Q&A: How can health workers and other responders manage heat stress while wearing personal protective equipment (PPE)?

Updated: 17 May 2020

Answer

There are three ways to reduce heat stress while wearing PPE:

  • start cool
  • reduce rises in body core temperature at work
  • improve thermal tolerance through acclimatization and fitness

Under some circumstances it may be possible to supply PPE that is less likely to lead to heat stress in health workers and other responders.

What can be done?

1. Learn how to identify symptoms of heat-related illness in yourself and others.

2. Before work: start cool

  • Start hydrated and avoid alcohol during time away from work.
  • Drink cold fluids or ice slurry prior to donning your PPE.
  • Become heat acclimatized to lower your starting body core temperature. You become heat acclimatized when you work in the heat for more than an hour each day for at least 7 days.
  • Cool down, hydrate and recover between shifts, as heat stress can increase with consecutive days of exposure.

3. During work: reduce rises in body core temperature.

  • Recognize signs of heat stress in yourself and don’t wait to feel unwell before taking a break
  • Stay hydrated and eat regularly to ensure electrolyte balance is maintained, when sweating heavily or for prolonged periods.
  • Reduce clothing layers underneath PPE.
  • Reduce additional heat from exertion: minimize the equipment you carry, be efficient in your movements, pace yourself.
  • Cool down: drink cold fluids or ice slurry during breaks, find cool spots to rest in.
  • Use work/rest schedules to minimize an excessive rise in body heat.
  • Consider using cooling devices under your protective garment like a vest with phase change materials, ice etc.

4. In general

  • Be aware of your individual vulnerability level as a result of your age, physical condition, health problems, medications, pregnancy or lack of heat-acclimatization.
  • Engage in acclimatization activities.
  • Maintain or improve your aerobic fitness where possible.

Evidence

To protect against the COVID-19 virus, protective garments are worn by medical and other exposed personnel. These garments generally consist of a fluid resistant surgical face mask, plastic apron and gloves, and sometimes a visor/goggles, or hazmat suit, depending on the activity. While essential for protecting workers from the virus, these items make it more difficult to lose body heat; in particular, because sweat cannot evaporate easily. Working in protective clothing not only reduces a person’s endurance and physical performance, the increase in body core temperature can also reduce cognitive performance.1

To optimize endurance and cognitive performance while wearing PPE, workers should seek to: lower their body’s core temperature at the onset of work and attenuate it during work.2

Start cool: precooling with a cold drink or ice slurry reduces body core temperature by about 0.5°C3 and 0.2°C for heat acclimation4, thus enhancing the capacity of the body to store heat that is generated during work. Cool down, hydrate and recover between shifts, as heat stress can increase with consecutive days of exposure.5

Stay cool: A progressive attenuation in body core temperature responses is reported with increasing levels of fluid replacement during work.6 Reduction in the weight of clothing reduces metabolic heat production and thus enhances work capacity.7 Use active cooling methods if practicable. A recent review shows the potential of cooling garments during work8 although there are concerns about the difficulty of controlling for contamination and hygiene, and some COVID-19 response centres report cooling as too aggressive.

Heat tolerance: Body core temperature tolerance is considerably higher in people with high, rather than medium, levels of aerobic fitness.9 Aerobic fitness is also a key factor in limiting the age-related decline in heat tolerance.10 General health/chronic medical conditions, specific medications, sleep deprivation, previous incidences of heat-related illness and alcohol/drug consumption may negatively impact the response to heat stress and should be controlled for accordingly.11  

Disclaimer

Levels of heat acclimatization, thermal tolerance, environmental conditions, workload and PPE will vary significantly within and between workforces wearing PPE. As such, these are general principles to be considered in light of your specific context and requirements.

References

  1. Zhang, F., De Dear, R. & Hancock, P. 2019. Effects of moderate thermal environments on cognitive performance: A multidisciplinary review. Applied energy, 236, 760-777.

  2. Alhadad, S. B., Tan, P. M. & Lee, J. K. 2019. Efficacy of heat mitigation strategies on core temperature and endurance exercise: a meta-analysis. Frontiers in physiology, 10.

  3. Lee, J. K., Shirreffs, S. M. & Maughan, R. J. 2008. Cold drink ingestion improves exercise endurance capacity in the heat. Medicine & Science in Sports & Exercise, 40, 1637-1644. doi: 10.1249/MSS.0b013e318178465d

  4. Weller, A.S., et al., Quantification of the decay and re-induction of heat acclimation in dry-heat following 12 and 26 days without exposure to heat stress. European Journal of Applied Physiology, 2007. 102(1): p. 57-66.

  5. Notley, S. R., Meade, R. D., D’Souza, A. W., McGarr, G. W. & Kenny, G. P. 2018. Cumulative effects of successive workdays in the heat on thermoregulatory function in the aging worker. Temperature, 5, 293-295.

  6. Montain, S. J. & Coyle, E. F. 1992. Fluid ingestion during exercise increases skin blood flow independent of increases in blood volume. Journal of Applied Physiology, 73, 903-910.

  7. Dorman, L. E. & Havenith, G. 2009. The effects of protective clothing on energy consumption during different activities. European journal of applied physiology, 105, 463-470.

  8. Bach, A. J., Maley, M. J., Minett, G. M., Zietek, S. A., Stewart, K. L. & Stewart, I. B. 2019. An evaluation of personal cooling systems for reducing thermal strain whilst working in chemical/biological protective clothing. Frontiers in physiology, 10, 424.

  9. McLellan, T. M., Daanen, H. A. & Cheung, S. S. 2013. Encapsulated Environment. Comprehensive Physiology, 3, 1363-1391. DOI: 10.1002/cphy.c130002

  10. Meade, R. D., Notely, S. R. & Kenny, G. P. 2019. Aging and human heat dissipation during exercise-heat stress: An update and future directions. Current Opinion in Physiology, 219-225.

  11. Jacklitch, B., Williams, J., Musolin, K., Coca, A., Kim, J.-H. & Turner, N. 2016. Criteria for a recommended standard: occupational exposure to heat and hot environments. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health.