey Cavanaugh Grant

Impacts of Disasters: Lessons from a Medical Perspective
José Luis Zeballos






Click a link below to view table in article context.


1. Definitions of disaster types
2. 25-yr average # victims by type & region-natural trigger
3. 25-yr average # victims by type & region-non-natural trigger
4. 25-yr average # victims by type-natural trigger (1969-1993)
5. 25-yr average # victims by type-non-natural trigger (1969-1993)
6. Natural trigger from 1969 to 1993: Events over 25 years
7. Non-natural trigger from 1969 to 1993: Events over 25 years
8. Natural trigger: Number by global region & type in 1994
9. Non-natural trigger: Number by global region & type in 1994
10. Examples of industrial explosions
11. Examples of major fires
12. Examples of major toxic releases
13. Role of major hazard installations management in hazard control
14. Working methods for hazard assessment
15. EC Directive criteria for major hazard  installations
16. Priority chemicals used in identifying major hazard installations
17. Weather-related occupational risks
18. Typical radionuclides, with their radioactive half-lives
19. Comparison of different nuclear accidents
20. Contamination in Ukraine, Byelorussia & Russia after Chernobyl
21. Contamination strontium-90 after the Khyshtym accident (Urals 1957)
22. Radioactive sources that involved the general public
23. Main accidents involving industrial irradiators
24. Oak Ridge (US) radiation accident registry (worldwide, 1944-88)
25. Pattern of occupational exposure to ionizing radiation worldwide
26. Deterministic effects: thresholds for selected organs
27. Patients with acute irradiation syndrome (AIS) after Chernobyl
28. Epidemiological cancer studies of high dose external irradiation
29. Thyroid cancers in children in Belarus, Ukraine & Russia, 1981-94
30. International scale of nuclear incidents
31. Generic protective measures for general population
32. Criteria for contamination zones
33. Major disasters in Latin America & the Caribbean, 1970-93
34. Losses due to six natural disasters
35. Hospitals & hospital beds damaged/ destroyed by 3 major disasters
36. Victims in 2 hospitals collapsed by the 1985 earthquake in Mexico
37. Hospital beds lost resulting from the March 1985 Chilean earthquake
38. Risk factors for earthquake damage to hospital infrastructure



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Thursday, 27 October 2011 19:36

Case Study: What does dose mean?

Written by

There are several ways to define a dose of ionizing radiation, each appropriate for different purposes.

Absorbed dose

Absorbed dose resembles pharmacological dose the most closely. While pharmacological dose is the quantity of substance administered to a subject per unit weight or surface, radiological absorbed dose is the amount of energy transmitted by ionizing radiation per unit mass. Absorbed dose is measured in Grays (1 Gray = 1 joule/kg).

When individuals are exposed homogeneously—for example, by external irradiation by cosmic and terrestrial rays or by internal irradiation by potassium-40 present in the body—all organs and tissues receive the same dose. Under these circumstances, it is appropriate to speak of whole-body dose. It is, however, possible for exposure to be non-homogenous, in which case some organs and tissues will receive significantly higher doses than others. In this case, it is more relevant to think in terms of organ dose. For example, inhalation of radon daughters results in exposure of essentially only the lungs, and incorporation of radioactive iodine results in irradiation of the thyroid gland. In these cases, we may speak of lung dose and thyroid dose.

However, other units of dose that take into account differences in the effects of different types of radiation and the different radiation sensitivities of tissues and organs, have also been developed.

Equivalent dose

The development of biological effects (e.g., inhibition of cell growth, cell death, azoospermia) depends not only on the absorbed dose, but also on the specific type of radiation. Alpha radiation has a greater ionizing potential than beta or gamma radiation. Equivalent dose takes this difference into account by applying radiation-specific weighting factors. The weighting factor for gamma and beta radiation (low ionizing potential), is equal to 1, while that for alpha particles (high ionizing potential) is 20 (ICRP 60). Equivalent dose is measured in Sieverts (Sv).

Effective dose

In cases involving non-homogenous irradiation (e.g., the exposure of various organs to different radionuclides), it may be useful to calculate a global dose that integrates the doses received by all organs and tissues. This requires taking into account the radiation sensitivity of each tissue and organ, calculated from the results of epidemiological studies of radiation-induced cancers. Effective dose is measured in Sieverts (Sv) (ICRP 1991). Effective dose was developed for the purposes of radiation protection (i.e., risk management) and is thus inappropriate for use in epidemiological studies of the effects of ionizing radiation.

Collective dose

Collective dose reflects the exposure of a group or population and not of an individual, and is useful for evaluating the consequences of exposure to ionizing radiation at the population or group level. It is calculated by summing the individual received doses, or by multiplying the average individual dose by the number of exposed individuals in the groups or populations in question. Collective dose is measured in man-Sieverts (man Sv).



ILO 80th Session, 2nd June 1993

ILO 80th Session, 2nd June 1993


Article 1

1. The purpose of this Convention is the prevention of major accidents involving hazardous substances and the limitation of the consequences of such accidents.…

Article 3

For the purposes of this Convention:

(a)    the term “hazardous substance” means a substance or mixture of substances which by virtue of chemical, physical or toxicological properties, either singly or in combination, constitutes a hazard;

(b)    the term “threshold quantity” means for a given hazardous substance or category of substances that quantity, prescribed in national laws and regulations by reference to specific conditions, which if exceeded identifies a major hazard installation;

(c)    the term “major hazard installation” means one which produces, processes, handles, uses, disposes of or stores, either permanently or temporarily, one or more hazardous substances or categories of substances in quantities which exceed the threshold quantity;

(d)    the term “major accident” means a sudden occurrence—such as a major emission, fire or explosion—in the course of an activity within a major hazard installation, involving one or more hazardous substances and leading to a serious danger to workers, the public or the environment, whether immediate or delayed;

(e)    the term “safety report“ means a written presentation of the technical, management and operational information covering the hazards and risks of a major hazard installation and their control and providing justification for the measures taken for the safety of the installation;

(f)    the term “near miss” means any sudden event involving one or more hazardous substances which, but for mitigating effects, actions or systems, could have escalated to a major accident.


Article 4

1. In the light of national laws and regulations, conditions and practices, and in consultation with the most representative organizations of employers and workers and with other interested parties who may be affected, each Member shall formulate, implement and periodically review a coherent national policy concerning the protection of workers, the public and the environment against the risk of major accidents.

2. This policy shall be implemented through preventive and protective measures for major hazard installations and, where practicable, shall promote the use of the best available safety technologies.

Article 5

1. The competent authority, or a body approved or recognized by the competent authority, shall, after consulting the most representative organizations of employers and workers and other interested parties who may be affected, establish a system for the identification of major hazard installations as defined in Article 3(c), based on a list of hazardous substances or of categories of hazardous substances or of both, together with their respective threshold quantities, in accordance with national laws and regulations or international standards.

2. The system mentioned in paragraph 1 above shall be regularly reviewed and updated.

Article 6

The competent authority, after consulting the representative organizations of employers and workers concerned, shall make special provision to protect confidential information transmitted or made available to it in accordance with Articles 8, 12, 13 or 14, whose disclosure would be liable to cause harm to an employer’s business, so long as this provision does not lead to serious risk to the workers, the public or the environment.


Article 7

Employers shall identify any major hazard installation within their control on the basis of the system referred to in Article 5.


Article 8

1. Employers shall notify the competent authority of any major hazard installation which they have identified:

(a)            within a fixed time-frame for an existing installation;

(b)            before it is put into operation in the case of a new installation.

2. Employers shall also notify the competent authority before any permanent closure of a major hazard installation.

Article 9

In respect of each major hazard installation employers shall establish and maintain a documented system of major hazard control which includes provision for:

(a)    the identification and analysis of hazards and the assessment of risks including consideration of possible interactions between substances;

(b)    technical measures, including design, safety systems, construction, choice of chemicals, operation, maintenance and systematic inspection of the installation;

(c)    organizational measures, including training and instruction of personnel, the provision of equipment in order to ensure their safety, staffing levels, hours of work, definition of responsibilities, and controls on outside contractors and temporary workers on the site of the installation;

(d)    emergency plans and procedures, including:

(i)        the preparation of effective site emergency plans and procedures, including
emergency medical procedures, to be applied in case of major accidents or threat
thereof, with periodic testing and evaluation of their effectiveness and revision as

(ii)        the provision of information on potential accidents and site emergency plans to
authorities and bodies responsible for the preparation of emergency plans and
procedures for the protection of the public and the environment outside the site of
the installation;

(iii)        any necessary consultation with such authorities and bodies;

(e)    measures to limit the consequences of a major accident;

(f)    consultation with workers and their representatives;

(g)    improvement of the system, including measures for gathering information and analysing accidents and near misses. The lessons so learnt shall be discussed with the workers and their representatives and shall be recorded in accordance with national law and practice.…

*  *  *



Article 15

Taking into account the information provided by the employer, the competent authority shall ensure that emergency plans and procedures containing provisions for the protection of the public and the environment outside the site of each major hazard installation are established, updated at appropriate intervals and coordinated with the relevant authorities and bodies.

Article 16

The competent authority shall ensure that:

(a)    information on safety measures and the correct behaviour to adopt in the case of a major accident is disseminated to members of the public liable to be affected by a major accident without their having to request it and that such information is updated and redisseminated at appropriate intervals;

(b)    warning is given as soon as possible in the case of a major accident;

(c)    where a major accident could have transboundary effects, the information required in (a) and (b) above is provided to the States concerned, to assist in cooperation and coordination arrangements.

Article 17

The competent authority shall establish a comprehensive siting policy arranging for the appropriate separation of proposed major hazard installations from working and residential areas and public facilities, and appropriate measures for existing installations. Such a policy shall reflect the General Principles set out in Part II of the Convention.


Article 18

1. The competent authority shall have properly qualified and trained staff with the appropriate skills, and sufficient technical and professional support, to inspect, investigate, assess, and advise on the matters dealt with in this Convention and to ensure compliance with national laws and regulations.

2. Representatives of the employer and representatives of the workers of a major hazard installation shall have the opportunity to accompany inspectors supervising the application of the measures prescribed in pursuance of this Convention, unless the inspectors consider, in the light of the general instructions of the competent authority, that this may be prejudicial to the performance of their duties.

Article 19

The competent authority shall have the right to suspend any operation which poses an imminent threat of a major accident.


Article 20

The workers and their representatives at a major hazard installation shall be consulted through appropriate cooperative mechanisms in order to ensure a safe system of work. In particular, the workers and their representatives shall:

(a)    be adequately and suitably informed of the hazards associated with the major hazard installation and their likely consequences;

(b)    be informed of any orders, instructions or recommendations made by the competent authority;

(c)    be consulted in the preparation of, and have access to, the following documents:

(i)    the safety report;

(ii)    emergency plans and procedures;

(iii)    accident reports;

(d)    be regularly instructed and trained in the practices and procedures for the prevention of major accidents and the control of developments likely to lead to a major accident and in the emergency procedures to be followed in the event of a major accident;

(e)    within the scope of their job, and without being placed at any disadvantage, take corrective action and if necessary interrupt the activity where, on the basis of their training and experience, they have reasonable justification to believe that there is an imminent danger of a major accident, and notify their supervisor or raise the alarm, as appropriate, before or as soon as possible after taking such action;

(f)    discuss with the employer any potential hazards they consider capable of generating a major accident and have the right to notify the competent authority of those hazards.

Article 21

Workers employed at the site of a major hazard installation shall:

(a)    comply with all practices and procedures relating to the prevention of major accidents and the control of developments likely to lead to a major accident within the major hazard installation;

(b)    comply with all emergency procedures should a major accident occur.


Article 22

When, in an exporting member State, the use of hazardous substances, technologies or processes is prohibited as a potential source of a major accident, the information on this prohibition and the reasons for it shall be made available by the exporting member State to any importing country.

Source: Excerpts, Convention No. 174 (ILO 1993).



This article was adapted, with permission, from Zeballos 1993b.

Latin America and the Caribbean have not been spared their share of natural disasters. Almost every year catastrophic events cause deaths, injuries and enormous economic damage. Overall, it is estimated that the major natural disasters of the last two decades in this region caused property losses affecting nearly 8 million people, some 500,000 injuries and 150,000 deaths. These figures rely heavily on official sources. (It is quite difficult to obtain accurate information in sudden-onset disasters, because there are multiple information sources and no standardized information system.) The Economic Commission for Latin America and the Caribbean (ECLAC) estimates that during an average year, disasters in Latin America and the Caribbean cost US$1.5 billion and take 6,000 lives (Jovel 1991).

Table 1 lists major natural disasters that struck countries of the region in the 1970-93 period. It should be noted that slow- onset disasters, such as droughts and floods, are not included.

Table 1. Major disasters in Latin America and the Caribbean, 1970-93



Type of

No.of deaths

Est. no. of
people affected


















Hurricane (Allen)





Volcanic eruption










Volcanic eruption




El Salvador






Hurricane (Gilbert)





Hurricane (Gilbert)





Hurricane (Joan)





Hurricane (Hugo)









Costa Rica











Tropical storm



Source: PAHO 1989; OFDA (USAID),1989; UNDRO 1990.

Economic Impact

In recent decades, ECLAC has carried out extensive research on the social and economic impacts of disasters. This has clearly demonstrated that disasters have negative repercussions on social and economic development in developing countries. Indeed, the monetary losses caused by a major disaster often exceed the total annual gross income of the affected country. Not surprisingly, such events can paralyze affected countries and foster widespread political and social turmoil.

In essence, disasters have three kinds of economic impacts:

  • direct impacts on the affected population’s property
  • indirect impacts caused by lost economic production and services
  • secondary impacts that become apparent after the disaster—such as reduced national income, increased inflation, foreign trade problems, heightened financial expenses, a resulting fiscal deficit, decreased monetary reserves and so on (Jovel 1991).


Table 2 shows the estimated losses caused by six major natural disasters. While such losses might not seem particularly devastating for developed countries with strong economies, they can have a serious and lasting impact on the weak and vulnerable economies of developing countries (PAHO 1989).

Table 2. Losses due to six natural disasters




Total losses
(US$ millions)






El Salvador







Volcanic eruption (Nevado del Ruiz)




Floods, drought (“El Niño”)

Peru, Ecuador, Bolivia



Hurricane (Joan)




Source: PAHO 1989; ECLAC.

The Health Infrastructure

In any major disaster-related emergency, the first priority is to save lives and provide immediate emergency care for the injured. Among the emergency medical services mobilized for these purposes, hospitals play a key role. Indeed, in countries with a standardized emergency response system (one where the concept of “emergency medical services” encompasses provision of emergency care through the coordination of independent subsystems involving paramedics, fire-fighters and rescue teams) hospitals constitute the major component of that system (PAHO 1989).

Hospitals and other health care facilities are densely occupied. They house patients, personnel and visitors, and they operate 24 hours a day. Patients may be surrounded by special equipment or connected to life-support systems dependent on power supplies. According to project documents available from the Inter-American Development Bank (IDB) (personal communication, Tomas Engler, IDB), the estimated cost of one hospital bed in a specialized hospital varies from country to country, but the average runs from US$60,000 to US$80,000 and is greater for highly specialized facilities.

In the United States, particularly California, with its extensive experience in seismic-resistant engineering, the cost of one hospital bed can exceed US$110,000. In sum, modern hospitals are highly complex facilities combining the functions of hotels, offices, laboratories and warehouses (Peisert et al. 1984; FEMA 1990).

These health care facilities are highly vulnerable to hurricanes and earthquakes. This has been amply demonstrated by past experience in Latin America and the Caribbean. For example, as table 3 shows, just three disasters of the 1980s damaged 39 hospitals and destroyed some 11,332 hospital beds in El Salvador, Jamaica and Mexico. Besides damage to these physical plants at critical times, the loss of human life (including the death of highly qualified local professionals with promising futures) needs to be considered (see table 4 and table 5).

Table 3. Number of hospitals and hospital beds damaged or destroyed by three major natural disasters

Type of disaster

No. of hospitals
damaged or destroyed

No. of beds lost

Earthquake, Mexico (Federal District, September 1985)



Earthquake, El Salvador (San Salvador, October 1986)



Hurricane Gilbert (Jamaica, September 1988)






Source: PAHO 1989; OFDA(USAID) 1989; ECLAC.

Table 4. Victims in two hospitals collapsed by the 1985 earthquake in Mexico


Collapsed hospitals


General hospital

Juarez hospital
























Source: PAHO 1987.

Table 5. Hospital beds lost as a result of the March 1985 Chilean earthquake


No. of existing  hospitals

No. of beds

Beds lost in region




Metropolitan Area





Region 5 (Viña del Mar, Valparaíso,
San Antonio)





Region 6 (Rancagua)





Region 7 (Ralca, Meula)










Source: Wyllie and Durkin 1986.

At present the ability of many Latin American hospitals to survive earthquake disasters is uncertain. Many such hospitals are housed in old structures, some dating from Spanish colonial times; and while many others occupy contemporary buildings of appealing architectural design, lax application of building codes makes their ability to resist earthquakes questionable.

Risk Factors in Earthquakes

Of the various types of sudden natural disasters, earthquakes are by far the most damaging to hospitals. Of course, each earthquake has its own characteristics relating to its epicentre, type of seismic waves, geological nature of the soil through which the waves travel and so on. Nevertheless, studies have revealed certain common factors that tend to cause death and injuries and certain others that tend to prevent them. These factors include structural characteristics related to building failure, various factors related to human behaviour and certain characteristics of nonstructural equipment, furnishings and other items inside buildings.

In recent years, scholars and planners have been paying special attention to identification of risk factors affecting hospitals, in hopes of framing better recommendations and norms to govern the building and organization of hospitals in highly vulnerable zones. A brief listing of relevant risk factors is shown in table 6. These risk factors, particularly those related to the structural aspects, were observed to influence patterns of destruction during a December 1988 earthquake in Armenia that killed some 25,000 people, affected 1,100,000 and destroyed or severely damaged 377 schools, 560 health facilities and 324 community and cultural centres (USAID 1989).

Table 6. Risk factors associated with earthquake damage to hospital infrastructure





 Medical equipment

 Public information

 Quality of construction    

 Laboratory equipment



 Office equipment



 Cabinets, shelves

 Educational programmes      

 Soil conditions

 Stoves, refrigerators, heaters    

 Health care staff training

 Seismic characteristics

 X-ray machines


 Time of the event

 Reactive materials


 Population density



Damage on a similar scale occurred in June 1990, when an earthquake in Iran killed about 40,000 people, injured 60,000 others, left 500,000 homeless, and collapsed 60 to 90% of buildings in affected zones (UNDRO 1990).

To address these and like calamities, an international seminar was held in Lima, Peru, in 1989 on the planning, design, repair and management of hospitals in earthquake-prone areas. The seminar, sponsored by PAHO, Peru’s National University of Engineering and the Peruvian-Japanese Center for Seismic Research (CISMID), brought together architects, engineers and hospital administrators to study issues related to health facilities located in these areas. The seminar approved a core of technical recommendations and commitments directed at carrying out vulnerability analyses of hospital infrastructures, improving the design of new facilities and establishing safety measures for existing hospitals, with emphasis on those located in high-risk earthquake areas (CISMID 1989).

Recommendations on Hospital Preparedness

As the foregoing suggests, hospital disaster preparedness constitutes an important component of PAHO’s Office of Emergency Preparedness and Disaster Relief. Over the last ten years, member countries have been encouraged to pursue activities directed toward this end, including the following:

  • classifying hospitals according to their risk factors and vulnerabilities
  • developing internal and external hospital response plans and training personnel
  • developing contingency plans and establishing safety measures for the professional and technical hospital staffs
  • strengthening lifeline backup systems that help hospitals to function during emergency situations.


More broadly, a principal aim of the current International Decade for Natural Disaster Reduction (IDNDR) is to attract, motivate and commit national health authorities and policy-makers around the world, thereby encouraging them to strengthen the health services directed at coping with disasters and to reduce the vulnerability of those services in the developing world.

Issues Concerning Technological Accidents

During the last two decades, developing countries have entered into intense competition to achieve industrial development. The main reasons for this competition are as follows:

  • to attract capital investment and to generate jobs
  • to satisfy domestic demand for products at a lower cost and to alleviate dependency on the international market
  • to compete with international and subregional markets
  • to establish foundations for development.


Unfortunately, efforts made have not always resulted in obtaining the intended objectives. In effect, flexibility in attracting capital investment, lack of sound regulation with respect to industrial safety and environmental protection, negligence in the operation of industrial plants, use of obsolete technology, and other aspects have contributed to increasing the risk of technological accidents in certain areas.

In addition, the lack of regulation regarding the establishment of human settlements near or around industrial plants is an additional risk factor. In major Latin American cities it is common to see human settlements practically surrounding industrial complexes, and the inhabitants of these settlements are ignorant of the potential risks (Zeballos 1993a).

In order to avoid accidents such as those that occurred in Guadalajara (Mexico) in 1992, the following guidelines are suggested for the establishment of chemical industries, to protect industrial workers and the population at large:

  • selection of appropriate technology and study of alternatives
  • appropriate location of industrial plants
  • regulation of human settlements in the neighbourhood of industrial plants
  • security considerations for technology transfer
  • routine inspection of industrial plants by local authorities
  • expertise provided by specialized agencies
  • role of workers in compliance with security rules
  • rigid legislation
  • classification of toxic materials and close supervision of their use
  • public education and training of workers
  • establishment of response mechanisms in case of emergency
  • training of health workers in emergency plans for technological accidents.



Saturday, 26 February 2011 01:17

Case Study: The Kader Toy Factory Fire

Written by

A tragic industrial fire in Thailand has focused worldwide attention on the need to adopt and enforce state-of-the-art codes and standards in industrial occupancies.

On May 10, 1993, a major fire at the Kader Industrial (Thailand) Co. Ltd. factory located in the Nakhon Pathom Province of Thailand killed 188 workers (Grant and Klem 1994). This disaster stands as the world’s worst accidental loss-of-life fire in an industrial building in recent history, a distinction held for 82 years by the Triangle Shirtwaist factory fire that killed 146 workers in New York City (Grant 1993). Despite the years between these two disasters, they share striking similarities.

Various domestic and international agencies have focused on this incident following its occurrence. With respect to fire protection concerns, the National Fire Protection Association (NFPA) cooperated with the International Labour Organization (ILO) and with the Bangkok Police Fire Brigade in documenting this fire.

Questions for a Global Economy

In Thailand, the Kader fire has created a great deal of interest about the country’s fire safety measures, particularly its building code design requirements and enforcement policies. Thai Prime Minister Chuan Leekpai, who travelled to the scene on the evening of the fire, has pledged that the government will address fire safety issues. According to the Wall Street Journal (1993), Leekpai has called for tough action against those who violate the safety laws. Thai Industry Minister Sanan Kachornprasart is quoted as saying that “Those factories without fire prevention systems will be ordered to install one, or we will shut them down”.

The Wall Street Journal goes on to state that labour leaders, safety experts and officials say that the Kader fire may help tighten building codes and safety regulations, but they fear that lasting progress is still far off as employers flout rules and governments allow economic growth to take priority over worker safety.

Because the majority of the shares of Kader Industrial (Thailand) Co. Ltd. are owned by foreign interests, the fire has also fuelled international debate about foreign investors’ responsibilities for ensuring the safety of the workers in their sponsoring country. Twenty per cent of the Kader shareholders are from Taiwan, and 79.96% are from Hong Kong. A mere 0.04% of Kader is owned by Thai nationals.

Moving into a global economy implies that products are manufactured at one location and used at other locations throughout the world. Desire for competitiveness in this new market should not lead to compromise in fundamental industrial fire safety provisions. There is a moral obligation to provide workers with an adequate level of fire protection, no matter where they are located.

The Facility

The Kader facility, which manufactured stuffed toys and plastic dolls primarily intended for export to the United States and other developed countries, is located in the Sam Phran District of Nakhon Pathom Province. This is not quite halfway between Bangkok and the nearby city of Kanchanaburi, the site of the infamous Second World War railroad bridge over the River Kwai.

The structures that were destroyed in the blaze were all owned and operated directly by Kader, which owns the site. Kader has two sister companies that also operate at the location on a lease arrangement.

The Kader Industrial (Thailand) Co. Ltd. was first registered on 27 January 1989, but the company’s licence was suspended on 21 November 1989, after a fire on 16 August 1989 destroyed the new plant. This fire was attributed to the ignition of polyester fabric used in the manufacture of dolls in a spinning machine. After the plant was rebuilt, the Ministry of Industry allowed it to reopen on 4 July 1990.

Between the time the factory reopened and the May 1993 fire, the facility experienced several other, smaller fires. One of them, which occurred in February 1993, did considerable damage to Building Three, which was still being repaired at the time of the fire in May 1993. The February fire occurred late at night in a storage area and involved polyester and cotton materials. Several days after this blaze a labour inspector visited the site and issued a warning that pointed out the plant’s need for safety officers, safety equipment and an emergency plan.

Initial reports following the May 1993 fire noted that there were four buildings on the Kader site, three of which were destroyed by the fire. In a sense this is true, but the three buildings were actually a single E-shaped structure (see figure 1), the three primary portions of which were designated Buildings One, Two and Three. Nearby was a one-storey workshop and another four-storey structure referred to as Building Four.

Figure 1. Site plan of the Kader toy factory


The E-shaped building was a four-storey structure composed of concrete slabs supported by a structural steel frame. There were windows around the perimeter of each floor and the roof was a gently sloped, peaked arrangement. Each portion of the building had a freight elevator and two stairwells that were each 1.5 metres (3.3 feet) wide. The freight elevators were caged assemblies.

Each building at the plant was equipped with a fire alarm system. None of the buildings had automatic sprinklers, but portable extinguishers and hose stations were installed on outside walls and in the stairwells of each building. None of the structural steel in the building was fireproofed.

There is conflicting information about the total number of workers at the site. The Federation of Thai Industries had pledged to help 2,500 plant employees displaced by the fire, but it is unclear how many employees were at the site at any one time. When the fire occurred, it was reported that there were 1,146 workers in Building One. Thirty-six were on the first floor, 10 were on the second, 500 were on the third, and 600 were on the fourth. There were 405 workers in Building Two. Sixty of them were on the first floor, 5 were on the second, 300 were on the third and 40 were on the fourth. It is not clear how many workers                                                                                                                     were in Building Three since a portion of it was still being                                                                                                                                 refurbished. Most of the workers at the plant were women.

The Fire

Monday, May 10, was a normal workday at the Kader facility. At approximately 4:00 p.m., as the end of the day shift approached, someone discovered a small fire on the first floor near the south end of Building One. This portion of the building was used to package and store the finished products, so it contained a considerable fuel load (see figure 2). Each building at the facility had a fuel load composed of fabric, plastics and materials used for stuffing, as well as other normal workplace materials.

Figure 2. Internal layout of buildings one, two and three


Security guards in the vicinity of the fire tried unsuccessfully to extinguish the flames before they called the local police fire brigade at 4:21 p.m. Authorities received two more calls, at 4:30 p.m. and 4:31 p.m. The Kader facility is just beyond the jurisdictional boundaries of Bangkok, but fire apparatus from Bangkok, as well as apparatus from Nakhon Pathom Province, responded.

As the workers and security guards tried in vain to extinguish the fire, the building began filling with smoke and other products of combustion. Survivors reported that the fire alarm never sounded in Building One, but many workers grew concerned when they saw smoke on the upper floors. Despite the smoke, security guards reportedly told some workers to stay at their stations because it was a small fire that would soon be under control.

The fire spread rapidly throughout Building One, and the upper floors soon became untenable. The blaze blocked the stairwell at the south end of the building, so most of the workers rushed to the north stairwell. This meant that approximately 1,100 people were trying to leave the third and fourth floors through a single stairwell.

The first fire apparatus arrived at 4:40 p.m., their response time having been extended because of the relatively remote location of the facility and the gridlock conditions typical of Bangkok traffic. Arriving fire-fighters found Building One heavily involved in                                                                                                                                 flames and already beginning to collapse, with people jumping                                                                                                                       from the third and fourth floors.

Despite the fire-fighters’ efforts, Building One collapsed completely at approximately 5:14 p.m. Fanned by strong winds blowing toward the north, the blaze spread quickly into Buildings Two and Three before the fire brigade could effectively defend them. Building Two reportedly collapsed at 5:30 p.m., and Building Three at 6:05 p.m. The fire brigade successfully kept the fire from entering Building Four and the smaller, one-storey workshop nearby, and the fire-fighters had the blaze under control by 7:45 p.m. Approximately 50 pieces of fire apparatus were involved in the battle.

The fire alarms in Buildings Two and Three reportedly functioned properly, and all the workers in those two buildings escaped. The workers in Building One were not so fortunate. A large number of them jumped from the upper floors. In all, 469 workers were taken to the hospital, where 20 died. The other dead were found during the post-fire search of what had been the north stairwell of the building. Many of them apparently succumbed to lethal products of combustion before or during the building’s collapse. According to the latest information available, 188 people, most of them female, have died as a result of this fire.

Even with the help of six large hydraulic cranes that were moved to the site to facilitate the search for victims, it was several days before all the bodies could be removed from the rubble. There were no fatalities among the fire-fighters, although there was one injury.

Traffic in the vicinity, which is normally congested, made transporting the victims to hospitals difficult. Nearly 300 injured workers were taken to the nearby Sriwichai II Hospital, although many of them were transferred to alternate medical facilities when the number of victims exceeded the hospital’s capacity to treat them.

The day after the fire, Sriwichai II Hospital reported that it had kept 111 fire victims. The Kasemrat Hospital received 120; Sriwichai Pattanana received 60; Sriwichai I received 50; Ratanathibet I received 36; Siriraj received 22; and Bang Phai received 17. The remaining 53 injured workers were sent to various other medical facilities in the area. In all, 22 hospitals throughout Bangkok and Nakhon Pathom Province participated in treating victims of the disaster.

Sriwichai II Hospital reported that 80% of their 111 victims suffered serious injuries and that 30% required surgery. Half of the patients suffered only from smoke inhalation, while the remainder also suffered burns and fractures that ranged from broken ankles to fractured skulls. At least 10% of the injured Kader workers admitted to Sriwichai II Hospital risk permanent paralysis.

Determining the cause of this fire became a challenge because the portion of the facility in which it began was totally destroyed and the survivors have provided conflicting information. Since the fire started near a large electrical control panel, investigators first thought that problems with the electrical system might have been the cause. They also considered arson. At this time, however, Thai authorities feel that a carelessly discarded cigarette may have been the source of ignition.

Analysing the Fire

For 82 years, the world has recognized the 1911 Triangle Shirtwaist factory fire in New York City as the worst accidental loss-of-life industrial fire in which the fatalities were limited to the building of fire origin. With 188 fatalities, however, the Kader factory fire now replaces the Triangle fire in the record books.

When analysing the Kader fire, a direct comparison with the Triangle fire provides a useful benchmark. The two buildings were similar in a number of ways. The arrangement of the exits was poor, the fixed fire protection systems were insufficient or ineffective, the initial fuel package was readily combustible, and the horizontal and vertical fire separations were inadequate. In addition, neither company had provided its workers with adequate fire safety training. However, there is one distinct difference between these two fires: the Triangle Shirtwaist factory building did not collapse and the Kader buildings did.

Inadequate exit arrangements were perhaps the most significant factor in the high loss of life at both the Kader and the Triangle fires. Had the exiting provisions of NFPA 101, the Life Safety Code, which was established as a direct result of the Triangle fire, been applied at the Kader facility, substantially fewer lives would have been lost (NFPA 101, 1994).

Several fundamental requirements of the Life Safety Code pertain directly to the Kader fire. For example, the Code requires that every building or structure be constructed, arranged and operated in such a way that its occupants are not placed in any undue danger by fire, smoke, fumes or the panic that may occur during an evacuation or during the time it takes to defend the occupants in place.

The Code also requires that every building have enough exits and other safeguards of the proper size and at the proper locations to provide an escape route for every occupant of a building. These exits should be appropriate to the individual building or structure, taking into account the character of the occupancy, the capabilities of the occupants, the number of occupants, the fire protection available, the height and type of building construction and any other factor necessary to provide all the occupants with a reasonable degree of safety. This was obviously not the case in the Kader facility, where the blaze blocked one of Building One’s two stairwells, forcing approximately 1,100 people to flee the third and fourth floors through a single stairwell.

In addition, the exits should be arranged and maintained so that they provide free and unobstructed egress from all parts of a building whenever it is occupied. Each of these exits should be clearly visible, or the route to every exit should be marked in such a way that every occupant of the building who is physically and mentally able readily knows the direction of escape from any point.

Every vertical exit or opening between the floors of a building should be enclosed or protected as necessary to keep the occupants reasonably safe while they exit and to prevent fire, smoke and fumes from spreading from floor to floor before the occupants have had a chance to use the exits.

The outcomes of both the Triangle and the Kader fires were significantly affected by the lack of adequate horizontal and vertical fire separations. The two facilities were arranged and built in such a way that a fire on a lower floor could spread rapidly to the upper floors, thus trapping a large number of workers.

Large, open work spaces are typical of industrial facilities, and fire-rated floors and walls must be installed and maintained to slow the spread of fire from one area to another. Fire also must be kept from spreading externally from the windows on one floor to those on another floor, as it did during the Triangle fire.

The most effective way to limit vertical fire spread is to enclose stairwells, elevators, and other vertical openings between floors. Reports of features such as caged freight elevators at the Kader factory raise significant questions about the ability of the buildings’ passive fire protection features to prevent vertical spread of fire and smoke.

Fire Safety Training and Other Factors

Another factor that contributed to the large loss of life in both the Triangle and Kader fires was the lack of adequate fire safety training, and the rigid security procedures of both companies.

After the fire at the Kader facility, survivors reported that fire drills and fire safety training were minimal, although the security guards had apparently had some incipient fire training. The Triangle Shirtwaist factory had no evacuation plan, and fire drills were not implemented. Furthermore, post-fire reports from Triangle survivors indicate that they were routinely stopped as they left the building at the end of the work day for security purposes. Various post-fire accusations by Kader survivors also imply that security arrangements slowed their exit, although these accusations are still being investigated. In any case, the lack of a well-understood evacuation plan seems to have been an important factor in the high loss of life sustained in the Kader fire. Chapter 31 of the Life Safety Code addresses fire drills and evacuation training.

The absence of fixed automatic fire protection systems also affected the outcome of both the Triangle and the Kader fires. Neither facility was equipped with automatic sprinklers, although the Kader buildings did have a fire alarm system. According to the Life Safety Code, fire alarms should be provided in buildings whose size, arrangement or occupancy make it unlikely that the occupants themselves will notice a fire immediately. Unfortunately, the alarms reportedly never operated in Building One, which resulted in a significant delay in evacuation. There were no fatalities in Buildings Two and Three, where the fire alarm system functioned as intended.

Fire alarm systems should be designed, installed and maintained in accordance with documents like NFPA 72, the National Fire Alarm Code (NFPA 72, 1993). Sprinkler systems should be designed and installed in accordance with documents like NFPA 13, Installation of Sprinkler Systems, and maintained in accordance with NFPA 25, Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems (NFPA 13, 1994; NFPA 25, 1995).

The initial fuel packages in both the Triangle and Kader fires were similar. The Triangle fire started in rag bins and quickly spread to combustible clothing and garments before involving wood furnishings, some of which were impregnated with machine oil. The initial fuel package at the Kader plant consisted of polyester and cotton fabrics, various plastics, and other materials used to manufacture stuffed toys, plastic dolls, and other related products. These are materials that can typically be ignited easily, can contribute to rapid fire growth and spread, and have a high heat release rate.

Industry will probably always handle materials that have challenging fire protection characteristics, but manufacturers should recognize these characteristics and take the necessary precautions to minimize associated hazards.

The Building’s Structural Integrity

Probably the most notable difference between the Triangle and Kader fires is the effect they had on the structural integrity of the buildings involved. Even though the Triangle fire gutted the top three floors of the ten-storey factory building, the building remained structurally intact. The Kader buildings, on the other hand, collapsed relatively early in the fire because their structural steel supports lacked the fireproofing that would have allowed them to maintain their strength when exposed to high temperatures. A post-fire review of the debris at the Kader site showed no indication that any of the steel members had been fireproofed.

Obviously, building collapse during a fire presents a great threat to both the building’s occupants and to the fire-fighters involved in controlling the blaze. However, it is unclear whether the collapse of the Kader building had any direct effect on the number of fatalities, since the victims may have already succumbed to the effects of heat and products of combustion by the time the building collapsed. If the workers on the upper floors of Building One had been shielded from the products of combustion and heat while they were trying to escape, the building’s collapse would have been a more direct factor in the loss of life.

Fire Focused Attention on Fire Protection Principles

Among the fire protection principles on which the Kader fire has focused attention are exit design, occupant fire safety training, automatic detection and suppression systems, fire separations and structural integrity. These lessons are not new. They were first taught more than 80 years ago at the Triangle Shirtwaist fire and again, more recently, in a number of other fatal workplace fires, including those at the chicken-processing plant in Hamlet, North Carolina, USA, that killed 25 workers; at a doll factory in Kuiyong, China, that killed 81 workers; and at the electrical power plant in Newark, New Jersey, USA, that killed all 3 workers in the plant (Grant and Klem 1994; Klem 1992; Klem and Grant 1993).

The fires in North Carolina and New Jersey, in particular, demonstrate that the mere availability of state-of-the-art codes and standards, such as NFPA’s Life Safety Code, cannot prevent tragic losses. These codes and standards must also be adopted and rigorously enforced if they are to have any effect.

National, state and local public authorities should examine the way they enforce their building and fire codes to determine whether new codes are needed or existing codes need to be updated. This review should also determine whether a building plan review and inspection process is in place to ensure that the appropriate codes are followed. Finally, provisions must be made for periodic follow-up inspections of existing buildings to ensure that the highest levels of fire protection are maintained throughout the life of the building.

Building owners and operators must also be aware that they are responsible for ensuring that their employees’ working environment is safe. At the very least, the state-of-the-art fire protection design reflected in fire codes and standards must be in place to minimize the possibility of a catastrophic fire.

Had the Kader buildings been equipped with sprinklers and working fire alarms, the loss of life might not have been so high. Had Building One’s exits been better designed, hundreds of people might not have been injured jumping from the third and fourth floors. Had vertical and horizontal separations been in place, the fire might not have spread so quickly throughout the building. Had the buildings’ structural steel members been fireproofed, the buildings might not have collapsed.

Philosopher George Santayana has written: “Those who forget the past are condemned to repeat it.” The Kader Fire of 1993 was unfortunately, in many ways, a repeat of the Triangle Shirtwaist Fire of 1911. As we look to the future, we need to recognize all that we need to do, as a global society, to prevent history from repeating itself.



Massive contamination of agricultural lands by radionuclides occurs, as a rule, due to large accidents at the enterprises of nuclear industry or nuclear power stations. Such accidents occurred at Windscale (England) and South Ural (Russia). The largest accident happened in April 1986 at the Chernobyl nuclear power station. The latter entailed intensive contamination of soils over several thousands of square kilometres.

The major factors contributing to radiation effects in agricultural areas are as follows:

  • whether radiation is from a single or a long-term exposure
  • total quantity of radioactive substances entering the environment
  • ratio of radionuclides in the fallout
  • distance from the source of radiation to agricultural lands and settlements
  • hydrogeological and soil characteristics of agricultural lands and the purpose of their use
  • peculiarities of work of the rural population; diet, water supply
  • time since the radiological accident.


As a result of the Chernobyl accident more than 50 million Curies (Ci) of mostly volatile radionuclides entered the environment. At the first stage, which covered 2.5 months (the “iodine period”), iodine-131 produced the greatest biological hazard, with significant doses of high-energy gamma radiation.

Work on agricultural lands during the iodine period should be strictly regulated. Iodine-131 accumulates in the thyroid gland and damages it. After the Chernobyl accident, a zone of very high radiation intensity, where no one was permitted to live or work, was defined by a 30 km radius around the station.

Outside this prohibited zone, four zones with various rates of gamma radiation on the soils were distinguished according to which types of agricultural work could be performed; during the iodine period, the four zones had the following radiation levels measured in roentgen (R):

  • zone 1—less than 0.1 mR/h
  • zone 2—0.1 to 1 mR/h
  • zone 3—1.0 to 5 mR/h
  • zone 4—5 mR/h and more.


Actually, due to the “spot” contamination by radionuclides over the iodine period, agricultural work in these zones was performed at levels of gamma irradiation from 0.2 to 25 mR/h. Apart from uneven contamination, variation in gamma radiation levels was caused by different concentrations of radionuclides in different crops. Forage crops in particular are exposed to high levels of gamma emitters during harvesting, transportation, ensilage and when they are used as fodder.

After the decay of iodine-131, the major hazard for agricultural workers is presented by the long-lived nuclides caesium-137 and strontium-90. Caesium-137, a gamma emitter, is a chemical analogue of potassium; its intake by humans or animals results in uniform distribution throughout the body and it is relatively quickly excreted with urine and faeces. Thus, the manure in the contaminated areas is an additional source of radiation and it must be removed as quickly as possible from stock farms and stored in special sites.

Strontium-90, a beta emitter, is a chemical analogue of calcium; it is deposited in bone marrow in humans and animals. Strontium-90 and caesium-137 can enter the human body through contaminated milk, meat or vegetables.

The division of agricultural lands into zones after the decay of short-lived radionuclides is carried out according to a different principle. Here, it is not the level of gamma radiation, but the amount of soil contamination by caesium-137, strontium-90 and plutonium-239 that are taken into account.

In the case of particularly severe contamination, the population is evacuated from such areas and farm work is performed on a 2-week rotation schedule. The criteria for zone demarcation in the contaminated areas are given in table 1.

Table 1. Criteria for contamination zones

Contamination zones

Soil contamination limits

Dosage limits

Type of action

1. 30 km zone

Residing of
population and
agricultural work
are prohibited.

2. Unconditional

15 (Ci)/km2
caesium- 137
3 Ci/km2
strontium- 90
0.1 Ci/km2 plutonium

0.5 cSv/year

Agricultural work is performed with 2-week rotation schedule under strict radiological control.

3. Voluntary

5–15 Ci/km2
0.15–3.0 Ci/km2
0.01–0.1 Ci/km2


Measures are undertaken to reduce
contamination of
upper soil layer;
agricultural work
is carried out under strict radiological

4. Radio- ecological

1–5 Ci/km2
0.02–0.15 Ci/km2
0.05–0.01 Ci/km2

0.01 cSv/year

Agricultural work is
carried out in usual way but under
radiological control.


When people work on agricultural lands contaminated by radionuclides, the intake of radionuclides by the body through respiration and contact with soil and vegetable dusts may occur. Here, both beta emitters (strontium-90) and alpha emitters are extremely dangerous.

As a result of accidents at nuclear power stations, part of radioactive materials entering the environment are low-dispersed, highly active particles of the reactor fuel—“hot particles”.

Considerable amounts of dust containing hot particles are generated during agricultural work and in windy periods. This was confirmed by the results of investigations of tractor air filters taken from machines which were operated on the contaminated lands.

The assessment of dose loads on the lungs of agricultural workers exposed to hot particles revealed that outside the 30 km zone the doses amounted to several millisieverts (Loshchilov et al. 1993).

According to the data of Bruk et al. (1989) the total activity of caesium-137 and caesium-134 in the inspired dust in machine operators amounted to 0.005 to 1.5 nCi/m3. According to their calculations, over the total period of field work the effective dose to lungs ranged from 2 to
70 cSv.

The relation between the amount of soil contamination by caesium-137 and radioactivity of work zone air was established. According to the data of the Kiev Institute for Occupational Health it was found that when the soil contamination by caesium-137 amounted to 7.0 to 30.0 Ci/km2 the radioactivity of the breathing zone air reached 13.0 Bq/m3. In the control area, where the density of contamination amounted to 0.23 to 0.61 Ci/km3, the radioactivity of work zone air ranged from 0.1 to 1.0 Bq/m3 (Krasnyuk, Chernyuk and Stezhka 1993).

The medical examinations of agricultural machine operators in the “clear” and contaminated zones revealed an increase in cardiovascular diseases in workers in the contaminated zones, in the form of ischaemic heart disease and neurocirculatory dystonia. Among other disorders dysplasia of the thyroid gland and an increased level of monocytes in the blood were registered more frequently.

Hygienic Requirements

Work schedules

After large accidents at nuclear power stations, temporary regulations for the population are usually adopted. After the Chernobyl accident temporary regulations for a period of one year were adopted, with the TLV of 10 cSv. It is assumed that workers receive 50% of their dose due to external radiation during work. Here, the threshold of intensity of radiation dose over the eight-hour work day should not exceed 2.1 mR/h.

During agricultural work, the radiation levels at workplaces can fluctuate significantly, depending on the concentrations of radioactive substances in soils and plants; they also fluctuate during technological processing (siloing, preparation of dry fodder and so on). In order to reduce dosages to workers, regulations of time limits for agricultural work are introduced. Figure 1 shows regulations which were introduced after the Chernobyl accident.

Figure 1. Time limits for agricultural work depending on intensity of gamma-ray  radiation at workplaces.



When carrying out agricultural work in conditions of high contamination of soils and plants, it is necessary to strictly observe measures directed at prevention of dust contamination. The loading and unloading of dry and dusty substances should be mechanized; the neck of the conveyer tube should be covered with fabric. Measures directed at the decrease of dust release must be undertaken for all types of field work.

Work using agricultural machinery should be carried out taking due account of cabin pressurization and the choice of the proper direction of operation, with the wind at the side being preferable. If possible it is desirable to first water the areas being cultivated. The wide use of industrial technologies is recommended so as to eliminate manual work on the fields as much as possible.

It is appropriate to apply substances to the soils which can promote absorption and fixation of radionuclides, changing them into insoluble compounds and thus preventing the transfer of radionuclides into plants.

Agricultural machinery

One of the major hazards for the workers is agricultural machinery contaminated by radionuclides. The allowable work time on the machines depends on the intensity of gamma radiation emitted from the cabin surfaces. Not only is the thorough pressurization of cabins required, but due control over ventilation and air conditioning systems as well. After work, wet cleaning of cabins and replacement of filters should be carried out.

When maintaining and repairing the machines after decontamination procedures, the intensity of gamma radiation at the outer surfaces should not exceed 0.3 mR/h.


Routine wet cleaning should be done inside and outside buildings. Buildings should be equipped with showers. When preparing fodder which contains dust components, it is necessary to adhere to procedures aimed at prevention of dust intake by the workers, as well as to keep the dust off the floor, equipment and so on.

Pressurization of the equipment should be under control. Workplaces should be equipped with effective general ventilation.

Use of pesticides and mineral fertilizers

The application of dust and granular pesticides and mineral fertilizers, as well as spraying from aeroplanes, should be restricted. Machine spraying and application of granular chemicals as well as liquid mixed fertilizers are preferable. The dust mineral fertilizers should be stored and transported only in tightly closed containers.

Loading and unloading work, preparation of pesticide solutions and other activities should be performed using maximum individual protective equipment (overalls, helmets, goggles, respirators, rubber gauntlets and boots).

Water supply and diet

There should be special closed premises or motor vans without draughts where workers can take their meals. Before taking meals workers should clean their clothes and thoroughly wash their hands and faces with soap and running water. During summer periods field workers should be supplied with drinking water. The water should be kept in closed containers. Dust must not enter containers when filling them with water.

Preventive medical examinations of workers

Periodic medical examinations should be carried out by a physician; laboratory analysis of blood, ECG and tests of respiratory function are compulsory. Where radiation levels do not exceed permissible limits, the frequency of medical examinations should be not less than once every 12 months. Where there are higher levels of ionizing radiation the examinations should be carried out more frequently (after sowing, harvesting and so on) with due account of radiation intensity at workplaces and the total absorbed dose.

Organization of Radiological Control over Agricultural Areas

The major indices characterizing the radiological situation after fallout are gamma radiation intensity in the area, contamination of agricultural lands by the selected radionuclides and content of radionuclides in agricultural products.

The determination of gamma radiation levels in the areas allows the drawing of the borders of severely contaminated areas, estimation of doses of external radiation to people engaged in agricultural work and the establishing of corresponding schedules providing for radiological safety.

The functions of radiological monitoring in agriculture are usually the responsibility of radiological laboratories of the sanitary service as well as veterinary and agrochemical radiological laboratories. The training and education of the personnel engaged in dosimetric control and consultations for the rural population are carried out by these laboratories.



Friday, 25 February 2011 17:12

Radiation Accidents

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Description, Sources, Mechanisms

Apart from the transportation of radioactive materials, there are three settings in which radiation accidents can occur:

  • use of nuclear reactions to produce energy or arms, or for research purposes
  • industrial applications of radiation (gamma radiography, irradiation)
  • research and nuclear medicine (diagnosis or therapy).


Radiation accidents may be classified into two groups on the basis of whether or not there is environmental emission or dispersion of radionuclides; each of these types of accident affects different populations.

The magnitude and duration of the exposure risk for the general population depends on the quantity and the characteristics (half-life, physical and chemical properties) of the radionuclides emitted into the environment (table 1). This type of contamination occurs when there is rupture of the containment barriers at nuclear power plants or industrial or medical sites which separate radioactive materials from the environment. In the absence of environmental emissions, only workers present onsite or handling radioactive equipment or materials are exposed.

Table 1. Typical radionuclides, with their radioactive half-lives



Radiation emitted

Physical half-life*

Biological half-life
after incorporation




10.7 y

65 d




284 d

263 d




30 y

109 d




5.3 y

1.6 y




8 d

7.5 d




24,065 y

50 y




138 d

27 d




29.1 y

18 y




12.3 y

10 d

* y = years; d = days.

Exposure to ionizing radiation may occur through three routes, regardless of whether the target population is composed of workers or the general public: external irradiation, internal irradiation, and contamination of skin and wounds.

External irradiation occurs when individuals are exposed to an extracorporeal radiation source, either point (radiotherapy, irradiators) or diffuse (radioactive clouds and fallout from accidents, figure 1). Irradiation may be local, involving only a portion of the body, or whole body.

Figure 1. Exposure pathways to ionizing radiation after an accidental release of radioactivity in the environment


Internal radiation occurs following incorporation of radioactive substances into the body (figure 1) through either inhalation of airborne radioactive particles (e.g., caesium-137 and iodine-131, present in the Chernobyl cloud) or ingestion of radioactive materials in the food chain (e.g., iodine-131 in milk). Internal irradiation may affect the whole body or only certain organs, depending on the characteristics of the radionuclides: caesium-137 distributes itself homogeneously throughout the body, while iodine-131 and strontium-90 concentrate in the thyroid and the bones, respectively.

Finally, exposure may also occur through direct contact of radioactive materials with skin and wounds.

Accidents involving nuclear power plants

Sites included in this category include power-generating stations, experimental reactors, facilities for the production and processing or reprocessing of nuclear fuel and research laboratories. Military sites include plutonium breeder reactors and reactors located aboard ships and submarines.

Nuclear power plants

The capture of heat energy emitted by atomic fission is the basis for the production of electricity from nuclear energy. Schematically, nuclear power plants can be thought of as comprising: (1) a core, containing the fissile material (for pressurized-water reactors, 80 to 120 tonnes of uranium oxide); (2) heat-transfer equipment incorporating heat-transfer fluids; (3) equipment capable of transforming heat energy into electricity, similar to that found in power plants that are not nuclear.

Strong, sudden power surges capable of causing core meltdown with emission of radioactive products are the primary hazards at these installations. Three accidents involving reactor-core meltdown have occurred: at Three Mile Island (1979, Pennsylvania, United States), Chernobyl (1986, Ukraine), and Fukushima (2011, Japan) [Edited, 2011].

The Chernobyl accident was what is known as a criticality accident—that is, a sudden (within the space of a few seconds) increase in fission leading to a loss of process control. In this case, the reactor core was completely destroyed and massive amounts of radioactive materials were emitted (table 2). The emissions reached a height of 2 km, favouring their dispersion over long distances (for all intents and purposes, the entire Northern hemisphere). The behaviour of the radioactive cloud has proven difficult to analyse, due to meteorological changes during the emission period (figure 2) (IAEA 1991).

Table 2. Comparison of different nuclear accidents


Type of facility


Total emitted
radioactivity (GBq)

of emission

Main emitted

dose (hSv)

Khyshtym 1957

Storage of high-
activity fission

Chemical explosion





Windscale 1957




23 hours

Iodine-131, polonium-210,


Three Mile Island

PWR industrial

Coolant failure





Chernobyl 1986

RBMK industrial 



More than 10 days

Iodine-131, iodine-132, 
caesium-137, caesium-134, 
strontium-89, strontium-90


Fukushima 2011


The final report of the Fukushima Assessment Task Force will be submitted in 2013.






Source: UNSCEAR 1993.

Figure 2. Trajectory of emissions from the Chernobyl accident, 26 April-6 May 1986


Contamination maps were drawn up on the basis of environmental measurements of caesium-137, one of the main radioactive emission products (table 1 and table 2). Areas of Ukraine, Byelorussia (Belarus) and Russia were heavily contaminated, while fallout in the rest of Europe was less significant (figure  3 and figure 4 (UNSCEAR 1988). Table 3 presents data on the area of the contaminated zones, characteristics of the exposed populations and routes of exposure.

FIgure 3. Caesium-137 deposition in Byelorussia, Russia and Ukraine following the Chernobyl accident.


Figure 4. Caesium-137 fallout (kBq/km2) in Europe following the Chernobyl accident


Table 3. Area of contaminated zones, types of populations exposed and modes of exposure in Ukraine, Byelorussia and Russia following the Chernobyl accident

Type of population

Surface area ( km2 )

Population size (000)

Main modes of exposure

Occupationally exposed populations:

Employees onsite at
the time of the

Clean-up and relief





External irradiation,
inhalation, skin
from the damaged
reactor, fragments
of the reactor
dispersed throughout
the site, radioactive
vapours and dusts

External irradiation,
inhalation, skin

General public:

Evacuated from the
prohibited zone in
the first few days

Residents of 
( Mbq/m2 ) - ( Ci/km2 )
>1.5              (>40)
0.6–1.5      (15–40)
0.2–0.6        (5–15)
0.04–0.2        (1–5)
Residents of other zones <0.04mbq/m2




External irradiation by
the cloud, inhalation
of radioactive
elements present
in the cloud

External radiation from
fallout, ingestion of

External irradiation
by fallout, ingestion
of contaminated

* Individuals participating in clean-up within 30 km of the site. These include fire-fighters, military personnel, technicians and engineers who intervened during the first weeks, as well as physicians and researchers active at a later date.

** Caesium-137 contamination.

Source: UNSCEAR 1988; IAEA 1991.


The Three Mile Island accident is classified as a thermal accident with no reactor runaway, and was the result of a reactor-core coolant failure lasting several hours. The containment shell ensured that only a limited quantity of radioactive material was emitted into the environment, despite the partial destruction of the reactor core (table 2). Although no evacuation order was issued, 200,000 residents voluntarily evacuated the area.

Finally, an accident involving a plutonium production reactor occurred on the west coast of England in 1957 (Windscale, table 2). This accident was caused by a fire in the reactor core and resulted in environmental emissions from a chimney 120 metres high.

Fuel-processing facilities

Fuel production facilities are located “upstream” from nuclear reactors and are the site of ore extraction and the physical and chemical transformation of uranium into fissile material suitable for use in reactors (figure 5). The primary accident hazards present in these facilities are chemical in nature and related to the presence of uranium hexafluoride (UF6), a gaseous uranium compound which may decompose upon contact with air to produce hydrofluoric acid (HF), a very corrosive gas.

Figure 5. Nuclear fuel processing cycle.


“Downstream” facilities include fuel storage and reprocessing plants. Four criticality accidents have occurred during chemical reprocessing of enriched uranium or plutonium (Rodrigues 1987). In contrast to accidents occurring at nuclear power plants, these accidents involved small quantities of radioactive materials—tens of kilograms at most—and resulted in negligible mechanical effects and no environmental emission of radioactivity. Exposure was limited to very high dose, very short term (of the order of minutes) external gamma ray and neutron irradiation of workers.

In 1957, a tank containing highly radioactive waste exploded at Russia’s first military-grade plutonium production facility, located in Khyshtym, in the south Ural Mountains. Over 16,000 km2 were contaminated and 740 PBq (20 MCi) were emitted into the atmosphere (table  2 and table 4).

Table 4. Surface area of the contaminated zones and size of population exposed after the Khyshtym accident (Urals 1957), by strontium-90 contamination

Contamination ( kBq/m2 )

( Ci/km2 )

Area ( km2 )


≥ 37,000

≥ 1,000



≥ 3,700




≥ 74

≥ 2



≥ 3.7

≥ 0.1




Research reactors

Hazards at these facilities are similar to those present at nuclear power plants, but are less serious, given the lower power generation. Several criticality accidents involving significant irradiation of personnel have occurred (Rodrigues 1987).

Accidents related to the use of radioactive sources in industry and medicine (excluding nuclear plants) (Zerbib 1993)

The most common accident of this type is the loss of radioactive sources from industrial gamma radiography, used, for example, for the radiographic inspection of joints and welds. However, radioactive sources may also be lost from medical sources (table 5). In either case, two scenarios are possible: the source may be picked up and kept by a person for several hours (e.g., in a pocket), then reported and restored, or it may be collected and carried home. While the first scenario causes local burns, the second may result in long-term irradiation of several members of the general public.

Table 5. Accidents involving the loss of radioactive sources and which resulted in exposure of the general public

Country (year)

Number of

Number of
receiving high

Number of deaths**

Radioactive material involved

Mexico (1962)





China (1963)




Cobalt 60

Algeria (1978)





Morocco (1984)





(Juarez, 1984)





(Goiânia, 1987)





(Xinhou, 1992)





United States
(Indiana, 1992)





* Individuals exposed to doses capable of causing acute or long-term effects or death.
** Among individuals receiving high doses.

Source: Nénot 1993.


The recovery of radioactive sources from radiotherapy equipment has resulted in several accidents involving the exposure of scrap workers. In two cases—the Juarez and Goiânia accidents—the general public was also exposed (see table 5 and box below).

The Goiвnia Accident, 1987

Between 21 September and 28 September 1987, several people suffering from vomiting, diarrhoea, vertigo and skin lesions at various parts of the body were admitted to the hospital specializing in tropical diseases in Goiânia, a city of one million inhabitants in the Brazilian state of Goias. These problems were attributed to a parasitic disease common in Brazil. On 28 September, the physician responsible for health surveillance in the city saw a woman who presented him with a bag containing debris from a device collected from an abandoned clinic, and a powder which emitted, according to the woman “a blue light”. Thinking that the device was probably x-ray equipment, the physician contacted his colleagues at the hospital for tropical diseases. The Goias Department of the Environment was notified, and the next day a physicist took measurements in the hygiene department’s yard, where the bag was stored overnight. Very high radioactivity levels were found. In subsequent investigations the source of radioactivity was identified as a caesium-137 source (total activity: approximately 50 TBq (1,375 Ci)) which had been contained within radiotherapy equipment used in a clinic abandoned since 1985. The protective housing surrounding the caesium had been disassembled on 10 September 1987 by two scrapyard workers and the caesium source, in powder form, removed. Both the caesium and the fragments of the contaminated housing were gradually dispersed throughout the city. Several people who had transported or handled the material, or who had simply come to see it (including parents, friends and neighbours) were contaminated. In all, over 100,000 people were examined, of whom 129 were very seriously contaminated; 50 were hospitalized (14 for medullary failure), and 4, including a 6-year-old girl, died. The accident had dramatic economic and social consequences for the entire city of Goiânia and the state of Goias: 1/1000 of the city’s surface area was contaminated, and the price of agricultural produce, rents, real estate, and land all fell. The inhabitants of the entire state suffered real discrimination.

Source: IAEA 1989a

The Juarez accident was discovered serendipitously (IAEA 1989b). On 16 January 1984, a truck entering the Los Alamos (New Mexico, United States) scientific laboratory loaded with steel bars triggered a radiation detector. Investigation revealed the presence of cobalt-60 in the bars and traced the cobalt-60 to a Mexican foundry. On January 21, a heavily contaminated scrapyard in Juarez was identified as the source of the radioactive material. Systematic monitoring of roads and highways by detectors resulted in the identification of a heavily contaminated truck. The ultimate radiation source was determined to be a radiotherapy device stored in a medical centre until December 1983, at which time it was disassembled and transported to the scrapyard. At the scrapyard, the protective housing surrounding the cobalt-60 was broken, freeing the cobalt pellets. Some of the pellets fell into the truck used to transport scrap, and others were dispersed throughout the scrapyard during subsequent operations, mixing with the other scrap.

Accidents involving the entry of workers into active industrial irradiators (e.g., those used to preserve food, sterilize medical products, or polymerize chemicals) have occurred. In all cases, these have been due to failure to follow safety procedures or to disconnected or defective safety systems and alarms. The dose levels of external irradiation to which workers in these accidents were exposed were high enough to cause death. Doses were received within a few seconds or minutes (table 6).

Table 6. Main accidents involving industrial irradiators

Site, date


Number of

Exposure level
and duration

Affected organs
and tissues

Dose  received (Gy),

Medical effects

Forbach, August 1991



several  deciGy/

Hands, head, trunk

40, skin

Burns  affecting  25–60% of
body area

Maryland, December 1991





55, hands

Bilateral finger amputation

Viet nam, November 1992



1,000 Gy/minute


1.5, whole  body

Amputation of the right hand and a finger of the left hand

Italy, May 1975



Several minutes

Head, whole body

8, bone marrow


San Salvador, February 1989




Whole body, legs,

3–8, whole body

2 leg  amputations, 1 death

Israel, June 1990



1 minute

Head, whole body



Belarus, October 1991



Several minutes

Whole body



* EA: electron accelerator CI: cobalt-60 irradiator.

Source: Zerbib 1993; Nénot 1993.


Finally, medical and scientific personnel preparing or handling radioactive sources may be exposed through skin and wound contamination or inhalation or ingestion of radioactive materials. It should be noted that this type of accident is also possible in nuclear power plants.

Public Health Aspects of the Problem

Temporal patterns

The United States Radiation Accident Registry (Oak Ridge, United States) is a worldwide registry of radiation accidents involving humans since 1944. To be included in the registry, an accident must have been the subject of a published report and have resulted in whole-body exposure exceeding 0.25 Sievert (Sv), or skin exposure exceeding 6 Sv or exposure of other tissues and organs exceeding 0.75 Sv (see "Case Study: What does dose mean?" for a definition of dose). Accidents that are of interest from the point of view of public health but which resulted in lower exposures are thus excluded (see below for a discussion of the consequences of exposure).

Analysis of the registry data from 1944 to 1988 reveals a clear increase in both the frequency of radiation accidents and the number of exposed individuals starting in 1980 (table 7). The increase in the number of exposed individuals is probably accounted for by the Chernobyl accident, particularly the approximately 135,000 individuals initially residing in the prohibited area within 30 km of the accident site. The Goiânia (Brazil) and Juarez (Mexico) accidents also occurred during this period and involved significant exposure of many people (table 5).

Table 7. Radiation accidents listed in the Oak Ridge (United States) accident registry (worldwide, 1944-88)





Total number of accidents




Number of individuals involved




Number of individuals exposed to doses exceeding
exposure criteria*




Number of deaths (acute effects)




* 0.25 Sv for whole-body exposure, 6 Sv for skin exposure, 0.75 Sv for other tissues and organs.


Potentially exposed populations

From the point of view of exposure to ionizing radiation, there are two populations of interest: occupationally exposed populations and the general public. United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR 1993) estimates that 4 million workers worldwide were occupationally exposed to ionizing radiation in the period 1985-1989; of these, approximately 20% were employed in the production, use and processing of nuclear fuel (table 8). IAEA member countries were estimated to possess 760 irradiators in 1992, of which 600 were electron accelerators and 160 gamma irradiators.

Table 8. Temporal pattern of occupational exposure to ionizing radiation worldwide (in thousands)





Nuclear fuel processing*




Military applications**




Industrial applications




Medical applications








* Production and reprocessing of fuel: 40,000; reactor operation: 430,000.
** including 190,000 shipboard personnel.

Source: UNSCEAR 1993.


The number of nuclear sites per country is a good indicator of the potential for exposure of the general public (figure 6).

Figure 6. Distribution of power-generating reactors and fuel  reprocessing plants in the world, 1989-90


Health Effects

Direct health effects of ionizing radiation

In general, the health effects of ionizing radiation are well known and depend on the dose level received and the dose rate (received dose per unit of time (see "Case Study: What does dose mean?").

Deterministic effects

These occur when the dose exceeds a given threshold and the dose rate is high. The severity of the effects is proportional to the dose, although the dose threshold is organ specific (table 9).

Table 9. Deterministic effects: thresholds for selected organs

Tissue or effect

Equivalent single dose
received at the organ (Sv)


Temporary sterility


Permanent sterility





Crystalline lens:

Detectable opacities


Impaired vision (cataracts)


Bone marrow:

Depression of haemopoiesis


Source: ICRP 1991.

In the accidents such as those discussed above, deterministic effects may be caused by local intense irradiation, such as that caused by external irradiation, direct contact with a source (e.g., a misplaced source picked up and pocketed) or skin contamination. All these result in radiological burns. If the local dose is of the order of 20 to 25 Gy (table 6, "Case Study: What does dose mean?") tissue necrosis may ensue. A syndrome known as acute irradiation syndrome, characterized by digestive disorders (nausea, vomiting, diarrhoea) and bone marrow aplasia of variable severity, may be induced when the average whole-body irradiation dose exceeds 0.5 Gy. It should be recalled that whole-body and local irradiation may occur simultaneously.

Nine of 60 workers exposed during criticality accidents at nuclear fuel processing plants or research reactors died (Rodrigues 1987). Decedents received 3 to 45 Gy, while survivors received 0.1 to 7 Gy. The following effects were observed in survivors: acute irradiation syndrome (gastro-intestinal and haematological effects), bilateral cataracts and necrosis of limbs, requiring amputation.

At Chernobyl, power plant personnel, as well as emergency response personnel not using special protective equipment, suffered high beta and gamma radiation exposure in the initial hours or days following the accident. Five hundred people required hospitalization; 237 individuals who received whole-body irradiation exhibited acute irradiation syndrome, and 28 individuals died despite treatment (table 10) (UNSCEAR 1988). Others received local irradiation of the limbs, in some cases affecting over 50% of the body surface and continue to suffer, many years later, multiple skin disorders (Peter, Braun-Falco and Birioukov 1994).

Table 10. Distribution of patients exhibiting acute irradiation syndrome (AIS) after the Chernobyl accident, by severity of condition

Severity of AIS

Equivalent dose

Number of

Number of
deaths (%)

Average survival
period (days)







1 (1.8)





7 (33.3)





20 (95.2)


Source: UNSCEAR 1988.

Stochastic effects

These are probabilistic in nature (i.e., their frequency increases with received dose), but their severity is independent of dose. The main stochastic effects are:

  • Mutation. This has been observed in animal experiments but has been difficult to document in humans.
  • Cancer. The effect of irradiation on the risk of developing cancer has been studied in patients receiving radiation therapy and in survivors of the Hiroshima and Nagasaki bombings. UNSCEAR (1988, 1994) regularly summarizes the results of these epidemiological studies. The duration of the latency period is typically 5 to 15 years from the date of exposure depending on organ and tissue. Table 11 lists the cancers for which an association with ionizing radiation has been established. Significant cancer excesses have been demonstrated among survivors of the Hiroshima and Nagasaki bombings with exposures above 0.2 Sv.
  • Selected benign tumours. Benign thyroid adenomas.


Table 11. Results of epidemiological studies of the effect of high dose rate of external irradiation on cancer

Cancer site


Other studies
No. positive/
total No.





Haematopoietic system






Lymphoma (not specified)




Non-Hodgkin lymphoma








Oral cavity




Salivary glands




Digestive system










Small intestine















Gall bladder






Respiratory system





Trachea, bronchi, lungs






Not specified






Other cancers




Breast (women)




Reproductive system


Uterus (non-specific)




Uterine body







Other (women)







Urinary system












Central nervous system











Connective tissue



All cancers, excluding leukaemias



+ Cancer sites studied in the Hiroshima and Nagasaki survivors.
* Positive association with ionizing radiation.
1 Cohort (incidence or mortality) or case-control studies.

Source: UNSCEAR 1994.


Two important points concerning the effects of ionizing radiation remain controversial.

Firstly, what are the effects of low-dose irradiation (below 0.2 Sv) and low dose rates? Most epidemiological studies have examined survivors of the Hiroshima and Nagasaki bombings or patients receiving radiation therapy—populations exposed over very short periods to relatively high doses—and estimates of the risk of developing cancer as a result of exposure to low doses and dose rates depends essentially on extrapolations from these populations. Several studies of nuclear power plant workers, exposed to low doses over several years, have reported cancer risks for leukaemia and other cancers that are compatible with extrapolations from high-exposure groups, but these results remain unconfirmed (UNSCEAR 1994; Cardis, Gilbert and Carpenter 1995).

Secondly, is there a threshold dose (i.e., a dose below which there is no effect)? This is currently unknown. Experimental studies have demonstrated that damage to genetic material (DNA) caused by spontaneous errors or environmental factors are constantly repaired. However, this repair is not always effective, and may result in malignant transformation of cells (UNSCEAR 1994).

Other effects

Finally, the possibility of teratogenic effects due to irradiation during pregnancy should be noted. Microcephaly and mental retardation have been observed in children born to female survivors of the Hiroshima and Nagasaki bombings who received irradiation of at least 0.1 Gy during the first trimester (Otake, Schull and Yoshimura 1989; Otake and Schull 1992). It is unknown whether these effects are deterministic or stochastic, although the data do suggest the existence of a threshold.

Effects observed following the Chernobyl accident

The Chernobyl accident is the most serious nuclear accident to have occurred to date. However, even now, ten years after the fact, not all the health effects on the most highly exposed populations have been accurately evaluated. There are several reasons for this:

  • Some effects appear only many years after the date of exposure: for example, solid-tissue cancers typically take 10 to 15 years to appear.
  • As some time elapsed between the accident and the commencement of epidemiological studies, some effects occurring in the initial period following the accident may not have been detected.
  • Useful data for the quantification of the cancer risk were not always gathered in a timely fashion. This is particularly true for data necessary to estimate the exposure of the thyroid gland to radioactive iodides emitted during the incident (tellurium-132, iodine-133) (Williams et al. 1993).
  • Finally, many initially exposed individuals subsequently left the contaminated zones and were probably lost for follow-up.


Workers. Currently, comprehensive information is unavailable for all the workers who were strongly irradiated in the first few days following the accident. Studies on the risk to clean-up and relief workers of developing leukaemia and solid-tissue cancers are in progress (see table 3). These studies face many obstacles. Regular follow-up of the health status of clean-up and relief workers is greatly hindered by the fact that many of them came from different parts of the ex-USSR and were redispatched after working on the Chernobyl site. Further, received dose must be estimated retrospectively, as there are no reliable data for this period.

General population. The only effect plausibly associated with ionizing radiation in this population to date is an increase, starting in 1989, of the incidence of thyroid cancer in children younger than 15 years. This was detected in Byelorussia (Belarus) in 1989, only three years after the incident, and has been confirmed by several expert groups (Williams et al. 1993). The increase was particularly noteworthy in the most heavily contaminated areas of Belarus, especially the Gomel region. While thyroid cancer was normally rare in children younger than 15 years, (annual incidence rate of 1 to 3 per million), its incidence increased tenfold on a national basis and twentyfold in the Gomel area (table 12, figure 7), (Stsjazhko et al. 1995). A tenfold increase of the incidence of thyroid cancer was subsequently reported in the five most heavily contaminated areas of Ukraine, and an increase in thyroid cancer was also reported in the Bryansk (Russia) region (table 12). An increase among adults is suspected but has not been confirmed. Systematic screening programmes undertaken in the contaminated regions allowed latent cancers present prior to the accident to be detected; ultrasonographic programmes capable of detecting thyroid cancers as small as a few millimetres were particularly helpful in this regard. The magnitude of the increase in incidence in children, taken together with the aggressiveness of the tumours and their rapid development, suggests that the observed increases in thyroid gland cancer are partially due to the accident.

Table 12. Temporal pattern of the incidence and total number of thyroid cancers in children in Belarus, Ukraine & Russia, 1981-94


Incidence* (/100,000)

Number of cases







Entire country





Gomel area






Entire country





Five most heavily
contaminated areas






Entire country





Bryansk and
Kaluga areas





* Incidence: the ratio of the number of new cases of a disease during a given period to the size of the population studied in the same period.

Source: Stsjazhko et al. 1995.


Figure 7. Incidence of cancer of the thyroid in children younger than 15 years in Belarus


In the most heavily contaminated zones (e.g., the Gomel region), the thyroid doses were high, particularly among children (Williams et al. 1993). This is consistent with the significant iodine emissions associated with the accident and the fact that radioactive iodine will, in the absence of preventive measures, concentrate preferentially in the thyroid gland.

Exposure to radiation is a well-documented risk factor for thyroid cancer. Clear increases in the incidence of thyroid cancer have been observed in a dozen studies of children receiving radiation therapy to the head and neck. In most cases, the increase was clear ten to 15 years after exposure, but was detectable in some cases within three to seven years. On the other hand, the effects in children of internal irradiation by iodine-131 and by short half-life iodine isotopes are not well established (Shore 1992).

The precise magnitude and pattern of the increase in the coming years of the incidence of thyroid cancer in the most highly exposed populations should be studied. Epidemiological studies currently under way should help to quantify the association between the dose received by the thyroid gland and the risk of developing thyroid cancer, and to identify the role of other genetic and environmental risk factors. It should be noted that iodine deficiency is widespread in the affected regions.

An increase in the incidence of leukaemia, particularly juvenile leukaemia (since children are more sensitive to the effects of ionizing radiation), is to be expected among the most highly exposed members of the population within five to ten years of the accident. Although no such increase has yet been observed, the methodological weaknesses of the studies conducted to date prevent any definitive conclusions from being drawn.

Psychosocial effects

The occurrence of more or less severe chronic psychological problems following psychological trauma is well established and has been studied primarily in populations faced with environmental disasters such as floods, volcanic eruptions and earthquakes. Post-traumatic stress is a severe, long-lasting and crippling condition (APA 1994).

Most of our knowledge on the effect of radiation accidents on psychological problems and stress is drawn from studies conducted in the wake of the Three Mile Island accident. In the year following the accident, immediate psychological effects were observed in the exposed population, and mothers of young children in particular exhibited increased sensitivity, anxiety and depression (Bromet et al. 1982). Further, an increase in depression and anxiety-related problems was observed in power-plant workers, compared to workers in another power plant (Bromet et al. 1982). In the following years (i.e., after the reopening of the power plant), approximately one-quarter of the surveyed population exhibited relatively significant psychological problems. There was no difference in the frequency of psychological problems in the rest of the survey population, compared to control populations (Dew and Bromet 1993). Psychological problems were more frequent among individuals living close to the power plant who were without a social support network, had a history of psychiatric problems, or who had evacuated their home at the time of the accident (Baum, Cohen and Hall 1993).

Studies are also under way among populations exposed during the Chernobyl accident and for whom stress appears to be an important public health issue (e.g., clean-up and relief workers and individuals living in a contaminated zone). For the moment, however, there are no reliable data on the nature, severity, frequency and distribution of psychological problems in the target populations. The factors that must be taken into account when evaluating the psychological and social consequences of the accident on residents of the contaminated zones include the harsh social and economic situation, the diversity of the available compensation systems, the effects of evacuation and resettlement (approximately 100,000 additional people were resettled in the years following the accident), and the effects of lifestyle limitations (e.g., modification of nutrition).

Principles of Prevention and Guidelines

Safety principles and guidelines

Industrial and medical use of radioactive sources

While it is true that the major radiation accidents reported have all occurred at nuclear power plants, the use of radioactive sources in other settings has nevertheless resulted in accidents with serious consequences for workers or the general public. The prevention of accidents such as these is essential, especially in light of the disappointing prognosis in cases of high-dose exposure. Prevention depends on proper worker training and on the maintenance of a comprehensive life-cycle inventory of radioactive sources which includes information on both the sources’ nature and location. The IAEA has established a series of safety guidelines and recommendations for the use of radioactive sources in industry, medicine and research (Safety Series No. 102). The principles in question are similar to those presented below for nuclear power plants.

Safety in nuclear power plants (IAEA Safety Series No. 75, INSAG-3)

The goal here is to protect both humans and the environment from the emission of radioactive materials under any circumstance. To this end, it is necessary to apply a variety of measures throughout the design, construction, operation and decommissioning of nuclear power plants.

The safety of nuclear power plants is fundamentally dependent on the “defence in depth” principle—that is, the redundancy of systems and devices designed to compensate for technical or human errors and deficiencies. Concretely, radioactive materials are separated from the environment by a series of successive barriers. In nuclear power production reactors, the last of these barriers is the containment structure (absent on the Chernobyl site but present at Three Mile Island). To avoid the breakdown of these barriers and to limit the consequences of breakdowns, the following three safety measures should be practised throughout the power plant’s operational life: control of the nuclear reaction, cooling of fuel, and containment of radioactive material.

Another essential safety principle is “operating experience analysis”—that is, using information gleaned from events, even minor ones, occurring at other sites to increase the safety of an existing site. Thus, analysis of the Three Mile Island and Chernobyl accidents has resulted in the implementation of modifications designed to ensure that similar accidents do not occur elsewhere.

Finally, it should be noted that significant efforts have been expended to promote a culture of safety, that is, a culture that is continually responsive to safety concerns related to the plant’s organization, activities and practices, as well as to individual behaviour. To increase the visibility of incidents and accidents involving nuclear power plants, an international scale of nuclear events (INES), identical in principle to scales used to measure the severity of natural phenomena such as earthquakes and wind, has been developed (table 12). This scale is not however suitable for the evaluation of a site’s safety or for performing international comparisons.

Table 13. International scale of nuclear incidents




Protective structure

7—Major accident

Major emission,
extensive health
and environmental


6—Serious accident

Significant emission,
may necessitate the application of all counter-measures.



Limited emission,
may necessitate
the application of
some counter-

Serious damage to
reactors and protective structures



Low emission, public
exposure approaching exposure limits

Damage to reactors
and protective
structures, fatal
exposure of workers


3—Serious incident

Very low emission,
public exposure
lower than exposure limits

contamination level, serious effects on
workers’ heath

Accident barely avoided



Serious contamination
level, over-exposure of workers

Serious failures of safety measures



Abnormality beyond
normal functional limits


No significance from
the point of view of safety



Principles of the protection of the general public from exposure to radiation

In cases involving the potential exposure of the general public, it may be necessary to apply protective measures designed to prevent or limit exposure to ionizing radiation; this is particularly important if deterministic effects are to be avoided. The first measures which should be applied in emergency are evacuation, sheltering and administration of stable iodine. Stable iodine should be distributed to exposed populations, since this will saturate the thyroid and inhibit its uptake of radioactive iodine. To be effective, however, thyroid saturation must occur before or soon after the start of exposure. Finally, temporary or permanent resettlement, decontamination, and control of agriculture and food may eventually be necessary.

Each of these countermeasures has its own “action level” (table 14), not to be confused with the ICRP dose limits for workers and the general public, developed to ensure adequate protection in cases of non-accidental exposure (ICRP 1991).

Table 14. Examples of generic intervention levels for protective measures for general population

Protective measure

Intervention level (averted dose)



10 mSv


50 mSv

Distribution of stable iodine

100 mGy


Temporary resettlement

30 mSv in 30 days; 10 mSv in the next 30 days

Permanent resettlement

1 Sv lifetime

Source: IAEA 1994.

Research Needs and Future Trends

Current safety research concentrates on improving the design of nuclear power-generating reactors—more specifically, on the reduction of the risk and effects of core meltdown.

The experience gained from previous accidents should lead to improvements in the therapeutic management of seriously irradiated individuals. Currently, the use of bone marrow cell growth factors (haematopoietic growth factors) in the treatment of radiation-induced medullary aplasia (developmental failure) is being investigated (Thierry et al. 1995).

The effects of low doses and dose rates of ionizing radiation remains unclear and needs to be clarified, both from a purely scientific point of view and for the purposes of establishing dose limits for the general public and for workers. Biological research is necessary to elucidate the carcinogenic mechanisms involved. The results of large-scale epidemiological studies, especially those currently under way on workers at nuclear power plants, should prove useful in improving the accuracy of cancer risk estimates for populations exposed to low doses or dose rates. Studies on populations which are or have been exposed to ionizing radiation due to accidents should help further our understanding of the effects of higher doses, often delivered at low dose rates.

The infrastructure (organization, equipment and tools) necessary for the timely collection of data essential for the evaluation of the health effects of radiation accidents must be in place well in advance of the accident.

Finally, extensive research is necessary to clarify the psychological and social effects of radiation accidents (e.g., the nature and frequency of, and risk factors for, pathological and non-pathological post-traumatic psychological reactions). This research is essential if the management of both occupationally and non-occupationally exposed populations is to be improved.



The industries and economies of nations depend, in part, on the large numbers of hazardous materials transported from the supplier to the user and, ultimately, to the waste disposer. Hazardous materials are transported by road, rail, water, air and pipeline. The vast majority reach their destination safely and without incident. The size and scope of the problem is illustrated by the petroleum industry. In the United Kingdom it distributes around 100 million tons of product every year by pipeline, rail, road and water. Approximately 10% of those employed by the UK chemical industry are involved in distribution (i.e., transport and warehousing).

A hazardous material can be defined as “a substance or material determined to be capable of posing an unreasonable risk to health, safety or property when transported”. “Unreasonable risk” covers a broad spectrum of health, fire and environmental considerations. These substances include explosives, flammable gases, toxic gases, highly flammable liquids, flammable liquids, flammable solids, substances which become dangerous when wet, oxidizing substances and toxic liquids.

The risks arise directly from a release, ignition, and so on, of the dangerous substance(s) being transported. Road and rail threats are those which could give rise to major accidents “which could affect both employees and members of the public”. These dangers can occur when materials are being loaded or unloaded or are en route. The population at risk is people living near the road or railway and the people in other road vehicles or trains who might become involved in a major accident. Areas of risk include temporary stopover points such as railway marshalling yards and lorry parking areas at motorway service points. Marine risks are those linked to ships entering or leaving ports and loading or discharging cargoes there; risks also arise from coastal and straits traffic and inland waterways.

The range of incidents which can occur in association with transport both while in transit and at fixed installations include chemical overheating, spillage, leakage, escape of vapour or gas, fire and explosion. Two of the principal events causing incidents are collision and fire. For road tankers other causes of release may be leaks from valves and from overfilling. Generally, for both road and rail vehicles, non-crash fires are much more frequent than crash fires. These transport-associated incidents can occur in rural, urban industrial and urban residential areas, and can involve both attended and unattended vehicles or trains. Only in the minority of cases is an accident the primary cause of the incident.

Emergency personnel should be aware of the possibility of human exposure and contamination by a hazardous substance in accidents involving railways and rail yards, roads and freight terminals, vessels (both ocean and inland based) and associated waterfront warehouses. Pipelines (both long distance and local utility distribution systems) can be a hazard if damage or leakage occurs, either in isolation or in association with other incidents. Transportation incidents are often more dangerous than those at fixed facilities. The materials involved may be unknown, warning signs may be obscured by rollover, smoke or debris, and knowledgeable operatives may be absent or casualties of the event. The number of people exposed depends on population density, both by day and night, on the proportions indoors and outdoors, and on the proportion who may be considered particularly vulnerable. In addition to the population who are normally in the area, personnel of the emergency services who attend the accident are also at risk. It is not uncommon in an incident involving transport of hazardous materials that a significant proportion of the casualties include such personnel.

In the 20-year period 1971 through 1990, about 15 people were killed on the roads of the United Kingdom because of dangerous chemicals, compared with the annual average of 5,000 persons every year in motor accidents. However, small quantities of dangerous goods can cause significant damage. International examples include:

  • A plane crashed near Boston, USA, because of leaking nitric acid.
  • Over 200 people were killed when a road tanker of propylene exploded over a campsite in Spain.
  • In a rail accident involving 22 rail cars of chemicals in Mississauga, Canada, a tanker containing 90 tonnes of chlorine was ruptured and there was an explosion and a large fire. There were no fatalities, but 250,000 persons were evacuated.
  • A rail collision alongside the motorway in Eccles, United Kingdom, resulted in three deaths and 68 injuries from the collision, but none from the resulting serious fire of the petroleum products being transported.
  • A petrol tanker went out of control in Herrborn, Germany, burning down a large part of the town.
  • In Peterborough, United Kingdom, a vehicle carrying explosives killed one person and almost destroyed an industrial centre.
  • A petrol tanker exploded in Bangkok, Thailand, killing a large number of people.


The largest number of serious incidents have arisen with flammable gas or liquids (partially related to the volumes moved), with some incidents from toxic gases and toxic fumes (including products of combustion).

Studies in the UK have shown the following for road transport:

  • frequency of accident while conveying hazardous materials: 0.12 x 10–6/km
  • frequency of release while conveying hazardous materials: 0.027 x 10–6/km
  • probability of a release given a traffic accident: 3.3%.


These events are not synonymous with hazardous material incidents involving vehicles, and may constitute only a small proportion of the latter. There is also the individuality of accidents involving the road transport of hazardous materials.

International agreements covering the transport of potentially hazardous materials include:

Regulations for the Safe Transport of Radioactive Material 1985 (as amended 1990): International Atomic Energy Agency, Vienna, 1990 (STI/PUB/866). Their purpose is to establish standards of safety which provide an acceptable level of control of the radiation hazards to persons, property and the environment that are associated with the transport of radioactive material.

The International Convention for the Safety of Life at Sea 1974 (SOLAS 74). This sets basic safety standards for all passenger and cargo ships, including ships carrying hazardous bulk cargoes.

The International Convention for the Prevention of Pollution from Ships 1973, as modified by the Protocol of 1978 (MARPOL 73/78). This provides regulations for the prevention of pollution by oil, noxious liquid substances in bulk, pollutants in packaged form or in freight containers, portable tanks or road and rail wagons, sewage and garbage. Regulation requirements are amplified in the International Maritime Dangerous Goods Code.

There is a substantial body of international regulation of the transportation of harmful substances by air, rail, road and sea (converted into national legislation in many countries). Most are based on standards sponsored by the United Nations, and cover the principles of identification, labelling, prevention and mitigation. The United Nations Committee of Experts on the Transport of Dangerous Goods has produced Recommendations on the Transport of Dangerous Goods. They are addressed to governments and international organizations concerned with the regulation of the transport of dangerous goods. Among other aspects, the recommendations cover principles of classification and definitions of classes, listing of the content of dangerous goods, general packing requirements, testing procedures, making, labelling or placarding, and transport documents. These recommendations—the “Orange Book”—do not have the force of law, but form the basis of all the international regulations. These regulations are generated by various organizations:

  • the International Civil Aviation Organization: Technical Instructions for Safe Transport of Dangerous Goods by Air (Tis)
  • the International Maritime Organization: International Maritime Dangerous Goods Code (IMDG Code)
  • the European Economic Community: The European Agreement Concerning the International Carriage of Dangerous Goods by Road (ADR)
  • the Office of International Rail Transport: Regulations Concerning the International Carriage of Dangerous Goods by Rail (RID).


The preparation of major emergency plans to deal with and mitigate the effects of a major accident involving dangerous substances is as much needed in the transportation field as for fixed installations. The planning task is made more difficult in that the location of an incident will not be known in advance, thus requiring flexible planning. The substances involved in a transport accident cannot be foreseen. Because of the nature of the incident a number of products may be mixed together at the scene, causing considerable problems to the emergency services. The incident may occur in an area which is highly urbanized, remote and rural, heavily industrialized, or commercialized. An added factor is the transient population who may be unknowingly involved in an event because the accident has caused a backlog of vehicles either on the public highway or where passenger trains are stopped in response to a rail incident.

There is therefore a necessity for the development of local and national plans to respond to such events. These must be simple, flexible and easily understood. As major transport accidents can occur in a multiplicity of locations the plan must be appropriate to all potential scenes. For the plan to work effectively at all times, and in both remote rural and heavily populated urban locales, all organizations contributing to the response must have the ability to maintain flexibility while conforming to the basic principles of the overall strategy.

The initial responders should obtain as much information as possible to try to identify the hazard involved. Whether the incident is a spillage, a fire, a toxic release, or a combination of these will determine responses. The national and international marking systems used to identify vehicles transporting hazardous substances and carrying hazardous packaged goods should be known to the emergency services, who should have access to one of the several national and international databases which can help to identify the hazard and the problems associated with it.

Rapid control of the incident is vital. The chain of command must be identified clearly. This may change during the course of the event from the emergency services through the police to the civil government of the affected area. The plan must be able to recognize the effect on the population, both those working in or resident in the potentially affected area and those who may be transients. Sources of expertise on public health matters should be mobilized to advise on both the immediate management of the incident and on the potential for longer-term direct health effects and indirect ones through the food chain. Contact points for obtaining advice on environmental pollution to water courses and so on, and the effect of weather conditions on the movement of gas clouds must be identified. Plans must identify the possibility of evacuation as one of the response measures.

However, the proposals must be flexible, as there may be a range of costs and benefits, both in incident management and in public health terms, which will have to be considered. The arrangements must outline clearly the policy with respect to keeping the media fully informed and the action being taken to mitigate the effects. The information must be accurate and timely, with the spokesperson being knowledgeable as to the overall response and having access to experts to respond to specialized queries. Poor media relations can disrupt the management of the event and lead to unfavourable and sometimes unjustified comments on the overall handling of the episode. Any plan must include adequate mock disaster drills. These enable the responders to and managers of an incident to learn each other’s personal and organizational strengths and weaknesses. Both table-top and physical exercises are required.

Although the literature dealing with chemical spills is extensive, only a minor part describes the ecological consequences. Most concern case studies. The descriptions of actual spills have focused on human health and safety problems, with ecological consequences described only in general terms. The chemicals enter the environment predominantly through the liquid phase. In only a few cases did accidents having ecological consequences also affect humans immediately, and the effects on the environment were not caused by identical chemicals or by identical release routes.

Controls to prevent risk to human health and life from the transport of hazardous materials include quantities carried, direction and control of means of transport, routing, as well as authority over interchange and concentration points and developments near such areas. Further research is required into risk criteria, quantification of risk, and risk equivalence. The United Kingdom Health and Safety Executive has developed a Major Incident Data Service (MHIDAS) as a database of major chemical incidents worldwide. It currently holds information on over 6,000 incidents.

Case Study: Transport of Hazardous Materials

An articulated road tanker carrying about 22,000 litres of toluene was travelling on a main arterial road which runs through Cleveland, UK. A car pulled into the path of the vehicle, and, as the truckdriver took evasive action, the tanker overturned. The manlids of all five compartments sprang open and toluene spilled on the roadway and ignited, resulting in a pool fire. Five cars travelling on the opposite carriageway were involved in the fire but all occupants escaped.

The fire brigade arrived within five minutes of being called. Burning liquid had entered the drains, and drain fires were evident approximately 400m from the main incident. The County Emergency Plan was put into action, with social services and public transport put on alert in case evacuation was needed. Initial action by the fire brigade concentrated on extinguishing car fires and searching for occupants. The next task was identifying an adequate water supply. A member of the chemical company’s safety team arrived to coordinate with the police and fire commanders. Also in attendance were staff from the ambulance service and the environmental health and water boards. Following consultation it was decided to permit the leaking toluene to burn rather than extinguish the fire and have the chemical emitting vapours. Police put out warnings over a four-hour period utilizing national and local radio, advising people to stay indoors and close their windows. The road was closed for eight hours. When the toluene fell below the level of the manlids, the fire was extinguished and the remaining toluene removed from the tanker. The incident was concluded approximately 13 hours after the accident.

Potential harm to humans existed from thermal radiation; to the environment, from air, soil and water pollution; and to the economy, from traffic disruption. The company plan which existed for such a transportation incident was activated within 15 minutes, with five persons in attendance. A county offsite plan existed and was instigated with a control centre coming into being involving police and the fire brigade. Concentration measurement but not dispersion prediction was performed. The fire brigade response involved over 50 persons and ten appliances, whose major actions were fire-fighting, washing down and spillage retention. Over 40 police officers were committed in traffic direction, warning the public, security and press control. The health service response encompassed two ambulances and two onsite medical staff. Local government reaction involved environmental health, transport and social services. The public were informed of the incident by loudspeakers, radio and word of mouth. The information focused on what to do, especially on sheltering indoors.

The outcome to humans was two admissions to a single hospital, a member of the public and a company employee, both injured in the crash. There was noticeable air pollution but only slight soil and water contamination. From an economic perspective there was major damage to the road and extensive traffic delays, but no loss of crops, livestock or production. Lessons learned included the value of rapid retrieval of information from the Chemdata system and the presence of a company technical expert enabling correct immediate action to be taken. The importance of joint press statements from responders was highlighted. Consideration needs to be given to the environmental impact of fire-fighting. If the fire had been fought in the initial stages, a considerable amount of contaminated liquid (firewater and toluene) potentially could have entered the drains, water supplies and soil.




Friday, 25 February 2011 16:57

Avalanches: Hazards and Protective Measures

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Ever since people began to settle in mountainous regions, they have been exposed to the specific hazards associated with mountain living. Among the most treacherous hazards are avalanches and landslides, which have taken their toll of victims even up to the present day.

When the mountains are covered with several feet of snow in winter, under certain conditions, a mass of snow lying like a thick blanket on the steep slopes or mountain tops can become detached from the ground underneath and slide downhill under its own weight. This can result in huge quantities of snow hurtling down the most direct route and settling into the valleys below. The kinetic energy thus released produces dangerous avalanches, which sweep away, crush or bury everything in their path.

Avalanches can be divided into two categories according to the type and condition of the snow involved: dry snow or “dust” avalanches, and wet snow or “ground” avalanches. The former are dangerous because of the shock waves they set off, and the latter because of their sheer volume, due to the added moisture in the wet snow, flattening everything as the avalanche rolls downhill, often at high speeds, and sometimes carrying away sections of the subsoil.

Particularly dangerous situations can arise when the snow on large, exposed slopes on the windward side of the mountain is compacted by the wind. Then it often forms a cover, held together only on the surface, like a curtain suspended from above, and resting on a base that can produce the effect of ball-bearings. If a “cut” is made in such a cover (e.g., if a skier leaves a track across the slope), or if for any reason, this very thin cover is torn apart (e.g., by its own weight), then the whole expanse of snow can slide downhill like a board, usually developing into an avalanche as it progresses.

In the interior of the avalanche, enormous pressure can build up, which can carry off, smash or crush locomotives or entire buildings as though they were toys. That human beings have very little chance of surviving in such an inferno is obvious, bearing in mind that anyone who is not crushed to death is likely to die from suffocation or exposure. It is not surprising, therefore, in cases where people have been buried in avalanches, that, even if they are found immediately, about 20% of them are already dead.

The topography and vegetation of the area will cause the masses of snow to follow set routes as they come down to the valley. People living in the region know this from observation and tradition, and therefore keep away from these danger zones in the winter.

In earlier times, the only way to escape such dangers was to avoid exposing oneself to them. Farmhouses and settlements were built in places where topographical conditions were such that avalanches could not occur, or which years of experience had shown to be far removed from any known avalanche paths. People even avoided the mountain areas altogether during the danger period.

Forests on the upper slopes also afford considerable protection against such natural disasters, as they support the masses of snow in the threatened areas and can curb, halt or divert avalanches that have already started, provided they have not built up too much momentum.

Nevertheless, the history of mountainous countries is punctuated by repeated disasters caused by avalanches, which have taken, and still take, a heavy toll of life and property. On the one hand, the speed and momentum of the avalanche is often underestimated. On the other hand, avalanches will sometimes follow paths which, on the basis of centuries of experience, have not previously been considered to be avalanche paths. Certain unfavourable weather conditions, in conjunction with a particular quality of snow and the state of the ground underneath (e.g., damaged vegetation or erosion or loosening of the soil as a result of heavy rains) produce circumstances that can lead to one of those “disasters of the century”.

Whether an area is particularly exposed to the threat of an avalanche depends not only on prevailing weather conditions, but to an even greater extent on the stability of the snow cover, and on whether the area in question is situated in one of the usual avalanche paths or outlets. There are special maps showing areas where avalanches are known to have occurred or are likely to occur as a result of topographical features, especially the paths and outlets of frequently occurring avalanches. Building is prohibited in high-risk areas.

However, these precautionary measures are no longer sufficient today, as, despite the prohibition of building in particular areas, and all the information available on the dangers, increasing numbers of people are still attracted to picturesque mountain regions, causing more and more building even in areas known to be dangerous. In addition to this disregard or circumvention of building bans, one of the manifestations of the modern leisure society is that thousands of tourists go to the mountains for sport and recreation in winter, and to the very areas where avalanches are virtually pre-programmed. The ideal ski slope is steep, free of obstacles and should have a sufficiently thick carpet of snow—ideal conditions for the skier, but also for the snow to sweep down into the valley.

If, however, risks cannot be avoided or are to a certain extent consciously accepted as an unwelcome “side-effect” of the enjoyment gained from the sport, then it becomes necessary to develop ways and means of coping with these dangers in another manner.

To improve the chances of survival for people buried in avalanches, it is essential to provide well-organized rescue services, emergency telephones near the localities at risk and up-to-date information for the authorities and for tourists on the prevailing situation in dangerous areas. Early warning systems and excellent organization of rescue services with the best possible equipment can considerably increase chances of survival for people buried in avalanches, as well as reducing the extent of the damage.

Protective Measures

Various methods of protection against avalanches have been developed and tested all over the world, such as cross-frontier warning services, barriers and even the artificial triggering-off of avalanches by blasting or firing guns over the snow fields.

The stability of the snow cover is basically determined by the ratio of mechanical stress to density. This stability can vary considerably according to the type of stress (e.g., pressure, tension, shearing strain) within a geographical region (e.g., that part of the snow field where an avalanche might start). Contours, sunshine, winds, temperature and local disturbances in the structure of the snow cover—resulting from rocks, skiers, snowploughs or other vehicles—can also affect stability. Stability can therefore be reduced by deliberate local intervention such as blasting, or increased by the installation of additional supports or barriers. These measures, which can be of a permanent or temporary nature, are the two main methods used for protection against avalanches.

Permanent measures include effective and durable structures, support barriers in the areas where the avalanche might start, diversionary or braking barriers on the avalanche path, and blocking barriers in the avalanche outlet area. The object of temporary protective measures is to secure and stabilize the areas where an avalanche might start by deliberately triggering off smaller, limited avalanches to remove the dangerous quantities of snow in sections.

Support barriers artificially increase the stability of the snow cover in potential avalanche areas. Drift barriers, which prevent additional snow from being carried by the wind to the avalanche area, can reinforce the effect of support barriers. Diversionary and braking barriers on the avalanche path and blocking barriers in the avalanche outlet area can divert or slow down the descending mass of snow and shorten the outflow distance in front of the area to be protected. Support barriers are structures fixed in the ground, more or less perpendicular to the slope, which put up sufficient resistance to the descending mass of snow. They must form supports reaching up to the surface of the snow. Support barriers are usually arranged in several rows and must cover all parts of the terrain from which avalanches could, under various possible weather conditions, threaten the locality to be protected. Years of observation and snow measurement in the area are required in order to establish correct positioning, structure and dimensions.

The barriers must have a certain permeability to let minor avalanches and surface landslides flow through a number of barrier rows without getting larger or causing damage. If permeability is not sufficient, there is the danger that the snow will pile up behind the barriers, and subsequent avalanches will slide over them unimpeded, carrying further masses of snow with them.

Temporary measures, unlike the barriers, can also make it possible to reduce the danger for a certain length of time. These measures are based on the idea of setting off avalanches by artificial means. The threatening masses of snow are removed from the potential avalanche area by a number of small avalanches deliberately triggered off under supervision at selected, predetermined times. This considerably increases the stability of the snow cover remaining on the avalanche site, by at least reducing the risk of further and more dangerous avalanches for a limited period of time when the threat of avalanches is acute.

However, the size of these artificially produced avalanches cannot be determined in advance with any great degree of accuracy. Therefore, in order to keep the risk of accidents as low as possible, while these temporary measures are being carried out, the entire area to be affected by the artificial avalanche, from its starting point to where it finally comes to a halt, must be evacuated, closed off and checked beforehand.

The possible applications of the two methods of reducing hazards are fundamentally different. In general, it is better to use permanent methods to protect areas that are impossible or difficult to evacuate or close off, or where settlements or forests could be endangered even by controlled avalanches. On the other hand, roads, ski runs and ski slopes, which are easy to close off for short periods, are typical examples of areas in which temporary protective measures can be applied.

The various methods of artificially setting off avalanches involve a number of operations which also entail certain risks and, above all, require additional protective measures for persons assigned to carry out this work. The essential thing is to cause initial breaks by setting off artificial tremors (blasts). These will sufficiently reduce the stability of the snow cover to produce a snow-slip.

Blasting is especially suitable for releasing avalanches on steep slopes. It is usually possible to detach small sections of snow at intervals and thus avoid major avalanches, which take a long distance to run their course and can be extremely destructive. However, it is essential that the blasting operations be carried out at any time of day and in all types of weather, and this is not always possible. Methods of artificially producing avalanches by blasting differ considerably according to the means used to reach the area where the blasting is to take place.

Areas where avalanches are likely to start can be bombarded with grenades or rockets from safe positions, but this is successful (i.e., produces the avalanche) in only 20 to 30% of cases, as it is virtually impossible to determine and to hit the most effective target point with any accuracy from a distance, and also because the snow cover absorbs the shock of the explosion. Besides, shells may fail to go off.

Blasting with commercial explosives directly into the area where avalanches are likely to start is generally more successful. The most successful methods are those whereby the explosive is carried on stakes or cables over the part of the snow field where the avalanche is to start, and detonated at a height of 1.5 to 3 m above the snow cover.

Apart from the shelling of the slopes, three different methods have been developed for getting the explosive for the artificial production of avalanches to the actual location where the avalanche is to start:

  • dynamite cableways
  • blasting by hand
  • throwing or lowering the explosive charge from helicopters.


The cableway is the surest and at the same time the safest method. With the help of a special small cableway, the dynamite cableway, the explosive charge is carried on a winding rope over the blasting location in the area of snow cover in which the avalanche is to start. With proper rope control and with the help of signals and markings, it is possible to steer accurately towards what are known from experience to be the most effective locations, and to get the charge to explode directly above them. The best results with respect to triggering off avalanches are achieved when the charge is detonated at the correct height above the snow cover. Since the cableway runs at a greater height above the ground, this requires the use of lowering devices. The explosive charge hangs from a string wound around the lowering device. The charge is lowered to the correct height above the site selected for the explosion with the help of a motor which unwinds the string. The use of dynamite cableways makes it possible to carry out the blasting from a safe position, even with poor visibility, by day or night.

Because of the good results obtained and the relatively low production costs, this method of setting off avalanches is used extensively in the entire Alpine region, a licence being required to operate dynamite cableways in most Alpine countries. In 1988, an intensive exchange of experience in this field took place between manufacturers, users and government representatives from the Austrian, Bavarian and Swiss Alpine areas. The information gained from this exchange of experience has been summarized in leaflets and legally binding regulations. These documents basically contain the technical safety standards for equipment and installations, and instructions on carrying out these operations safely. When preparing the explosive charge and operating the equipment, the blasting crew must be able to move as freely as possible around the various cableway controls and appliances. There must be safe and easily accessible footpaths to enable the crew to leave the site quickly in case of emergency. There must be safe access routes up to cableway supports and stations. In order to avoid failure to explode, two fuses and two detonators must be used for every charge.

In the case of blasting by hand, a second method for artificially producing avalanches, which was frequently done in earlier times, the dynamiter has to climb to the part of the snow cover where the avalanche is to be set off. The explosive charge can be placed on stakes planted in the snow, but more generally thrown down the slope towards a target point known from experience to be particularly effective. It is usually imperative for helpers to secure the dynamiter with a rope throughout the entire operation. Nonetheless, however carefully the blasting team proceeds, the danger of falling or of encountering avalanches on the way to the blasting site cannot be eliminated, as these activities often involve long ascents, sometimes under unfavourable weather conditions. Because of these hazards, this method, which is also subject to safety regulations, is rarely used today.

Using helicopters, a third method, has been practised for many years in the Alpine and other regions for operations to set off avalanches. In view of the dangerous risks for persons on board, this procedure is used in most Alpine and other mountainous countries only when it is urgently needed to avert an acute danger, when other procedures cannot be used or would involve even greater risk. In view of the special legal situation arising from the use of aircraft for such purposes and the risks involved, specific guidelines on setting off avalanches from helicopters have been drawn up in the Alpine countries, with the collaboration of the aviation authorities, the institutions and authorities responsible for occupational health and safety, and experts in the field. These guidelines deal not only with matters concerning the laws and regulations on explosives and safety provisions, but also are concerned with the physical and technical qualifications required of persons entrusted with such operations.

Avalanches are set off from helicopters either by lowering the charge on a rope and detonating it above the snow cover or by dropping a charge with its fuse already lit. The helicopters used must be specially adapted and licensed for such operations. With regard to safely carrying out the operations on board, there must be a strict division of responsibilities between the pilot and the blasting technician. The charge must be correctly prepared and the length of fuse selected according to whether it is to be lowered or dropped. In the interests of safety, two detonators and two fuses must be used, as in the case of the other methods. As a rule, the individual charges contain between 5 and 10 kg of explosive. Several charges can be lowered or dropped one after the other during one operational flight. The detonations must be visually observed in order to check that none has failed to go off.

All these blasting processes require the use of special explosives, effective in cold conditions and not sensitive to mechanical influences. Persons assigned to carry out these operations must be specially qualified and have the relevant experience.

Temporary and permanent protective measures against avalanches were originally designed for distinctly different areas of application. The costly permanent barriers were mainly constructed to protect villages and buildings especially against major avalanches. The temporary protective measures were originally limited almost exclusively to protecting roads, ski resorts and amenities which could be easily closed off. Nowadays, the tendency is to apply a combination of the two methods. To work out the most effective safety programme for a given area, it is necessary to analyse the prevailing situation in detail in order to determine the method that will provide the best possible protection.



Friday, 25 February 2011 16:53

Weather-Related Problems

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It was long accepted that weather-related problems were a natural phenomenon and death and injury from such events were inevitable (see table 1). It is only in the past two decades that we have begun to look at factors contributing to weather-related death and injury as a means of prevention. Because of the short duration of study in this area, the data are limited, particularly as they pertain to the number and circumstances of weather-related deaths and injuries among workers. The following is an overview of the findings thus far.

Table 1. Weather-related occupational risks

Weather event

Type of worker

Biochemical agents

Traumatic injuries



Vehicle accidents

Mental stress


emergency personnel






















emergency personnel













Light forest fires








*degree of risk.

Floods, Tidal Waves

Definitions, sources and occurrences

Flooding results from a variety of causes. Within a given climatic region, tremendous variations of flooding occur because of fluctuations within the hydrological cycle and other natural and synthetic conditions (Chagnon, Schict and Semorin 1983). The US National Weather Service has defined flash floods as those that follow within a few hours of heavy or excessive rain, a dam or levee failure or a sudden release of water impounded by an ice or log jam. Although most flash floods are the result of intense local thunderstorm activity, some occur in conjunction with tropical cyclones. Forerunners to flash floods usually involve atmospheric conditions that influence the continuation and intensity of rainfall. Other factors that contribute to flash floods include steepness of slopes (mountain terrain), absence of vegetation, lack of infiltration capability of the soil, floating debris and ice jams, rapid snow melt, dam and levee failures, rupture of a glacial lake, and volcanic disturbances (Marrero 1979). River flooding can be influenced by factors which cause flash flooding, but more insidious flooding may be caused by stream channel characteristics, character of soil and subsoil, and degree of synthetic modification along its path (Chagnon, Schict and Semorin 1983; Marrero 1979). Coastal flooding can result from storm surge, which is the result of a tropical storm or cyclone, or ocean waters driven inland by wind-generated storms. The most devastating type of coastal flooding is the tsunami, or tidal wave, which is generated by submarine earthquakes or certain volcanic eruptions. Most recorded tsunamis have occurred in the Pacific and Pacific coast regions. The islands of Hawaii are particularly prone to tsunami damage because of their location in the mid-Pacific (Chagnon, Schict and Semorin 1983; Whitlow 1979).

Factors influencing morbidity and mortality

It has been estimated that floods account for 40% of all the world’s disasters, and they do the greatest amount of damage. The most lethal flood in recorded history struck the Yellow River in 1887, when the river overflowed 70-foot-high levees, destroying 11 cities and 300 villages. An estimated 900,000 people were killed. Several hundred thousand may have died in China’s Shantung Province in 1969 when storm surges pushed flood tides up the Yellow River Valley. A sudden flood in January 1967 in Rio de Janeiro killed 1,500 people. In 1974 heavy rains flooded Bangladesh and caused 2,500 deaths. In 1963 heavy rains caused an enormous landslide that fell into the lake behind the Vaiont Dam in Northern Italy, sending 100 million tons of water over the dam and causing 2,075 deaths (Frazier 1979). In 1985 an estimated 7 to 15 inches of rain fell in a ten-hour period in Puerto Rico, killing 180 people (French and Holt 1989).

River flooding has been curtailed by engineering controls and increased forestation of watersheds (Frazier 1979). However, flash floods have increased in recent years, and are the number one weather-related killer in the United States. The increased toll from flash floods is attributed to increased and more urbanized populations on sites that are ready targets for flash floods (Mogil, Monro and Groper 1978). Fast-flowing water accompanied by such debris as boulders and fallen trees account for the primary flood-related morbidity and mortality. In the United States studies have shown a high proportion of car-related drownings in floods, due to people driving into low-lying areas or across a flooded bridge. Their cars may stall in high water or be blocked by debris, trapping them in their cars while high levels of fast-flowing water descend upon them (French et al. 1983). Follow-up studies of flood victims show a consistent pattern of psychological problems up to five years after the flood (Melick 1976; Logue 1972). Other studies have shown a significant increase in the incidence of hypertension, cardiovascular disease, lymphoma and leukaemia in flood victims, which some investigators feel are stress related (Logue and Hansen 1980; Janerich et al. 1981; Greene 1954). There is a potential for increased exposure to biological and chemical agents when floods cause disruption of water purification and sewage-disposal systems, rupture of underground storage tanks, overflowing of toxic waste sites, enhancement of vector-breeding conditions and dislodgement of chemicals stored above ground (French and Holt 1989).

Although, in general, workers are exposed to the same flood-related risks as the general population, some occupational groups are at higher risk. Clean-up workers are at high risk of exposure to biological and chemical agents following floods. Underground workers, particularly those in confined places, may be trapped during flash floods. Truck drivers and other transportation workers are at high risk from vehicle-related flood mortality. As in other weather-related disasters, fire-fighters, police and emergency medical personnel are also at high risk.

Prevention and control measures and research needs

Prevention of death and injury from floods can be accomplished by identifying flood-prone areas, making the public aware of these areas and advising them on appropriate prevention actions, conducting dam inspections and issuing dam safety certification, identifying meteorological conditions that will contribute to heavy precipitation and runoff, and issuing early warnings of floods for a specific geographic area within a specific time frame. Morbidity and mortality from secondary exposures can be prevented by assuring that water and food supplies are safe to consume and are not contaminated with biological and chemical agents, and by instituting safe human waste disposal practices. Soil surrounding toxic waste sites and storage lagoons should be inspected to determine if there has been contamination from overflowing storage areas (French and Holt 1989). Although mass vaccination programmes are counterproductive, clean-up and sanitation workers should be properly immunized and instructed in appropriate hygienic practices.

There is a need to improve technology so that early warnings for flash floods can be more specific in terms of time and place. Conditions should be assessed to determine whether evacuation should be by car or on foot. Following a flood a cohort of workers engaged in flood-related activities should be studied to assess the risk of adverse physical and mental health effects.

Hurricanes, Cyclones, Tropical Storms

Definitions, sources and occurrences

A hurricane is defined as a rotating wind system that whirls counterclockwise in the northern hemisphere, forms over tropical water, and has sustained wind speeds of at least 74 miles per hour (118.4 km/h). This whirling accumulation of energy is formed when circumstances involving heat and pressure nourish and nudge the winds over a large area of ocean to wrap themselves around an atmospheric low-pressure zone. A typhoon is comparable to a hurricane except that it forms over Pacific waters. Tropical cyclone is the term for all wind circulations rotating around an atmospheric low over tropical waters. A tropical storm is defined as a cyclone with winds from 39 to 73 mph (62.4 to 117.8 km/h), and a tropical depression is a cyclone with winds less than 39 mph (62.4 km/h).

It is presently thought that many tropical cyclones originate over Africa, in the region just south of the Sahara. They start as an instability in a narrow east to west jet stream that forms in that area between June and December, as a result of the great temperature contrast between the hot desert and the cooler, more humid region to the south. Studies show that the disturbances generated over Africa have long lifetimes, and many of them cross the Atlantic (Herbert and Taylor 1979). In the 20th century an average of ten tropical cyclones each year whirl out across the Atlantic; six of these become hurricanes. As the hurricane (or typhoon) reaches its peak intensity, air currents formed by the Bermuda or Pacific high-pressure areas shift its course northward. Here the ocean waters are cooler. There is less evaporation, less water vapour and energy to feed the storm. If the storm hits land, the supply of water vapour is cut off entirely. As the hurricane or typhoon continues to move north, its winds begin to diminish. Topographical features such as mountains may also contribute to the breakup of the storm. The geographic areas at greatest risk for hurricanes are the Caribbean, Mexico, and the eastern seaboard and Gulf Coast states of the United States. A typical Pacific typhoon forms in the warm tropical waters east of the Philippines. It may move westward and strike the Chinese mainland or veer to the north and approach Japan. The storm’s path is determined as it moves around the western edge of the Pacific high-pressure system (Understanding Science and Nature: Weather and Climate 1992).

The destructive power of a hurricane (typhoon) is determined by the way storm surge, wind and other factors are combined. Forecasters have developed a five-category disaster potential scale to make the predicted hazards of approaching hurricanes clearer. Category 1 is a minimum hurricane, category 5 a maximum hurricane. In the period 1900-1982, 136 hurricanes struck the United States directly; 55 of these were of at least category 3 intensity. Florida felt the effects of both the highest number and the most intense of these storms, with Texas, Louisiana and North Carolina following in descending order (Herbert and Taylor 1979).

Factors influencing morbidity and mortality

Although winds do much damage to property, the wind is not the biggest killer in a hurricane. Most victims die from drowning. The flooding that accompanies a hurricane may come from the intense rain or from the storm surges. The US National Weather Service estimates that storm surges cause nine of every ten hurricane-associated fatalities (Herbert and Taylor 1979). The occupational groups most heavily impacted by hurricanes (typhoons) are those related to boating and shipping (which would be affected by the unusually rough seas and high winds); utility line workers who are called into service to repair damaged lines, often while the storm is still raging; fire-fighters and police officers, who are involved in evacuations and protecting the property of evacuees; and emergency medical personnel. Other occupational groups are discussed in the section on floods.

Prevention and control, research needs

The incidence of deaths and injuries associated with hurricanes (typhoons) has dropped dramatically in the past twenty years in those areas where sophisticated advanced warning systems have been put into effect. The principal steps to follow for preventing death and injury are: to identify meteorological precursors of these storms and track their course and potential development into hurricanes, to issue early warnings to provide for timely evacuation when indicated, to enforce stringent land use management practices and building codes in high-risk areas, and to develop emergency contingency plans in high-risk areas to provide for an orderly evacuation and adequate shelter capacity for evacuees.

Because the meteorological factors contributing to hurricanes have been well studied, a good deal of information is available. More information is needed on the variable pattern of incidence and intensity of hurricanes over time. The effectiveness of existing contingency plans should be assessed following each hurricane, and it should be determined if buildings protected from wind speed are also protected from storm surges.


Formation and patterns of occurrence

Tornadoes are formed when layers of air of different temperature, density and windflow combine to produce powerful updrafts forming huge cumulonimbus clouds which are transformed into rotating tight spirals when strong cross winds blow through the cumulonimbus cloud. This vortex draws even more warm air into the cloud, which makes the air spin faster until a funnel cloud packing explosive force drops out of the cloud (Understanding Science and Nature: Weather and Climate 1992). The average tornado has a track approximately 2 miles long and 50 yards wide, affecting about 0.06 square miles and with wind speeds as high as 300 mph. Tornadoes occur in those areas where warm and cold fronts are apt to collide, causing unstable conditions. Although the probability that a tornado will strike any specific location is extremely small (probability 0.0363), some areas, such as the Midwest states in the United States, are particularly vulnerable.

Factors influencing morbidity and mortality

Studies have shown that people in mobile homes and in lightweight cars when tornadoes strike are at particularly high risk. In the Wichita Falls, Texas, Tornado Study, occupants of mobile homes were 40 times more likely to sustain a serious or fatal injury than those in permanent dwellings, and occupants of automobiles were at approximately five times greater risk (Glass, Craven and Bregman 1980). The leading cause of death are craniocerebral trauma, followed by crushing wounds of the head and trunk. Fractures are the most frequent form of non-fatal injury (Mandlebaum, Nahrwold and Boyer 1966; High et al. 1956). Those workers who spend a major part of their working time in lightweight automobiles, or whose offices are in mobile homes, would be at high risk. Other factors relating to clean-up operators discussed in the flood section would apply here.

Prevention and control

The issuing of appropriate warnings, and the need for the population to take appropriate action on the basis of those warnings, are the most important factors in preventing tornado-related death and injury. In the United States, the National Weather Service has acquired sophisticated instrumentation, such as Doppler radar, which permits them to identify conditions conducive to the formation of a tornado and to issue warnings. A tornado watch means that conditions are conducive to tornado formation in a given area, and a tornado warning means that a tornado has been sighted in a given area and those residing in that area should take appropriate shelter, which entails going to the basement if one exists, going to an inside room or closet, or if outside, going to a ditch or gully.

Research is needed to assess whether warnings are effectively disseminated and the extent to which people heed those warnings. It should also be determined whether the prescribed shelter areas really provide adequate protection from death and injury. Information should be gathered on the number of deaths and injuries to tornado workers.

Lightning and Forest Fires

Definitions, sources and occurrences

When a cumulonimbus cloud grows into a thunderstorm, different sections of the cloud accumulate positive and negative electric charges. When the charges have built up, the negative charges flow toward the positive charges in a lightning flash that travels within the cloud or between the cloud and the ground. Most lightning travels from cloud to cloud, but 20% travels from cloud to ground.

A lightning flash between a cloud and the ground can be either positive or negative. Positive lightning is more powerful and is more likely to start forest fires. A lightning strike will not start a fire unless it meets easily ignitable fuel like pine needles, grass and pitch. If the fire hits decaying wood, it can burn unnoticed for a long period of time. Lightning ignites fires more often when it touches the ground and the rain within the thunder cloud evaporates before it reaches the ground. This is called dry lightning (Fuller 1991). It is estimated that in dry, rural areas such as Australia and the western United States, 60% of forest fires are caused by lightning.

Factors causing morbidity and mortality

Most of the fire-fighters who die in a fire die in truck or helicopter accidents or from being hit by falling snags, rather than from the fire itself. However, fighting fire can cause heat stroke, heat exhaustion and dehydration. Heat stroke, caused by the body temperature rising to over 39.4°C, can cause death or brain damage. Carbon monoxide is also a threat, particularly in smouldering fires. In one test, researchers found that the blood of 62 of 293 fire-fighters had carboxyhaemoglobin levels above the maximum allowable level of 5% after eight hours on the fire line (Fuller 1991).

Prevention, control and research needs

Because of the danger and the mental and physical stress associated with fire-fighting, crews should not work for more than 21 days, and must have one day off for every 7 days worked within that time. In addition to wearing appropriate protective gear, fire-fighters must learn safety factors such as planning safety routes, keeping in communication, watching for hazards, keeping track of the weather, making sure of directions and acting before a situation becomes critical. The standard fire-fighting orders emphasize knowing what the fire is doing, posting lookouts and giving clear, understandable instructions (Fuller 1991).

Factors relating to prevention of lightning forest fires include limiting fuels such as dry underbrush or fire-susceptible trees like eucalyptus, preventing building in fire-prone areas and early detection of forest fires. Early detection has been enhanced by the development of new technology such as an infrared system which is mounted on helicopters to check whether lightning strikes reported from aerial lookout and detection systems have actually started fires and to map hot spots for ground crews and helicopter drops (Fuller 1991).

More information is needed on the number and circumstances of deaths and injuries associated with lightning-related forest fires.



Friday, 25 February 2011 16:50

Post-Disaster Activities

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Industrial accidents may affect groups of workers exposed in the workplace as well as the population living around the plant where the accident takes place. When pollution caused by accident occurs, the size of the affected population is likely to be orders of magnitude greater than the workforce, posing complex logistic problems. The present article focuses on these problems, and applies to agricultural accidents as well.

Reasons for quantifying health effects of an accident include:

  • the need to ensure that all exposed persons have received medical attention (regardless of whether or not treatment was actually needed by each of them). Medical attention may consist of the search for and alleviation of clinically recognizable adverse consequences (if any) as well as implementation of means for preventing possible delayed effects and complications. This is obligatory when an accident occurs within a plant; then all the people working there will be known and full follow-up is feasible
  • the need to identify persons deserving of compensation as victims of the accident. This implies that individuals must be characterized as to the severity of disease and the credibility of a causal association between their condition and the disaster.
  • the acquisition of new knowledge on disease pathogenesis in humans
  • the scientific interest of unravelling mechanisms of toxicity in humans, including those aspects which may help in reassessing, for a given exposure, doses considered to be “safe” in humans.


Characterization of Accidents in Relation to Health Consequences

Environmental accidents include a broad range of events occurring under the most diverse of circumstances. They may be first noticed or suspected because of environmental changes or because of the occurrence of disease. In both situations, the evidence (or suggestion) that “something may have gone wrong” may appear suddenly (e.g., the fire in the Sandoz storehouse in Schweizerhalle, Switzerland, in 1986; the epidemic of the condition later labelled as “toxic oil syndrome” (TOS) in Spain in 1981) or insidiously (e.g., excesses of mesothelioma following environmental—non-occupational—exposure to asbestos in Wittenoom, Australia). In all circumstances, at any given moment, uncertainty and ignorance surround both key questions: “Which health consequences have occurred so far?” and “What can be predicted to occur?”

In assessing the impact of an accident on human health, three types of determinants may interact:

  1. the agent(s) being released, its hazardous properties and the risk created by its release
  2. the individual disaster experience
  3. the response measures (Bertazzi 1991).


The nature and quantity of the release might be difficult to determine, as well as the ability of the material to enter into the different compartments of the human environment, such as the food chain and water supply. Twenty years after the accident, the amount of 2,3,7,8-TCDD released in Seveso on July 10, 1976, remains a matter of dispute. In addition, with the limited knowledge about the toxicity of this compound, in the early days after the accident, any prediction of risk was necessarily questionable.

Individual disaster experience consists of fear, anxiety and distress (Ursano, McCaughey and Fullerton 1994) consequent to the accident, irrespective of the nature of the hazard and of the actual risk. This aspect covers both conscious—not necessarily justified—behavioural changes (e.g., the marked decrease in birth rates in many Western European Countries in 1987, following the Chernobyl accident) and psychogenic conditions (e.g., symptoms of distress in school children and Israeli soldiers following the escape of hydrogen sulphide from a faulty latrine in a school on the West Bank of Jordan in 1981). Attitudes towards the accident are also influenced by subjective factors: in Love Canal, for instance, young parents with little experience of contact with chemicals in the workplace were more prone to evacuate the area than were older people with grown-up children.

Finally, an accident may have an indirect impact on the health of those exposed, either creating additional hazards (e.g., distress associated with evacuation) or, paradoxically, leading to circumstances with some potential for benefit (such as people who stop smoking tobacco as a consequence of contact with the milieu of health workers).

Measuring the Impact of an Accident

There is no doubt that each accident requires an assessment of its measurable or potential consequences on the exposed human population (and animals, domestic and/or wild), and periodic updates of such assessment may be required. In fact, many factors influence the detail, extent and nature of the data which can be collected for such an assessment. The amount of available resources is critical. Accidents of the same severity may be granted different levels of attention in different countries, in relation to the ability to divert resources from other health and social issues. International cooperation may partly mitigate this discrepancy: in fact, it is limited to episodes which are particularly dramatic and/or present unusual scientific interest.

The overall impact of an accident upon health ranges from negligible to severe. Severity depends on the nature of the conditions which are produced by the accident (which may include death), on the size of the exposed population, and on the proportion that develop disease. Negligible effects are more difficult to demonstrate epidemiologically.

Sources of data to be used for evaluating health consequences of an accident include in the first place current statistics which exist already (attention to their potential use should always precede any suggestion of creating new population databases). Additional information can be derived from analytical, hypothesis-centred epidemiological studies for the purpose of which current statistics may or may not be useful. If in an occupational setting no health surveillance of the workers is present, the accident can provide the opportunity to establish a surveillance system which will eventually help to protect workers from other potential health hazards.

For the purposes of clinical surveillance (short or long term) and/or provision of compensation, the exhaustive enumeration of the exposed persons is a sine qua non. This is relatively simple in the case of intra-factory accidents. When the affected population can be defined by the place where they live, the list of residents in administrative municipalities (or smaller units, when available) provides a reasonable approach. The construction of a roster may be more problematic under other circumstances, particularly when the need is for a list of people showing symptoms possibly attributable to the accident. In the TOS episode in Spain, the roster of persons to be included in the long-term clinical follow-up was derived from the list of the 20,000 persons applying for financial compensation, subsequently corrected through a revision of the clinical records. Given the publicity of the episode, it is believed that this roster is reasonably complete.

A second requirement is that activities aiming at the measure of the impact of an accident be rational, clear-cut and easy to explain to the affected population. Latency may range between days and years. If some conditions are met, the nature of disease and probability of occurrence can be hypothesized a priori with a precision sufficient for the adequate design of a clinical surveillance programme and ad hoc studies aiming at one or more of the goals mentioned at the beginning of this article. These conditions include the rapid identification of the agent released by the accident, availability of adequate knowledge on its short- and long-term hazardous properties, a quantification of the release, and some information on inter-individual variation in susceptibility to the agent’s effects. In fact, these conditions are rarely met; a consequence of the underlying uncertainty and ignorance is that the pressure of public opinion and the media for prevention or definite medical intervention of doubtful usefulness is more difficult to resist.

Finally, as soon as possible after the occurrence of an accident has been established, a multidisciplinary team (including clinicians, chemists, industrial hygienists, epidemiologists, human and experimental toxicologists) needs to be established, which will be responsible to the political authority and the public. In the selection of experts, it must be borne in mind that the range of chemicals and technology which may underlie an accident is very large, so that different types of toxicity involving a variety of biochemical and physiological systems may result.

Measuring the Impact of Accidents through Current Statistics

Current health status indicators (such as mortality, natality, hospital admissions, sickness absence from work and physician visits) have the potential to provide early insight on the consequences of an accident, provided they are stratifiable for the affected region, which often will not be possible because affected areas can be small and not necessarily overlapping with administrative units. Statistical associations between the accident and an excess of early events (occurring within days or weeks) detected through existing health status indicators are likely to be causal, but do not necessarily reflect toxicity (e.g., an excess of physician visits may be caused by fear rather than by actual occurrence of disease). As always, care must be exercised when interpreting any change in health status indicators.

Although not all accidents produce death, mortality is an easily quantifiable endpoint, either by direct count (e.g., Bhopal) or through comparisons between observed and expected number of events (e.g., acute episodes of air pollution in urban areas). Ascertaining that an accident has not been associated with an early excess of mortality may help in assessing the severity of its impact and in addressing attention to non-lethal consequences. Further, the statistics needed in order to calculate expected numbers of deaths are available in most countries and allow for estimates in areas as small as those which are usually affected by an accident. Assessing mortality from specific conditions is more problematic, because of possible bias in certifying causes of death by health officers who are aware of the diseases expected to increase after the accident (diagnostic suspicion bias).

From the foregoing, the interpretation of health status indicators based on existing data sources requires a careful design of ad hoc analyses, including a detailed consideration of possible confounding factors.

On occasions, early after an accident, the question is posed whether the creation of a conventional population-based cancer registry or a registry of malformations is warranted. For these specific conditions, such registries may provide more reliable information than other current statistics (such as mortality or hospital admissions), particularly if newly created registries are run according to internationally acceptable standards. Nevertheless, their implementation requires the diversion of resources. In addition, if a population-based registry of malformations is established de novo after an accident, probably within nine months it will hardly be capable of producing data comparable to those produced by other registries and a series of inferential problems (particularly statistical error of the second type) will ensue. In the end, the decision largely relies on the evidence of carcinogenicity, embryotoxicity or teratogenicity of the hazard(s) which have been released, and on possible alternative uses of the available resources.

Ad Hoc Epidemiological Studies

Even in areas covered by the most accurate systems for monitoring the reasons for patients’ contacts with physicians and/or hospital admissions, indicators from these areas will not provide all the information needed in order to assess the health impact of an accident and the adequacy of the medical response to it. There are specific conditions or markers of individual response which either do not require contact with the medical establishment or do not correspond to the disease classifications conventionally used in current statistics (so that their occurrence would hardly be identifiable). There may be the need for counting as “victims” of the accident, subjects whose conditions are borderline between occurrence and non-occurrence of disease. It is often necessary to investigate (and evaluate the efficacy of) the range of therapeutical protocols which are used. The problems noted here are but a sampling and do not cover all those which might create the need for an ad hoc investigation. In any case, procedures should be established in order to receive additional complaints.

Investigations differ from the provision of care in that they are not directly related to the individual’s interest as a victim of the accident. An ad hoc investigation should be shaped in order to fulfil its purposes—to provide reliable information and/or demonstrate or disprove a hypothesis. Sampling may be reasonable for research purposes (if accepted by the affected population), but not in the provision of medical care. For instance, in the case of a spill of an agent suspected of damaging bone marrow, there are two totally different scenarios in order to respond to each of the two questions: (1) whether the chemical actually induces leukopenia, and (2) whether all exposed persons have been exhaustively screened for leukopenia. In an occupational setting both questions can be pursued. In a population, the decision also will depend on the possibilities for constructive intervention to treat those affected.

In principle, there is a need to have sufficient epidemiological skill locally to contribute to the decision on whether ad hoc studies ought to be carried out, to design them and to supervise their conduct. However, health authorities, media and/or the population may not consider the epidemiologists of the affected area to be neutral; thus, help from outside may be needed, even at a very early stage. The same epidemiologists should contribute to the interpretation of descriptive data based on the currently available statistics, and to the development of causal hypotheses when needed. If epidemiologists are not available locally, collaboration with other institutions (usually, National Institutes of Health, or WHO) is necessary. Episodes which are unravelled because of the lack of epidemiological skill are regrettable.

If an epidemiological study is believed to be necessary, however, attention should be addressed to some preliminary questions: To what use will predictable results be put? Might the desire for a more refined inference resulting from the planned study unduly delay clean-up procedures or other preventive measures? Must the proposed research programme first be fully documented and evaluated by the multidisciplinary scientific team (and perhaps by other epidemiologists)? Will there be adequate provision of details to the persons to be studied to ensure their fully informed, prior and voluntary consent? If a health effect is found, what treatment is available and how will it be delivered?

Finally, conventional prospective cohort mortality studies ought to be implemented when the accident has been severe and there are reasons to fear later consequences. Feasibility of these studies differs between countries. In Europe, they range between the possibility of nominal “flagging” of persons (e.g., rural populations in Shetland, UK, following the Braer Oil Spill) and the need for systematic contacts with the victims’ families in order to identify dying persons (e.g., TOS in Spain).

Screening for Prevalent Conditions

Offering affected people medical attention is a natural reaction to an accident which may have caused them harm. The attempt to identify all those in the exposed population who exhibit conditions related to the accident (and give them medical care if needed) corresponds to the conventional concept of screening. Basic principles, potentialities and limitations common to any screening programme (regardless of the population to which it is addressed, the condition to be identified and the tool used as a diagnostic test) are as valid after an environmental accident as in any other circumstance (Morrison 1985).

Estimating participation and understanding reasons for non-response are just as crucial as measuring sensitivity, specificity and predictive value of the diagnostic test(s), designing a protocol for subsequent diagnostic procedures (when needed) and the administration of therapy (if required). If these principles are neglected, short- and/or long-term screening programmes may produce more harm than benefit. Unnecessary medical examinations or laboratory analyses are a waste of resources and a diversion from providing necessary care to the population as a whole. Procedures for ensuring a high level of compliance have to be carefully planned and evaluated.

Emotional reactions and uncertainties surrounding environmental accidents may further complicate things: physicians tend to loose specificity when diagnosing borderline conditions, and some “victims” may consider themselves entitled to receive medical treatment regardless of whether or not it is actually needed or even useful. In spite of the chaos which often follows an environmental accident, some sine qua non for any screening programme should be borne in mind:

  1. Procedures should be laid down in a written protocol (including second level diagnostic tests and therapy to be provided to those who are found to be affected or sick).
  2. One person should be identified as responsible for the programme.
  3. There should be a preliminary estimate of specificity and sensitivity of the diagnostic test.
  4. There should be coordination between clinicians participating in the programme.
  5. Participation rates should be quantified and reviewed at regular intervals.


Some a priori estimates of efficacy of the whole programme would also help in deciding whether or not the programme is worth implementing (e.g., no programme for anticipating the diagnosis of a lung cancer should be encouraged). Also, a procedure should be established in order to recognize additional complaints.

At any stage, screening procedures may have a value of a different type—to estimate the prevalence of conditions, as a basis for an assessment of the consequences of the accident. A major source of bias in these estimates (which becomes more severe with time) is the representativeness of the exposed persons submitting themselves to the diagnostic procedures. Another problem is the identification of adequate control groups for comparing the prevalence estimates which are obtained. Controls drawn from the population may suffer from as much selection bias as the exposed person’s sample. Nevertheless, under some circumstances, prevalence studies are of the utmost importance (particularly when the natural history of the disease is not known, such as in TOS), and control groups external to the study, including those assembled elsewhere for other purposes, may be used when the problem is important and/or serious.

Use of Biological Materials for Epidemiological Purposes

For descriptive purposes, the collection of biological materials (urine, blood, tissues) from members of the exposed population can provide markers of internal dose, which by definition are more precise than (but do not replace totally) those obtainable through estimates of the concentration of the pollutant in the relevant compartments of the environment and/or through individual questionnaires. Any evaluation ought to take into account possible bias ensuing from the lack of representativeness of those members of the community from whom the biological samples were obtained.

Storing biological samples may prove useful, at a later stage, for the purpose of ad hoc epidemiological studies requiring estimates of internal dose (or early effects) at the individual level. Collecting (and properly preserving) the biological samples early after the accident is crucial, and this practice should be encouraged even in the absence of precise hypotheses for their use. The informed consent process must ensure that the patient understands that his or her biological material is to be stored for use in tests hitherto undefined. Here it is helpful to exclude the use of such specimens from certain tests (e.g., identification of personality disorders) to better protect the patient.


The rationale for medical intervention and epidemiological studies in the population affected by an accident ranges between two extremes—assessing the impact of agents which are proved to be potential hazards and to which the affected population is (or has been) definitely exposed, and exploring the possible effects of agents hypothesized to be potentially hazardous and suspected to be present in the area. Differences between experts (and between people in general) in their perception of the relevance of a problem are inherent to humanity. What matters is that any decision has a recorded rationale and a transparent plan of action, and is supported by the affected community.