Metalworking involves casting, welding, brazing, forging, soldering, fabrication and surface treatment of metal. Metalworking is becoming even more common as artists in developing countries are also starting to use metal as a basic sculptural material. While many art foundries are commercially run, art foundries are also often part of college art programmes.

Hazards and Precautions

Casting and foundry

Artists either send work out to commercial foundries, or can cast metal in their own studios. The lost wax process is often used for casting small pieces. Common metals and alloys used are bronze, aluminium, brass, pewter, iron and stainless steel. Gold, silver and sometimes platinum are used for casting small pieces, particularly for jewellery.

The lost wax process involves several steps:

1. making the positive form
2. making the investment mould
3. burning out of the wax
4. melting the metal
5. slagging
6. pouring the molten metal into the mould
7. removing the mould

The positive form can be made directly in wax; it can also be made in plaster or other materials, a negative mould made in rubber and then the final positive form cast in wax. Heating the wax can result in fire hazards and in decomposition of the wax from overheating.

The mould is commonly made by applying an investment containing the cristobalite form of silica, creating the risk of silicosis. A 50/50 mixture of plaster and 30-mesh sand is a safer substitute. Moulds can also be made using sand and oil, formaldehyde resins and other resins as binders. Many of these resins are toxic by skin contact and inhalation, requiring skin protection and ventilation.

The wax form is burnt out in a kiln. This requires local exhaust ventilation to remove the acrolein and other irritating wax decomposition products.

Melting the metal is usually done in a gas-fired crucible furnace. A canopy hood exhausted to the outside is needed to remove carbon monoxide and metal fumes, including zinc, copper, lead, aluminium and so on.

The crucible containing the molten metal is then removed from the furnace, the slag on the surface removed and the molten metal poured into the moulds (figure 1). For weights under 80 pounds of metal, manual lifting is normal; for greater weights, lifting equipment is needed. Ventilation is needed for the slagging and pouring operations to remove metal fumes. Resin sand moulds can also produce hazardous decomposition products from the heat. Face shields protecting against infrared radiation and heat, and personal protective clothing resistant to heat and molten metal splashes are essential. Cement floors must be protected against molten metal splashes by a layer of sand.

Figure 1. Pouring molten metal in art foundry.

Ted Rickard

Breaking away the mould can result in exposure to silica. Local exhaust ventilation or respiratory protection is needed. A variation of the lost wax process called the foam vaporization process involves using polystyrene or polyurethane foam instead of wax, and vaporizing the foam during pouring of the molten metal. This can release hazardous decomposition products, including hydrogen cyanide from polyurethane foam. Artists often use scrap metal from a variety of sources. This practice can be dangerous due to possible presence of lead- and mercury-containing paints, and to the possible presence of metals like cadmium, chromium, nickel and so on in the metals.

Fabrication

Metal can be cut, drilled and filed using saws, drills, snips and metal files. The metal filings can irritate the skin and eyes. Electric tools can cause electric shock. Improper handling of these tools can result in accidents. Goggles are needed to protect the eyes from flying chips and filings. All electrical equipment should be properly grounded. All tools should be carefully handled and stored. Metal to be fabricated should be securely clamped to prevent accidents.

Forging

Cold forging utilizes hammers, mallets, anvils and similar tools to change the shape of metal. Hot forging involves additionally heating the metal. Forging can create great amounts of noise, which can cause hearing loss. Small metal splinters may damage the skin or eyes if precautions are not taken. Burns are also a hazard with hot forging. Precautions include good tools, eye protection, routine clean-up, proper work clothing, isolation of the forging area and wearing ear plugs or ear muffs.

Hot forging involves the burning of gas, coke or other fuels. A canopy hood for ventilation is needed to exhaust carbon monoxide and possible polycyclic aromatic hydrocarbon emissions, and to reduce heat build-up. Infrared goggles should be worn for protection against infrared radiation.

Surface treatment

Mechanical treatment (chasing, repousse) is done with hammers, engraving with sharp tools, etching with acids, photoetching with acids and photochemicals, electroplating (plating a metallic film onto another metal) and electroforming (plating a metallic film onto a non-metallic object) with acids and cyanide solutions and metal colouring with many chemicals.

Electroplating and electroforming often use cyanide salts, ingestion of which can be fatal. Accidental mixing of acids and the cyanide solution will produce hydrogen cyanide gas. This is hazardous through both skin absorption and inhalation—death can occur within minutes. Disposal and waste management of spent cyanide solutions is strictly regulated in many countries. Electroplating with cyanide solutions should be done in a commercial plant; otherwise use substitutes that do not contain cyanide salts or other cyanide-containing materials.

Acids are corrosive, and skin and eye protection is needed. Local exhaust ventilation with acid-resistant ductwork is recommended.

Anodizing metals such as titanium and tantalum involves oxidizing these at the anode of an electrolytic bath to colour them. Hydrofluoric acid can be used for precleaning. Avoid using hydrofluoric acid or use gloves, goggles and a protective apron.

Patinas used to colour metals can be applied cold or hot. Lead and arsenic compounds are very toxic in any form, and others can give off toxic gases when heated. Potassium ferricyanide solutions will give off hydrogen cyanide gas when heated, arsenic acid solutions give off arsine gas and sulphide solutions give off hydrogen sulphide gas. Very good ventilation is needed for metal colouring (figure 2). Arsenic compounds and heating of potassium ferrocyanide solutions should be avoided.

Figure 2. Applying a patina to metal with slot exhaust hood.

Ken Jones

Finishing processes

Cleaning, grinding, filing, sandblasting and polishing are some final treatments for metal. Cleaning involves the use of acids (pickling). This involves the hazards of handling acids and of the gases produced during the pickling process (such as nitrogen dioxide from nitric acid). Grinding can result in the production of fine metal dusts (which can be inhaled) and heavy flying particles (which are eye hazards).

Sandblasting (abrasive blasting) is very hazardous, particularly with actual sand. Inhalation of fine silica dust from sandblasting can cause silicosis in a short time. Sand should be replaced with glass beads, aluminium oxide or silicon carbide. Foundry slags should be used only if chemical analysis shows no silica or dangerous metals such as arsenic or nickel. Good ventilation or respiratory protection is needed.

Polishing with abrasives such as rouge (iron oxide) or tripoli can be hazardous since rouge can be contaminated with large amounts of free silica, and tripoli contains silica. Good ventilation of the polishing wheel is needed.

Welding

Physical hazards in welding include the danger of fire, electric shock from arc-welding equipment, burns caused by molten metal sparks, and injuries caused by excessive exposure to infrared and ultraviolet radiation. Welding sparks can travel 40 feet.

Infrared radiation can cause burns and eye damage. Ultraviolet radiation can cause sunburn; repeated exposure may lead to skin cancer. Electric arc welders in particular are subject to pink eye (conjunctivitis), and some have cornea damage from UV exposure. Skin protection and welding goggles with UV- and IR-protective lenses are needed.

Oxyacetylene torches produce carbon monoxide, nitrogen oxides and unburned acetylene, which is a mild intoxicant. Commercial acetylene contains small amounts of other toxic gases and impurities.

Compressed gas cylinders can be both explosive and fire hazards. All cylinders, connections and hoses must be carefully maintained and inspected. All gas cylinders must be stored in a location which is dry, well ventilated and secure from unauthorized persons. Fuel cylinders must be stored separately from oxygen cylinders.

Arc welding produces enough energy to convert the air’s nitrogen and oxygen to nitrogen oxides and ozone, which are lung irritants. When arc welding is done within 20 feet of chlorinated degreasing solvents, phosgene gas can be produced by the UV radiation.

Metal fumes are generated by the vaporization of metals, metal alloys and the electrodes used in arc welding. Fluoride fluxes produce fluoride fumes.

Ventilation is needed for all welding processes. While dilution ventilation may be adequate for mild steel welding, local exhaust ventilation is necessary for most welding operations. Moveable flanged hoods, or lateral slot hoods should be used. Respiratory protection is needed if ventilation is not available.

Many metal dusts and fumes can cause skin irritation and sensitization. These include brass dust (copper, zinc, lead and tin), cadmium, nickel, titanium and chromium.

In addition, there are problems with welding materials that may be coated with various substances (e.g., lead or mercury paint).

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Since the first sustained flight of a powered aircraft at Kitty Hawk, North Carolina (United States), in 1903, aviation has become a major international activity. It is estimated that from 1960 to 1989, the annual number of air passengers of regularly scheduled flights increased from 20 million to over 900 million (Poitrast and deTreville 1994). Military aircraft have become indispensable weapons systems for the armed forces of many nations. Advances in aviation technology, in particular the design of life support systems, have contributed to the rapid development of space programmes with human crews. Orbital space flights occur relatively frequently, and astronauts and cosmonauts work in space vehicles and space stations for extended periods of time.

In the aerospace environment, physical stressors that may affect the health of aircrew, passengers and astronauts to some degree include reduced concentrations of oxygen in the air, decreased barometric pressure, thermal stress, acceleration, weightlessness and a variety of other potential hazards (DeHart 1992). This article describes aeromedical implications of exposure to gravity and acceleration during flight in the atmosphere and the effects of microgravity experienced in space.

Gravity and Acceleration

The combination of gravity and acceleration encountered during flight in the atmosphere produces a variety of physiological effects experienced by aircrew and passengers. At the surface of the earth, the forces of gravity affect virtually all forms of human physical activity. The weight of a person corresponds to the force exerted upon the mass of the human body by the earth’s gravitational field. The symbol used to express the magnitude of the acceleration of an object in free fall when it is dropped near the earth’s surface is referred to as g, which corresponds to an acceleration of approximately 9.8 m/s² (Glaister 1988a; Leverett and Whinnery 1985).

Acceleration occurs whenever an object in motion increases its velocity. Velocity describes the rate of movement (speed) and direction of motion of an object. Deceleration refers to acceleration that involves a reduction in established velocity. Acceleration (as well as deceleration) is a vector quantity (it has magnitude and direction). There are three types of acceleration: linear acceleration, a change of speed without change in direction; radial acceleration, a change in direction without a change of speed; and angular acceleration, a change in speed and direction. During flight, aircraft are capable of manoeuvring in all three directions, and crew and passengers may experience linear, radial and angular accelerations. In aviation, applied accelerations are commonly expressed as multiples of the acceleration due to gravity. By convention, G is the unit expressing the ratio of an applied acceleration to the gravitational constant (Glaister 1988a; Leverett and Whinnery 1985).

Biodynamics

Biodynamics is the science dealing with the force or energy of living matter and is a major area of interest within the field of aerospace medicine. Modern aircraft are highly manoeuvrable and capable of flying at very high speeds, causing accelerative forces upon the occupants. The influence of acceleration upon the human body depends upon the intensity, rate of onset and direction of acceleration. The direction of acceleration is generally described by the use of a three-axis coordinate system (x, y, z) in which the vertical (z) axis is parallel to the long axis of the body, the x axis is oriented from front to back, and the y axis oriented side to side (Glaister 1988a). These accelerations can be categorized into two general types: sustained and transitory.

Sustained acceleration

The occupants of aircraft (and spacecraft operating in the atmosphere under the influence of gravity during launch and re-entry) commonly experience accelerations in response to aerodynamic forces of flight. Prolonged changes in velocity involving accelerations lasting longer than 2 seconds may result from changes in an aircraft’s speed or direction of flight. The physiological effects of sustained acceleration result from the sustained distortion of tissues and organs of the body and changes in the flow of blood and distribution of body fluids (Glaister 1988a).

Positive or headward acceleration along the z axis (+G_z) represents the major physiological concern. In civil air transportation, G_z accelerations are infrequent, but may occasionally occur to a mild degree during some take-offs and landings, and while flying in conditions of air turbulence. Passengers may experience brief sensations of weightlessness when subject to sudden drops (negative G_z accelerations), if unrestrained in their seats. An unexpected abrupt acceleration may cause unrestrained aircrew or passengers to be thrown against internal surfaces of the aircraft cabin, resulting in injuries.

In contrast to civil transport aviation, the operation of high- performance military aircraft and stunt and aerial spray planes may generate significantly higher linear, radial and angular accelerations. Substantial positive accelerations may be generated as a high-performance aircraft changes its flight path during a turn or a pull-up manoeuvre from a steep dive. The +G_z performance characteristics of current combat aircraft may expose occupants to positive accelerations of 5 to 7 G for 10 to 40 seconds (Glaister 1988a). Aircrew may experience an increase in the weight of tissues and of the extremities at relatively low levels of acceleration of only +2 G_z. As an example, a pilot weighing 70 kg who performed an aircraft manoeuvre which generated +2 G_z would experience an increase of body weight from 70 kg to 140 kg.

The cardiovascular system is the most important organ system for determining the overall tolerance and response to +G_z stress (Glaister 1988a). The effects of positive acceleration on vision and mental performance are due to decreases in blood flow and delivery of oxygen to eye and brain. The capability of the heart to pump blood to the eyes and brain is dependent upon its capability to exceed the hydrostatic pressure of blood at any point along the circulatory system and the inertial forces generated by the positive G_z acceleration. The situation may be likened to that of pulling upward a balloon partially full of water and observing the downward distension of the balloon because of the resultant inertial force acting upon the mass of water. Exposure to positive accelerations may cause temporary loss of peripheral vision or complete loss of consciousness. Military pilots of high- performance aircraft may risk development of G-induced blackouts when exposed to rapid onset or extended periods of positive acceleration in the +G_z axis. Benign cardiac arrhythmias frequently occur following exposure to high sustained levels of +G_z acceleration, but usually are of minimal clinical significance unless pre-existing disease is present; –G_z acceleration seldom occurs because of limitations in aircraft design and performance, but may occur during inverted flight, outside loops and spins and other similar manoeuvres. The physiological effects associated with exposure to –G_z acceleration primarily involve increased vascular pressures in the upper body, head and neck (Glaister 1988a).

Accelerations of sustained duration which act at right angles to the long axis of the body are termed transverse accelerations and are relatively uncommon in most aviation situations, with the exception of catapult and jet- or rocket-assisted take-offs from aircraft carriers, and during launch of rocket systems such as the space shuttle. The accelerations encountered in such military operations are relatively small, and usually do not affect the body in a major fashion because the inertial forces act at right angles to the long axis of the body. In general, the effects are less pronounced than in G_z accelerations. Lateral acceleration in ±G_y axis are uncommon, except with experimental aircraft.

Transitory acceleration

The physiological responses of individuals to transitory accelerations of short duration are a major consideration in the science of aircraft accident prevention and crew and passenger protection. Transitory accelerations are of such brief duration (considerably less than 1 second) that the body is unable to attain a steady-state status. The most common cause of injury in aircraft accidents results from the abrupt deceleration that occurs when an aircraft impacts the ground or water (Anton 1988).

When an aircraft impacts the ground, a tremendous amount of kinetic energy applies damaging forces to the aircraft and its occupants. The human body responds to these applied forces by a combination of acceleration and strain. Injuries result from deformation of tissues and organs and trauma to anatomic parts caused by collision with structural components of the aircraft cockpit and/or cabin.

Human tolerance to abrupt deceleration is variable. The nature of injuries will depend on the nature of the applied force (whether it primarily involves penetrating or blunt impact). At impact, the forces which are generated are dependent on the longitudinal and horizontal decelerations which are generally applied to an occupant. Abrupt decelerative forces are often categorized into tolerable, injurious and fatal. Tolerable forces produce traumatic injuries such as abrasions and bruises; injurious forces produce moderate to severe trauma which may not be incapacitating. It is estimated that an acceleration pulse of approximately 25 G maintained for 0.1 second is the limit of tolerability along the +G_z axis, and that about 15 G for 0.1 sec is the limit for the –G_z axis (Anton 1988).

Multiple factors affect human tolerance to short-duration acceleration. These factors include the magnitude and duration of the applied force, the rate of onset of the applied force, its direction and the site of application. It should be noted that people can withstand much greater forces perpendicular to the long axis of the body.

Protective Countermeasures

Physical screening of crew members to identify serious pre- existing diseases which might put them at increased risk in the aerospace environment is a key function of aeromedical programmes. In addition, countermeasures are available to crew of high-performance aircraft to protect against the adverse effects of extreme accelerations during flight. Crew members must be trained to recognize that multiple physiological factors may decrease their tolerance to G stress. These risk factors include fatigue, dehydration, heat stress, hypoglycemia and hypoxia (Glaister 1988b).

Three types of manoeuvres which crew members of high- performance aircraft employ to minimize adverse effects of sustained acceleration during flight are muscle tensing, forced expiration against a closed or partially closed glottis (back of the tongue) and positive-pressure breathing (Glaister 1988b; DeHart 1992). Forced muscle contractions exert increased pressure on blood vessels to decrease venous pooling and increase venous return and cardiac output, resulting in increased blood flow to the heart and upper body. While effective, the procedure requires extreme, active effort and may rapidly result in fatigue. Expiration against a closed glottis, termed the Valsalva manoeuver (or M-1 procedure) can increase pressure in the upper body and raise the intrathoracic pressure (inside the chest); however, the result is short lived and may be detrimental if prolonged, because it reduces venous blood return and cardiac output. Forcibly exhaling against a partially closed glottis is a more effective anti-G straining manoeuver. Breathing under positive pressure represents another method to increase intrathoracic pressure. Positive pressures are transmitted to the small artery system, resulting in increased blood flow to the eyes and brain. Positive-pressure breathing must be combined with the use of anti-G suits to prevent excessive pooling in the lower body and limbs.

Military aircrew practise a variety of training methods to enhance G tolerance. Crews frequently train in a centrifuge consisting of a gondola attached to a rotating arm which spins and generates +G_z acceleration. Aircrew become familiar with the spectrum of physiological symptoms which may develop and learn the proper procedures to control them. Physical fitness training, particularly whole-body strength training, also has been found to be effective. One of the most common mechanical devices used as protective equipment to reduce the effects of +G exposure consists of pneumatically inflated anti-G suits (Glaister 1988b). The typical trouser-like garment consists of bladders over the abdomen, thighs and calves which automatically inflate by means of an anti-G valve in the aircraft. The anti-G valve inflates in reaction to an applied acceleration upon the aircraft. Upon inflation, the anti-G suit produces a rise in the tissue pressures of the lower extremities. This maintains peripheral vascular resistance, reduces the pooling of blood in the abdomen and lower limbs and minimizes downward displacement of the diaphragm to prevent the increase in the vertical distance between the heart and brain that may be caused by positive acceleration (Glaister 1988b).

Surviving transitory accelerations associated with aircraft crashes is dependent on effective restraint systems and the maintenance of the cockpit/cabin integrity to minimize intrusion of damaged aircraft components into the living space (Anton 1988). The function of lap belts, harnesses and other types of restraint systems are to limit the movement of the aircrew or passengers and to attenuate the effects of sudden deceleration during impact. The effectiveness of the restraint system depends on how well it transmits loads between the body and the seat or vehicle structure. Energy-attenuating seating and rearward facing seats are other features in aircraft design which limit injury. Other accident-protection technology includes the design of airframe components to absorb energy and improvements in seat structures to reduce mechanical failure (DeHart 1992; DeHart and Beers 1985).

Microgravity

Since the 1960s, astronauts and cosmonauts have flown numerous missions into space, including 6 lunar landings by Americans. Mission duration has been from several days to a number of months, with a few Russian cosmonauts logging approximately 1-year flights. Subsequent to these space flights, a large body of literature has been written by physicians and scientists describing in-flight and post-flight physiological aberrations. For the most part, these aberrations have been attributed to exposure to weightlessness or microgravity. Although these changes are transient, with total recovery within several days to several months after returning to Earth, nobody can say with complete certitude whether astronauts would be so fortunate after missions lasting 2 to 3 years, as envisioned for a round trip to Mars. The major physiological aberrations (and countermeasures) can be categorized as cardiovascular, musculoskeletal, neurovestibular, haematological and endocrinological (Nicogossian, Huntoon and Pool 1994).

Cardiovascular hazards

Thus far, there have been no serious cardiac problems in space, such as heart attacks or heart failure, although several astronauts have developed abnormal heart rhythms of a transient nature, particularly during extra-vehicular activity (EVA). In one case, a Russian cosmonaut had to return to Earth earlier than planned, as a precautionary measure.

On the other hand, microgravity seems to induce a lability of blood pressure and pulse. Although this does not cause impaired health or crew performance during flight, approximately half of astronauts immediately post-flight do become extremely dizzy and giddy, with some experiencing fainting (syncope) or near fainting (pre-syncope). The cause of this intolerance to being vertical is thought to be a drop in blood pressure upon re-entering the earth’s gravitational field, combined with the dysfunction of the body’s compensatory mechanisms. Hence, a low blood pressure and decreasing pulse unopposed by the body’s normal response to such physiological aberrations results in these symptoms.

Although these pre-syncopal and syncopal episodes are transient and without sequelae, there remains great concern for several reasons. First, in the event that a returning space vehicle were to have an emergency, such as a fire, upon landing, it would be extremely difficult for astronauts to rapidly escape. Second, astronauts landing on the moon after periods of time in space would be prone to some extent to pre-fainting and fainting, even though the moon’s gravitational field is one-sixth that of Earth. And finally, these cardiovascular symptoms might be far worse or even lethal after very long missions.

It is for these reasons that there has been an aggressive search for countermeasures to prevent or at least ameliorate the microgravity effects upon the cardiovascular system. Although there are a number of countermeasures now being studied that show some promise, none so far has been proven truly effective. Research has focused on in-flight exercise utilizing a treadmill, bicycle ergometer and rowing machine. In addition, studies are also being conducted with lower body negative pressure (LBNP). There is some evidence that lowering the pressure around the lower body (using compact special equipment) will enhance the body’s ability to compensate (i.e., raise blood pressure and pulse when they fall too low). The LBNP countermeasure might be even more effective if the astronaut drinks moderate amounts of specially constituted salt water simultaneously.

If the cardiovascular problem is to be solved, not only is more work needed on these countermeasures, but also new ones must be found.

Musculoskeletal hazards

All astronauts returning from space have some degree of muscle wasting or atrophy, regardless of mission duration. Muscles at particular risk are those of the arms and legs, resulting in decreased size as well as strength, endurance and work capacity. Although the mechanism for these muscle changes is still ill-defined, a partial explanation is prolonged disuse; work, activity and movement in microgravity are almost effortless, since nothing has any weight. This may be a boon for astronauts working in space, but is clearly a liability when returning to a gravitational field, whether it be that of the moon or Earth. Not only could a weakened condition impede post-flight activities (including work on the lunar surface), it could also compromise rapid ground emergency escape, if required upon landing. Another factor is the possible requirement during EVA to do space vehicle repairs, which can be very strenuous. Countermeasures under study include in-flight exercises, electrical stimulation and anabolic medication (testosterone or testosterone-like steroids). Unfortunately, these modalities at best only retard muscle dysfunction.

In addition to muscle wasting, there is also a slow but inexorable loss of bone in space (about 300 mg per day, or 0.5% of total bone calcium per month) experienced by all astronauts. This has been documented by post-flight x rays of bones, particularly of those that bear weight (i.e., the axial skeleton). This is due to a slow but unremitting loss of calcium into the urine and faeces. Of great concern is the continuing loss of calcium, regardless of flight duration. Consequently, this calcium loss and bone erosion could be a limiting factor of flight, unless an effective countermeasure can be found. Although the precise mechanism of this very significant physiological aberration is not fully understood, it undoubtedly is due in part to the absence of gravitational forces on bone, as well as disuse, similar to muscle wasting. If bone loss were to continue indefinitely, particularly over long missions, bones would become so brittle that eventually there would be risk of fractures with even low levels of stress. Furthermore, with a constant flow of calcium into the urine via the kidneys, a possibility of renal stone formation exists, with accompanying severe pain, bleeding and infection. Clearly, any of these complications would be a very serious matter were they to occur in space.

Unfortunately, there are no known countermeasures that effectively prevent calcium loss during space flight. A number of modalities are being tested, including exercise (treadmill, bicycle ergometer and rowing machine), the theory being that such voluntary physical stresses would normalize bone metabolism, thereby preventing or at least ameliorating bone loss. Other countermeasures under investigation are calcium supplements, vitamins and various medications (such as diphosphonates—a class of medications that has been shown to prevent bone loss in patients with osteoporosis). If none of these simpler countermeasures prove to be effective, it is possible that the solution lies in artificial gravity that could be produced by continuous or intermittent rotation of the space vehicle. Although such motion could generate gravitational forces similar to that of the earth, it would represent an engineering “nightmare”, in addition to major add-on costs.

Neurovestibular hazards

More than half of the astronauts and cosmonauts suffer from space motion sickness (SMS). Although the symptoms vary somewhat from individual to individual, most suffer from stomach awareness, nausea, vomiting, headache and drowsiness. Often there is an exacerbation of symptoms with rapid head movement. If an astronaut develops SMS, it usually occurs within a few minutes to a few hours after launch, with complete remission within 72 hours. Interestingly, the symptoms sometimes recur after returning to the earth.

SMS, particularly vomiting, can not only be disconcerting to the crew members, it also has the potential to cause performance decrement in an astronaut who is ill. Furthermore, the risk of vomiting while in a pressure suit doing EVA cannot be ignored, as the vomitus could cause the life-support system to malfunction. It is for these reasons that no EVA activities are ever scheduled during the first 3 days of a space mission. If an EVA becomes necessary, for example, to do emergency repairs on the space vehicle, the crew would have to take that risk.

Much neurovestibular research has been directed toward finding a way to prevent as well as to treat SMS. Various modalities, including anti-motion-sickness pills and patches, as well as using pre-flight adaptation trainers such as rotating chairs to habituate astronauts, have been attempted with very limited success. However, in recent years it has been discovered that the antihistamine phenergan, given by injection, is an extremely effective treatment. Hence, it is carried onboard all flights and given as required. Its efficacy as a preventive has yet to be demonstrated.

Other neurovestibular symptoms reported by astronauts include dizziness, vertigo, dysequilibrium and illusions of self-motion and motion of the surrounding environment, sometimes making walking difficult for a short time post-flight. The mechanisms for these phenomena are very complex and are not completely understood. They could be problematical, particularly after a lunar landing following several days or weeks in space. As of now, there are no known effective countermeasures.

Neurovestibular phenomena are most likely caused by dysfunction of the inner ear (the semicircular canals and utricle-saccule), because of microgravity. Either erroneous signals are sent to the central nervous system or signals are misinterpreted. In any event, the results are the aforementioned symptoms. Once the mechanism is better understood, effective countermeasures can be identified.

Haematological hazards

Microgravity has an effect upon the body’s red and white blood cells. The former serve as a conveyor of oxygen to the tissues, and the latter as an immunological system to protect the body from invading organisms. Hence, any dysfunction could cause deleterious effects. For reasons not understood, astronauts lose approximately 7 to 17% of their red blood cell mass early in flight. This loss appears to plateau within a few months, returning to normal 4 to 8 weeks post-flight.

So far, this phenomenon has not been clinically significant, but, rather, a curious laboratory finding. However, there is clear potential for this loss of red blood cell mass to be a very serious aberration. Of concern is the possibility that with very long missions envisioned for the twenty-first century, red blood cells could be lost at an accelerated rate and in far greater quantities. If this were to occur, anaemia could develop to the point that an astronaut could become seriously ill. It is hoped that this will not be the case, and that the red blood cell loss will remain very small, regardless of mission duration.

In addition, several components of the white blood cell system are affected by microgravity. For example, there is an overall increase in the white blood cells, mainly neutrophils, but a decrease in lymphocytes. There is also evidence that some white blood cells do not function normally.

As of now, in spite of these changes, no illness has been attributed to these white blood cell changes. It is unknown whether or not a long mission will cause further decrease in numbers as well as further dysfunction. Should this occur, the body’s immune system would be compromised, making astronauts very susceptible to infectious disease, and possibly incapacitated by even minor illness that would otherwise easily be fended off by a normally functioning immunological system.

As with the red blood cell changes, the white blood cell changes, at least on missions of approximately one year, are not of clinical significance. Because of the potential risk of serious illness in-flight or post-flight, it is critical that research continue on the effects of microgravity on the haematological system.

Endocrinological hazards

During space flight, it has been noted that there are a number of fluid and mineral changes within the body due in part to changes in the endocrine system. In general, there is a loss of total body fluids, as well as calcium, potassium and calcium. A precise mechanism for these phenomena has eluded definition, although changes in various hormonal levels offer a partial explanation. To further confound matters, laboratory findings are often inconsistent among the astronauts who have been studied, making it impossible to discern a unitary hypothesis as to the cause of these physiological aberrations. In spite of this confusion, these changes have caused no known impairment of health of astronauts and no performance decrement in flight. What the significance of these endocrine changes are for very long flight, as well as the possibility that they may be harbingers of very serious sequelae, is unknown.

Acknowledgements: The authors would like to recognize the work of the Aerospace Medical Association in this area.

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Teachers comprise a large and growing segment of the workforce in many countries. For example, over 4.2 million workers were classified as preschool through high school teachers in the United States in 1992. In addition to classroom teachers, other professional and technical workers are employed by schools, including custodial and maintenance workers, nurses, food service workers and mechanics.

Teaching has not traditionally been regarded as an occupation that entails exposure to hazardous substances. Consequently, few studies of occupationally related health problems have been carried out. Nevertheless, school teachers and other school personnel may be exposed to a wide variety of recognized physical, chemical, biological and other occupational hazards.

Indoor air pollution is an important cause of acute illnesses in teachers. A major source of indoor air pollution is inadequate maintenance of heating, ventilation and air conditioning systems (HVAC). Contamination of HVAC systems can cause acute respiratory and dermatological illnesses. Newly constructed or renovated school buildings release chemicals, dusts and vapours into the air. Other sources of indoor air pollution are roofing, insulation, carpets, drapes and furniture, paint, caulk and other chemicals. Unrepaired water damage, as from roof leakage, can lead to the growth of micro-organisms in building materials and ventilation systems and the release of bioaerosols that affect the respiratory systems of teachers and students alike. Contamination of school buildings by micro-organisms can cause severe health conditions such as pneumonia, upper respiratory infections, asthma and allergic rhinitis.

Teachers who specialize in certain technical fields may be exposed to specific occupational hazards. For example, arts and craft teachers frequently encounter a variety of chemicals, including organic solvents, pigments and dyes, metals and metal compounds, minerals and plastics (Rossol 1990). Other art materials cause allergic reactions. Exposure to many of these materials is strictly regulated in the industrial workplace but not in the classroom. Chemistry and biology teachers work with toxic chemicals such as formaldehyde and other biohazards in school laboratories. Shop teachers work in dusty environments and may be exposed to high levels of wood dust and cleaning materials, as well as high noise levels.

Teaching is an occupation that is often characterized by a high degree of stress, absenteeism and burnout. There are many sources of teacher stress, which may vary with grade level. They include administrative and curriculum concerns, career advancement, student motivation, class size, role conflict and job security. Stress may also arise from dealing with children’s misbehaviours and possibly violence and weapons in schools, in addition to physical or environmental hazards such as noise. For example, desirable classroom sound levels are 40 to 50 decibels (dB) (Silverstone 1981), whereas in one survey of several schools, classroom sound levels averaged between 59 and 65 dB (Orloske and Leddo 1981). Teachers who are employed in second jobs after work or during the summer may be exposed to additional workplace hazards that can affect performance and health. The fact that the majority of teachers are women (three-fourths of all teachers in the United States are women) raises the question of how the dual role of worker and mother may affect women’s health. However, despite perceived high levels of stress, the rate of cardiovascular disease mortality in teachers was lower than in other occupations in several studies (Herloff and Jarvholm 1989), which could be due to lower prevalence of smoking and less consumption of alcohol.

There is a growing concern that some school environments may include cancer-causing materials such as asbestos, electromagnetic fields (EMF), lead, pesticides, radon and indoor air pollution (Regents Advisory Committee on Environmental Quality in Schools 1994). Asbestos exposure is a special concern among custodial and maintenance workers. A high prevalence of abnormalities associated with asbestos-related diseases has been documented in school custodians and maintenance employees (Anderson et al. 1992). The airborne concentration of asbestos has been reported higher in certain schools than in other buildings (Lee et al. 1992).

Some school buildings were built near high-voltage transmission power lines, which are sources of EMF. Exposure to EMF also comes from video display units or exposed wiring. Excess exposure to EMF has been linked to the incidence of leukaemia as well as breast and brain cancers in some studies (Savitz 1993). Another source of concern is exposure to pesticides that are applied to control the spread of insect and vermin populations in schools. It has been hypothesized that pesticide residues measured in adipose tissue and serum of breast cancer patients may be related to the development of this disease (Wolff et al. 1993).

The large proportion of teachers who are women has led to concerns about possible breast cancer risks. Unexplained increased breast cancer rates have been found in several studies. Using death certificates collected in 23 states in the United States between 1979 and 1987, the proportionate mortality ratios (PMRs) for breast cancer were 162 for White teachers and 214 for Black teachers (Rubin et al. 1993). Increased PMRs for breast cancer were also reported among teachers in New Jersey and in the Portland-Vancouver area (Rosenman 1994; Morton 1995). While these increases in observed rates have so far not been linked either to specific environmental factors or to other known risk factors for breast cancer, they have given rise to heightened breast cancer awareness among some teachers’ organizations, resulting in screening and early detection campaigns.

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This article describes the basic health and safety concerns associated with the use of lasers, neon sculpture and computers in the arts. Creative artists often work very intimately with the technology, and in experimental ways. This scenario too often increases the risk of injury. The primary concerns are for eye and skin protection, for reducing the possibilities of electrical shock and for preventing exposure to toxic chemicals.

Lasers

Laser radiation may be hazardous to the eyes and skin of artists and audiences by both direct viewing and reflection. The degree of laser injury is a function of power. Higher-power lasers are more likely to cause serious injury and more hazardous reflections. Lasers are classified and labelled by their manufacturer in classes I to IV. Class I lasers exhibit no laser radiation hazard and Class IV are very dangerous.

Artists have used all laser classes in their work, and most use visible wavelengths. Besides the safety controls required of any laser system, artistic applications require special considerations.

In laser exhibits, it is important to isolate the audience from direct beam contact and scattered radiation, using plastic or glass enclosures and opaque beam stops. For planetariums and other indoor light shows, it is critical to maintain direct beam or reflected laser radiation at Class I levels where the audience is exposed. Class III or IV laser radiation levels must be kept at safe distances from performers and the audience. Typical distances are 3 m away when an operator controls the laser and 6 m away without continuous operator control. Written procedures are needed for set-up, alignment and testing of Class III and IV lasers. Required safety controls include warning in advance of energizing these lasers, key controls, fail-safe safety interlocks and manual reset buttons for Class IV lasers. For Class IV lasers, appropriate laser goggles should be worn.

Scanning laser art displays often used in the performing arts use rapidly moving beams that are generally safer since the duration of inadvertent eye or skin contact with the beam is short. Still, operators must employ safeguards to ensure exposure limits will not be exceeded if the scanning equipment fails. Outdoor displays cannot allow aircraft to fly through hazardous beam levels, or the illumination with greater than Class I levels of radiation of tall buildings or personnel in high-reach equipment.

Holography is the process of producing a three-dimensional photograph of an object using lasers. Most images are displayed off-axis from the laser beam, and intrabeam viewing is typically not a hazard. A transparent display case around the hologram can help reduce the possibilities of injury. Some artists create permanent images from their holograms, and many chemicals used in the development process are toxic and must be managed for accident prevention. These include pyrogallic acid, alkalis, sulphuric and hydrobromic acids, bromine, parabenzoquinone and dichromate salts. Safer substitutes are available for most of these chemicals.

Lasers also have serious non-radiological hazards. Most performance-level lasers use high voltages and amperage, creating significant risks of electrocution, particularly during design stages and maintenance. Dye lasers use toxic chemicals for the active lasing medium, and high-powered lasers may generate toxic aerosols, especially when the beam strikes a target.

Neon Art

Neon art uses neon tubes to produce lighted sculptures. Neon signage for advertising is one application. Producing a neon sculpture involves bending leaded glass to the desired shape, bombarding the evacuated glass tube at a high voltage to remove impurities from the glass tube, and adding small amounts of neon gas or mercury. A high voltage is applied across electrodes sealed into each end of the tube to give the luminous effect by exciting the gases trapped in the tube. To obtain a wider range of colours, the glass tube can be coated with fluorescent phosphors, which convert the ultraviolet radiation from the mercury or neon into visible light. The high voltages are achieved by using step-up transformers.

Electrical shock is a threat mostly when the sculpture is connected to its bombarding transformer to remove impurities from the glass tube, or to its electrical power source for testing or display (figure 1). The electrical current passing through the glass tube also causes the emission of ultraviolet light that in turn interacts with the phosphor-covered glass to form colours. Some near-ultraviolet radiation (UVA) may pass through the glass and present an eye hazard to those nearby; therefore, eyewear that blocks UVA should be worn.

Figure 1. Neon sculpture manufacture showing an artist behind a protective barrier.

Fred Tschida

Some phosphors that coat the neon tube are potentially toxic (e.g., cadmium compounds). Sometimes mercury is added to the neon gas to create a particularly vivid blue colour. Mercury is highly toxic by inhalation and is volatile at room temperature.

Mercury should be added to the neon tube with great care and stored in unbreakable sealed containers. The artist should use trays to contain spillage, and mercury spill kits should be available. Mercury should not be vacuumed up, as this may disperse a mist of mercury through the vacuum cleaner’s exhaust.

Computer Art

Computers are used in art for a variety of purposes, including painting, displaying scanned photographic images, producing graphics for printing and television (e.g., on-screen credits), and for a variety of animated and other special effects for motion pictures and television. The latter is a rapidly expanding use of computer art. This can bring about ergonomic problems, typically due to repetitive tasks and uncomfortably arranged components. The predominant complaints are discomfort in the wrists, arms, shoulders and neck, and vision problems. Most complaints are of a minor nature, but disabling injuries such as chronic tendinitis or carpal tunnel syndrome are possible.

Creating with computers often involves long periods manipulating the keyboard or mouse, designing or fine tuning the product. It is important that computer users take a break away from the screen periodically. Short, frequent breaks are more effective than long breaks every couple of hours.

Regarding the proper arrangement of components and the user, design solutions for correct posture and visual comfort are the key. Computer work station components should be easy to adjust for the variety of tasks and people involved.

Eye strain may be prevented by taking periodic visual breaks, preventing glare and reflection and by placing the top of the monitor so that it is at eye level. Vision problems may also be avoided if the monitor has a refresh rate of 70 Hz, so that image flicker is reduced.

Many kinds of radiation effects are possible. Ultraviolet, visible, infrared, radio frequency and microwave radiation emissions from computer hardware are generally at or below normal background levels. The possible health effects of lower-frequency waves from the electrical circuitry and electronic components are not well understood. To date, however, no solid evidence identifies a health risk from exposure to the electromagnetic fields associated with computer monitors. Computer monitors do not emit hazardous levels of x rays.

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