fire extinguishers should be readily available nearby. Self-contained impermeable suits, a self-contained breathing apparatus, and cartridge respirators may also be appropriate for spill response preparedness, depending on the physical properties and toxicity of the materials being used (see section 5.C.2.3).

Experiments conducted with highly toxic chemicals should be carried out in work areas designed to contain accidental releases (see also section 5.D.3). Hood trays and other types of secondary containers should be used to contain inadvertent spills, and careful technique must be observed to minimize the potential for spills and releases.

All toxicity and emergency response information about the highly toxic chemicals being used should be readily available both before and during experimentation and should be located outside the immediate work area to ensure accessibility in emergencies. All laboratory workers who could potentially be exposed must be properly trained to participate in first aid or emergency response operations. In some cases the frequency with which highly toxic chemicals are used or the quantities involved might make formal emergency response drills warranted. Such ''dry runs" may involve medical personnel as well as emergency cleanup crews.

(See also sections 5.C.11.5 and 5.C.11.6.)

5.D.7 Storage and Waste Disposal

Highly toxic chemicals should be stored in unbreakable secondary containers. If the materials are volatile or could react with moisture or air to form volatile toxic compounds, these secondary containers should be placed in a ventilated environment under negative pressure. All containers of highly toxic chemicals should be labeled clearly with chemical composition, known hazards, and warnings for handling. Chemicals that can combine to make highly toxic materials (e.g., acids and inorganic cyanides, which can generate hydrogen cyanide) should not be stored together in the same secondary container. A list of highly toxic compounds, their locations, and contingency plans for dealing with spills should be displayed prominently at any storage facility. Access to areas where highly toxic compounds are stored should be restricted to workers who are familiar with the risks they pose and who have been trained to handle these chemicals. Highly toxic chemicals that have a limited shelf life need to be tracked and monitored for deterioration in the storage facility. Those that require refrigeration should be stored in a ventilated refrigeration facility.

Procedures for disposal of highly toxic materials should be established before experiments begin, preferably before the chemicals are ordered. The procedures should address methods for decontamination of all laboratory equipment that contacts (or could contact) highly toxic chemicals. Waste should be accumulated in clearly labeled, impervious containers that are stored in unbreakable secondary containers. Volatile or reactive waste should always be covered to minimize release to the hood environment in which it is being handled.

It is the responsibility of the experimenter and the laboratory supervisor to ensure that waste is disposed of in a manner that renders it innocuous. This may involve pretreatment of the waste either before or during accumulation. In other circumstances, prudence might dictate that highly toxic compounds never be moved from an enclosed environment and might suggest in-laboratory destruction as the safest and most effective way of dealing with the waste. Regulatory requirements may have an impact on this decision (see Chapter 9). If waste cannot be rendered harmless in the laboratory, then accumulation in closed, impervious containers within secondary containment systems is prudent. The choice of methods for final disposal must ensure that these chemicals are completely destroyed or rendered harmless in some manner.

5.D.8 Multihazardous Materials

Some highly toxic materials present additional hazards because of their flammability (see Chapter 3, sections 3.D.1 and 3.D.4; see also section 5.F), volatility (see sections 5.E and 5.G.6), explosibility (see Chapter 3, section 3.D.3; see also section 5.G.4), or reactivity (see Chapter 3, section 3.D.2; see also section 5.G.2). These materials warrant special attention to ensure that risks are minimized and that plans to deal effectively with all potential hazards and emergency response are implemented. (Tables 3.9 and 3.14 give information regarding incompatible chemicals and substances requiring extreme caution.)

5.E WORKING WITH BIOHAZARDOUS AND RADIOACTIVE MATERIALS

5.E.1 Biohazardous Materials

For even the most experienced laboratory worker, a careful review of the publication Biosafety in Microbiological and Biomedical Laboratories (U.S. DHHS, 1993) should be a prerequisite for beginning any laboratory activity involving a microorganism. It defines four levels of control that are appropriate for safe laboratory work with microorganisms that present occupational risks ranging from no risk of disease for normal healthy individuals to high individual risk of life-threatening



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