Personal Risk Factors

Some workers handle heat stress less effectively than others. Heat intolerance happens for a variety of reasons. Personal risk factors include:

• Obesity (body mass index ≥ 30 kg/m²)
• Diabetes
• High blood pressure
• Heart disease
• Lower level of physical fitness
• Use of certain medications such as diuretics (water pills) and some psychiatric or blood pressure medicines
• Some medications can result in a worker's inability to feel heat conditions and/or the inability to sweat, so symptoms of heat stress may not be evident.
• Alcohol use
• Use of illicit drugs such as opioids, methamphetamine, or cocaine

The above list is not comprehensive. Other medical conditions can also predispose workers to heat-related illnesses.

Employers should recognize that not all workers tolerate heat the same way. Workplace controls should focus on making jobs safe for all the employees. An occupational medical monitoring program can identify workers who are at increased risk of heat illness, while maintaining the confidentiality of workers’ health information.

When heat hazards are present, workers should receive training about personal factors that can make them more susceptible to heat-related illness. When in doubt, workers should talk to their healthcare provider about whether they can work safely in the heat.

Physiologic Monitoring

Workers' bodies produce automatic responses to cope with heat stress. Heart rate increases. Sweating becomes more profuse. Eventually skin temperature and core body temperature rise.

These physiologic responses can be measured by workers or employers. Physiologic monitoring has several advantages over other methods of monitoring heat stress:

• Physiologic responses provide a direct and individualized measurement of each worker's response to heat stress.
• Physiologic measurements can be used to monitor the worker's level of heat tolerance. Impermeable clothing, such as chemical protective suits, prevents cooling by sweating and may contribute to heat illness at lower temperatures. Environmental monitoring (i.e., WBGT) does not give an accurate indication of these workers' heat stress. Physiologic monitoring, such as heart rate measurement, should be used to determine whether their heat stress is too high.

Heart rate is the easiest physiologic parameter to measure. A timepiece is the only required equipment. Workers can be trained to count their pulse. More sophisticated devices, such as heart rate monitor wristwatches, are also available.

Some employers also monitor weight changes during a work shift as a measure of water loss from sweating.

Body temperature can be measured by thermometers. Oral, skin, and aural (eardrum) thermometers are less invasive than core body temperature measurements. Caution should be used when interpreting temperature measurements, because environmental heat might affect some thermometers.

Please see the Additional Resources for more details about implementation and interpretation of physiologic monitoring.