should be equipped with flow-sensing devices that can show at a glance or by an audible signal whether they are performing adequately. When toxic chemicals are used in a glove box, it should be operated under negative pressure, and the gloves should be checked for integrity and appropriate composition before use. Any effluent from these reactions should be reactively or chemically scrubbed and/or cleaned with HEPA (high-efficiency particulate air) filters prior to discharge into the hood atmosphere. Hoods should not be used as waste disposal devices, particularly when toxic substances are involved. In order to offer maximum protection, hoods should be operated with sashes closed whenever possible, and experiments involving toxic materials should be shielded further. Monitoring equipment might include both active and passive devices to sample laboratory working environments. (See Chapter 8, section 8.C, for detailed discussion on hoods and environmental control.)
When working with toxic liquids or solids, it is critical that gloves be worn to protect the hands and forearms. These gloves must be carefully selected to ensure that they are impervious to the chemicals being used and are of appropriate thickness to allow reasonable dexterity while also ensuring adequate barrier protection. Double gloves can provide a multiple line of defense and are likely to be appropriate for many situations with highly toxic chemicals. When risks from toxicity are only one facet of working with a given chemical or experimental apparatus, it is important to find a glove or combination of gloves that addresses all of the hazards present.
When using gloves, it is important to exercise proper hygiene. Reusable gloves should be washed and inspected before and after each use. Gloves that might be contaminated with toxic materials should not be removed from the immediate area (usually a hood) in which the chemicals are located. They should never be worn when handling common items such as doorknobs, elevator buttons, handles, or switches on common equipment. Other types of personal protective equipment, such as aprons of reduced permeability and disposable laboratory coats, can offer additional safeguards when working with large quantities of toxic materials.
Face and eye protection is also essential in preventing ingestion, inhalation, and skin absorption of toxic chemicals in the case of unexpected events. Safety glasses with side shields are a minimum standard for all laboratory work. When using toxic substances that could generate vapors, aerosols, or dusts, additional levels of protection, including full-face shields and respirators, are appropriate, depending on the degree of hazard represented. Transparent explosion shields in hoods offer additional protection from splashes. Medical supervision or surveillance may be warranted when using some toxic substances, particularly when large quantities of chemicals are involved or experiments are conducted with smaller quantities over an extended period of time. Medical certification may also be required if respirators are worn.
Equipment used for the handling of highly toxic chemicals should be suitably isolated from the general laboratory environment. Laboratory vacuum pumps used with these substances should be protected by high-efficiency scrubbers or HEPA filters and vented into an exhaust hood. Motor-driven vacuum pumps are recommended because they are easy to decontaminate (decontamination should be conducted in a designated hood).
Good laboratory hygiene should never be compromised in laboratories where highly toxic chemicals are handled. After using toxic materials the laboratory worker should wash his or her face, hands, neck, and arms. Equipment (including personal protective equipment such as gloves) that might be contaminated must never be removed from the environment reserved for handling toxic materials without complete decontamination. When possible, laboratory equipment and glassware should be chosen with an eve toward the ease of cleaning and decontamination. Mixtures that contain toxic chemicals or substances of unknown toxicity must never be smelled or tasted.
Transportation of very toxic chemicals from one location to another should be planned carefully, and handling of these materials outside the specially designated laboratory area should be minimized. When these materials are transported, the full complement of personal protective equipment appropriate to the chemicals in question should be worn, and the samples should be carried in unbreakable secondary containers.
Emergency response procedures must cover highly toxic substances because such procedures provide the last line of defense in working with these chemicals. Spill control and appropriate emergency response kits should be nearby, and laboratory workers should be trained in their proper use. To avoid their being contaminated or made inaccessible in an emergency, these kits should not be located within the immediate area where highly toxic substances are handled. Spill control absorbents, impermeable ground covers (to prevent the spread of contamination while conducting emergency response), warning signs, emergency barriers, first aid supplies, and antidotes should be in these kits. The contents of the kits should be validated before starting experiments. Safety showers, eyewashes, and