Firefighters are faced with significant environmental and physically challenging responsibilities due to the nature of their jobs—lifting heavy equipment, navigating buildings and other premises, securing individuals who may be at risk, and managing unique heat conditions, to name a few. Research of tactical athletes, like firefighters, in their work environments can lead to important advances in injury prevention, recognition and treatment, which can ultimately help them perform their jobs more safely and efficiently.
Body temperature on scene
Exertional heat illness is a particular area of focus to ensure best prevention practices and immediate care of firefighters on scene. Exertional heat illnesses are conditions that commonly occur in hot environmental conditions, such as exercise-associated muscle cramps, heat exhaustion or exertional heat stroke. Of the distinct conditions, exertional heat stroke can have a high morbidity and mortality rate if not recognized or treated promptly. Corresponding fatalities of potential heat stroke events are reported annually in firefighters while on duty.1
In order to protect firefighters from exertional hyperthermia (having an above-normal body temperature), several safety procedures already exist, including work monitoring programs and PPE modifications. Further, NFPA 1584: Standard on the Rehabilitation Process for Members During Emergency Operations and Training specifically recommends rehabilitation intervals during sustained firefighting activity depending on the number of minutes actively engaged with the fire.2
Additionally, cooling devices used during work or rehabilitation intervals are commonly marketed to fire departments as an additional method of avoiding exertional hyperthermia. However, few have been researched by an external entity, and those that have been researched demonstrated an array of results, ranging from favorable to ineffective. This leads to inconsistent clinical bottom lines for firefighters, as well as athletic trainers working with fire departments, to make injury-prevention decisions.
Head cooling is one method that has been studied for core body temperature attenuation, but never in firefighters. Forearm cold-water immersion has been explored in firefighters, but the majority of studies were done in laboratories, making results hard to translate to the field setting.
With this in mind, researchers at the University of South Carolina conducted a study to evaluate the efficacy of two field cooling devices for firefighters with respect to their ability to slow the rise in body temperature during drills (head cooling) or reduce body temperature during rehabilitation (forearm cooling).
Study logistics
Our research team, composed of athletic trainers, used a randomized controlled trial to determine the efficacy of field cooling devices during simulated firefighting activity or rehabilitation. The study was conducted at the district’s Firefighter Training Center in Terre Haute, IN. Twenty-seven career firefighters from eight stations volunteered to participate in the study.
Gastrointestinal temperature was measured by an ingestible thermistor, which transmitted a signal to the athletic trainer’s handheld data receiver. Ingestible thermistors were distributed to firefighters after arrival at their station for their shift and were ingested 5 hours prior to their arrival time at the training facility. Heart rate straps sent a signal to the corresponding watch worn by researchers. Thermal sensation was measured by showing a visual scale numbered from 0 to 8 (0 = unbearably cold, 8 = unbearably hot). The firefighters indicated how they felt at the time, based on the scale descriptions.
Firefighters assigned to the head-cooling group inserted a head gel pack just removed from the freezer into the top of their helmet. Forearm cooling consisted of a collapsible chair with water immersion troughs built into the arm rests. Firefighters fully immersed the forearm from the elbow to the knuckles in 41 degrees F water.
The control group did not receive any cooling during firefighting activity drills or rehabilitation. Firefighters adorned a heart rate strap, bunker pants with suspenders, steel-toe boots and bunker coats before baseline measurements soon after arrival. They donned their remaining turnout gear, including Nomex hoods, gloves, helmets, Draegar SCBA with a mask and a 30-minute 4,500-psi air bottle immediately prior to commencing drills.
The modified combat challenge protocol3 included four 15-minute firefighting activity drills:
- Station one was an outdoor obstacle course in which firefighters crawled following a hose over and through various props and then used an armpit drag to move a Rescue Randy.
- Station two was a high-rise drill in which firefighters carried either a hose or an appliance kit (on alternating trips) up four flights of stairs to the top of a smoke-filled tower to the standpipe connection where the hose would be attached and then descended the stairs to the bottom of the tower.
- To simulate search and rescue, firefighters crawled through a smoke-filled, two-story residence while following a hose, crawling through props and up and down stairs.
- At the car extrication drill, firefighters performed car extrication skills outdoors in the sun without wearing SCBA.
The firefighters were allowed to self-pace completion of the task at each drill but kept repeating the task for the entire 15-minute timeframe. Firefighters completed the first firefighting activity drill, then reported to athletic trainers at an exchange area to replace their air cylinders.
Firefighters assigned to head-cooling received a new gel pack from the freezer at this time. Following the exchange, the firefighters rotated to the next drill in the sequence. Firefighters then reported to athletic trainers at the rehabilitation area for measurements and all groups rested for 15 minutes. At the end of rehab, firefighters redressed and completed the drill-exchange-drill-rehabilitation sequence a second time. Researchers recorded gastrointestinal temperature, heart rate, and thermal sensation at baseline and the end of each 15-minute firefighting activity drill and rehab.
Results and takeaways
Our study demonstrated that head cooling was ineffective at slowing the rise in gastrointestinal temperature, heart rate and thermal sensation compared to the control group. The inability of the head-cooling device to significantly reduce these variables may be explained by the device’s limited ability to maintain its original temperature4 and the size and type of surface area. The ability to effectively transfer heat away from the head may have been restricted by the small surface area of contact between the gel pack and the head. Although the firefighters in the head-cooling group reported feeling cooler, the difference was not statistically or practically significant.
The drop in gastrointestinal temperature from the end of the firefighting activity drill to the end of rehab was significantly greater in the forearm-cooling group compared to the head cooling and control groups. The absolute gastrointestinal temperature was significantly lower by the end of each rehabilitation as well. The 41 degree F water temperature used in the immersion arm troughs for our study was much lower than previous research examining this cooling mechanism. We were able to maintain the water temperature with periodic ice additions that ensured the temperature gradient remained substantial (41 degrees F versus ~102.2 degrees F) and resulted in a greater cooling rate per minute. This encouraged a significant amount of heat to be removed from the body at a faster rate within the rehabilitation period,5 ultimately impacting the gastrointestinal temperature. It is important to highlight that gastrointestinal temperature returned to baseline, or below, in the forearm-cooling group by the end of each rehabilitation timeframe. We feel the 41 degrees F water temperature was the key factor in our statistical and clinical findings as compared to previous research.6-10
Immersion of extremities is of interest to firefighter companies as a means to lower body temperature while in the field due to water’s effectiveness in reducing body temperature. Practically, firefighters needing to return to an emergency after a rehabilitation interval cannot remove bunker pants for leg immersion. However, forearm water immersion would allow bunker pants to stay on during rehab. Further, forearm-water immersion is cost-effective, as water and ice are readily available compared to freezer units needed to keep cooling vests stored appropriately. Thus, forearm water immersion alone is both practical and physiologically beneficial for field rehab scenarios.
Even though not measured, the firefighters in our study also did not complain that hand dexterity was impacted since fingers were not immersed. Forearm cooling did not slow the rise in gastrointestinal temperature during ensuing firefighting activity drills, suggesting that the observed reduction of gastrointestinal temperature during rehabilitation may have allowed these firefighters to work at a higher intensity during subsequent drills compared to the head-cooling and control groups.
In the current study, forearm cooling also resulted in a lower heart rate at the end of both rehab intervals, but a statistical difference was not present. Forearm immersion did not significantly lower thermal sensation. Research on the population of firefighters has previously noted that thermal sensation is a poor indicator and over-predicts body temperature 80 percent of the time.11 A cooling device that lowers body temperature but does not lead to inappropriately low thermal sensation could be considered safer cooling device.
Bottom line
The head-cooling device failed to slow the rise in gastrointestinal temperature during firefighting activity and, therefore, its use by fire departments for this purpose is not recommended. Use of the forearm-cooling device during rehabilitation can be recommended while actively engaged in the field to aid recovery of gastrointestinal temperature and physiological strain to baseline values. While this may not slow subsequent rise in gastrointestinal temperature during firefighting activities, it may allow for greater work and heat storage capacity (i.e., time before reaching critical temperatures greater than 104 degrees F) for the firefighter during subsequent firefighting activities. This field cooling device can be used in conjunction with other preventative measures to reduce the risk of an exertional heat illness of firefighters while on duty.
The full study, “Physiological and Perceived Effects of Forearm or Head Cooling During Simulated Firefighting Activity and Rehabilitation,” which was published in a special Journal of Athletic Training dedicated to tactical athletes, is available here.
Susan Yeargin, PhD, ATC, is an assistant professor in the Athletic Training Education Program of the University of South Carolina Department of Exercise Science. She is a member of the National Athletic Trainers’ Association. For more information about athletic trainers, please visit www.nata.org.
Acknowledgements
The authors would like to thank the Terre Haute, IN, Fire Department for their constant support throughout the project. We would also like to thank the firefighters who agreed to participate in the study and the large research team needed to execute the study.
1. U.S. Fire Administration. November 2014. Firefighter Fatalities in the United States in 2013. www.usfa.fema.gov/downloads/pdf/publications/ff_fat13.pdf.
2. NFPA 1584: Standard on the Rehabilitation Processes of Members During Emergency Operations and Training Exercises. 2008. www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards?mode=code&code=1584.
3. Davis P. Firefighter Combat Challenge. firefighter-challenge.com. Accessed Jan. 7, 2015.
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