Document d8qndoeXaBBY99k4a9zbgg19

806 T. F. HATCH HEAT CONTROL IN THE HOT INDUSTRIES 807 is because the older and more experienced men have learned how to get al in heat. They regulate their work rate and balance periods of exposure v periods of rest in cooler environments. In this way, they keep their over-all; posure within tolerable limits. In contrast, young, inexperienced men are ap; continue to work in excessive heat to the point of exhaustion. Such individua The proposed safe tolerance times are within the practical limits found in hot industries. ` kong-continued exposure is known to lead to deterioration of performance and morale Seven in the fittest and well acclimatized individuals. Any safe limits that may be set must, 'therefore, allow for a wide margin of safety to be generally acceptable. j?v Intermittent Rest Periods require supervision to avoid overexposure. 'Vf*Wl'v1' ' The length of recovery periods in a relatively cool environment will depend upon the rate B and duration of work, the severity of heat, and on individual constitutional factors. A. SAFE TOLERANCE LIMITS AND INTERMITTENT REST PERIODS In a review of thermal standards for industry, the APHA Committee Atmospheric Comfort* presented the following summary of findings and rec mendations respecting safe tolerance times and duration of intermittent,:1 , In laboratory experiments in which the rectal temperature was raised to between 100 and F. by working for an hour or so in a saturated atmosphere of 95 F., the resting period ^required to drop the rectal temperature to 99" F. in a room at 85' F. dry-bulb and 50 RH was U' 50 to 40 minutes starting with 100' F. rectal temperature, and 60 to 90 minutes starting with 102 F. rectal temperature. Recovery of heart rate was much faster. However, after repeated periods for persons exposed to extreme heat; exposures on the same day, neither the pulse nor the rectal temperature returned to normal | but stabilized at higher levels. Safe Tolerance Limits The tolerance contours (Figure 5) have been constructed from joint studies by the Ar can Society of Heating and Ventilating Engineers and the U. S, Bureau of Mines during 1 *. As a rule, the workers themselves set the pace and the length of recovery periods in jaw- industries. In mines where temperatures approach 95' F., with humidities close to the saturation point, men work only one-half to one-third of the shift time, alternating short periods of work in the heat with rest periods of 40 to 45 minutes in cooler areas. In aluminum and steel manufacturing processes in which environmental temperatures MS'.' between 120 and 160' F. with relative humidities of 3 to. 15% (ET, 90-100" F.) are encountered, 111611 ^9^8 light duties work for about one hour and rest for an equal period, while those engaged in heavy occupations work for about 30 minutes and rest during the next 30 minutes. B. MEDICAL SUPERVISION Proper selection of persons best fitted for heat exposure, proper acclimatizaQH-hefore.,undertaking--rout-ine-ex-posure-to-extreme-heat,-regulation of periods 5, ^ work and rest, control of fatigue, and maintenance of an adequate intake of fcsalt and water are essential measures for the protection'ofremployees in the hot ^industries. Preplacement and periodic examinations to detect; circulatory and other ,,_gj-TMJ4physiological deficiencies help to keep unfit men awayt'fft>m,excessive heat ex` Posures- Acclimatisation has dramatic benefits In preyjeii.Sn^j,early cases of heat 1 exhaustion. Maintenance of water and salt balance ik essential,to successful per- : SmB ^ormanoe 'n the heat. The water supply should be coii^efiientfy located and the W**^men encouraged to drink water beyond the digfj$s of-t^glimwiuc^iiaB-been found fin extreme heat exposures to be'an . direct safe exRosuRet hours Figure 5. Permitted duration of heat exposure at rest and at work, for various environmeni t.pmppjfl.t.nrpR and rplnfrivfl hnnviHif.jpg (fVmrt.PRy jAm 'J sRiLhl^'Np.nftb ^' ~ 1926. Safe tolerance time, for the purpose of this report, is defined as the average time req to raise the pulse rate to 125 beats per minute from initial rates of 70 to 80, and tKS'i temperature to 101 F. from initial levels of 98 to 99 F. Symptoms of heat distress d( appear in healthy persons until the pulse rate rises well above 130 and the rectal temper above 101 F., in exposure lasting more than one hour. |(;0hapterV). ;V S|c- There is evidence that the stress of physiological disturbances from causes other than heat is added to the heat stress, so that men ,ifith'teS^'i^'ar.y respiraiBlItory infection, digestiye,dis.turhance.,.andmtherJepart^res trom hnvma.1. health are ^.^.^o^^^Pttbltrtirheat exhausfion; during periods of such disturbances haul, py. jjjjjjjn posures should be limited. This is a responsibility of medical supervision, as is the continued observation of men exposed to heat to detect signs of long-term impair|| ment, as in the circulatory system.