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sary. However,, vests do not encumber the loads, and frequent replacement is neces worker and thus permit maximum mobility. Cooling with ice is also relatively inexpensive. 2. Wetted clothing is another simple and inexpensive personal cooling technique. It f i is effective when reflective or other impermeable protective clothing is worn. The clothing may i -be wetted terry cloth coveralls or wetted two-piece, whole-body cotton suits. This approach to auxiiiary cooling can be quite effective under conditions of high temperature and low humidity, where evaporation from the wetted garment is not restricted. 3. Water-cooled garments range from a hood, which cools only the head, to vests and "long johns`," which offer partial or complete body cooling. Use of this equipment requires a battery- driven circulating pump, liquid-ice coolant, and^a container. Although this system has the advantage of allowing wearer mobility, the weight of the components limits the amount,of ice that can be carried and thus reduces the effective use l time. The heat transfer rate in liquid cooling systems may limit their use to low-activity jobs; even in such jobs, their service time is only about 20 minutes per pound'of cooling ice. To keep outside heat from melting the ice, an outer insulating jacket should be an integral part of t these systems. 4.- Circulating air is the most highly effective, as well as the most complicated, personal cooling system. 'By directing compressed air around the body from a supplied air system, both evaporative and convective cooling is improved. 'The greatest advantage occurs when circulating air is used with impermeable garments or double cotton overalls. One type, used when"respiratory protection is also necessary, forces exhaust air from a l� supplied-air hood ("bubble hood") around the neck and down inside an impermeable suit. The air then escapes through openings in the suit. Air can also be supplied directly10 the suit r . without using a hood in three ways:% i • by a single inlet; • by a distribution tree; or • by a perforated vest. In addition, a vortex tube can be used to reduce the'temperature of circulating air. The cooled air from this tube can be introduced'either under the clothing or into a bubble hood. The use of a vortex tube separates the air stream into a hot and cold stream; these tubes also can be used to-supply heat in i cold climates. Circulating air, however, is noisy and requires a constant source of compressed air supplied through an attached air hose. r I� One problem with this system is the limited mobility of workers whose suits are attached to an air hose. Another is that of getting air to the work area itself. These systems should therefore be used in work areas where workers are not`required to move around much or to climb. Another concern with these systems is that they can lead to dehydration. The cool, dry air'feels comfortable and the worker may not realize that it is important to drink liquids frequently. RESPIRATOR USAGE l The weight of a self-contained breathing apparatus (SCBA) increases stress on a worker, and this stress contributes to overall heat stress. Chemical protective clothing such as totally encapsulating chemical protection suits will also add to the heat stress problem. STANTEC Consulting Corporation Attachment 8 r T