Best Working Temperatures

Man as a working machine held the attention of the American Institute of Mining & Metallurgical Engineers at their Manhattan meeting last week, just as he always interests every user of his productive capacities. The particular question which held the engineers was what condition of air--temperature and humidity--is best for man's work. Dr. William John McConnell of Metropolitan Life Insurance Co. told them.

The best general conditions are: temperature range between 40DEG F. and 75DEG F.; humidity 60.* Because individuals respond with varying ease to changes of humidity and temperature, the individual optimum is best indicated by his pulse rate. The nearer to normal his pulse goes the more efficient he is. The normal pulse rate for men is 68 to 75 a minute.

Mr. Connell reached these conclusions with engineering finesse. He placed men and women in a special cork-lined heat chamber built by the U. S. Bureau of Mines and operated jointly with the American Society of Heating & Ventilating Engineers. While the specimens rested and worked in still and moving air he made observations:

A person resting in still, humid air is comfortable until the temperature reaches 90DEG F.; a light breeze lets him stay so until 95DEG. However if he is working his muscles he feels discomfort at 80DEG. At 100DEG a man can do four times as much work if the air is dry (humidity 30) than if it were saturated (humidity 100). With humidity at the ordinary 60, the subjects did five times more work at 90DEG than at 120DEG.

Warm blooded animals accommodate themselves efficiently to changes in temperature. They are continually manufacturing heat themselves and getting rid of it. Thus they maintain normal temperatures. The smaller the animal the higher is likely to be its body temperature. Temperature of a mouse is 105.8DEG, rabbit 102.0DEG, dog 100.0DEG to 102.0DEG, man 98.6DEG, horse 96.8DEG to 98.6DEG. Children are about one degree warmer than adults.

Dissipation of the body manufactured heat depends on the surroundings. The drier the air the more moisture-bound heat it can absorb. The faster the air moves the faster can it carry heat from the body. But if the air is hot, humid and still, the body must struggle to throw off heat. The harder it struggles, the harder the heart must work. The pulse rate indicates the heart efforts, and thus the body efforts. High pulse rate is an index of unwise, inefficient overexertion. Dr. McConnell found that when his subjects in the cork-lined test room developed a pulse of 135 a minute, they complained of discomfort. Their heads ached, their hearts palpitated. A metallic taste came into their mouths. They could speak only with effort. At 160 pulses a minute they felt as though they were "floating on air" and were at the verge of heat stroke. Dr. McConnell endangered them no further.

The significance of his observations meant to his engineer audience that wise employers should keep their workrooms at comfortable temperature and humidity by means of artificial aids--radiators, pans of water, fans, ducts of washed air.

*Humidity, more exactly relative humidity, is the amount of water vapor in the air. The warmer the air at any height the more vapor it can carry. A humidity of 60 means that the atmosphere is 60% saturated.

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