Document zQY751yqQB8o0Y71JwkgOEjnB

48 Chapter 2 1945 Guide the ieucocyte count of the blood-and-other -factor? -dealing-with man-'smechanism of defense against infection. Another of the deleterious effects of high temperatures is that the blood is diverted from the internal organs to the surface capillaries, in order to serve in the process of cooling. This affects the stomach, heart, lungs and other vital organs, and it is suggested that the feeling of lassitude and discomfort experienced is due in part to the anaemic condition of the brain. The stomach loses some of its power to act upon the food, owing to a diminished secretion of gastric juice, and there is a corresponding loss in the antiseptic and antifermentive action which favors the growth of bacteria in the intestinal tract23. These are considered- to be the potent factors in the increased susceptibility to gastro-intestinal disorders in hot summer weather. In warm atmospheres, particularly during physical work, a considerable'' v amount of chloride is lost from the system through sweating. The loss of this substance may lead to attacks of cramps, unless the salts are replaced in the drinking water. In order to relieve both cramps and fatigue, it is recommended that 6 g of sodium chloride and 4 g of potassium chloride be added to a gallon of water24. _ . The_deleterious physiologic effects of high temperatures exert a power ful influence upon physical activity, accidents, sickness and mortality. Both laboratory and field data show that physical work in warm atmos pheres is a great, effort, and that production falls progressively as the tem perature rises. The incidence of industrial accidents reaches a minimum at about 68 F, increasing above and below that temperature. Sickness and mortality rates increase progressively as the temperature rises. The need of air conditioning for workers in hot industries is growing rapidly and this should become an important field for the air conditioning engineer. The hot conditions may be remedied by any of the recognized comfort cooling applications. The choice of the type of system and cycle to be used in a given instance must be determined by the air conditioning engineer after a study of surrounding conditions. In some hot industries where a small number of workers are engaged in spaces of large volumetric capacity the worker himself, rather than the entire environment, can be cooled by either placing him in a small cooled and ventilated booth, by blowing cooled air over him, or by circulating cooled air through a loose-fitting suit.25 RELATION OF AIR CONDITIONING NEEDS TO METABOLISM The major objective of heating and ventilation is to balance heat losses , from the human body. The basic factor is metabolism. The desirable environment, from the standpoint of heat loss, depends directly on the heat produced in the body and this heat may be over ten times as great when a man is exercising violently as when he is reclining and at rest. Therefore, there is no absolute optimum of air temperature or other environmental conditions, which will meet all cases. With moderate, (45 per cent) relative humidity and minimum air movement, an air tem perature of 80 F has been found ideal for die lightly clothed subject at rest in a semi-reclining position, while normally clothed, healthy persons "Influence of Effective Temperature upon Bactericidal Action of Gastro-intestinal Tract, by Arnold and Brody (Proceedings Society Exp. Biol. Med., Vol. 24, 1927, p. $32). "Some Effects of High Air Temperatures Upon the Miner, by K. N. Moss (Transactions Institute <4 Mining Engineers. Vol. 66, 1924, p. 284). "A.S.H.V.E. Research Report No. 1188--Local Cooling of Workers in Hot Industry, by F. C. Hough-, ten, M. B. Ferderber and Carl Gutberlet (A.S.H.V.E. Transactions, Vol. 47, 1941,,p. 403). --have been found comfortable~at 72 and 77 F with 45 per cent relative humidity (or 67 and 71 deg ET, respectively) for winter and summer conditions. In factories where light work is performed in summer time, the ideal has been found to be about 76 F. For children (who have a high Table 3. Relation Between Metabolic Rate and Activity1 Actrvitt tc lvq a iT d, ob Hocblt Hodblt Sensibu3 Latent Heat Dua- Heat Dis SIPATED sipated, at 79 F, at 79 F, Btu fee Btu per Hour Hour Moisture Dissipated per Hour fsb Person Grains Pounds Seated at Rest............._.... -- Reading Aloud (Seated)-----:......................... Standing at Rest-------------- ---------....... -...... Hand Sewing (Seated)..TM--................... ...... Knitting 23 stitches per minute on Sweater.. Dressing and Undressing.--............... Singing.-------------------------- ------------Office Worker Moderately Active.-- Light Work Standing.;-- Typewriting Rapidly.-----Ironing with 5 lb iron.-...................... .............. Dishwashing--Plates, Bowls, Cups and Saucers Clerk Moderately Active Standing at Counter.. Book Binder.-.............................. ..................... Shoemaker........................... --..........vv--........ Sweeping Bare Floor 38 Strokes per Minute.... Pool Player........... ............................. Walking 2 mph, Light Dancing.____ Light Metal Worker (at Bench)... Painter of Furniture (at Bench)... Carpenter___ _____ Restaurant Serving... Pulling Weight.__________________________ Walking 3 mph:_______________ ________ __ Walking 4 mph. Active Dancing, Roller Skating] Walking Down Stairs________ Stdne Mason.Bowling._________ Man Sawing Wood Swimming...... .................. Running 5.3 mph________: Walking 5 mph.__ 1________________ ____ Walking Very Fast 5.3 mph._____--...I.... ..... Walking Upstairs...___________________ I 4365 Maximum Exertion Different People.--.... ...... ) 3000-4800 145 225 225 225 225 225 225 225 225 225 225 225 225 225 225 225 225 229 230 250 277 280 307 325 335 339 452 467 485 490 ,590 145 978 0.140 159 1072 0.153 195 206 216 1315 0.188 1389 0.198 1457 0.208 237 243 1598 0.228 1639 0.234 257 261 1733 0.248 1760 0.251 265 324 1787 0.255 2185 0.312 333 2246 0.321 345 2326 0.332 375 2529 0.361 375 401 2529 2704 0.361 0.386 436 22940 0.420 443 52987 0.427 450 S 0.434 511 3 0.492 585 3 0.564 596 4 0.574 647 4 0.623 675 4 0.650 708 4 0.682 711 4 0.685 938 6 0.904 977 6. 0.941 1005 6 0.968 1010 6 0.973 1210 8 1.166 ..... ueai dissipation into l_a_t_e_n_t_and se.anvsjiublesratimteastiessbcaasseeddounpaocntuvaalrtioeustsdcaotna_s_ai_d_ne_dr_ao_t_nio_nvsa-r,.i^ouD*sivccistocinkosuniadioetrfeastthtiaoe,nitsro^otfmaolr metabolic rates up to 1250 Btu per hour, and extrapolated for higher rates. Values for total brat dissipa tion for a person at rest apply for a dry-bulb temperature range from approximately tO to 90 F; for other than rest conditions the values apply for a similar but lower temperature range.. Below these temperature irnacnrgeeassemseltiagbhotllyicarnadtestoatnadl htoetaatldriastseispaotfiohnearat tdeisssdipecarteioanseinrcarpeaidsley,.whDilievisaiboonveofthteostealradnisgseispamtieotnabraotleicsraintetos sensible and latent heat holds only for a dry-bulb temperature of 79 F. For lower temperatures, sensible beat dissipation increases and latent heat decreases, while for higher temperatures the reverse is true. metabolism) at school, in winter clothing, 70 F has been considered correct; while in a gymnasium, 55 F has been recommended. The wide variations in metabolic activities with which the engineer must be prepared to cope and the influence of such variations in metabo lism on the heat load contributed by the human body to the environment