During severe disease outbreaks such as the 2014 Ebola virus epidemic in West Africa, wearing special gear can protect healthcare workers from exposure. This personal protective equipment covers the face and body to provide a physical barrier against germs.

In addition, a respirator prevents the inhalation of airborne germs. Since many types of personal protective equipment worn during the Ebola response are made of heavy, fluid-resistant material, which can prevent sweat from evaporating and cooling the body, heat stress is a concern in hot weather.

At NIOSH, the safe use of personal protective equipment is a priority. Two studies recently published in the journal Disaster Medicine and Public Health Preparedness focused specifically on preventing heat stress while wearing this equipment in hot, humid environments.

Volunteer study participants included six healthy, young men who received medical clearance by a licensed physician. To simulate working in the hot and humid conditions of West Africa, participants walked on a treadmill for 60 minutes in a special environmental chamber set to 90 degrees F (32 degrees C) and 92% relative humidity.

Personal Protective Equipment Does Not Take the Heat Equally

After comparing three commonly used ensembles, NIOSH investigators found that different types of personal protective equipment were linked to increases in heart rate and body temperature during exertion.

The first ensemble tested included a face shield and a fluid-resistant surgical gown. The other, more elaborate, ensembles included goggles, coveralls, and a separate hood for the second one, and highly fluid-resistant coveralls, a separate hood, and a surgical mask cover over a NIOSH approved N95 respirator for the third one. Participants wore each of the ensembles over standard medical scrubs.

It is important to balance work in hot conditions with adequate rest periods and to use heat-prevention strategies such as cooling vests.
Compared to participants wearing the first ensemble, those wearing the second and third ensembles had significantly higher heart rates and body temperatures after exercising on the treadmill. In addition, participants wearing the second and third ensembles reported feeling hotter and more tired.

These findings underscore the importance of training healthcare workers and regulating agencies in proper selection of personal protective equipment to prevent heat stress.

In addition to training, it is important to balance work in hot conditions with adequate rest periods and to use heat-prevention strategies such as cooling vests.

Cooling Vests Linked to Fewer Signs of Heat Stress

Study participants wearing special vests fitted with ice packs, phase-change materials, or water hoses under personal protective equipment had fewer signs of heat stress than participants who did not wear the cooling devices, according to a related study.

These results highlight the importance of cooling vests for healthcare workers wearing personal protective equipment in hot, humid environments.

For this study, participants tested four different styles of cooling vests that were are made of fabric and fitted with cooling packs or water-circulation hoses.

Two of the vests contained cooling packs made of a special material designed to stay cold for long periods. One of these contained gel ice packs, and one contained a battery-operated pump and small hoses to deliver cold water throughout the vest. Participants wore the vests over standard medical scrubs and under personal protective equipment.

At the end of the treadmill tests, participants who were not wearing a cooling vest had significantly higher body temperatures and heart rates than did those who wore one.

Furthermore, participants lost more weight during the exercise test when they were not wearing a cooling vest.

Smaller increases in body temperatures and heart rates occurred among participants wearing the cooling vests with the gel ice packs and water hoses, compared to those wearing vests containing the special cooling material.

In addition to measuring body temperature, weight, and heart rate, the investigators used a questionnaire to measure five subjective feelings of exertion: heat sensation, thermal comfort, rating of perceived exertion, breathing comfort, and wetness.

They found that three of the five feelings—heat sensation, rating of perceived exertion, and breathing comfort—improved when participants wore a cooling vest.

Investigators noted that future research should look at the effects of wearing cooling vests on posture, balance, and mobility and the physical effects of wearing circulating-water vests prior to wearing the personal protective equipment. In addition, further research with larger populations that include women is necessary.