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PHYSIOLOGICAL EFFECTS OF HIGH TEMPERATURES AND HUMIDITIES WITH AND WITHOUT AIR MOVEMENT.

Effects on Body Temperature and Pulse Rate of Subjects at Rest.

By R. R. Sayers, Surgeon, United States Public Health Service, Chief Surgeon, Bureau of Mines, Department of the Interior; and D. Harrington, Supervising Mining Engineer, Bureau of Miues, Department of the Interior.

INTRODUCTION.

For several years the writers have been studying various problems of the effect of air conditions in metal mines upon underground workers. In 1918 a short study was made in certain hot and deep mines, and brief reports were published in the Engineering and Mining Journal (August, 1920) and in the Public Health Reports (vol. 36, No. 4, January 28, 1921).1

In 1921 a more extended study was made (also in hot and deep metal mines) for the purpose of ascertaining the limiting conditions imposed upon underground workers by the physiological effect of various air movements, temperatures, and humidities. The determinations were made both with the subjects at work and at rest. It is intended to report this later investigation in a series of short papers, each paper to consider one particular phase of the work. The present paper deals with the effect on body temperature and pulse rate of subjects in still air as compared with moving air, at temperatures from 90° to 100° F., and of 100 per cent relative humidity, the subjects at rest.

SUBJECTS USED IN THE INVESTIGATION.

In order to avoid the criticism that data taken upon investigators working in mines only intermittently would not be representative of results taken on everyday mine workers, there were used in the 1921 study, in addition to one of the previous investigators, two miners, one having just left employment as general mine laborer in some of the worst places in one of the hottest mines in the district, and the other having been employed in various capacities in the mines in which the experimental work was being conducted. These three subjects, who were the reagents supplying most of the data, were vigorous and in good health, and thoroughly accustomed to mining work in hot, humid air. All of them remained in good physical condition throughout the period of making the tests. In addition, during the underground field work, data were taken on various other underground employees of the mines entered.

1 A preliminary study of the physiological effects of high temperatures and hitih humidities in metal mines, Public Health Reports, vol. 3i, No. 4, Jan. 23, 1921, pp. 116 129. Reprint No. C39.

DATA RECORDED.

Blood pressure (taken with a Tycos sphygmomanometer'), pulse rate, and rectal body temperature, together with any symptoms of dizziness, headache, weakness, perspiration, etc., were recorded. The air temperature and humidity were taken by a sling psychrometer, and the air velocities by an anemometer. The exact time of taking the readings was also noted. One of the investigators acted as recorder of all the data taken.

The outside, or surface, air temperature and humidity were usually observed before going underground, and the air temperature, body temperature, pulse rate, and blood pressure were taken in the washhouse or "dry" just before going underground. After going underground and before entering the place chosen for the test, a full set of readings was made in a near-by place where it was quiet enough to use the blood pressure apparatus. Such data were also taken in the test place, when feasible.

Incident to taking the physiological data on the subjects, Doctor Sayers necessarily participated in the stay in the hot places and, therefore, was able not only to observe the effect of conditions on the subjects, but also to experience the symptoms himself. Engineering data, such as psychrometric, barometric, and anemometric readings, were made by Mr. Harrington, who also acted as one of the subjects throughout the investigation.

The subjects sat still in the hot or test places, and during the test period exerted no physical effort other than the small amount involved in taking readings of blood pressure, pulse rate, body temperature, psychrometric data, etc. Often it was found necessary to omit taking blood pressure and pulse in the actual test place, in which cases this was done just before entering and just after leaving the test place. In a few instances the data obtained during the test were greatly influenced by a very slight amount of work done by a subject just before beginning the test.

In practically all of the above experimental work samples of the air were taken, the analyses of which showed nearly normal air as far as carbon dioxide and oxygen were concerned, and no carbon monoxide or other poisonous gases were found. The air in the place where the tests at 95° F. or over were made was as nearly absolutely saturated as can be obtained underground, and psychrometric readings were taken frequently enough to make certain that any changes occurring during the test would be discovered.

Figure 1 shows the effect on the body temperature of one subject (No. 5) of still air at 95°, 96°, and 100° F., and of moving air at 91J°, 95°, 98^°, and 100° F. The effect of these various air temperatures is shown on the graph by using zero to represent the subject's ternperature at the time of starting the test and then indicating the elevation during the stay in the test place by degrees above zero. The time is calculated in minutes, beginning with zero as the time of entering the test place. The solid lines on the graph represent the air temperatures without any air movement; the dotted lines indicate those with air movement.

A similar graph made for the other subjects would show practically the same general results, so that the one representing the effects on the temperature of subject No. 5 may be considered fairly typical.

EFFECT WITHOUT AIK MOVEMENT.

Still saturated air at 91}° F. caused the following symptoms in a subject: (1) A definite rise in body temperature; (2) moderate increase in pulse rate (18); (3) profuse sweating and feeling of weakness. The after effects were dizziness and weakness.

Although subject No. 5 was the least readily affected of the three (2, 4, and 5), Figure 1 shows that there was a decided increase in his

[graphic]

13 — 38 4$

Ttmc (minutes).

Fio. 1.—Effect of high temperatures and humidities on a subject In still and moving air.

body temperature in the still, saturated air—at the close of the experiment, the rise above the entrance temperature being as follows: At 95° there was an increase of 1.4°; at 96° an increase of 2.3°, and at 100° an increase of 3.4°. The effect of the still, saturated air on the pulse rate was similar to that on the temperature. The rate of increase at 95° and 9t>° was practically the same, although the rate at the end of the test in still, saturated air was slightly higher at 95° temperature than at 90°, probably due to slightly more exertion by the subject during the 95° test than during the 96° test. The 100° still, saturated air increased the pulse rate very rapidly, the rate being 20 beats above that at 95° and 96° at the end of the test, or a total increase of 74 beats above normal.

While sitting approximately an hour in still, saturated air, with temperature at 95° (Table I A), all the subjects were decidedly distressed, the body temperature going to 101.4° with subject No. 5, to 101.5° with subject No. 2, to 102.5° with subject No. 1, and to 102.5° with subject No. 4, the two latter being somewhat adversely affected by having exerted»a little more effort than Nos. 2 and 5 (No. 1 in taking the readings and No. 4 in walking and climbing previous to undergoing the test).

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