To determine core temperature (Tc) elevations in hazardous materials (HazMat) technicians wearing level-A fully encapsulated, chemically resistive suits (FECRSs) during training scenarios.

Cross-sectional, observational feasibility study with Institutional Review Board approval.

HazMat training scenarios held during the summer of 1994. Weather conditions included both rainy and sunny days, with a mean ambient temperature of 75.8°F(24.3°C) (range 69–83° F [20.6–28.3°C).

Nine male firefighters participating in training scenarios in the Midwestern United States.

Each volunteer swallowed a capsule containing a Tc sensor developed by the National Aeronautics and Space Administration. The capsule continuously monitored Tc and stored data in an ambulatory recorder worn under the level-A FECRS during training.

Mean age of the volunteers was 34 years, mean weight was 92.6 kg, and average baseline Tc was 36.7°C (97.1°F) (range 35.3–38.2°C [95.5–100°F]). Time in the FECRS averaged 25.4 minutes (range 14–35 minutes). All subjects demonstrated increased Tc while in the suit; the mean Tc increase was 0.8°C (1.4°F) (range 0.2–1.3°C [0.4–2.3°F]). The Tc continued to increase during wet decontamination procedures and after suit removal. Mean heat storage values (ΔTcx LBMx 3.47 kJ) were calculated, and found to be moderately elevated to 3.6 kJ/kg (range 2.1–4.6 kJ/kg).

These observations support the validity and significance of implementing prophylactic measures for firefighters using protective clothing. Simple protective measures include enforced time limitations, hydration, and efforts to minimize heat buildup by avoiding both direct sunlight and unnecessary time encapsulated in the suit.