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Firefighters entering the heat chamber to begin a search task.

Monitoring practices of firefighter safety when working in the heat

Firefighters work hard, in environments characterised by high levels of ambient and radiant heat. To further add to their thermal strain, urban firefighters wear heavy, impermeable protective clothing in a range of operating conditions.

Despite structural firefighting PPC being designed for internal fire attack, it is not uncommon to see firefighters wearing this clothing to a range of events, including motor vehicle accidents, where the risk of heat illness by and large outweighs the risk of thermal injury resulting from a fire. The human body aims to dissipate body heat, mainly through a process of evaporation of sweat from the skin surface. However, modern PPC is designed specifically with the purpose of reducing chemical and steam ingress from the environment. Unfortunately, this comes with a trade-off, in that evaporation cannot occur, with sweat creating a humid micro-environment within the PPC, leading to increased body temperatures, dehydration and thermal strain for operators.

Ready for a break. Firefighters exiting the heat chamber at the end of the first work cycle (20 minutes).

Ready for a break. Firefighters exiting the heat chamber at the end of the first work cycle (20 minutes).

The internal heat load sustained by firefighters comes from the environment, through radiation, convection and conduction during firefighting operations. This heat is then augmented by the metabolic heat produced as a by-product of working (exercising). Naturally, each individual may be working at different rates, based on their fitness, their technical ability and their motivation to perform. This will then result in differing thermal loads leading to a range of body temperatures during work programs, making work/rest times problematic as a definitive tool to manage heat stress of firefighters on the fireground. To compound this problem, individuals have varying tolerances for body temperatures, making a “one size-fits all” model difficult. Guidelines for workers have been developed for working in the heat in other jurisdictions, however approaches to managing firefighters at fire scenes are not universal among different fire services in Australia.

Both the International Organisation for Standardisation (ISO) and the National Fire Protection Association (NFPA) recommend that body temperatures for workers are limited to less than 38.5 ∞C during work tasks. Furthermore, allowing individuals to work at those temperatures require that they are “medically screened, heat acclimated and medically monitored (ISO 9886).” It is currently unclear whether this practice is actually followed in Australian fire services, raising questions regarding the ongoing safety of an ageing workforce delivering emergency response capabilities in the heat. Anecdotally, as a general rule, reentry is guided by the question “are you right to go mate” rather than actual physiological data. Thus, the focus of this article, will therefore be on whether, in the absence of formal monitoring, current practices for redeployment of firefighters during long-duration events can give a reasonable estimate of their safety.

In order to understand the extent of thermal strain on firefighters, ACT Fire & Rescue, led by Dr Walker, undertook a number of research projects, based out of a purpose built heat chamber operated at their training centre in Canberra. Temperatures were set at approximately 100 ∞C, with 145 volunteers from that service completing two 20-minute search and rescue tasks in smoke and darkness, separated by a 10-minute passive recovery where they removed their jackets and drank cool water. This protocol closely replicates those conditions likely to be encountered by urban firefighters during an emergency firefighting response. Firefighters were monitored for core temperatures using ingestible thermometers, heart rates and skin temperatures. These measurement tools were then compared with perceptual responses (How hard are you working – Rate of perceived exertion? How hot are you- thermal sensation?) given at 5-minute intervals during work and rest.

Figure 1: Mean (SD) Perceived exertion of firefighters during two simulated work tasks in the heat.

Figure 1: Mean (SD) Perceived exertion of firefighters during two simulated work tasks in the heat.

Some results to consider

  • Core temperatures (Figure 3) reached an average of 38.9 ∞C at the conclusion of the second work task. This is well in excess of safe working limits. Furthermore, 3 participants recorded temperatures in excess of 40 ∞C. Continued to rise during the rest period, in spite of removing PPC.
  • Skin temperatures were elevated during work tasks and dropped significantly during rest. (Figure 3) This is due to removing PPC and evaporation of sweat beginning
  • Heart rates of participants reached approximately 90 % of their maximum (established during lab testing, not by estimation). The work tasks were standardized, meaning that increasing heart rates were due to elevated core temperatures
  • Both perceived exertion and physiological strain (Figure 1 and 2) increased during the work tasks and dropped during the rest period. This is in spite of core temperatures continuing to rise and is therefore linked with skin temperatures
Figure 2: Mean (SD) Thermal strain of firefighters during two simulated work tasks in the heat.

Figure 2: Mean (SD) Thermal strain of firefighters
during two simulated work tasks in the heat.

When incident controllers make assessments of firefighter wellbeing based on their perception of wellness, this research indicates that this is likely an unsafe practice. Firefighter’s perceptions of their wellness are linked with their skin temperatures, which in turn are affected by exposure to hot environments, wearing PPC. It is therefore intuitive to expect that, when they remove their jackets and sit in the shade they will believe that they are recovering, however this research indicates that this is not the case. In lieu of providing physiological monitoring on the fireground, which at this point in time can be expensive and impractical, a strategy could be to enforce work/rest cycles in line with NFPA 1584. This document states that firefighters should enter rehab sectors following a second work cylinder in the heat. Based on the results of this study, this seems entirely practical and appropriate for Australian firefighters working in the heat.

Figure 3: Temperatures (core and skin) of firefighters during two simulated work tasks in the heat.

Figure 3: Temperatures (core and skin) of firefighters during two simulated work tasks in the heat.

Overall recommendations

  • Firefighters must be properly conditioned to work in the heat with high heart rates expected to occur. They must therefore be medically screened as those with existing cardiac risk factors are likely to experience elevated risk
  • Fire services and incident controllers must plan for adequate resourcing to ensure that firefighters can maintain safe work/rest cycles during emergency responses.
  • In line with NFPA 1584, fire services must provide evidence-based effective post-incident cooling practices. As evidenced by this research, the current practice of removing PPC and providing only water is both ineffective and unsafe. Practical solutions include iced slush drinks and cold-water immersion (multiple body segments – ie lower body at a minimum)
  • Research activity in the future should focus on the development of a practical, cost effective tool for measuring core temperatures in the field. Relying on perceptions of wellbeing as a sole measure may be unsafe

For more information, email anthony.walker@canberra.edu.au

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Dr Anthony Walker has worked as a firefighter with ACT Fire & Rescue for the past 10 years. After experiencing, and witnessing a number of heat related events at work, he chose to pursue a research program into thermal stress experienced by operational firefighters with the aim to make firefighters safer. This program culminated in him completing a PhD through the University of Canberra, awarded his doctorate in 2015. Anthony has published extensively in the field of thermal physiology and regularly presents at both local and international conferences on firefighter safety at work and bringing research from the athletic field into the work environment.