posure to these monohalomethanes, none of which is a simple industrial hygiene or management decision. Careful planning and thought should be used prior to implementation.
When feasible, substitution of an alternative material with a lower potential health risk is an important method for reducing exposure. Extreme care must be used when selecting substitutes. Possible health effects from potential exposure to alternatives for these monohalomethanes should be fully evaluated prior to selection.
Engineering controls should be used to eliminate the potential for monohalomethane exposure in the workplace and to prevent fires and explosions. Achieving and maintaining reduced concentrations of airborne monohalomethanes in the workplace depend upon the implementation of engineering control measures, such as properly constructed and maintained closed system operations and ventilation, with appropriate safety designs.
Closed system operations provide the most effective means for minimizing worker exposures to these monohalomethanes. Closed system equipment should be used for manufacturing, storing, and processing these monohalomethanes because of their volatility. Where closed systems cannot be employed or do not effectively control monohalomethane emissions, local exhaust ventilation should be provided to direct vapors and gases away from workers and to prevent the recirculation of contaminated exhaust air. Exhaust ventilation systems for quality control laboratories or laboratories where samples are prepared for analyses should be designed to adequately capture and contain monohalomethane vapors or gases. Special consideration should be given to the releasing of these compounds from pressurized sampling containers. Guidance for designing local exhaust ventilation systems can be found in Recommended Industrial Ventilation Guidelines,58 Industrial Ventilation--A Manual of Recommended Practice,59 and Fundamentals Governing the Design and Operation of Local Exhaust Systems, ANSI Z92-1971.60
Ventilation equipment should be checked at least every three months to ensure adequate performance. System effectiveness should also be checked when there are any changes in production, process, or control that might result in significant increases in airborne exposure to these monohalomethanes.
If feasible, workers may be isolated from direct contact with the work environment by the use of automated equipment operated from a closed control booth or room. The control room should be maintained at a greater air pressure than that surrounding the process equipment so that air flows out of, rather than into, the room. This type of control will not protect workers who must perform process checks, adjustments, maintenance, assembly-line tasks, and related operations. Therefore, special precautions are often necessary to prevent or limit worker exposure in these situations and frequently involve the use of personal protective equipment.
Personal Protective Equipment
In a liquid state, all of the monohalomethanes discussed in this document may be injurious to both the skin and eyes upon direct contact. Liquefied methyl chloride and bromide are injurious to the skin because of rapid evaporation and the subsequent cooling effect which produces localized "burns" or "frostbite." Liquid methyl bromide has reportedly produced skin lesions and itching after skin contact and has resulted in conjunctivitis when accidentally splashed into the eyes.61 Other similar cases have been attributed to penetration of clothing by liquid methyl bromide.19,48,62
In one report on methyl iodide,29 it was noted that a soaked cloth pad applied to the forearm produced severe persistent lesions. These lesions were described as resembling those caused by mustard gas. These reports emphasize the importance of avoiding direct skin or eye contact with any liquid form of these monohalomethanes.29,63 This may be accomplished through the proper use of monohalomethane-resistant gloves, aprons, boots, or entire worksuits, depending on the nature and extent of the hazard. Faceshields or che