SAFETY

 

Given below is a short reminder list of basic safety principles and specific warnings about hazards that can occur in a physical chemistry laboratory. Items 1 and 2 are crucially important. Knowing how to respond effectively in the unlikely event of a serious accident is essential. Safety information should be displayed prominently in the laboratory—find it and read it before beginning any experimental work.

Following the list is a discussion of many safety issues that are pertinent to physical chemistry. A detailed treatment of all aspects of safety is given in Prudent Practices for Handling Hazardous Chemicals in Laboratories, prepared by the National Research Council Committee on Hazardous Sub­stances and published by the National Academy Press in 1981.

1.     Review experimental procedures and identify possible safety hazards before beginning laboratory work.

2.     Learn the location and proper use of all safety equipment available in the laboratory as well as the fastest method of obtaining emergency medical assistance.

3.     Never work alone in the laboratory.

4.     Beware of high-voltage electricity.

5.     Never pipette chemicals by mouth; use a pipetting bulb.

6.     Wear safety glasses or goggles in the laboratory at all times.

7.     Limit the use of open flames and never use them in the presence of flammable materials.

8.     Avoid looking directly into any laser beam. A laser beam or even a reflected part of such a beam that enters the eye can cause permanent eye damage.

9.     Beware of possible explosions due to gas overpressures, especially in glass systems.

10.         Do not eat, drink, or smoke in the laboratory.

Electrical hazards: Several experiments make use of 110-V ac electrical power and employ apparatus in which exposed metal parts are "live." If the laboratory table has a metal surface, cover it with an insulating sheet of plywood or other material before assembling an electrical circuit. Remember that metal fixtures of all kinds and pipes or tubes of any kind that carry water are usually grounded. Turn off all electrical apparatus before altering circuits, if possible; if apparatus must be left on, use properly insulated test prods and leads. Be on the lockout for charged condensers, which may not be discharged owing to a broken circuit or a defective bleeder resistor. Naturally, 220V represents a greater hazard than 110 V. It should be kept in mind that the laboratory is often served with 220V in a three-wire system, with 110 V each side of ground. If 110-V outlets are supplied with a ground wire and one side of the 220-V line, as much as a 220-V difference can be obtained in accidental contact between circuits plugged into outlets serviced by opposite sides of the 220-V line. Shock, if it does occur, can be a serious matter; medical help should be summoned at once. Keep the victim quiet and comfortable administer no stimulants of any kind.

Chemical hazards: These are many and varied. It should be taken for granted that any chemical substance taken by mouth or inhaled is toxic until and unless definite assurance has been given to the contrary. Reactions that evolve toxic fumes or vapors or entail risk of fire should always take place in a fume hood. As a matter of standard safety practice, never pipette any liquid or solution by mouth; use a rubber pipetting bulb. Mercury vapor can attain a hazardous concentration in the laboratory atmosphere. Mercury should be kept in covered vessels at all times. Spills should be carefully cleaned up (a capillary tube attached to a suction flask is convenient for this), and inaccessible droplets in floor cracks and hard-to-reach places should be covered with a light dusting of powdered sulfur. Another insidious hazard is that of vapors from organic solvents. Such solvents should not be used indiscriminately for cleaning purposes, and spills should be avoided. Good ventilation is important.

Environmental exposure to chemical hazards is currently a subject of concern and awareness. Zero exposure or zero risk of exposure is impossible in practice either in the chemical laboratory or elsewhere. Part of the professions role of chemists is to acquire knowledge and to develop judgement as to which precautions are necessary to limit these risks. One should not be blindly afraid of every chemical in the laboratory, nor should one be foolishly fearless. Man chemical hazards can be avoided by simply not eating or drinking in the laboratory, or breathing large volumes of vapors. Most chemical poisons are eliminated from the body, so that the effects of exposure gradually diminish. However, some poisons are not eliminated completely, and they accumulate, usually in particular tissues.

Recently, chronic exposure to low levels of certain chemicals has bee shown to increase significantly the incidence of cancer. Such chemicals are referred to as carcinogens. The following list gives those chemicals classified as strong carcinogens by SHA (Occupational Safety and Health Administration):

1.     2-Acetylaminofluorene

2.     4,4'-Methylene-bis(2-chloroaniline)

3.     Acrylonitrile

4.     a-Naphthylamine

5.     4-Aminobiphenyl

6.     b-Naphthylamine

7.     Benzidine (salts implied)

8.     4-Nitrobiphenyl

9.     Bis(chloromethyl) ether

10.         N-Nitrosodimethylamine

11.         Chloromethyl methyl ether

12.         b-Propiolactone

13.         3,3'-Dichlorobenzidine

14.         Vinyl chloride

15.         4-Dimethylaminoazobenzene

16.         Asbestos

17.         Ethylenimine

18.         Inorganic arsenic

None of these chemicals is used in the experiments described in this book. There are other chemicals thought to be weak carcinogens on the basis of statistical inferences involving data from long-term studies on large numbers of subjects. In these cases, there may be a hazard in industrial settings from chronic exposure to vapors or direct contact with the skin, but the risk from brief use in a research or educational setting is not serious.

Chemical bums: Strong acids (particularly oxidizing acids such as chromic acid cleaning solution) and bases may cause severe bums to the skin. If skin contact is made, wash copiously with water. If the exposure is to a strong acid, washing with a very dilute weak base (ammonia) is helpful; for a strong base use a very dilute weak acid (acetic acid). Particular attention should be directed to eye protection; safety glasses, safety goggles, or a face shield must be worn in the laboratory at all times. Prompt and effective action is essential if any chemical agent gets into the eyes; a strong base such as sodium hydroxide can permanently destroy the cornea in a few seconds. Speed is all-important in getting the exposed individual to an eyewash fountain or other source of copiously flowing (but low-pressure) water and thoroughly bathing the eyeball. The eyelids should be lifted away from the eyeball to facilitate effective washing. Use nothing but water. Get medical help promptly.

Fire and explosion: Any flammable substance provides a potential fire hazard. In experiments that make use of hydrogen gas or other flammable gases, not only open flames but also cigarettes and sparking electrical contacts provide the possibility of explosion. If used in large quantities, such gases must be vented into the open air outside the building. A direct exhaust line from the experiment to a nearby window is best, but an exhaust fan and cross-ventilation will serve. The distillation of flammable liquids must be carried out in the absence of open flames; use a steam bath or electrical heating mantle. If an experiment involves an irreducible risk of fire or explosion, arrange for an adequate barrier. Safety goggles are required in all circumstances in which fire or explosion is a possible eventuality. Know the location of the nearest water supply and fire extinguishers (use water only on paper or cloth fires). In the event of serious burns, do not apply ointments or medications; get medical help.

Radiation hazards: Ultraviolet light from a mercury lamp or carbon arc is highly damaging to the eyes. Ordinary glasses give some protection, but the experimental arrangement should be well shielded so as to decrease the possibility of accidental exposure to a minimum. Prolonged exposure of the skin to such radiation can produce severe "sunburn." An optical laser beam, even from a laser of very low power, which enters directly into the eye or is accidentally reflected into the eye by a surface, can cause irreparable damage to the retina as a result of focusing by the lens of the eye. Eyeglasses provide no protection from this hazard, and the appropriate laser safety goggles should be worn when working with such sources (see Exp. 37). Exposure to strong radiofrequency or microwave fields can "cook" tissue and produce deep internal burns. Exposure to x-rays and to the radiation from radioactive materials must be carefully guarded against in experiments dealing with them. Any such experiments should be done under the direct supervision of an experienced research worker who will assume personal responsibility for all required safety measures, and under an appropriate license if radioactive materials are involved.

Mechanical and other hazards: Most mechanical hazards are too clearly apparent to warrant mention here. The danger lies in forgetfulness or casual disregard of risks. Vacuum systems often carry a hazard of collapse or implosion; bulbs more than 1 liter in volume should be surrounded by a metal screen or else wrapped with strong tape to reduce hazard from flying glass particles in the event of implosion. The bursting of a container due to overpressure is a frequent cause of accident or injury. A compressed-air line (usual pressure of the order of 50 psi) should never be connected to a closed system containing rubber tubing or glass bulbs. No closed system, except a properly designed combustion bomb, should be attached to a cylinder of compressed gas (usual maximum pressure: about 3000 psi) unless a suitable reducing valve is attached; even then, a relief valve should be provided to guard against accidental overpressure. Gas cylinders must be chained or strapped to prevent their falling over. The protective cap must be in place whenever a gas cylinder is being moved; cylinders should be moved with an appropriate hand truck, not dragged across the floor. Mechanical pumps must have belt guards.

Unattended operations must be planned with automatic safety switches that prevent serious damage (fire, flooding, explosion) in case of accidental equipment failure or interruption of utility services such as electricity, water, or gas supplies. Of special concern are the constant flow of cooling water and the operation of high-temperature baths. In the case of water flow, a device should be installed in the water line to (1) automatically regulate the water pressure (so as to avoid surges that might disconnect or rupture a water hose), and (2) automatically turn off electrical connections and water-supply valves in case of a total loss of water supply. In the case of hot thermostat baths or ovens, a sensor/control device should be installed that automatically turns off the electrical power to all heaters if the temperature exceeds some preset upper limit.

Safety equipment: Safety glasses or goggles have been mentioned in this appendix and in other places in this book in connection with specific hazards. However, use of safety glasses equipped with side shields, or other approved means of eye protection (plastic goggles alone or over ordinary prescription glasses, plastic face shields) is usually mandatory at all times in instructional laboratories, just as it is in industrial research laboratories. The use of safety goggles is strongly recommended as standard laboratory policy. Their use is essential in all circumstances where there exists the possibility of fire, explosion, and implosion, spattering of caustic chemicals, or flying fragments from machine-shop operations. Fortunately, very few of these risks exist in the experiments described in this book, and explicit warnings are given in each case where hazards do occur.

The laboratory should be equipped with a conveniently accessible safety shower and an eyewash fountain; there should be more than one of each in a large laboratory. Increasingly, the fixed type of eyewash fountain is being superseded by a spray nozzle at the end of an extensible hose; there should be one of these on each laboratory bench. In lieu of such devices—or in addition to them—2- or 3-ft lengths of rubber hose (nor small-bore pressure tubing) attached with wire or clamps to water faucets are certainly better than nothing.

The laboratory should have convenient access to one or more fume hoods (with a face velocity of at least 100 ft/min) for any operations involving more than insignificant quantities of volatile chemicals in open containers.

An approved fire extinguisher [the "dry chemical" (bicarbonate) type is preferred, but the CO; type is satisfactory] should be mounted near at least one exit and refilled after every use, no matter how small. The laboratory should be arranged so as to provide two or more avenues of escape from any experimental setup in case of emergency. A first-aid kit containing Band-Aids, sterile gauze, adhesive tape, petroleum jelly, a mild antiseptic, sterile cotton swabs, tweezers, a set of sewing needles, a packet of razor blades, and a quick-reference first-aid manual will provide adequately for most minor emergencies.

The location of an inhalator, a stretcher, and other rescue equipment, if not in the laboratory itself, should be known. The telephone number of the nearest medical emergency room and the local ambulance service should be posted conspicuously. Instructions for emergency evacuation, including special procedures for evacuating physically handicapped persons, should also be posted. An evacuation drill held near the beginning of each academic term is recommended.

Under no circumstances should a person be allowed to work in the laboratory alone.

Finally, safety depends on habits that must be gained outside the laboratory as well as inside. Thus, on your way to and from the laboratory, look both ways before crossing the street; after finishing the writing of that laboratory report, don't smoke in bed (or anywhere else!).