Always assume that a voltage potential exists within a device while servicing it, even if it is deenergized and disconnected from its power source. A device may contain capacitors, for example, and could retain a potentially harmful electrical charge.

   Work with only one hand, if it is not awkward or otherwise unsafe to do so, while keeping the other hand at your side or in a pocket away from all conducting materials. This precaution reduces the likelihood of accidents that result in current passing through the chest cavity.

   Avoid becoming grounded by staying at least 6 in. away from walls, water, and all metal materials including pipes.

   Use voltmeters and test equipment with ratings and leads sufficient to measure the highest potential voltage to be found inside the equipment being serviced.

7.C.2 Vacuum Pumps

The use of water aspirators is discouraged. Their use in filtration or solvent-removal operations involving volatile organic solvents presents a hazard that volatile chemicals will contaminate the wastewater and the sewer, even if traps are in place. Water and sewer contamination may result in violation of local, state, or federal law. These devices also consume large volumes of water, present a flooding hazard, and can compromise local conservation measures.

Distillation or similar operations requiring a vacuum must use a trapping device to protect the vacuum source, personnel, and the environment. This requirement also applies to oil-free Teflon-lined diaphragm pumps. Normally the vacuum source is a cold trap cooled with dry ice or liquid nitrogen. Even with the use of a trap, the oil in a mechanical vacuum trap can become contaminated and the waste oil must be treated as a hazardous waste.

Vent the output of each pump to a proper air exhaust system. This procedure is essential when the pump is being used to evacuate a system containing a volatile toxic or corrosive substance. Failure to observe this precaution results in pumping the untrapped substances into the laboratory atmosphere. Scrubbing or absorbing the gases exiting the pump is also recommended. Even with these precautions, volatile toxic or corrosive substances may accumulate in the pump oil and thus be discharged into the laboratory atmosphere during future pump use. Avoid this hazard by draining and replacing the pump oil when it becomes contaminated. Follow procedures recommended by the institution’s environmental health and safety office for the safe disposal of pump oil contaminated with toxic or corrosive substances. General-purpose laboratory vacuum pumps should have a record of use to prevent cross-contamination or reactive chemical incompatibility problems.

Belt-driven mechanical pumps must have protective guards. Such guards are particularly important for pumps installed on portable carts or tops of benches where laboratory personnel might accidentally entangle clothing or fingers in the moving belt or wheels. Glassware under vacuum is at risk for implosion, which could result in flying glass. (For more information about working under vacuum, see Chapter 4, section 4.E.4.)

7.C.3 Refrigerators and Freezers

The potential hazards posed by laboratory refrigerators include release of vapors from the contents, the possible presence of incompatible chemicals, and spillage. As general precautions, laboratory refrigerators should be placed against fire-resistant walls, should have heavy-duty power cords, and preferably should be protected by their own circuit breaker. Enclose the contents of a laboratory refrigerator in unbreakable secondary containment. Because there is almost never a satisfactory way to continuously vent the interior atmosphere of a refrigerator, any vapors escaping from vessels placed in one will accumulate in the refrigerated space and gradually be absorbed into the surrounding insulation. Thus, the atmosphere in a refrigerator could contain an explosive mixture of air and the vapor of a flammable substance or a dangerously high concentration of the vapor of a toxic substance or both. The impact of exposure to toxic substances can be aggravated when a person inserts his or her head inside a refrigerator to search for a particular sample. Placing potentially explosive (see Chapter 6, sections 6.C and 6.G) or highly toxic substances (see Chapter 6, sections 6.D and 6.E) in a laboratory refrigerator is strongly discouraged. As noted in Chapter 6, section 6.C, laboratory refrigerators are never used to store food or beverages for human consumption. Add permanent labels warning against the storage of food and beverages to all laboratory refrigerators and freezers.

Potential ignition sources, (e.g., electrical sparks) must be eliminated from the inside of laboratory refrigerators used to store flammable chemicals. Use explosion-proof refrigerators for the storage of flammable materials; they are sold for this purpose and are labeled and hardwired. Only refrigerators that have been UL- or FM (Factory Mutual)-approved for flammable storage should be used for this purpose. A labeled hardwired explosion-proof refrigerator is mandatory for a renovated or new laboratory where flammable materials need refrigeration. Because of the



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