Page 53 - OHS, September 2022

thermometers must be kept in a cool insulated container or immersed in alcohol. With the advent of digital oral thermometers, oral temperature measurements may be obtained within 30 seconds, thus avoiding some of the issues found with standard oral thermometers. Evaluation of any oral temperature must follow established medical and occupational hygiene guidelines.
Data indicate that nearly 95 percent of the time, oral temperature was below 99.5 degrees Fahrenheit when the recovery heart rate was 124 bpm or less, and 50 percent of the time oral temperature was below 99.5 degrees Fahrenheit when the heart rate was less than 145 bpm. If the heart rate is below 90 bpm, the heat stress condition is considered satisfactory. When the heart rate approximates 90 bpm and/or the recovery is about 10 bpm, it indicates that the work level is high but there is little increase in the core body temperature. If the heart rate is greater than 90 bpm and/or recovery rate is less than 10 bpm, it indicates a no-recovery pattern—that is, the heat stress exceeds acceptable levels and corrective actions should be taken to prevent heat- related illness.
Skin Physiological Measurements
Skin temperature can be used to assess the severity of heat strain and estimate tolerance, which is supported by thermodynamically and field-derived data. To remove body heat from the deep
tissues (core body) to the skin (shell), where it is dissipated to the ambient environment, requires an adequate heat gradient.
As the skin temperature rises and approaches the core body temperature, this temperature gradient is decreased and the rate of heat removed from the body core to the shell is decreased and the rate of core heat loss is reduced. To restore the rate of heat loss or core skin heat gradient, the core body temperature needs to increase. Circulation of warm blood from central (core) body to the skin results in an increase in skin temperature. An increase in skin temperature results in heat transfer to the ambient environment through conduction, convection, and radiation.
As heat is transferred to the environment, blood near the skin surface cools and returns to the body core resulting in a decrease in core body temperature. Under certain environmental conditions, insufficient heat is transferred from the skin to the environment which can result in an increase in core body temperature. As core body temperature increases above 100.4 degrees Fahrenheit, the risk of an ensuing heat-related illness is increased. From these clinical observations, it has been suggested that a reasonable estimate of tolerance time for hot work could be made from the skin temperature. Where evaporative heat exchange is not restricted, skin temperature should not increase much, if at all. In such situations, the maintenance of an acceptable core body temperature may not be jeopardized, except under very high metabolic loads or restricted heat transfer from clothing.
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