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Firefighters wear structural turnout gear and other components of personal protective equipment (PPE) to provide protection against multiple hazards, most notably thermal injury. The use of such protection is absolutely necessary, but it also imposes a physiological burden. Specifically, the weight and insulative properties of the gear increase the cardiovascular and thermoregulatory strain of performing work.
National Fire Protection Association (NFPA) 1971, Standard on Protective Ensembles for Structural Firefighting and Proximity Firefighting, includes a thermal protection performance (TPP) test to ensure a minimum amount of thermal protection as well as a total heat loss (THL) test to ensure minimum level of heat dissipation. However, current NFPA standards for TPP and THL consider only the turnout gear worn during emergency operations. In fact, the clothing worn under the turnout gear (including base layers and station uniform) may also contribute to thermal protection and may limit heat dissipation.
Effects of stationwear
There is currently no standard practice in the United States as to the clothing worn under structural turnout gear. Many firefighters wear a cotton T-shirt issued by the department. Some departments also require that firefighters wear a station uniform shirt over the cotton T-shirt, although this may only be required during “business hours.”
Although wearing a station uniform shirt may be desirable for the sake of tradition and professionalism, it is not known if the station uniform shirt has beneficial or detrimental effects on physiological response or comfort during work. Previous research has shown that adding clothing layers in athletic and military settings increases thermal stress by increasing thermal insulation and decreasing evaporative cooling efficiency. However, increasing layers may also increase protection against thermal injury, thus being of some benefit to firefighters.
In order to understand the influence of wearing a station shirt, we performed a research study that included both human performance and materials performance testing. For both types of testing, we considered all layers of the clothing worn by the firefighter (baselayer, station uniform, structural turnout gear) as an integrated clothing ensemble.
Ten male participants participated in the human performance testing component of the research study. Testing was done in a thermoneutral laboratory (69.8 degrees Fahrenheit; 58.0% relative humidity). On different days, participants wore station pants and either a cotton T-shirt alone (511 Tactical Services, Modesto, CA; weight, 6.81 ounces; thickness, 0.022 inches) or a cotton T-shirt AND a short-sleeved station uniform shirt (Topps Safety Apparel, Rochester, NY; weight, 4.37 ounces; thickness, 0.017 inches; NOMEX) under full firefighting personal protective equipment (PPE; G-XTREME turnout pants and jacket Globe Manufacturing Co., Pittsfield, NH; weight, 20.57 ounces; thickness, 0.084 inches; outer shell, GEMINI PBI Matrix; moisture barrier, CROSSTECH 2C; thermal barrier, QUANTUM3D two-layer). Participants also wore other protective equipment, including boots, flash hood, helmet, gloves and self-contained breathing apparatus (SCBA) during an alternating work/recovery protocol lasting 110 minutes.
A 110-minute alternating work/recovery protocol consisting of three 20-minute bouts of work, with bouts separated by recovery periods of 10, 20 and 20 minutes, was used to mimic a realistic work cycle for firefighters. Work entailed walking on a treadmill at a moderate intensity level (~70% of age-predicted maximal heart rate) while wearing PPE. Personal protective equipment was doffed and a fan was used to cool participants during the recovery periods to mimic recommendations during planned cooling periods of emergency operations.