Physiological Monitoring as a Determinant of Heat Stress
Physiologic monitoring can help protect all workers from heat-related illness.
- By Bernard Fontaine
- Sep 01, 2022
Physiologic monitoring may be used in conjunction with other environmental measurements as a means to determine the heath impact of heat stress. Such techniques include oral, skin, and aural measurements that can be done at the worksite rather than a clinical setting. The effects from heat stress should be considered whenever the Wet Bulb Globe Temperature (WBGT) exceeds the American Conference of Governmental Industrial Hygienist (ACGIH) Threshold Limit Values (TLVs) or the National Institute for Occupational Safety and Health Recommended Action Limit (RAL) or Recommended Exposure Limit (REL). These occupational exposure limits provide a validated reference for working in hot environments indoors and outdoors.
Heart rate, skin and core body temperature, and total body water loss from sweating can be measured as a physiologic response to heat exposure. More advanced methods and new tools are available for physiologic monitoring. When the NIOSH Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments was first published in 1972, physiologic monitoring was not considered a viable adjunct to the WBGT index and control of heat stress.
In 1986, it was proposed that monitoring core body temperature and/or the work and recovery heart rate of workers exposed to environmental conditions in excess of the ACGIH TLVs could be a safe and relatively simple approach. Heat stress indices assume that most workers will not incur heat related illnesses or injuries if they are exposed to hot work conditions that do not exceed the permissible value. Inherent in this assumption is that some exposed workers may still develop heat-related illness.
The NIOSH REL and the ACGIH TLV are intended to protect nearly all healthy heat-acclimatized workers at heat stress levels that do not exceed the occupational exposure guideline. Physiologic monitoring can help protect all workers, including new hires, workers on medication or suffering from illness or disease along with heat-intolerant workers.
Oral Physiological Measurements
Oral temperatures are easily obtained with inexpensive disposable oral thermometers. However, to obtain reliable oral temperature requires a strictly controlled procedure. The thermometer must be correctly placed under the tongue for three to five minutes before taking the reading, mouth breathing is not permitted during this period, nor should hot or cold liquids be consumed for at least 15-minutes beforehand.
This article originally appeared in the September 1, 2022 issue of Occupational Health & Safety.