Probability of hyperthermia in a hot environment while wearing a liquid cooling garment underneath firefighters' protective clothing

Abstract

Firefighters’ protective clothing (FPC) can limit human thermoregulation due to limited water vapor permeability and insulation. This study investigated the effect of cooling on the physiological responses and probability of hyperthermia in subjects wearing FPC during exercise in a hot environment. Twelve males participated in this study. A maximal graded treadmill exercise test was performed to measure maximal oxygen uptake ($\dot{V}$O_2max) and to assess subjects’ capacity to perform the assigned exercise. Exercise included treadmill walking at 40% $\dot{V}$O_2max in warm (30 °C) and humid (70% RH) conditions for 40 min while wearing FPC. Subjects participated in two randomly counterbalanced assigned experimental protocols: control (no cooling) and intervention (cooling). The experimental intervention consisted of a cooling garment infused with cooled water (18 °C) through silastic tubing sewn into the fabric and worn underneath FPC. Each subject served as their own control and, therefore, completed both the control and intervention of the protocol. A logistic regression model was used to analyze the interaction effect of cooling on the probability of progression to hyperthermia (T_c ≥ 38 °C). Subjects’ physiological responses increased during exercise in a warm and humid environment. Active cooling decreased (p < 0.05) the thermal stress thereby reducing the probability of hyperthermia while exercising in hot and humid conditions. The results indicate that when cooling was used each subject, on average, was 91% less likely to reach the lower threshold limit of hyperthermia. Exercise in hot environments while wearing FPC results in significant physiological strain, which may lead to hyperthermia. Utilization of a cooling garment reduced physiological strain and the probability of hyperthermia.

Keywords:

• Continuous cooling
• firefighters
• heat stress
• PPE
• work physiology

Acknowledgments

The data used in this study is a subset of a larger study derived from Dr. Aljaroudi’s Ph.D. dissertation work at the University of Cincinnati, conducted during his pre-doctoral research at the National Personal Protective Technology Laboratory (NPPTL). The authors thank the subjects for their time and participation. The authors also thank Aitor Coca, Ph.D., Jung-Hyun Kim, Ph.D., and Tianzhou Wu, M.S. for their support during data collection. We also thank Ms. Lorenna Altman and Ms. Cyndy Cox from the University of Cincinnati for their technical support. We thank Dr. Raymond Roberge, MD for medical monitoring and screening during data collection.

Disclosure statement

The authors report no conflict of interest. The findings and conclusions in this report are those of the author(s) and do not necessarily represent the official position of the National Institute for Occupational Safety and Health, Center for Disease Control and Prevention. Mention of a product or use of a photo does not constitute NIOSH endorsement.

Additional information

Funding

This study was funded in part from the NIOSH ERC University of Cincinnati Grant #T420H008432 and with NIOSH/NPPTL internal discretionary funding.