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646 Heat Injury and Illness Prevention: Supervisor Skip to main content

Physiological Monitoring

What It Is

Physiological monitoring involves regularly tracking indicators like heart rate, core temperature, and skin temperature to directly assess how a worker’s body is responding to heat, rather than relying solely on environmental measures.

ARMOR Heat Monitor

When to Use It

  • When standard limits (WBGT or Heat Index) may not protect acclimatized or unacclimatized workers under heavy workloads.
  • For vulnerable workers with personal risk factors or those wearing encapsulating suits.
  • In emergency conditions or when workers are isolated (no buddy system).

How to Monitor

Below are the physiological alert thresholds for workers:

  • Heart Rate: 180 beats per minute (bpm) subtract the age of the worker (180 bpm - age) sustained for several minutes; compare against the worker's' baseline.
  • Recovery Heart Rate: A heart rate greater than 120 bpm one minute after peak effort.
  • Core Temperature: Increase of more than 1.8°F above pre-shift, or greater than 101.3°F for acclimatized workers and greater than 100.4°F for unacclimatized workers.

Action Levels

If any metric exceeds its limit, stop work immediately and move the worker to cool rest and recovery before resuming.

By embedding physiological monitoring into your heat-stress program, you ensure real-time protection tailored to each worker's individual tolerance level.

Knowledge Check Choose the best answer for the question.

3-9. What should be done if a worker's recovery heart rate remains above 120 bpm one minute after peak effort?