Assess workers carefully to determine risk in heat

By Lilly Ramphal-Naley, MD, MPH

Medical Director

WorkMed, the occupational health program of Wilson N. Jones Hospital

Sherman, TX

Many health factors contribute to workers’ susceptibility to heat stress, including age, overall level of fitness, presence of other illnesses, use of certain medications, and the individual’s ability to acclimatize to extreme temperatures. An individual worker’s susceptibility to extreme heat may not be known until you perform a thorough assessment of these and other factors.

Acclimatization is defined as the time needed for physiological adaptation to extreme temperature changes. An average individual takes about one or two weeks to adapt to extreme cold or hot temperatures. Successful acclimatization occurs if the physiologic mechanisms of the cardiovascular, pulmonary, and renal systems interrelate effectively to adjust the body’s core temperature by using evaporative heat loss or conservation. The process of acclimatization requires intact and responsive cardiovascular and renal systems.

The National Institute on Occupational Safety and Health in Cincinnati recommends that the focus of pre-placement and surveillance exams for heat stress should include a complete history and physical examination. I suggest screening more specifically for relative or absolute contraindications to hot environments. Factors which may contribute to the tendency to develop heat-related illnesses are considered relative contraindications to heat stress exposure and should be evaluated on a case-by-case basis. Absolute contraindications are factors that are known to contribute to heat-related illnesses.

Relative and absolute contraindications

These are some relative contraindications to heat stress exposure:

- renal disease;

- thyroid disease;

- diabetes or endocrine disorders;

- heart disease or arrhythmia;

- hypertension;

- other chronic illnesses;

- dehydration;

- obesity;

- a history of previously documented heat-related illness;

- use of beta blockers, phenothiazines, diuretics, and some other medications.

These are some absolute contraindications to heat stress exposure:

- pregnancy;

- congestive heart failure;

- unstable angina or arrhythmia;

- severe hypertension;

- renal failure;

- end-stage pulmonary disease;

- core body temperature of more than 100.4 degrees Fahrenheit;

- infertility. (Infertility does not increase the risk of heat stress, but heat stress can exacerbate infertility problems, especially in men.)

Humidity must be considered

Besides evaluating a worker with a complete history and physical exam, environmental monitoring with a wet bulb globe thermometer is recommended.

Recommended ambient temperature limits vary as the ambient humidity and convection factors vary. Based on this fact, recommended alert limits and recommended exposure limits are encouraged by the federal Occupational Safety and Health Administration in Washington, DC. When workers are exposed to heat stress, biological monitoring with the three-minute pulse recovery test is recommended during the hottest two-hour period of the day.

An excessively rapid pulse (more than 90 beats per minute) with slow recovery time (more than three minutes) and/or an elevated core temperature (more than 100.4 degrees Fahrenheit) indicates a rest period is needed to allow the worker to recover before re-entering the heat-stressed work area.

Baseline measurements can serve as an indication of whether or not a worker is fit to enter the heat-stressed environment at the beginning of the work day.