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61. Using, Storing and Transporting Chemicals
Chapter Editors: Jeanne Mager Stellman and Debra Osinsky
Case Study: Hazard Communication: The Chemical Safety Data Sheet or the Material Safety Data Sheet (MSDS)
Classification and Labelling Systems for Chemicals
Konstantin K. Sidorov and Igor V. Sanotskiy
Safe Handling and Storage of Chemicals
Compressed Gases: Handling, Storage and Transport
A. Türkdogan and K.R. Mathisen
Methods for Localized Control of Air Contaminants
The GESTIS Chemical Information System: A Case Study
Karlheinz Meffert and Roger Stamm
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The ILO Code of Practice
Much of the information and excerpts in this chapter are taken from the Code of Practice “Safety in the Use of Chemicals at Work” of the International Labour Organization (ILO 1993). The ILO Code provides practical guidelines on the implementation of the provisions of the Chemicals Convention, 1990 (No. 170), and Recommendation, 1990 (No. 177). The object of the Code is to provide guidance to those who may be engaged in the framing of provisions relating to the use of chemicals at work, such as competent authorities, the management in companies where chemicals are supplied or used, and emergency services, which should also offer guidelines to suppliers’, employers’ and workers’ organizations. The Code provides minimum standards and is not intended to discourage competent authorities from adopting higher standards. For more detailed information on individual chemicals and chemical families, see the “Guide to chemicals” in Volume IV of this “Encyclopaedia”.
The objective (section 1.1.1) of the ILO Code of Practice Safety in the Use of Chemicals at Work is to protect workers from the hazards of chemicals, to prevent or reduce the incidence of chemically- induced illnesses and injuries resulting from the use of chemicals at work, and consequently to enhance the protection of the general public and the environment by providing guidelines for:
Section 2 of the ILO Code of Practice outlines the general obligations, responsibilities and duties of the competent authority, the employer and the worker. The section also details the general responsibilities of suppliers and the rights of workers, and it offers guidelines regarding special provisions for the employer’s disclosure of confidential information. The final recommendations address the need for cooperation among employers, workers and their representatives.
General Obligations, Responsibilities and Duties
It is the responsibility of the appropriate governmental agency to follow existing national measures and practices, in consultation with the most representative organizations of employers and workers concerned, in order to assure safety in the use of chemicals at work. National practices and laws should be viewed in the context of international regulations, standards and systems, and with the measures and practices recommended by the ILO Code of Practice and the ILO Convention No. 170 and Recommendation No. 177.
The major focus of such measures which provide for safety of workers are, in particular:
There are various means by which the competent authority may achieve this aim. It may enact national laws and regulations; adopt, approve or recognize existing standards, codes or guidelines; and, where such standards, codes or guidelines do not exist, an authority may encourage their adoption by another authority, which can then be recognized. The governmental agency may also require that employers justify the criteria by which they are working.
According to the Code of Practice (section 2.3.1), it is the responsibility of employers to set out, in writing, their policy and arrangements on safety in the use of chemicals, as part of their general policy and arrangements in the field of occupational safety and health, and the various responsibilities exercised under these arrangements, in accordance with the objectives and principles of the Occupational Safety and Health Convention, 1981 (No. 155), and Recommendation, 1981 (No. 164). This information should be brought to the attention of their workers in a language the latter readily understand.
Workers, in turn, should take care of their own health and safety, and that of other persons who may be affected by their acts or omissions at work, as far as possible and in accordance with their training and with instructions given by their employer (section 2.3.2).
The suppliers of chemicals, whether manufacturers, importers or distributors, should ensure that, in accordance with the guidelines in the relevant paragraphs of the Code and in pursuance of the requirements of Convention No. 170 and Recommendation No. 177:
Operational Control Measures
Certain general principles exist for the operation control of chemicals at work. These are dealt with in Section 6 of the ILO Code of Practice, which prescribes that after reviewing the chemicals being used at work and obtaining information about their hazards and making an assessment of the potential risks involved, employers should take steps to limit exposure of workers to hazardous chemicals (on the basis of the measures outlined in sections 6.4 to 6.9 of the Code), in order to protect workers against hazards from the use of chemicals at work. The measures taken should eliminate or minimize the risks, preferably by substitution of non-hazardous or less hazardous chemicals, or by the choice of better technology. When neither substitution nor engineering control are feasible, other measures, such as safe working systems and practices, personal protective equipment (PPE) and the provision of information and training will further minimize risks and may have to be relied upon for some activities entailing the use of chemicals.
When workers are potentially exposed to chemicals that are hazardous to health, they must be safeguarded against the risk of injury or disease from these chemicals. There should be no exposure which exceeds exposure limits or other exposure criteria for the evaluation and control of the working environment established by the competent authority, or by a body approved or recognized by the competent authority in accordance with national or international standards.
Control measures to provide protection for workers could be any combination of the following:
1. good design and installation practice:
2. plants processes or work systems which minimize generation of, or suppress or contain, hazardous dust, fumes, etc., and which limit the area of contamination in the event of spills and leaks:
3. work systems and practices:
4. personal protection (where the above measures do not suffice, suitable PPE should be provided until such time as the risk is eliminated or minimized to a level that would not pose a threat to health)
5. prohibition of eating, chewing, drinking and smoking in contaminated areas
6. provision of adequate facilities for washing, changing and storage of clothing, including arrangements for laundering contaminated clothing
7. use of signs and notices
8. adequate arrangements in the event of an emergency.
Chemicals known to have carcinogenic, mutagenic or teratogenic health effects should be kept under strict control.
Record keeping is an essential element of the work practices which provide a safe use of chemicals. Records should be kept by employers on measurements of airborne hazardous chemicals. Such records should be clearly marked by date, work area and plant location. The following are some elements of section 12.4 of the ILO Code of Practice, which deals with record-keeping requirements.
Besides the numerical results of measurements, the monitoring data should include, for example:
Records should be kept for a specified period of time determined by the competent authority. Where this has not been prescribed, it is recommended that the employer keep the records, or a suitable summary, for:
Information and Training
Correct instruction and quality training are essential components of a successful hazard communication programme. The ILO Code of Practice Safety in the Use of Chemicals at Work provides general principles of training (sections 10.1 and 10.2). These include the following:
Review of training needs
The extent of the training and instruction received and required should be reviewed and updated simultaneously with the review of the working systems and practices referred to in section 8.2 (Review of work systems).
The review should include the examination of:
Hazard classification and labelling systems are included in legislation covering the safe production, transport, use and disposal of chemicals. These classifications are designed to provide a systematic and comprehensible transfer of health information. Only a small number of significant classification and labelling systems exist at the national, regional and international levels. Classification criteria and their definitions used in these systems vary in the number and degree of hazard scales, specific terminology and test methods, and the methodology for classifying mixtures of chemicals. The establishment of an international structure for harmonizing classification and labelling systems for chemicals would have a beneficial impact on chemical trade, on the exchange of information related to chemicals, on the cost of risk assessment and management of chemicals, and ultimately on the protection of workers, the general public and the environment.
The major basis for classification of chemicals is the assessment of exposure levels and environmental impact (water, air and soil). About half of the international systems contain criteria related to a chemical’s production volume or the effects of pollutant emissions. The most widespread criteria used in chemical classification are values of median lethal dose (LD50) and median lethal concentration (LC50). These values are evaluated in laboratory animals via three main pathways—oral, dermal and inhalation—with a one-time exposure. Values of LD50 and LC50 are evaluated in the same animal species and with the same exposure routes. The Republic of Korea considers LD50 with intravenous and intracutaneous administration as well. In Switzerland and Yugoslavia chemical management legislation requires quantitative criteria for LD50 with oral administration and adds a provision which specifies the possibility of different hazard classifications based on the route of exposure.
In addition, differences in the definitions of comparable hazard levels exist. While the European Community (EC) system utilizes a three-level acute toxicity scale (“very toxic”, “toxic” and “harmful”), the US Occupational Safety and Health Administration (OSHA) Hazard Communication Standard applies two acute toxicity levels (“highly toxic” and “toxic”). Most classifications apply either three categories (United Nations (UN), World Bank, International Maritime Organization (IMO), EC and others) or four (the former Council for Mutual Economic Assistance (CMEA), the Russian Federation, China, Mexico and Yugoslavia).
The following discussion of existing chemical classification and labelling systems focuses primarily on major systems with long application experience. Hazard assessments of pesticides are not covered in general chemical classifications, but are included in the Food and Agricultural Organization/World Health Organization (FAO/WHO) classification as well as in various national legislation (e.g., Bangladesh, Bulgaria, China, the Republic of Korea, Poland, the Russian Federation, Sri Lanka, Venezuela and Zimbabwe).
Transport classifications, which are broadly applied, serve as a basis for regulations governing labelling, packaging and transport of dangerous cargoes. Among these classifications are the UN Recommendations on the Transport of Dangerous Goods (UNRTDG), the International Maritime Dangerous Goods Code developed within the IMO, the classification established by the Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP) for hazardous chemicals carried by ship, as well as national transport classifications. National classifications as a rule comply with UN, IMO and other classifications within international agreements on transportation of dangerous goods by air, rail, road and inland navigation, harmonized with the UN system.
The United Nations Recommendations on the Transport of Dangerous Goods and related transport modal authorities
The UNRTDG create a widely accepted global system which provides a framework for intermodal, international and regional transport regulations. These Recommendations are increasingly being adopted as the basis of national regulations for domestic transport. The UNRTDG is rather general on issues such as notification, identification and hazard communication. The scope has been restricted to the transport of hazardous substances in packaged form; the Recommendations do not apply to exposed hazardous chemicals or to transport in bulk. Originally the objective was to prevent dangerous goods from causing acute injury to workers or the general public, or damage to other goods or the means of transport employed (aircraft, vessel, railcar or road vehicle). The system has now been extended to include asbestos and substances hazardous to the environment.
The UNRTDG focus primarily on hazard communication based on labels which include a combination of graphic symbols, colours, warning words and classification codes. They also provide key data for emergency response teams. The UNRTDG are relevant for the protection of such transport workers as aircrew, mariners and the crews of trains and road vehicles. In many countries the Recommendations have been incorporated in legislation for the protection of dock workers. Parts of the system, such as the Recommendations on explosives, have been adapted to regional and national regulations for the workplace, generally including manufacturing and storage. Other UN organizations concerned with transport have adopted the UNRTDG. The transport classification systems of dangerous goods of Australia, Canada, India, Jordan, Kuwait, Malaysia and United Kingdom basically comply with the major principles of these Recommendations, for example.
The UN classification subdivides chemicals into nine classes of hazards:
The packaging of goods for the purpose of transport, an area specified by the UNRTDG, is not covered as comprehensively by other systems. In support of the Recommendations, organizations such as IMO and International Civil Aviation Organization (ICAO) carry out very significant programmes aimed at training dock workers and airport personnel in the recognition of label information and packaging standards.
The International Maritime Organization
The IMO, with a mandate from the 1960 Conference on Safety of Life at Sea (SOLAS 1960), has developed the International Maritime Dangerous Goods (IMDG) Code. This code supplements the mandatory requirements of chapter VII (Carriage of Dangerous Goods) of SOLAS 74 and those of Annex III of the Maritime Pollution Convention (MARPOL 73/78). The IMDG Code has been developed and kept up to date for more than 30 years in close cooperation with the UN Committee of Experts on Transport of Dangerous Goods (CETG) and has been implemented by 50 IMO members representing 85% of the world’s merchant tonnage.
Harmonization of the IMDG Code with the UNRTDG ensures compatibility with the national and international rules applicable to the transport of dangerous goods by other modes, in so far as these other modal rules are also based on the recommendations of the UNCETG—that is, ICAO Technical Instructions for the Safe Transport of Dangerous Goods by Air and the European Regulations concerning the international carriage of dangerous goods by road (ADR) and by rail (RID).
In 1991 the 17th IMO Assembly adopted a Resolution on the Coordination of Work in Matters Relating to Dangerous Goods and Hazardous Substances, urging, inter alia, UN bodies and governments to coordinate their work in order to ensure the compatibility of any legislation on chemicals, dangerous goods and hazardous substances with established international transport rules.
Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal, 1989
The Convention’s Annexes define 47 categories of wastes, including domestic wastes. Although the hazard classification parallels that of the UNRTDG, a significant difference includes the addition of three categories reflecting more specifically the nature of toxic wastes: chronic toxicity, liberation of toxic gases from interaction of wastes with air or water, and capacity of wastes to yield secondary toxic material after disposal.
National classification systems related to the hazard assessment of pesticides tend to be quite comprehensive because of the wide use of these chemicals and the potential long-term damage to the environment. These systems may identify from two to five hazard classifications. The criteria are based on median lethal doses with different routes of exposure. While Venezuela and Poland recognize only one route of exposure, ingestion, the WHO and various other countries identify both ingestion and skin application.
The criteria for hazard assessment of pesticides in East European countries, Cyprus, Zimbabwe, China and others are based on median lethal doses via inhalation. Bulgaria’s criteria, however, include skin and eye irritation, sensitization, accumulation ability, persistence in environmental media, blastogenic and teratogenic effects, embryotoxicity, acute toxicity and medical treatment. Many classifications of pesticides also include separate criteria based on median lethal doses with different aggregative states. For example, criteria for liquid pesticides are usually more severe than those for solid ones.
WHO Recommended Classification of Pesticides by Hazard
This Classification was first issued in 1975 by the WHO and updated subsequently on a regular basis by the United Nations Environment Programme, the ILO and the WHO (UNEP/ILO/WHO) International Programme on Chemical Safety (IPCS) with input from the Food and Agriculture Organization (FAO). It consists of one hazard category or classification criterion, acute toxicity, divided in four classification levels based on LD50 (rat, oral and dermal values for liquid and solid forms) and ranging from extremely to slightly hazardous. Apart from general considerations, no specific labelling rules are provided. The 1996–97 update contains a guide to classification which includes a list of classified pesticides and comprehensive safety procedures. (See the chapter Minerals and agricultural chemicals.)
FAO International Code of Conduct on the Distribution and Use of Pesticides
The WHO Classification is supported by another document, the FAO International Code of Conduct on the Distribution and Use of Pesticides. Although it is only a recommendation, this classification is applied most widely in developing countries, where it is often included into pertinent national legislation. With regard to labelling, the FAO has published Guidelines on Good Labelling Practice for Pesticides as an addendum to these guidelines.
Regional Systems (EC, EFTA, CMEA)
The EC Council Directive 67/548/EEC has been in application for over two decades and has harmonized the pertinent legislation of 12 countries. It has evolved into a comprehensive system which includes an inventory of existing chemicals, a notification procedure for new chemicals prior to marketing, a set of hazard categories, classification criteria for each category, testing methods, and a hazard communication system including labelling with codified risk and safety phrases and hazard symbols. Chemical preparations (mixtures of chemicals) are regulated by Council Directive 88/379/EEC. The definition of the chemical safety data sheet data elements is practically identical to that defined in ILO Recommendation No. 177, as discussed earlier in this chapter. A set of classification criteria and a label for chemicals that are dangerous to the environment have been produced. The Directives regulate chemicals placed on the market, with the goal of protecting human health and the environment. Fourteen categories are divided into two groups related respectively to physico-chemical properties (explosive, oxidizing, extremely flammable, highly flammable, flammable) and toxicological properties (very toxic, toxic, harmful, corrosive, irritant, carcinogenic, mutagenic, toxic to reproduction, properties dangerous to health or the environment).
The Commission of European Communities (CEC) has an extension to the system specifically addressed to the workplace. In addition, these measures on chemicals should be considered within the overall framework of the protection of the health and safety of workers provided for under Directive 89/391/EEC and its individual Directives.
With the exception of Switzerland, the countries in EFTA follow the EC system to a large degree.
Former Council for Mutual Economic Assistance (CMEA)
This system was elaborated under the umbrella of the Standing Commission for Cooperation in Public Health of the CMEA, which included Poland, Hungary, Bulgaria, the former USSR, Mongolia, Cuba, Romania, Vietnam and Czechoslovakia. China still uses a system which is similar in concept. It consists of two classification categories, namely toxicity and hazard, using a four-level ranking scale. Another element of the CMEA system is its requirement for the preparation of a “toxicological passport of new chemical compounds subjected to introduction in the economy and domestic life”. Criteria for irritancy, allergic effects, sensitization, carcinogenicity, mutagenicity, teratogenicity, antifertility and ecological hazards are defined. However, the scientific basis and the testing methodology related to the classification criteria are significantly different from those used by the other systems.
Provisions for workplace labelling and hazard symbols are also different. The UNRTDG system is used for labelling goods for transport, but there does not seem to be any linkage between the two systems. There are no specific recommendations for chemical safety data sheets. The system is described in detail in the UNEP International Register of Potentially Toxic Chemicals (IRPTC) International Survey of Classification Systems. While the CMEA system contains most of the basic elements of the other classification systems, it differs significantly in the area of hazard assessment methodology, and uses exposure standards as one of the hazard classification criteria.
Examples of National Systems
Australia has enacted legislation for the notification and assessment of industrial chemicals, the Industrial Chemicals Notification and Assessment Act of 1989, with similar legislation enacted in 1992 for agricultural and veterinary chemicals. The Australian system is similar to that of the EC. The differences are mainly due to its utilization of the UNRTDG classification (i.e., the inclusion of the categories compressed gas, radioactive and miscellaneous).
The Workplace Hazardous Materials Information System (WHMIS) was implemented in 1988 by a combination of federal and provincial legislation designed to enforce the transfer of information about hazardous materials from producers, suppliers and importers to employers and in turn to workers. It applies to all industries and workplaces in Canada. WHMIS is a communication system aimed primarily at industrial chemicals and composed of three interrelated hazard communication elements: labels, chemical safety data sheets and worker education programmes. A valuable support to this system was the earlier creation and commercial distribution worldwide of a computerized database, now available on compact disc, containing over 70,000 chemical safety data sheets voluntarily submitted to the Canadian Centre for Occupational Health and Safety by manufacturers and suppliers.
In Japan, the control of chemicals is covered mainly by two laws. First, the Chemical Substances Control Law, as amended in 1987, is aimed at preventing environmental contamination by chemical substances that are low in biodegradability and harmful to human health. The law defines a premarket notification procedure and three “hazard” classes:
Control measures are defined, and a list of existing chemicals is provided.
The second regulation, the Industrial Safety and Health Law, is a parallel system with its own list of “Specified chemical substances” which require labelling. Chemicals are classified into four groups (lead, tetraalkyl lead, organic solvents, specified chemical substances). The classification criteria are (1) possible occurrence of serious health impairment, (2) possible frequent occurrence of health impairment and (3) actual health impairment. Other laws dealing with the control of hazardous chemicals include the Explosives Control Law; the High Pressure Gas Control Law; the Fire Prevention Law; the Food Sanitation Law; and the Drugs, Cosmetics and Medical Instruments Law.
The Hazard Communication Standard (HCS), a mandatory standard promulgated by OSHA, is a workplace-oriented binding regulation which refers to other existing laws. Its goal is to ensure that all chemicals produced or imported are evaluated, and that information related to their hazards is transmitted to employers and to workers through a comprehensive hazard communication programme. The programme includes labelling and other forms of warning, chemical safety data sheets and training. Label and data sheet minimum contents are defined, but the use of hazard symbols is not mandatory.
Under the Toxic Substances Control Act (TSCA), administered by the Environmental Protection Agency (EPA), an inventory listing approximately 70,000 existing chemicals is maintained. The EPA is developing regulations to complement the OSHA HCS which would have similar hazard evaluation and worker communication requirements for the environmental hazards of chemicals on the inventory. Under TSCA, prior to manufacture or import of chemicals which are not on the inventory, the manufacturer must submit a premanufacture notice. The EPA may impose testing or other requirements based on the premanufacture notice review. As new chemicals are introduced into commerce, they are added to the inventory.
Labels on containers of hazardous chemicals provide the first alert that a chemical is hazardous, and should provide basic information about safe handling procedures, protective measures, emergency first aid and the chemical’s hazards. The label should also include the identity of the hazardous chemical(s) and the name and address of the chemical manufacturer.
Labelling consists of phrases as well as graphic and colour symbols applied directly on the product, package, label or tag. The marking should be clear, easily comprehensible and able to withstand adverse climatic conditions. The labelling should be placed against a background that contrasts with the product’s accompanying data or package colour. The MSDS provides more detailed information on the nature of the chemical product’s hazards and the appropriate safety instructions.
While presently there are no globally harmonized labelling requirements, there are established international, national and regional regulations for labelling hazardous substances. Requirements for labelling are incorporated into the Law on Chemicals (Finland), the Act on Dangerous Products (Canada) and EC Directive N 67/548. Minimum label content requirements of the European Union, United States and Canadian systems are relatively similar.
Several international organizations have established labelling content requirements for handling chemicals at the workplace and in transport. The labels, hazard symbols, risk and safety phrases, and emergency codes of the International Organization for Standardization (ISO), the UNRTDG, the ILO and EU are discussed below.
The section on labelling in the ISO/IEC guide 51, Guidelines for Inclusion of Safety Aspects in Standards, includes commonly recognized pictograms (drawing, colour, sign). In addition, short and plain warning phrases alert the user to potential hazards and provide information on preventive safety and health measures.
The guidelines recommend the use of the following “signal” words to alert the user:
The UNRTDG establish five main pictograms for easy visible recognition of dangerous goods and significant hazard identification:
These symbols are supplemented by other representations such as:
The Chemicals Convention, 1990 (No. 170), and Recommendation, 1990 (No. 177), were adopted at the 77th Session of the International Labour Conference (ILC). They establish requirements for the labelling of chemicals to ensure the communication of basic hazard information. The Convention states that label information should be easily understandable and should convey the potential risks and appropriate precautionary measures to the user. Regarding the transport of dangerous goods, the Convention refers to the UNRTDG.
The Recommendation outlines labelling requirements in accordance with existing national and international systems, and establishes criteria for classification of chemicals including chemical and physical properties; toxicity; necrotic and irritating properties; and allergic, teratogenic, mutagenic and reproductive effects.
The EC Council Directive N 67/548 stipulates the form of label information: graphic hazard symbols and pictograms including risk and safety phrases. Hazards are coded by the Latin letter R accompanied with combinations of Arabic numerals from 1 to 59. For example, R10 corresponds with “flammable”, R23 with “toxic by inhalation”. The hazard code is given with a safety code consisting of the Latin letter S and combinations of numerals from 1 to 60. For example, S39 means “Wear eye/face protection”. The EC labelling requirements serve as a reference for chemical and pharmaceutical companies throughout the world.
Despite significant efforts in chemical hazard data acquisition, evaluation and organization by different international and regional organizations, there is still a lack of coordination of these efforts, particularly in the standardization of assessment protocols and methods and interpretation of data. The ILO, the Organization for Economic Cooperation and Development (OECD), the IPCS and other concerned bodies have initiated a number of international activities aimed toward establishing a global harmonization of chemical classification and labelling systems. The establishment of an international structure to monitor chemical hazard assessment activities would greatly benefit workers, the general public and the environment. An ideal harmonization process would reconcile the transport, marketing and workplace classification and labelling of hazardous substances, and address consumer, worker and environmental concerns.
Adapted from 3rd edition, Encyclopaedia of Occupational Health and Safety
Before a new hazardous substance is received for storage, information concerning its correct handling should be provided to all users. Planning and maintaining of storage areas are necessary to avoid material losses, accidents and disasters. Good housekeeping is essential, and special attention should be paid to incompatible substances, suitable location of products and climatic conditions.
Written instructions of storage practices should be provided, and the chemicals’ material safety data sheets (MSDSs) should be available in storage areas. Locations of the different classes of chemicals should be illustrated in a storage map and in a chemical register. The register should contain the maximum allowed quantity of all chemical products and the maximum allowed quantity of all chemical products per class. All substances should be received at a central location for distribution to the storerooms, stockrooms and laboratories. A central receiving area is also helpful in monitoring substances that may eventually enter the waste-disposal system. An inventory of substances contained in the storerooms and stockrooms will give an indication of the quantity and nature of substances targeted for future disposal.
Stored chemicals should be examined periodically, at least annually. Chemicals with expired shelf lives and deteriorated or leaking containers should be disposed of safely. A “first in, first out” system of keeping stock should be used.
The storage of dangerous substances should be supervised by a competent, trained person. All workers required to enter storage areas should be fully trained in appropriate safe work practices, and a periodic inspection of all storage areas should be carried out by a safety officer. A fire alarm should be situated in or near the outside of the storage premises. It is recommended that persons should not work alone in a storage area containing toxic substances. Chemical storage areas should be located away from process areas, occupied buildings and other storage areas. In addition, they should not be in proximity of fixed sources of ignition.
Labelling and Relabelling Requirements
The label is the key to organizing chemical products for storage. Tanks and containers should be identified with signs indicating the name of the chemical product. No containers or cylinders of compressed gases should be accepted without the following identifying labels:
The label may also offer precautions for correct storage, such as “Keep in a cool place” or “Keep container dry”. When certain dangerous products are delivered in tankers, barrels or bags and repackaged at the workplace, each new container should be relabelled so that the user will be able to identify the chemical and recognize the risks immediately.
Explosive substances include all chemicals, pyrotechnics and matches which are explosives per se and also those substances such as sensitive metallic salts which, by themselves or in certain mixtures or when subject to certain conditions of temperature, shock, friction or chemical action, may transform and undergo an explosive reaction. In the case of explosives, most countries have stringent regulations regarding safe storage requirements and precautions to be taken in order to prevent theft for use in criminal activities.
The storage places should be situated far away from other buildings and structures so as to minimize damage in case of an explosion. Manufacturers of explosives issue instructions as to the most suitable type of storage. The storerooms should be of solid construction and kept securely locked when not in use. No store should be near a building containing oil, grease, waste combustible material or flammable material, open fire or flame.
In some countries there is a legal requirement that magazines should be situated at least 60 m from any power plant, tunnel, mine shaft, dam, highway or building. Advantage should be taken of any protection offered by natural features such as hills, hollows, dense woods or forests. Artificial barriers of earth or stone walls are sometimes placed around such storage places.
The storage place should be well ventilated and free from dampness. Natural lighting or portable electric lamps should be used, or lighting provided from outside the storehouse. Floors should be constructed of wood or other non-sparking material. The area surrounding the storage place should be kept free of dry grass, rubbish or any other material likely to burn. Black powder and explosives should be stored in separate storehouses, and no detonators, tools or other materials should be kept in an explosive store. Non-ferrous tools should be used for opening cases of explosives.
Oxidizing substances provide sources of oxygen, and thus are capable of supporting combustion and intensifying the violence of any fire. Some of these oxygen suppliers give off oxygen at storage-room temperature, but others require the application of heat. If containers of oxidizing materials are damaged, the contents may mix with other combustible materials and start a fire. This risk can be avoided by storing oxidizing materials in a separate storage place. However, this practice may not always be available, as, for example, in dock warehouses for goods in transit.
It is dangerous to store powerful oxidizing substances near liquids that even have a low flash point or even slightly flammable materials. It is safer to keep all flammable materials away from a place where oxidizing substances are stored. The storage area should be cool, well ventilated and of fire-resisting construction.
A gas is deemed to be flammable if it burns in the presence of air or oxygen. Hydrogen, propane, butane, ethylene, acetylene, hydrogen sulphide and coal gas are among the most common flammable gases. Some gases such as hydrogen cyanide and cyanogen are both flammable and poisonous. Flammable materials should be stored in places which are cool enough to prevent accidental ignition if the vapours mix with the air.
Vapours of flammable solvents may be heavier than air and may move along the floor to a distant ignition source. Flammable vapours from spilled chemicals have been known to descend into stairwells and elevator shafts and ignite at a lower storey. It is therefore essential that smoking and open flames be prohibited where these solvents are handled or stored.
Portable, approved safety cans are the safest vessels for storing flammables. Quantities of flammable liquids greater than 1 litre should be stored in metal containers. Two-hundred-litre drums are commonly used to ship flammables, but are not intended as long-term storage containers. The stopper should be removed carefully and replaced by an approved pressure-relief vent to avoid increased internal pressure from heat, fire or exposure to sunlight. When transferring flammables from metal equipment, the worker should use an enclosed transfer system or have adequate exhaust ventilation.
The storage area should be situated away from any source of heat or fire hazard. Highly flammable substances should be kept apart from powerful oxidizing agents or from materials which are susceptible to spontaneous combustion. When highly volatile liquids are stored, any electric light fittings or apparatus should be of certified flameproof construction, and no open flames should be permitted in or near the storage place. Fire extinguishers and absorbent inert materials, such as dry sand and earth, should be available for emergency situations.
The walls, ceilings and floors of the storage room should consist of materials with at least a 2-hour fire resistance. The room should be fitted with self-closing fire doors. The storage-room installations should be electrically grounded and periodically inspected, or equipped with automatic smoke- or fire-detection devices. Control valves on storage vessels containing flammable liquids should be clearly labelled, and pipelines should be painted with distinctive safety colours to indicate the type of liquid and the direction of flow. Tanks containing flammable substances should be situated on ground sloping away from the main buildings and plant installations. If they are on level ground, protection against fire spread can be obtained by adequate spacing and the provision of dykes. The dyke capacity should preferably be 1.5 times that of the storage tank, as a flammable liquid may be likely to boil over. Provision should be made for venting facilities and flame arrestors on such storage tanks. Adequate fire extinguishers, either automatic or manual, should be available. No smoking should be allowed.
Toxic chemicals should be stored in cool, well ventilated areas out of contact with heat, acids, moisture and oxidizing substances. Volatile compounds should be stored in spark-free freezers (–20 °C) to avoid evaporation. Because containers may develop leaks, storerooms should be equipped with exhaust hoods or equivalent local ventilation devices. Open containers should be closed with tape or other sealant before being returned to the storeroom. Substances which can react chemically with each other should be kept in separate stores.
Corrosive substances include strong acids, alkalis and other substances which will cause burns or irritation of the skin, mucous membranes or eyes, or which will damage most materials. Typical examples of these substances include hydrofluoric acid, hydrochloric acid, sulphuric acid, nitric acid, formic acid and perchloric acid. Such materials may cause damage to their containers and leak into the atmosphere of the storage area; some are volatile and others react violently with moisture, organic matter or other chemicals. Acid mists or fumes may corrode structural materials and equipment and have a toxic action on personnel. Such materials should be kept cool but well above their freezing point, since a substance such as acetic acid may freeze at a relatively high temperature, rupture its container and then escape when the temperature rises again above its freezing point.
Some corrosive substances also have other dangerous properties; for example, perchloric acid, in addition to being highly corrosive, is also a powerful oxidizing agent which can cause fire and explosions. Aqua regia has three dangerous properties: (1) it displays the corrosive properties of its two components, hydrochloric acid and nitric acid; (2) it is a very powerful oxidizing agent; and (3) application of only a small amount of heat will result in the formation of nitrosyl chloride, a highly toxic gas.
Storage areas for corrosive substances should be isolated from the rest of the plant or warehouses by impervious walls and floor, with provision for the safe disposal of spillage. The floors should be made of cinder blocks, concrete that has been treated to reduce its solubility, or other resistant material. The storage area should be well ventilated. No store should be used for the simultaneous storage of nitric acid mixtures and sulphuric acid mixtures. Sometimes it is necessary to store corrosive and poisonous liquids in special types of containers; for example, hydrofluoric acid should be kept in leaden, gutta percha or ceresin bottles. Since hydrofluoric acid interacts with glass, it should not be stored near glass or earthenware carboys containing other acids.
Carboys containing corrosive acids should be packed with kieselguhr (infusorial earth) or other effective inorganic insulating material. Any necessary first-aid equipment such as emergency showers and eyewash bottles should be provided in or immediately close to the storage place.
Some chemicals, such as sodium and potassium metals, react with water to produce heat and flammable or explosive gases. Certain polymerization catalysts, such as alkyl aluminium compounds, react and burn violently on contact with water. Storage facilities for water-reactive chemicals should not have water in the storage area. Non-water automatic sprinkler systems should be employed.
Detailed legislation has been drawn up in many countries to regulate the manner in which various dangerous substances may be stored; this legislation includes the following specifications:
In many countries there is no central authority concerned with the supervision of the safety precautions for the storage of all dangerous substances, but a number of separate authorities exist. Examples include mine and factory inspectorates, dock authorities, transport authorities, police, fire services, national boards and local authorities, each of which deals with a limited range of dangerous substances under various legislative powers. It is usually necessary to obtain a licence or permit from one of these authorities for the storage of certain types of dangerous substances such as petroleum, explosives, cellulose and cellulose solutions. The licensure procedures require that storage facilities comply with specified safety standards.
Adapted from 3rd edition, Encyclopaedia of Occupational Health and Safety
Gases in their compressed state, and particularly compressed air, are almost indispensable to modern industry, and are also used widely for medical purposes, for the manufacture of mineral waters, for underwater diving and in connection with motor vehicles.
For purposes of the present article, compressed gases and air are defined as being those with a gauge pressure exceeding 1.47 bar or as liquids having a vapour pressure exceeding 2.94 bar. Thus, consideration is not given to such cases as natural gas distribution, which is dealt with elsewhere in this Encyclopaedia.
Table 1. Gases often found in compressed form
*These gases are flammable.
All the above gases present either an irritant, asphyxiant or highly toxic respiratory hazard and may also be flammable and an explosive when compressed. Most countries provide for a standard colour-coding system whereby different coloured bands or labels are applied to the gas cylinders to indicate the type of hazard to be expected. Particularly toxic gases, such as hydrogen cyanide, are also given special markings.
All compressed gas containers are so constructed that they are safe for the purposes for which they are intended when first put into service. However, serious accidents may result from their misuse, abuse or mishandling, and the greatest care should be exercised in the handling, transport, storage and even in the disposal of such cylinders or containers.
Characteristics and Production
Depending on the characteristics of the gas, it may be introduced into the container or cylinder in liquid form or simply as a gas under high pressure. In order to liquefy a gas, it is necessary to cool it to below its critical temperature and to subject it to an appropriate pressure. The lower the temperature is reduced below the critical temperature, the less the pressure required.
Certain of the gases listed in table 1 have properties against which precautions must be taken. For example, acetylene can react dangerously with copper and should not be in contact with alloys containing more than 66% of this metal. It is usually delivered in steel containers at about 14.7 to 16.8 bar. Another gas that has a highly corrosive action on copper is ammonia, which must also be kept out of contact with this metal, use being made of steel cylinders and authorized alloys. In the case of chlorine, no reaction takes place with copper or steel except in the presence of water, and for this reason all storage vessels or other containers must be kept free from contact with moisture at all times. Fluorine gas, on the other hand, although reacting readily with most metals, will tend to form a protective coating, as, for example, in the case of copper, where a layer of copper fluoride over the metal protects it from further attack by the gas.
Among the gases listed, carbon dioxide is one of the most readily liquefied, this taking place at a temperature of 15 °C and a pressure of about 14.7 bar. It has many commercial applications and may be kept in steel cylinders.
The hydrocarbon gases, of which liquefied petroleum gas (LPG) is a mixture formed mainly of butane (about 62%) and propane (about 36%), are not corrosive and are generally delivered in steel cylinders or other containers at pressures of up to 14.7 to 19.6 bar. Methane is another highly flammable gas that is also generally delivered in steel cylinders at a pressure of 14.7 to 19.6 bar.
Storage and transport
When a filling, storage and dispatch depot is being selected, consideration must be given to the safety of both the site and the environment. Pump rooms, filling machinery and so on must be located in fire-resistant buildings with roofs of light construction. Doors and other closures should open outwards from the building. The premises should be adequately ventilated, and a system of lighting with flameproof electrical switches should be installed. Measures should be taken to ensure free movement in the premises for filling, checking and dispatch purposes, and safety exits should be provided.
Compressed gases may be stored in the open only if they are adequately protected from the weather and direct sunlight. Storage areas should be located at a safe distance from occupied premises and neighbouring dwellings.
During the transport and distribution of containers, care must be taken to ensure that valves and connections are not damaged. Adequate precautions should be taken to prevent cylinders from falling off the vehicle and from being subjected to rough usage, excessive shocks or local stress, and to prevent excessive movement of liquids in large tanks. Every vehicle should be equipped with a fire extinguisher and an electrically conductive strip for earthing static electricity, and should be clearly marked “Flammable liquids”. Exhaust pipes should have a flame-control device, and engines should be halted during loading and unloading. The maximum speed of these vehicles should be rigorously limited.
The main dangers in the use of compressed gases arise from their pressure and from their toxic and/or flammable properties. The principal precautions are to ensure that equipment is used only with those gases for which it was designed, and that no compressed gases are used for any purpose other than that for which their use has been authorized.
All hoses and other equipment should be of good quality and should be examined frequently. The use of non-return valves should be enforced wherever necessary. All hose connections should be in good condition and no joints should be made by forcing together threads that do not exactly correspond. In the case of acetylene and combustible gases, a red hose should be used; for oxygen the hose should be black. It is recommended that for all flammable gases, the connection-screw thread shall be left-handed, and for all other gases, it shall be right-handed. Hoses should never be interchanged.
Oxygen and some anaesthetic gases are often transported in large cylinders. The transfer of these compressed gases to small cylinders is a hazardous operation, which should be done under competent supervision, making use of the correct equipment in a correct installation.
Compressed air is widely used in many branches of industry, and care should be taken in the installation of pipelines and their protection from damage. Hoses and fittings should be maintained in good condition and subjected to regular examinations. The application of a compressed air hose or jet to an open cut or wound through which air can enter the tissues or the bloodstream is particularly dangerous; precautions should also be taken against all forms of irresponsible behaviour which could result in a compressed air jet coming in contact with any openings in the body (the result of which can be fatal). A further hazard exists when compressed air jets are used to clean machined components or workplaces: flying particles have been known to cause injury or blindness, and precautions against such dangers should be enforced.
Labelling and marking
4.1.1. The competent authority, or a body approved or recognized by the competent authority, should establish requirements for the marking and labelling of chemicals to enable persons handling or using chemicals to recognize and distinguish between them, both when receiving and when using them, so that they may be used safely (see paragraph 2.1.8 (criteria and requirements)). Existing criteria for marking and labelling established by other competent authorities may be followed where they are consistent with the provisions of this paragraph and are encouraged where this may assist uniformity of approach.
4.1.2. Suppliers of chemicals should ensure that chemicals are marked and hazardous chemicals are labelled, and that revised labels are prepared and provided to employers whenever new relevant safety and health information becomes available (see paragraphs 2.4.1 (suppliers’ responsibilities) and 2.4.2 (classification)).
4.1.3. Employers receiving chemicals that have not been labelled or marked should not use them until the relevant information is obtained from the supplier or from other reasonably available sources. Information should be obtained primarily from the supplier but may be obtained from other sources listed in paragraph 3.3.1 (sources of information), with a view to marking and labelling in accordance with the requirements of the national competent authority, prior to use. ...
4.3.2. The purpose of the label is to give essential information on:
The information should refer to both acute and chronic exposure hazards.
4.3.3. Labelling requirements, which should be in conformity with national requirements, should cover:
(a) the information to be given on the label, including as appropriate:
(b) the legibility, durability and size of the label;
(c) the uniformity of labels and symbols, including colours.
Source: ILO 1993, Chapter 4.
Labelling and marking should be in accordance with standard practice in the country or region in question. The use of one gas for another by mistake, or the filling of a container with a gas different from that which it previously contained, without the necessary cleaning and decontamination procedures, may cause serious accidents. Colour marking is the best method of avoiding such errors, painting specific areas of containers or piping systems in accordance with the colour code stipulated in national standards or recommended by the national safety organization.
For convenience in handling, transportation and storage, gases are commonly compressed in metal gas cylinders at pressures that range from a few atmospheres overpressure to 200 bar or even more. Alloy steel is the material most commonly used for the cylinders, but aluminium is also widely used for many purposes—for example, for fire extinguishers.
The hazards met with in handling and using compressed gases are:
Cylinder manufacture. Steel cylinders may be seamless or welded. The seamless cylinders are made from high-quality alloy steels and carefully heat-treated in order to obtain the desired combination of strength and toughness for high-pressure service. They may be forged and hot-drawn from steel billets or hot-formed from seamless tubes. Welded cylinders are made from sheet material. The pressed top and bottom parts are welded to a cylindrical seamless or welded tube section and heat-treated to relieve material stresses. Welded cylinders are extensively used in low-pressure service for liquefiable gases and for dissolved gases such as acetylene.
Aluminium cylinders are extruded in large presses from special alloys that are heat-treated to give the desired strength.
Gas cylinders must be designed, produced and tested according to strict norms or standards. Every batch of cylinders should be checked for material quality and heat treatment, and a certain number of cylinders tested for mechanical strength. Inspection is often aided by sophisticated instruments, but in all cases the cylinders should be inspected and hydraulically tested to a given test pressure by an approved inspector. Identification data and the inspector’s mark should be permanently stamped on the cylinder neck or another suitable place.
Periodic inspection. Gas cylinders in use may be affected by rough treatment, corrosion from inside and outside, fire and so on. National or international codes therefore require that they shall not be filled unless they are inspected and tested at certain intervals, which mostly range between two and ten years, depending on the service. Internal and external visual inspection together with a hydraulic pressure test is the basis for the approval of the cylinder for a new period in a given service. The test date (month and year) is stamped on the cylinder.
Disposal. A large number of cylinders are scrapped every year for various reasons. It is equally important that these cylinders be disposed of in such a way that they will not find their way back into use through uncontrolled channels. The cylinders should therefore be made completely unserviceable by cutting, crushing or a similar safe procedure.
Valves. The valve and any safety attachment must be regarded as a part of the cylinder, which must be kept in good working condition. Neck and outlet threads should be intact, and the valve should close tight without the use of undue force. Shut-off valves are often equipped with a pressure-relief device. This may be in the form of a resetting safety valve, bursting disc, fuse plug (melt plug) or a combination of bursting disc and fuse plug. The practice varies from country to country, but cylinders for low-pressure liquefied gases are always equipped with safety valves connected to the gas phase.
Different transport codes classify gases as compressed, liquefied or dissolved under pressure. For the purpose of this article, it is useful to use the type of hazard as a classification.
High pressure. If cylinders or equipment burst, damage and injuries may be caused by flying debris or by the gas pressure. The more a gas is compressed, the higher is the stored energy. This hazard is always present with compressed gases and will increase with temperature if the cylinders are heated. Hence:
Low temperature. Most liquefied gases will evaporate rapidly under atmospheric pressure, and may reach very low temperatures. A person whose skin is exposed to such liquid may sustain injuries in the form of “cold burns”. (Liquid CO2 will form snow particles when expanded.) Correct protective equipment (e.g., gloves, goggles) should therefore be used.
Oxidation. The hazard of oxidation is most evident with oxygen, which is one of the most important compressed gases. Oxygen will not burn on its own, but is necessary for combustion. Normal air contains 21% oxygen by volume.
All combustible materials will ignite more easily and burn more vigorously when the oxygen concentration is increased. This is noticeable with even a slight increase in oxygen concentration, and utmost care must be taken to avoid oxygen enrichment in the working atmosphere. In confined spaces small oxygen leaks may lead to dangerous enrichment.
The danger with oxygen increases with increasing pressure to the point where many metals will burn vigorously. Finely divided materials may burn in oxygen with explosive force. Clothing that is saturated with oxygen will burn very rapidly and be difficult to extinguish.
Oil and grease have always been regarded as dangerous in combination with oxygen. The reason is that they react readily with oxygen, their existence is common, the ignition temperature is low and the developed heat may start a fire in the underlying metal. In high-pressure oxygen equipment the necessary ignition temperature may easily be reached by the compression shock that may result from rapid valve opening (adiabatic compression).
Flammability. The flammable gases have flashpoints below room temperature and will form explosive mixtures with air (or oxygen) within certain limits known as the lower and upper explosion limits.
Escaping gas (also from safety valves) may ignite and burn with a shorter or longer flame depending on the pressure and amount of gas. The flames may again heat nearby equipment, which may burn, melt or explode. Hydrogen burns with an almost invisible flame.
Even small leaks may cause explosive mixtures in confined spaces. Some gases, such as liquefied petroleum gases, mostly propane and butane, are heavier than air and are difficult to vent away, as they will concentrate in the lower parts of buildings and “float” through channels from one room to another. Sooner or later, the gas may reach an ignition source and explode.
Ignition may be caused by hot sources, but also by electrical sparks, even very small ones.
Acetylene takes a special place among the combustible gases because of its properties and wide use. If heated, the gas may start to decompose with the development of heat even without the presence of air. If allowed to proceed, this may lead to cylinder explosion.
Acetylene cylinders are, for safety reasons, filled with a highly porous mass which also contains a solvent for the gas. Outside heating from a fire or welding torch, or in certain cases internal ignition by strong backfires from welding equipment, may start a decomposition within the cylinder. In such cases:
Acetylene cylinders in several countries are equipped with fuse (melting) plugs. These will release the gas pressure when they melt (usually at about 100 °C) and prevent cylinder explosion. At the same time there is a risk that the released gas may ignite and explode.
Common precautions to observe in respect of combustible gases are as follows:
Toxicity. Certain gases, if not the most common, may be toxic. At the same time, they may be irritating or corrosive to the skin or eyes.
Persons who handle these gases should be well trained and aware of the danger involved and the necessary precautions. The cylinders should be stored in a well ventilated area. No leaks should be tolerated. Suitable protective equipment (gas masks or breathing equipment) should be used.
Inert gases. Gases such as argon, carbon dioxide, helium and nitrogen are widely used as protective atmospheres to prevent unwanted reactions in welding, chemical plants, steel works and so on. These gases are not labelled as being hazardous, and serious accidents may happen because only oxygen can support life.
When any gas or gas mixture displaces the air so that the breathing atmosphere becomes deficient in oxygen, there is a danger of asphyxiation. Unconsciousness or death may result very rapidly when there is little or no oxygen, and there is no warning effect.
Confined spaces where the breathing atmosphere is deficient in oxygen must be ventilated before entering. When breathing equipment is used, the person entering must be supervised. Breathing equipment must be used even in rescuing operations. Normal gas masks give no protection against oxygen deficiency. The same precaution must be observed with large, permanent firefighting installations, which are often automatic, and those who may be present in such areas should be warned of the danger.
Cylinder filling. Cylinder filling involves the operation of high-pressure compressors or liquid pumps. The pumps may operate with cryogenic (very low-temperature) liquids. The filling stations may also incorporate large storage tanks of liquid gases in a pressurized and/or deeply refrigerated state.
The gas filler should check that the cylinders are in acceptable condition for filling, and should fill the correct gas in not more than the approved amount or pressure. The filling equipment should be designed and tested for the given pressure and type of gas, and protected by safety valves. Cleanliness and material requirements for oxygen service must be observed strictly. When filling flammable or toxic gases, special attention should be given to the safety of the operators. The primary requirement is good ventilation combined with correct equipment and technique.
Cylinders which are contaminated with other gases or liquids by the customers constitute a special hazard. Cylinders with no residual pressure may be purged or evacuated before filling. Special care should be taken to ensure that medical gas cylinders are free from any harmful matter.
Transport. Local transport tends to become more mechanized through the use of fork-lift trucks and so on. Cylinders should be transported only with the caps on and secured against falling from the vehicles. Cylinders must not be dropped from trucks directly onto the ground. For hoisting with cranes, suitable lifting cradles should be used. Magnetic lifting devices or caps with uncertain threads should not be used for lifting cylinders.
When cylinders are manifolded into larger packages, great care should be taken to avoid strain on the connections. Any hazard will be increased because of the greater amount of gas involved. It is good practice to divide larger units into sections and to place shut-off valves where they can be operated in any emergency.
The most frequently occurring accidents in cylinder handling and transport are injuries caused by the hard, heavy and difficult-to-handle cylinders. Safety shoes should be worn. Trolleys should be provided for longer transport of single cylinders.
In international transport codes, compressed gases are classified as dangerous goods. These codes give details about which gases may be transported, cylinder requirements, allowed pressure, marking and so on.
Identification of content. The most important requirement for safe handling of compressed gases is the correct identification of the gas content. Stamping, labelling, stencilling and colour marking are the means that are used for this purpose. Certain requirements for marking are covered in International Organization for Standardization (ISO) standards. The colour marking of medical gas cylinders follows the ISO standards in most countries. Standardized colours are also used in many countries for other gases, but this is not a sufficient identification. In the end only the written word can be regarded as a proof of the cylinder content.
Standardized valve outlets. The use of a standardized valve outlet for a certain gas or group of gases strongly reduces the chance of connecting cylinders and equipment made for different gases. Adapters should therefore not be used, as this sets aside the safety measures. Only normal tools and no excessive force should be used when making connections.
Safe Practice for Users
The safe use of compressed gases entails applying the safety principles outlined in this chapter and the ILO Code of Practice Safety in the Use of Chemicals at Work (ILO 1993). This is not possible unless the user has some basic knowledge of the gas and the equipment that he or she is handling. In addition the user should take the following precautions:
Occupational exposure to hazardous chemicals in laboratories 1990 OSHA Laboratory Standard 29 CFR 1910.1450
The following description of a laboratory chemical hygiene plan corresponds with Section (e:1-4), Chemical hygiene plan-General, of the 1990 OSHA Laboratory Standard. This plan should be made readily available to employees and employee representatives.The chemical hygiene plan shall include each of the following elements and shall indicate specific measures that the employer will take to ensure laboratory employee protection:
(a) establishment of a designated area;
(b) use of containment devices such as fume hoods or glove boxes;
(c) procedures for safe removal of contaminated waste; and
(d) decontamination procedures.
The employer shall review and evaluate the effectiveness of the chemical hygiene plan at least annually and update it as necessary.
Setting up a Safe and Healthy Laboratory
A laboratory can only be safe and hygienic if the work practices and procedures that are followed there are safe and hygienic. Such practices are fostered by first giving responsibility and authority for laboratory safety and chemical hygiene to a laboratory safety officer who, together with a safety committee of laboratory personnel, decides what tasks must be accomplished and assigns responsibility for carrying out each of them.
The safety committee’s specific tasks include conducting periodic laboratory inspections and summarizing the results in a report submitted to the laboratory safety officer. These inspections are properly done with a checklist. Another important aspect of safety management is periodic inspections of safety equipment to ensure that all equipment is in good working order and in designated locations. Before this can be done, an annual inventory of all the safety equipment must be made; this includes a brief description, including size or capacity and manufacturer. Of no less importance is a semiannual inventory of all laboratory chemicals, including proprietary products. These should be classified into groups of chemically similar substances and also classified according to their fire hazard. Another essential safety classification depends on the degree of hazard associated with a substance, since the treatment a substance receives is directly related to the harm it can cause and the ease with which the harm is unleashed. Each chemical is put into one of three hazard classes chosen on the basis of grouping according to the order of magnitude of risk involved; they are:
Ordinary hazard substances are those that are relatively easily controlled, are familiar to laboratory personnel and present no unusual risk. This class ranges from innocuous substances such as sodium bicarbonate and sucrose to concentrated sulphuric acid, ethylene glycol and pentane.
High-hazard substances present much greater hazards than ordinary hazards. They require special handling or, sometimes, monitoring, and present high fire or explosion hazards or severe health risks. In this group are chemicals that form unstable explosive compounds on standing (e.g., hydroperoxides formed by ethers) or substances that have high acute toxicities (e.g., sodium fluoride, which has an oral toxicity of 57 mg/kg in mice), or that have chronic toxicities such as carcinogens, mutagens or teratogens. Substances in this group often have the same kind of hazard as those in the group that follows. The difference is one of degree—those in group 3, the extremely hazardous materials, have either a greater intensity of hazard, or their order of magnitude is much greater, or the dire effects can be released far more easily.
Extremely hazardous materials, when not handled correctly, can very readily cause a serious accident resulting in severe injury, loss of life or extensive property damage. Extreme caution must be exercised in dealing with these substances. Examples of this class are nickel tetracarbonyl (a volatile, extremely poisonous liquid, the vapours of which have been lethal in concentrations as low as 1 ppm) and triethylaluminium (a liquid that spontaneously ignites on exposure to air and reacts explosively with water).
One of the most important of the safety committee’s tasks is to write a comprehensive document for the laboratory, a laboratory safety and chemical hygiene plan, that fully describes its safety policy and standard procedures for carrying out laboratory operations and fulfilling regulatory obligations; these include guidelines for working with substances that may fall into any of the three hazard categories, inspecting safety equipment, responding to a chemical spill, chemical waste policy, standards for laboratory air quality and any recordkeeping required by regulatory standards. The laboratory safety and chemical hygiene plan must be kept in the laboratory or must be otherwise easily accessible to its workers. Other sources of printed information include: chemical information sheets (also called material safety data sheets, MSDSs), a laboratory safety manual, toxicological information and fire hazard information. The inventory of laboratory chemicals and three associated derivative lists (classification of chemicals according to chemical class, fire safety class and the three degrees of hazard) must also be kept with these data.
A file system for records of safety-related activities is also required. It is not necessary that this file either be in the laboratory or be immediately accessible to laboratory workers. The records are mainly for the use of laboratory personnel who oversee laboratory safety and chemical hygiene and for the perusal of regulatory agency inspectors. It should thus be easily available and kept up to date. It is advisable that the file be kept outside the laboratory in order to reduce the possibility of its destruction in the event of a fire. The documents on file should include: records of laboratory inspections by the safety committee, records of inspections by any local regulatory agencies including fire departments and state and federal agencies, records dealing with hazardous waste disposal, records of taxes levied on various classes of hazardous waste, where applicable, a second copy of the inventory of laboratory chemicals, and copies of other pertinent documents dealing with the facility and its personnel (e.g., records of attendance of personnel at annual laboratory safety sessions).
Causes of Illness and Injury in the Laboratory
Measures for the prevention of personal injury, illness and anxiety are an integral part of the plans for the day-to-day operation of a well-run laboratory. The people who are affected by unsafe and unhygienic conditions in a laboratory include not only those who work in that laboratory but also neighbouring personnel and those who provide mechanical and custodial services. Since personal injuries in laboratories stem largely from inappropriate contact between chemicals and people, inappropriate mixing of chemicals or inappropriate supply of energy to chemicals, protecting health entails preventing such undesirable interactions. This, in turn, means suitably confining chemicals, combining them properly and closely regulating the energy supplied to them. The main kinds of personal injury in the laboratory are poisoning, chemical burns and injury resulting from fires or explosions. Fires and explosions are a source of thermal burns, lacerations, concussions and other severe bodily harm.
Chemical attack on the body. Chemical attack takes place when poisons are absorbed into the body and interfere with its normal function through disturbance of metabolism or other mechanisms. Chemical burns, or the gross destruction of tissue, usually occur by contact with either strong acids or strong alkalis. Toxic materials that have entered the body by absorption through the skin, eyes or mucous membranes, by ingestion or by inhalation, can cause systemic poisoning, usually by being spread via the circulatory system.
Poisoning is of two general types—acute and chronic. Acute poisoning is characterized by ill effects appearing during or directly after a single exposure to a toxic substance. Chronic poisoning becomes evident only after the passage of time, which may take weeks, months, years or even decades. Chronic poisoning is said to occur when each of these conditions is met: the victim must have been subjected to multiple exposures over long periods of time and to metabolically significant amounts of a chronic poison.
Chemical burns, usually encountered when liquid corrosives are spilled or splashed on the skin or in the eyes, also occur when those tissues come in contact with corrosive solids, ranging in size from powdery dusts to fairly large crystals, or with corrosive liquids dispersed in the air as mists, or with such corrosive gases as hydrogen chloride. The bronchial tubes, lungs, tongue, throat and epiglottis can also be attacked by corrosive chemicals in either the gaseous, liquid or solid states. Toxic chemicals also, of course, may be introduced into the body in any of these three physical states, or in the form of dusts or mists.
Injury through fires or explosions. Both fires or explosions may produce thermal burns. Some of the injuries caused by explosions, however, are particularly characteristic of them; they are injuries engendered either by the concussive force of the detonation itself or by such of its effects as glass fragments hurled through the air, causing loss of fingers or limbs in the first case, or skin lacerations or loss of vision, in the second.
Laboratory injuries from other sources. A third class of injuries may be caused neither by chemical attack nor by combustion. Rather they are produced by a miscellany of all other sources—mechanical, electrical, high-energy light sources (ultraviolet and lasers), thermal burns from hot surfaces, sudden explosive shattering of screw-capped glass chemical containers from the unexpected build-up of high internal gas pressures and lacerations from the sharp, jagged edges of newly broken glass tubing. Among the most serious sources of injury of a mechanical origin are tall, high-pressure gas cylinders tipping over and falling to the floor. Such episodes can injure legs and feet; in addition, should the cylinder stem break during the fall, the gas cylinder, propelled by the rapid, massive, uncontrolled escape of gas, becomes a deadly, undirected missile, a potential source of greater, more widespread harm.
Safety sessions and information dissemination. Injury prevention, dependent on performance of laboratory operations in a safe and prudent manner, is, in turn, dependent on laboratory workers being trained in correct laboratory methodology. Although they have received some of this training in their undergraduate and graduate education, it must be supplemented and reinforced by periodic laboratory safety sessions. Such sessions, which should emphasize understanding the physical and biological bases of safe laboratory practice, will enable laboratory workers to reject questionable procedures easily and to select technically sound methods as a matter of course. The sessions should also acquaint laboratory personnel with the kinds of data needed to design safe procedures and with sources of such information.
Workers must also be provided with ready access, from their work stations, to pertinent safety and technical information. Such materials should include laboratory safety manuals, chemical information sheets and toxicological and fire hazard information.
Prevention of poisoning and chemical burns. Poisoning and chemical burns have a common feature—the same four sites of entry or attack: (1) skin, (2) eyes, (3) mouth to stomach to intestines and (4) nose to bronchial tubes to lungs. Prevention consists in making these sites inaccessible to poisonous or corrosive substances. This is done by placing one or more physical barriers between the person to be protected and the hazardous substance or by ensuring that the ambient laboratory air is not contaminated. Procedures that use these methods include working behind a safety shield or using a fume hood, or utilizing both methods. The use of a glove box, of course, of itself affords a twofold protection. Minimization of injury, should contamination of tissue occur, is accomplished by removing the toxic or corrosive contaminant as quickly and completely as possible.
Prevention of acute poisoning and chemical burns in contrast with the prevention of chronic poisoning. Although the basic approach of isolation of the hazardous substance from the person to be protected is the same in preventing acute poisoning, chemical burns and chronic poisoning, its application must be somewhat different in preventing chronic poisoning. Whereas acute poisoning and chemical burns may be likened to massive assault in warfare, chronic poisoning has the aspect of a siege. Usually produced by much lower concentrations, exerting their influence through multiple exposures over long periods of time, its effects surface gradually and insidiously through sustained and subtle action. Corrective action involves either first detecting a chemical capable of causing chronic poisoning before any physical symptoms appear, or recognizing one or more aspects of a laboratory worker’s discomfort as possibly being physical symptoms connected with chronic poisoning. Should chronic poisoning be suspected, medical attention must be sought promptly. When a chronic poison is found at a concentration exceeding the allowable level, or even approaching it, steps must be taken either to eliminate that substance or, at the very least, to reduce its concentration to a safe level. Protection against chronic poisoning often requires that protective equipment be used for all or much of the workday; however, for reasons of comfort, the use of a glove box or a self-contained breathing apparatus (SCBA) is not always feasible.
Protection against poisoning or chemical burns. Protection against contamination of the skin by a particular splashed corrosive liquid or scattered poisonous airborne solid is best done by the use of safety gloves and a laboratory apron made of a suitable natural or synthetic rubber or polymer. The term suitable here is taken to mean a material which is neither dissolved, swelled nor in any other way attacked by the substance against which it must afford protection, nor should it be permeable to the substance. The use of a safety shield on the laboratory bench interposed between apparatus in which chemicals are being heated, reacted or distilled and the experimenter is a further safeguard against chemical burns and poisoning via skin contamination. Since the speed with which a corrosive or a poison is washed from the skin is a critical factor in preventing or minimizing the damage these substances can inflict, a safety shower, conveniently located in the laboratory, is an indispensable piece of safety equipment.
The eyes are best protected from splashed liquids by safety goggles or face shields. Airborne contaminants, in addition to gases and vapours, include solids and liquids when they are present in a finely subdivided state as dusts or mists. These are most effectively kept out of the eyes by conducting operations in a fume hood or glove box, although goggles afford some protection against them. To afford additional protection while the hood is being used, goggles may be worn. The presence of easily accessible eyewash fountains in the laboratory will often eliminate, and certainly will, at least, reduce eye damage through contamination by splashed corrosives or poisons.
The mouth to stomach to intestines route is usually connected with poisoning rather than with attack by corrosives. When toxic materials are ingested, it usually happens unwittingly through the chemical contamination of foods or cosmetics. Sources of such contamination are food stored in refrigerators with chemicals, food and beverages consumed in the laboratory, or lipstick kept or applied in the laboratory. Prevention of this kind of poisoning is done by avoiding practices known to cause it; this is feasible only when refrigerators to be used exclusively for food, and dining space outside of the laboratory, are made available.
The nose to bronchial tubes to lungs route, or respiratory route, of poisoning and chemical burns deals exclusively with airborne substances, whether gases, vapours, dusts or mists. These airborne materials may be kept from the respiratory systems of people within and outside of the laboratory by the concurrent practices of: (1) confining operations that either use or produce them to the fume hood (2) adjusting the laboratory air supply so that the air is changed 10 to 12 times per hour and (3) keeping the laboratory air pressure negative with respect to that of the corridors and rooms around it. Fume- or dust-producing operations that involve very bulky pieces of apparatus or containers the size of a 218-l drum, which are too large to be enclosed by an ordinary fume hood, should be done in a walk-in hood. In general, respirators or SCBA should not be used for any laboratory operations other than those of an emergency nature.
Chronic mercury poisoning, produced by the inhalation of mercury vapours, is occasionally found in laboratories. It is encountered when a pool of mercury that has accumulated in a hidden location—under floorboards, in drawers or a closet—has been emitting vapours over a long enough period of time to affect the health of laboratory personnel. Good laboratory housekeeping will avert this problem. Should a hidden source of mercury be suspected, the laboratory air must be checked for mercury either by the use of a special detector designed for the purpose or by sending an air sample for analysis.
Preventing fires and explosions and extinguishing fires. The principal cause of laboratory fires is the accidental ignition of flammable liquids. Flammable liquid is defined, in the fire safety sense, as being a liquid having a flashpoint of less than 36.7 °C. Ignition sources known to have caused this kind of laboratory fire include open flames, hot surfaces, electric sparks from switches and motors found in such equipment as stirrers, household-type refrigerators and electric fans, and sparks produced by static electricity. When ignition of a flammable liquid occurs, it takes place, not in the liquid itself, but above it, in the mixture of its vapours with air (when the concentration of vapour falls between certain upper and lower limits).
Preventing laboratory fires is accomplished by confining the vapours of flammables completely within the containers in which the liquids are kept or the apparatus in which they are used. If it is not possible to contain these vapours completely, their rate of escape should be made as low as possible and a continuous vigorous flow of air should be supplied to sweep them away, so as to keep their concentration at any given time well below the lower critical concentration limit. This is done both when reactions involving a flammable liquid are run in a fume hood and when drums of flammables are stored in safety solvent cabinets vented to an exhaust.
A particularly unsafe practice is the storage of such flammables as ethanol in a household-type refrigerator. These refrigerators will not keep vapours of stored flammable liquids from the sparks of its switches, motors and relays. No containers of flammables must ever be put in this type of refrigerator. This is especially true of open vessels and trays containing flammable liquids. However, even flammables in screw-capped bottles, kept in this type of refrigerator, have caused explosions, presumably by vapours leaking through a faulty seal or by the bottles breaking. Flammable liquids that require refrigeration must be kept only in explosion-proof refrigerators.
A significant source of fires that occur when large quantities of flammables are poured or siphoned from one drum to another is sparks produced through the accumulation of electric charge produced by a moving fluid. Spark generation of this sort can be prevented by electrically grounding both drums.
Most chemical and solvent fires that occur in the laboratory and are of manageable size, may be extinguished with either a carbon dioxide or dry-chemical type fire extinguisher. One or more 4.5 kg extinguishers of either kind should be supplied to a laboratory, according to its size. Certain special types of fires require other kinds of extinguishing agents. Many metal fires are put out with sand or graphite. Burning metal hydrides require graphite or powdered limestone.
When clothing is set afire in the laboratory, the flames must be put out quickly to minimize the injury caused by thermal burns. A wall-mounted wrap-around fire blanket extinguishes such fires effectively. It may be used for unassisted smothering of flames by the person whose clothing is on fire. Safety showers may also be used to extinguish these fires.
There are limits to the total volumes of flammable liquids that may be safely kept in a particular laboratory. Such limits, generally written into local fire codes, vary and depend on the materials of construction of the laboratory and on whether it is equipped with an automatic fire-extinguishing system. They usually range from about 55 to 135 litres.
Natural gas is often available from numbers of valves located throughout a typical laboratory. These are the most common sources of gas leaks, along with the rubber tubes and burners leading from them. Such leaks, when not detected soon after their onset, have led to severe explosions. Gas detectors, designed to indicate the level of gas concentration in the air, may be used to locate the source of such leakage quickly.
Prevention of injury from miscellaneous sources. Harm from tall, high-pressure gas cylinders falling, among the most familiar in this group of accidents, is avoided easily by strapping or chaining these cylinders securely to a wall or laboratory bench and putting cylinder caps on all unused and empty cylinders.
Most of the injuries from jagged edges of broken glass tubing are sustained through breakage while the tubing is being put into corks or rubber stoppers. They are avoided by lubricating the tube with glycerol and protecting the hands with leather work gloves.
Appendix A to 1910.1450—National Research Council recommendations concerning chemical hygiene in laboratories (non-mandatory)
The following guidelines concerning proper laboratory ventilation correspond with the information provided in Section C. The Laboratory Facility; 4. Ventilation - (a) General laboratory ventilation, Appendix A of the 1990 OSHA Laboratory Standard, 29 CFR 1910.1450.Ventilation
(a) General laboratory ventilation. This system should: Provide a source of air for breathing and for input to local ventilation devices; it should not be relied on for protection from toxic substances released into the laboratory; ensure that laboratory air is continually replaced, preventing increase of air concentrations of toxic substances during the working day; direct air flow into the laboratory from non-laboratory areas and out to the exterior of the building.
(b) Hoods. A laboratory hood with 2.5 linear feet (76 cm) of hood space per person should be provided for every 2 workers if they spend most of their time working with chemicals; each hood should have a continuous monitoring device to allow convenient confirmation of adequate hood performance before use. If this is not possible, work with substances of unknown toxicity should be avoided or other types of local ventilation devices should be provided.
(c) Other local ventilation devices. Ventilated storage cabinets, canopy hoods, snorkels, etc. should be provided as needed. Each canopy hood and snorkel should have a separate exhaust duct.
(d) Special ventilation areas. Exhaust air from glove boxes and isolation rooms should be passed through scrubbers or other treatment before release into the regular exhaust system. Cold rooms and warm rooms should have provisions for rapid escape and for escape in the event of electrical failure.
(e) Modifications. Any alteration of the ventilation system should be made only if thorough testing indicates that worker protection from airborne toxic substances will continue to be adequate.
(f) Performance. Rate: 4-12 room air changes/hour is normally adequate general ventilation if local exhaust systems such as hoods are used as the primary method of control.
(g) Quality. General air flow should not be turbulent and should be relatively uniform throughout the laboratory, with no high velocity or static areas; airflow into and within the hood should not be excessively turbulent; hood face velocity should be adequate (typically 60-100 lf/min) (152-254 cm/min).
(h) Evaluation. Quality and quantity of ventilation should be evaluated on installation, regularly monitored (at least every 3 months), and reevaluated whenever a change in local ventilation is made.
Incompatible materials are a pair of substances that, on contact or mixing, produce either a harmful or potentially harmful effect. The two members of an incompatible pair may be either a pair of chemicals or a chemical and a material of construction such as wood or steel. The mixing or contact of two incompatible materials leads either to a chemical reaction or to a physical interaction that generates a large amount of energy. Specific harmful or potentially harmful effects of these combinations, which can ultimately lead to serious injury or damage to the health, include liberation of large amounts of heat, fires, explosions, production of a flammable gas or generation of a toxic gas. Since a fairly extensive variety of substances is usually found in laboratories, the occurrence of incompatibles in them is quite common and presents a threat to life and health if they are not handled correctly.
Incompatible materials are seldom mixed intentionally. Most often, their mixing is the result of a simultaneous accidental breaking of two adjacent containers. Sometimes it is the effect of leakage or dripping, or results from the mixing of gases or vapours from nearby bottles. Although in many cases in which a pair of incompatibles is mixed, the harmful effect is easily observed, in at least one instance, a not readily detectable chronic poison is formed. This occurs as the result of the reaction of formaldehyde gas from 37% formalin with hydrogen chloride that has escaped from concentrated hydrochloric acid to form the potent carcinogen bis(chloromethyl) ether. Other instances of not immediately detectable effects are the generation of odourless, flammable gases.
Keeping incompatibles from mixing through the simultaneous breaking of adjacent containers or through escape of vapours from nearby bottles is simple—the containers are moved far apart. The incompatible pair, however, must first be identified; not all such identifications are simple or obvious. To minimize the possibility of overlooking an incompatible pair, a compendium of incompatibles should be consulted and scanned occasionally to acquire an acquaintance with less familiar examples. Preventing a chemical from coming in contact with incompatible shelving material, through dripping or through a bottle breaking, is done by keeping the bottle in a glass tray of sufficient capacity to hold all of its contents.
Occupational health professionals have generally relied on the following hierarchy of control techniques to eliminate or minimize worker exposures: substitution, isolation, ventilation, work practices, personal protective clothing and equipment. Usually a combination of two or more of these techniques is applied. Although this article focuses primarily on the application of ventilation techniques, the other approaches are briefly discussed. They should not be ignored when attempting to control exposure to chemicals by ventilation.
The occupational health professional should always think of the concept of source-path-receiver. The primary focus should be on control at the source with control of the path the second focus. Control at the receiver should be considered the last choice. Whether it is during the start-up or design phases of a process or during the evaluation of an existing process, the procedure for control of exposure to air contaminants should start at the source and progress to the receiver. It is likely that all or most of these control strategies will need to be used.
The principle of substitution is to eliminate or reduce the hazard by substituting non-toxic or less toxic materials or redesigning the process to eliminate escape of contaminants into the workplace. Ideally, substitute chemicals would be non-toxic or the process redesign would completely eliminate exposure. However, since this is not always possible the subsequent controls in the above hierarchy of controls are attempted.
Note that extreme care should be taken to assure that substitution does not result in a more hazardous condition. While this focus is on the toxicity hazard, the flammable and chemical reactivity of substitutes must also be considered when assessing this risk.
The principle of isolation is to eliminate or reduce the hazard by separating the process emitting the contaminant from the worker. This is accomplished by completely enclosing the process or locating it a safe distance away from people. However, to accomplish this, the process may need to be operated and/or controlled remotely. Isolation is particularly useful for jobs requiring few workers and when control by other methods is difficult. Another approach is to perform hazardous operations on off shifts where fewer workers may be exposed. Sometimes the use of this technique does not eliminate exposure but reduces the number of people who are exposed.
Two types of exhaust ventilation are commonly employed to minimize airborne exposure levels of contaminants. The first is called general or dilution ventilation. The second is referred to as source control or local exhaust ventilation (LEV) and is discussed in more detail later in this article.
These two types of exhaust ventilation should not be confused with comfort ventilation, whose main purpose is to provide measured amounts of outdoor air for breathing and to maintain design temperature and humidity. Various types of ventilation are discussed elsewhere in this Encyclopaedia.
Work practices control encompasses the methods workers employ to perform operations and the extent to which they follow the correct procedures. Examples of this control procedure are given throughout this Encyclopaedia wherever general or specific processes are discussed. General concepts such as education and training, principles of management and social support systems include discussions of the importance of work practices in controlling exposures.
Personal Protective Equipment
Personal protective equipment (PPE) is considered the last line of defence for control of worker exposure. It encompasses the use of respiratory protection and protective clothing. It is frequently used in conjunction with other control practices, particularly to minimize the effects of unexpected releases or accidents. These issues are discussed in more detail in the chapter Personal protection.
Local Exhaust Ventilation
The most efficient and cost-effective form of contaminant control is LEV. This involves capture of the chemical contaminant at its source of generation. There are three types of LEV systems:
Enclosures are the preferable type of hood. Enclosures primarily are designed to contain the materials generated within the enclosure. The more complete the enclosure the more completely the contaminant will be contained. Complete enclosures are those that have no openings. Examples of complete enclosures include glove boxes, abrasive blasting cabinets and toxic gas storage cabinets (see figure 1, figure 2 and figure 3). Partial enclosures have one or more sides open but the source is still inside the enclosure. Examples of partial enclosures are a spray paint booth (see figure 4) and a laboratory hood. Often it might appear that the design of enclosures is more art than science. The basic principle is to design a hood with the smallest opening possible. The volume of air required is usually based on the area of all openings and maintaining an airflow velocity into the opening of 0.25 to 1.0 m/s. The control velocity chosen will depend on the operation’s characteristics, including the temperature and the degree to which the contaminant is propelled or generated. For complex enclosures, extreme care must be taken to assure that the exhaust flow is evenly distributed throughout the enclosure, particularly if the openings are distributed. Many enclosure designs are evaluated experimentally and if demonstrated to be effective are included as design plates in the American Conference of Governmental Industrial Hygienists’ industrial ventilation manual (ACGIH 1992).
Figure 1. Complete enclosure: Glovebox
Figure 2. Complete enclosure: Toxic gas storage cabinet
Figure 3. Complete enclosure: Abrasive blasting cabinet
Figure 4. Partial enclosure: Spray paint booth
Often, total enclosure of the source is not possible, or is not necessary. In these cases, another form of local exhaust, an exterior or capture hood, can be used. An exterior hood prevents the release of toxic materials into the workplace by capturing or entraining them at or close to the source of generation, usually a work station or process operation. Considerably less air volume is usually required than for the partial enclosure. However, since the contaminant is generated outside the hood, it must be designed and used properly in order to be as effective as a partial enclosure. The most effective control is a complete enclosure.
To work effectively, the air inlet of an exterior hood must be of appropriate geometrical design and placed near the point of chemical release. The distance away will depend on the size and shape of the hood and the velocity of air needed at the generation source to capture the contaminant and bring it into the hood. Generally, the closer to the generation source, the better. Design face or slot velocities are typically in the range of 0.25 to 1.0 and 5.0 to 10.0 m/s, respectively. Many design guidelines exist for this class of exhaust hoods in Chapter 3 of the ACGIH manual (ACGIH 1992) or in Burgess, Ellenbecker and Treitman (1989). Two types of exterior hoods that find frequent application are “canopy” hoods and “slot” hoods.
Canopy hoods are used primarily for capture of gases, vapours and aerosols released in one direction with a velocity that can be used to aid capture. These are sometimes called “receiving” hoods. This type of hood is generally used when the process to be controlled is at elevated temperatures, to make use of the thermal updraft, or the emissions are directed upward by the process. Examples of operations that may be controlled in this manner include drying ovens, melting furnaces and autoclaves. Many equipment manufacturers recommend specific capture hood configurations that are suitable for their units. They should be consulted for advice. Design guidelines are also provided in the ACGIH manual, Chapter 3 (ACGIH 1992). For example, for an autoclave or oven where the distance between the hood and the hot source does not exceed approximately the diameter of the source or 1 m, whichever is smaller, the hood may be considered a low canopy hood. Under such conditions, the diameter or cross-section of the hot air column will be approximately the same as the source. The diameter or side dimensions of the hood therefore need only be 0.3 m larger than the source.
The total flow rate for a circular low canopy hood is
Qt=4.7 (Df)2.33 (Dt)0.42
Qt = total hood air flow in cubic feet per minute, ft3/min
Df = diameter of hood, ft
Dt = difference between temperature of the hood source, and the ambient, °F.
Figure 5. Canopy hood: Oven exhaust
Slot hoods are used for control of operations that cannot be performed inside a containment hood or under a canopy hood. Typical operations include barrel filling, electroplating, welding and degreasing. Examples are shown in figure 6 and figure 7.
Figure 6. Exterior hood: Welding
Figure 7. Exterior hood: Barrel filling
The required flow can be calculated from a series of equations determined empirically by the size and shape of the hood and the distance of the hood from the source. For example, for a flanged slot hood, the flow is determined by
Q = 0.0743LVX
Q = total hood air flow, m3/min
L = the length of the slot, m
V = the velocity needed at the source to capture it, m/min
X = distance from the source to the slot, m.
The velocity needed at the source is sometimes called “capture velocity” and is usually between 0.25 and 2.5 m/s. Guidelines for selecting an appropriate capture velocity are provided in the ACGIH manual. For areas with excessive cross-drafts or for high-toxicity materials, the upper end of the range should be selected. For particulates, higher capture velocities will be necessary.
Some hoods may be some combination of enclosure, exterior and receiving hoods. For example, the spray paint booth shown in figure 4 is a partial enclosure that is also a receiving hood. It is designed to provide efficient capture of particles generated by making use of the particle momentum created by the rotating grinding wheel in the direction of the hood.
Care must be used in selecting and designing local exhaust systems. Considerations should include (1) ability to enclose the operation, (2) source characteristics (i.e., point source vs. widespread source) and how the contaminant is generated, (3) capacity of existing ventilation systems, (4) space requirements and (5) toxicity and flammability of contaminants.
Once the hood is installed, a routine monitoring and maintenance programme for the systems shall be implemented to assure its effectiveness in preventing exposure to workers (OSHA 1993). Monitoring of the standard laboratory chemical hood has become standardized since the 1970s. However, there is no such standardized procedure for other forms of local exhaust; therefore, the user must devise his or her own procedure. The most effective would be a continuous flow monitor. This could be as simple as a magnetic or water pressure gauge measuring static pressure at the hood (ANSI/AIHA 1993). The required hood static pressure (cm of water) will be known from the design calculations, and flow measurements can be made at the time of installation to verify them. Whether or not a continuous flow monitor is present, there should be some periodic evaluation of the hood performance. This can be done with smoke at the hood to visualize capture and by measuring total flow in the system and comparing that to the design flow. For enclosures it is usually advantageous to measure face velocity through the openings.
Personnel must also be instructed in the correct use of these types of hoods, particularly where the distance from the source and the hood can be easily changed by the user.
If local exhaust systems are designed, installed and used correctly they can be an effective and economical means of controlling toxic exposures.
GESTIS, the hazardous substance information system of the Berufsgenossenschaften (BG, statutory accident insurance carriers) in Germany, is presented here as a case study of an integrated information system for the prevention of risks from workplace chemical substances and products.
With the enactment and application of the regulation on hazardous substances in Germany in the mid-1980s, there was a huge increase in demand for data and information on hazardous substances. This demand had to be met directly by the BG within the framework of their industrial advisory and supervisory activities.
Specialists, including persons working with technical inspection services of the BG, workplace safety engineers, occupational physicians and those cooperating with expert panels, require specific health data. However, information regarding chemical hazards and the necessary safety measures is no less important for the layperson working with hazardous products. In the factory the effectiveness of work protection rules is what finally counts; it is therefore essential that relevant information be easily accessible to the factory owner, safety personnel, workers and, if appropriate, the work committees.
Against this background GESTIS was set up in 1987. Individual BG institutions had maintained databases mostly for more than 20 years. Within the framework of GESTIS, these databases were combined and supplemented with new components, including a “fact” database on substances and products, and information systems specific to particular branches of industry. GESTIS is organized on a central and peripheral basis, with comprehensive data for and about industry in Germany. It is arranged and classified according to branches of industry.
GESTIS consists of four core databases located centrally with the Berufsgenossenschaften Association and their Institute for Occupational Safety (BIA), plus peripheral, branch-specific information systems and documentation on occupational medicine surveillance and interfaces with external databases.
The target groups for hazardous substance information, such as safety engineers and occupational physicians, require different forms and specific data for their work. The form of information directed towards employees should be understandable and related to the specific handling of substances. Technical inspectors may require other information. Finally, the general public has a right to and an interest in workplace health information, including the identification and status of particular risks and the incidence of occupational disease.
GESTIS must be able to satisfy the information needs of various target groups by providing accurate information that focuses on practice.
Which data and information are needed?
Core information on substances and products
Hard facts must be the primary foundation. In essence these are facts about pure chemical substances, based on scientific knowledge and legal requirements. The scope of the subjects and information in safety data sheets, as, for example, defined by the European Union in EU Directive 91/155/EEC, correspond to the requirements of work protection in the factory and provide a suitable framework.
These data are found in the GESTIS central substance and product database (ZeSP), an online database compiled since 1987, with an emphasis on substances and in cooperation with the governmental labour inspection services (i.e., the hazardous substance databases of the states). The corresponding facts on products (mixtures) are established only on the basis of valid data on substances. In practice, a large problem exists because producers of safety data sheets often do not identify the relevant substances in preparations. The above-mentioned EU directive provides for improvements in the safety data sheets and requires more precise data on the listing of components (depending on the concentration levels).
The compilation of safety data sheets within GESTIS is indispensable for combining the producer data with substance data that are independent of the producers. This result occurs both through the branch-specific recording activities of the BG and through a project in cooperation with producers, who ensure that the safety data sheets are available, up-to-date and largely in data-processed form (see figure 1) in the ISI database (Information System Safety datasheets).
Figure 1.Collection and information centre for safety data sheets - basic structure
Because safety data sheets often do not adequately consider the special use of a product, specialists in branches of industry compile information on product groups (e.g., cooling lubricants for practical work protection in the factory) from producers’ information and substance data. Product groups are defined according to their use and their chemical risk potential. The information made available on product groups is independent of the data provided by producers on the composition of individual products because it is based on general formulae of composition. Thus, the user has access to a supplementary independent information source in addition to the safety data sheet.
A characteristic feature of ZeSP is the provision of information on the safe handling of hazardous substances in the workplace, including specific emergency and preventive measures. Furthermore, ZeSP contains comprehensive information on occupational medicine in a detailed, understandable and practice-related form (Engelhard et al. 1994).
In addition to the practice-oriented information outlined above, further data are needed in connection with national and international expert panels in order to undertake risk assessments for chemical substances (e.g., the EU Existing Chemicals Regulation).
For the evaluation of risk, data are required for the handling of hazardous substances, including (1) the use category of substances or products; (2) the amounts used in production and handling, and the number of persons working with or exposed to the hazardous substance or product; and (3) exposure data. These data can be obtained from hazardous substance registers at the factory level, which are obligatory under European hazardous substance law, for pooling at a higher level to form branch or general trade registers. These registers are becoming increasingly indispensable for providing the required background for political decision- makers.
Exposure data (i.e., measurement values of hazardous substance concentrations) are obtained through the BG within the framework of the BG measurement system for hazardous substances (BGMG 1993), to carry out compliance measurements in view of threshold values in the workplace. Their documentation is necessary for considering the level of technology when establishing threshold values and for risk analyses (e.g., in connection with the determination of risks in existing substances), for epidemiological studies and for evaluating occupational diseases.
The measurement values determined as part of workplace surveillance are therefore documented in the Documentation for Measurement Data on Hazardous Substances in the Workplace (DOK-MEGA). Since 1972 more than 800,000 measurement values have become available from over 30,000 firms. At present about 60,000 of these values are being added annually. Particular features of the BGMG include a quality assurance system, education and training components, standardized procedures for sampling and analysis, a harmonized measurement strategy on a legal basis and tools supported by data processing for information gathering, quality assurance and evaluation (figure 2).
Figure 2. BG measurement system for hazardous substances (BGMG) —cooperation between the BIA and the BG.
Exposure measurement values must be representative, repeatable and compatible. Exposure data from workplace surveillance in the BGMG are viewed strictly as “representative” of the individual factory situation, since the selection of measurement sites is carried out according to technical criteria in individual cases, not in accordance with statistical criteria. The question of representativeness arises, however, when measurement values for the same or a similar workplace, or even for entire branches of industry, have to be pooled statistically. Measurement data determined as part of surveillance activity generally give higher average values than data that have initially been collected to obtain a representative cross-section of a branch of industry.
For each measurement, differentiated recording and documentation of the relevant factory, process and sampling parameters are required so that the measured values can be combined in a way that is statistically reasonable, and evaluated and interpreted in a technically adequate manner.
In DOK-MEGA this goal is achieved on the following bases of data recording and documentation:
The BIA makes use of its experience with DOK-MEGA in a EU research project with representatives of other national exposure databases with the aim of improving the comparability of exposure and measurement results. In particular, an attempt is being made here to define core information as a basis for comparability and to develop a “protocol” for data documentation.
In addition to facts about chemical substances and products and about the results of exposure measurements, information is needed on the health effects of actual exposure to hazardous substances in the workplace. Adequate conclusions concerning occupational safety on and beyond the corporate level can be drawn only from an overall view of risk potential, actual risk and effects.
A further component of GESTIS is therefore the occupational disease documentation (BK-DOK), in which all cases of occupational disease reported since 1975 have been registered.
Essential to occupational disease documentation in the area of hazardous substances is the unambiguous, correct determination and recording of the relevant substances and products associated with each case. As a rule the determination is very time-consuming, but acquiring knowledge for prevention is impossible without the accurate identification of substances and products. Thus, for respiratory and skin diseases, which present a particular need for better understanding of possible causative agents, particular effort must be given to record substance and product use information as accurately as possible.
The fourth component proposed for GESTIS was background information made available in the form of literature documents, so that the basic facts could be judged appropriately on the basis of current knowledge, and conclusions drawn. For this purpose an interface was developed with the literature database (ZIGUV-DOK), with a total of 50,000 references at present, of which 8,000 are on the subject of hazardous substances.
Linkage and Problem-oriented Preparation of Data
The components of GESTIS described above cannot stand in isolation if such a system is to be used efficiently. They require appropriate linkage possibilities, for example, between exposure data and cases of occupational disease. This linkage permits the creation of a truly integrated information system. The linkage occurs through core information that is available, coded in the standardized GESTIS coding system (see table 1).
Table 1. Standardized GESTIS code system
|Substance, product||ZVG central allocation number (BG)||SGS/PGS, substance/product group code (BG)|
|Workplace||IBA sphere of activity of individual factory (BG)||AB sphere of activity (BIA)|
|Exposed person||Activity (BIA, on the basis of the Federal Statistical Office’s systematic listing of occupations)|
Origins of codes appear in parentheses.
With the help of the GESTIS code both individual items of information can be linked to each other (e.g., measurement data from a particular workplace with a case of occupational disease that has occurred in the same or similar workplace) and statistically condensed, “typified” information (e.g., diseases related to particular work processes with average exposure data) can be obtained. With individual linkages of data (e.g., using the pension insurance number) the data protection laws must of course be strictly observed.
It is clear, therefore, that only a systematic coding system is capable of meeting these linkage requirements within the information system. Attention must, however, also be drawn to the possibility of linkage between various information systems and across national boundaries. These possibilities of linkage and comparison are crucially dependent on the use of internationally unified coding standards, if necessary in addition to national standards.
Preparation of problem-oriented and use-oriented information
The structure of GESTIS has at its centre the fact databases on substances and products, exposures, occupational diseases and literature, the data compiled both through specialists active at the centre and through the peripheral activities of the BG. For the application and use of the data, it is necessary to reach the users, centrally through publication in relevant journals (e.g., on the subject of the incidence of occupational disease), but also specifically through the advisory activities of the BG in their member firms.
For the most efficient possible use of information made available in GESTIS, the question arises regarding the problem-specific and target-group-specific preparation of facts as information. User-specific requirements are addressed in the fact databases on chemical substances and products—for example, in the depth of information or in the practice-oriented presentation of information. However, not all the specific requirements of possible users can be directly addressed in the fact databases. Target-group-specific and problem-specific preparation, if necessary supported by data processing, is required. Workplace-oriented information must be made available on the handling of hazardous substances. The most important data from the database must be extracted in a generally understandable and workplace-oriented form, for example, in the form of “workplace instructions”, which are prescribed in the occupational safety laws of many countries. Frequently too little attention is paid to this user-specific preparation of data as information for workers. Special information systems can prepare this information, but specialized information points which respond to individual queries also provide information and give the necessary support to firms. Within the framework of GESTIS this information- gathering and preparation proceeds, for instance, through branch-specific systems such as GISBAU (Hazardous Substances Information System of the Building Industry BG), GeSi (Hazardous Substances and Safety System), and through specialized information centres in the BG, in the BIA or in the association of the Berufsgenossenschaften.
GESTIS provides the relevant interfaces for data exchange and fosters cooperation by means of task-sharing:
The emphasis of further development will be on prevention. In cooperation with the producers, plans encompass a comprehensive and up-to-date preparation of product data; the establishment of statistically determined workplace characteristic values derived from the exposure measurement data and from the substance-specific and product-specific documentation; and an evaluation in the occupational disease documentation.
A systematic approach to safety requires an efficient flow of information from the suppliers to the users of chemicals on potential hazards and correct safety precautions. In addressing the need for a written hazard communication programme, the ILO Code of Practice Safety in the Use of Chemicals at Work (ILO 1993) states, “The supplier should provide an employer with essential information about hazardous chemicals in the form of a chemical safety data sheet.” This chemical safety data sheet or material safety data sheet (MSDS) describes the hazards of a material and provides instructions on how the material can be safely handled, used and stored. MSDSs are produced by the manufacturer or importer of hazardous products. The manufacturer must provide distributors and other customers with MSDSs upon first purchase of a hazardous product and if the MSDS changes. Distributors of hazardous chemicals must automatically provide MSDSs to commercial customers. Under the ILO Code of Practice, workers and their representatives should have a right to an MSDS and to receive the written information in forms or languages they easily understand. Because some of the required information might be intended for specialists, further clarification may be needed from the employer. The MSDS is only one source of information on a material and, therefore, it is best used along with technical bulletins, labels, training and other communications.
The requirements for a written hazard communication programme are outlined in at least three major international directives: the US Occupational Safety and Health Administration (OSHA) Hazard Communication Standard, Canada’s Workplace Hazardous Materials Information System (WHMIS) and the European Community’s Commission Directive 91/155/EEC. In all three directives, the requirements for preparing a complete MSDS are established. Criteria for the data sheets include information about the identity of the chemical, its supplier, classification, hazards, safety precautions and the relevant emergency procedures. The following discussion details the type of required information included in the 1992 ILO Code of Practice Safety in the Use of Chemicals at Work. While the Code is not intended to replace national laws, regulations or accepted standards, its practical recommendations are intended for all those who have a responsibility for ensuring the safe use of workplace chemicals.
The following description of chemical safety data sheet content corresponds with section 5.3 of the Code:
Chemical safety data sheets for hazardous chemicals should give information about the identity of the chemical, its supplier, classification, hazards, safety precautions and the relevant emergency procedures.
The information to be included should be that established by the competent authority for the area in which the employer’s premises are located, or by a body approved or recognized by that competent authority. Details of the type of information that should be required are given below.
(a) Chemical product and company identification
The name should be the same as that used on the label of the hazardous chemical, which may be the conventional chemical name or a commonly used trade name. Additional names may be used if these help identification. The full name, address and telephone number of the supplier should be included. An emergency telephone number should also be given, for contact in the event of an emergency. This number may be that of the company itself or of a recognized advisory body, so long as either can be contacted at all times.
(b) Information on ingredients (composition)
The information should allow employers to identify clearly the risks associated with a particular chemical so that they may conduct a risk assessment, as outlined in section 6.2 (Procedures for assessment) of this code. Full details of the composition should normally be given but may not be necessary if the risks can be properly assessed. The following should be provided except where the name or concentration of an ingredient in a mixture is confidential information which can be omitted in accordance with section 2.6:
(c) Hazard identification
The most important hazards, including the most significant health, physical and environmental hazards, should be stated clearly and briefly, as an emergency overview. The information should be compatible with that shown on the label.
(d) First-aid measures
First-aid and self-help measures should be carefully explained. Situations where immediate medical attention is required should be described and the necessary measures indicated. Where appropriate, the need for special arrangements for specific and immediate treatment should be emphasized.
(e) Firefighting measures
The requirements for fighting a fire involving a chemical should be included; for example:
Information should also be given on the properties of the chemical in the event of fire and on special exposure hazards as a result of combustion products, as well as the precautions to be taken.
(f) Accidental release measures
Information should be provided on the action to be taken in the event of an accidental release of the chemical. The information should include:
(g) Handling and storage
Information should be given about conditions recommended by the supplier for safe storage and handling, including:
(h) Exposure controls and personal protection
Information should be given on the need for personal protective equipment during use of a chemical, and on the type of equipment that provides adequate and suitable protection. Where appropriate, a reminder should be given that the primary controls should be provided by the design and installation of any equipment used and by other engineering measures, and information provided on useful practices to minimize exposure of workers. Specific control parameters such as exposure limits or biological standards should be given, along with recommended monitoring procedures.
(i) Physical and chemical properties
A brief description should be given of the appearance of the chemical, whether it is a solid, liquid or gas, and its colour and odour. Certain characteristics and properties, if known, should be given, specifying the nature of the test to determine these in each case. The tests used should be in accordance with the national laws and criteria applying at the employer’s workplace and, in the absence of national laws or criteria, the test criteria of the exporting country should be used as guidance. The extent of the information provided should be appropriate to the use of the chemical. Examples of other useful data include:
(j) Stability and reactivity
The possibility of hazardous reactions under certain conditions should be stated. Conditions to avoid should be indicated, such as:
Where hazardous decomposition products are given off, these should be specified along with the necessary precautions.
(k) Toxicological information
This section should give information on the effects on the body and on potential routes of entry into the body. Reference should be made to acute effects, both immediate and delayed, and to chronic effects from both short- and long-term exposure. Reference should also be made to health hazards as a result of possible reaction with other chemicals, including any known interactions, for example, resulting from the use of medication, tobacco and alcohol.
(l) Ecological information
The most important characteristics likely to have an effect on the environment should be described. The detailed information required will depend on the national laws and practice applying at the employer’s workplace. Typical information that should be given, where appropriate, includes the potential routes for release of the chemical which are of concern, its persistence and degradability, bioaccumulative potential and aquatic toxicity, and other data relating to ecotoxicity (e.g., effects on water treatment works).
(m) Disposal considerations
Safe methods of disposal of the chemical and of contaminated packaging, which may contain residues of hazardous chemicals, should be given. Employers should be reminded that there may be national laws and practices on the subject.
(n) Transport information
Information should be given on special precautions that employers should be aware of or take while transporting the chemical on or off their premises. Relevant information given in the United Nations Recommendations on the Transport of Dangerous Goods and in other international agreements may also be included.
(o) Regulatory information
Information required for the marking and labelling of the chemical should be given here. Specific national regulations or practices applying to the user should be referred to. Employers should be reminded to refer to the requirements of national laws and practices.
(p) Other information
Other information which may be important to workers’ health and safety should be included. Examples are training advice, recommended uses and restrictions, references, and sources of key data for compiling the chemical safety data sheet, the technical contact point and date of issue of the sheet.
3.1.1. The competent authority, or a body approved or recognised by the competent authority, should establish systems and specific criteria for classifying a chemical as hazardous and should progressively extend these systems and their application. Existing criteria for classification established by other competent authorities or by international agreement may be followed, if they are consistent with the criteria and methods outllined in this code, and this is encouraged where it may assist uniformity of approach. The results of the work of the UNEP/ILO/WHO International Programme on Chemical Safety (IPCS) coordinating group for the harmonisation of classification of chemicals should be considered when appropriate. The responsibilities and role of competent authorities concerning classification systems are set out in paragraphs 2.1.8 (criteria and requirements), 2.1.9 (consolidated list) and 2.1.10 (assessment of new chemicals).
3.1.2. Suppliers should ensure that chemicals they supplied have been classified or that they have been identified and their properties assessed (see paragraphs 2.4.3 (assessment) and 2.4.4 (classification)).
3.1.3. Manufacturers or importers, unless exempted, should give to the competent authority information about chemical elements and compounds not yet included in the consolidated classification list compiled by the competent authority, prior to their use at work (see paragraph 2.1.10 (assessment of new chemicals)).
3.1.4. The limited quantities of a new chemical required for research and development purposes may be produced by, handled in, and transported between laboratories and pilot plant before all hazards of this chemical are known in accordance with national laws and regulations. All available information found in literature or known to the employer from his or her experience with similar chemicals and applications should be fully taken into account, and adequate protection measures should be applied, as if the chemical were hazardous. The workers involved must be informed about the actual hazard information as it becomes known.
3.2. Criteria for classification
3.2.1. The criteria for the classification of chemicals should be based upon their intrinsic health and physical hazards, including:
3.3. Method of classification
3.3.1. The classification of chemicals should be based on available sources of information, e.g.:
3.3.2. Certain classification systems in use may be limited to particular classes of chemicals only. An example is the WHO Recommended classification of pesticides by hazard and guidelines to classification, which classifies pesticides by degree of toxicity only and principally by acute risks to health. Employers and workers should understand the limitations of any such system. Such systems can be useful to complement a more generally applicable system.
3.3.3. Mixtures of chemicals should be classified based on the hazards exhibited by the mixtures themselves. Only if mixtures have not been tested as a whole should they be classified on the basis of intrinsic hazards of their component chemicals.
Source: ILO 1993, Chapter 3.