a trap in the line to the pump. Vacuum pump oil contaminated with mercury must be treated as hazardous waste. (See Chapter 5, sections 5.C.11.8 and 5.D.)

The output of each pump should be vented to an 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 would result in pumping any of the substance that is not trapped into the laboratory atmosphere. It is also recommended to scrub or absorb the gases exiting the pump. Even with these precautions, however, volatile toxic or corrosive substances may accumulate in the pump oil and, thus, be discharged into the laboratory atmosphere during future pump use. This hazard can be avoided by draining and replacing the pump oil when it becomes contaminated. The contaminated pump oil should be disposed of by following standard RCRA procedures for the safe disposal of toxic or corrosive substances. General-purpose laboratory vacuum pumps should have a record of use in order to prevent cross-contamination or reactive chemical incompatibility problems.

Belt-driven mechanical pumps with exposed belts must have protective guards. Such guards are particularly important for pumps installed on portable carts or tops of benches where laboratory workers might accidentally entangle clothing or fingers in the moving belt, but they are not necessary for enclosed pumps.

6.C.3 Refrigerators and Freezers

The potential hazards posed by laboratory refrigerators involve 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 cords, and preferably should be protected by their own circuit breaker. The contents of a laboratory refrigerator should be enclosed in unbreakable secondary containers. Because there is almost never a satisfactory arrangement for continuously venting the interior atmosphere of a refrigerator, any vapors escaping from vessels placed in one will accumulate in the refrigerated space and will 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 potential for exposure to toxic substances can be aggravated when a worker places his or her head inside a refrigerator while searching for a particular sample. The placement of potentially explosive (see Chapter 5, sections 5.C and 5.G) or highly toxic substances (see Chapter 5, sections 5.D and 5.E) in a laboratory refrigerator is strongly discouraged. If this precaution must be violated, then a clear, prominent warning sign should be placed on the outside of the refrigerator door. Storage of these types of materials in a refrigerator should be kept to a minimum and monitored regularly. As noted in Chapter 5, section 5.C, laboratory refrigerators and freezers should never be used to store food or beverages for human consumption.

AMPOULE EXPLOSION IN A REFRIGERATOR

The door to a refrigerator used for storage of chemicals in a laboratory was left open for 10 minutes while a researcher searched through chemicals. Suddenly, an ampoule stored in the door exploded, spraying the contents in all directions, including toward the researcher. Fortunately, only one other container was ruptured, and the researcher received only a cut on his face from flying glass. A review of the incident concluded that the ampoule had been sealed at a relatively low temperature. When the ampoule warmed up in the open door, pressure built up inside it, causing it to rupture.

There should be no potential sources of electrical sparks on the inside of a laboratory refrigerator where volatile or flammable chemicals are stored. Only refrigerators that have been Underwriters-approved for flammable storage by the manufacturer should be used for this purpose. If this is not possible, all new or existing manual defrost refrigerators should be modified by

  • removing the interior light and switch mounted on the door frame, if present, and

  • moving the contacts of the thermostat controlling the fan and temperature outside the refrigerated compartment.

Although a prominent sign warning against the storage of flammable substances can be permanently attached to the door of an unmodified refrigerator, this alternative is less desirable than modifying the equipment by removing any spark sources from the refrigerated compartment. "Frost-free" refrigerators are not suitable for laboratory use, owing to the problems associated with attempts to modify them. Many of these refrigerators have a drain tube or hole that carries water (and any flammable material present) to an area adjacent to the compressor and, thus, present



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