Overview: Firefighters and law enforcement officers (LEOs) perform physically demanding occupational tasks in arduous conditions while wearing personal protective equipment (PPE) (6,14). Although PPE provides protection, it also increases internal strain. Accordingly, PPE has been shown to increase metabolic demand and decrease occupational performance in firefighters and LEOs (6,10,14,15). As such, this column describes specific investigations that evaluated the effect of PPE on occupational performance.

HEAT TOLERANCE DURING UNCOMPENSABLE HEAT STRESS IN MEN AND WOMEN WEARING FIREFIGHTER PERSONAL PROTECTIVE EQUIPMENT. APPLIED ERGONOMICS 101: 103702, 2020.

RENBERG, J, LIGNIER, MJ, WIGGEN, 0N, FAEREVIK, H, HELGERUD, J, AND SANDSUND, M.

Bottom Line Up Front (BLUF): Fit males and females (non­firefighters) respond to exercise heat stress similarly when performing aerobic exercise in PPE.

The percentage of women in the fire service has increased from 2% in 1999 to 9% in 2020 (13,14). This raises the importance of considering the physiological differences between male and female firefighters to promote a safe and supportive work environment (9). Both sexes are fully capable of performing rigorous firefighting duties; however, factors that influence performance can vary between the sexes (e.g., body size, muscle mass distribution, strength) (13). Occupational demands of firefighting often include prolonged heat exposure, which can lead to heat stress, disrupted thermoregulation, hypohydration, heat exhaustion, diminished cognitive function, and potentially life-threatening heat stroke (3,8). Yet, the relevance of sex-related differences regarding thermoregulation in PPE (standard helmet, structural gloves, boots, turnout coat, pants, and self-contained breathing apparatus) while working in a hot environment is unknown. Therefore, this investigation aimed to quantify heat tolerance among fit males and females while wearing firefighter PPE during physical activity.

Twelve male (age: 27±7 yr, body mass: 83±8 kg, V02max: 58.8±7.5 ml/kg/min) and 12 female (age: 28±7 yr, body mass: 66±5 kg, V02max: 51.7±4.7 ml/kg/min) healthy Norwegian non-firefighter participants volunteered to perform a heat tolerance assessment after passing the Norwegian Labour Inspection Authority (NLIA) aerobic fitness test and thus were considered fit for firefighter duty. A maximal treadmill graded exercise test was performed in athletic clothing to determine aerobic capacity (V02max). In addition, a workload capacity test was used to determine the velocity that corresponded with six watts per kilogram (body mass) workload, which was subsequently utilized in a heat tolerance test. Before starting the heat tolerance test, participants dressed in a shirt and pants, then sat for 20 min in room temperature (23.1±0.9 °C, 23±7% RH). After 20 min, participants donned regulation firefighter PPE (female PPE mass: 6.4±0.1 kg, male PPE mass: 6.9±0.2 kg) including a turnout jacket and trousers, fire hood, helmet, structural gloves, and running shoes, but did not wear a self-contained breathing apparatus. Participants sat in the PPE for an additional 10 min before entering the environmental chamber (39.7±0.3 °C, 14±1% RH). While in the environmental chamber, participants walked on the treadmill at the predetermined velocity until volitional exhaustion, a rectal temperature of 39.0 °C was indicated, or once 60 min had been completed.

The authors assessed heat tolerance on a continuum associated with a traffic light system determined by final rectal temperature. Five participants were found to be in the "green zone"(< 38.0 °C), 15 in the "yellow zone" (38.0 °C - 38.5 °C), and four in the "red zone" (> 38.5 °C). All participants (12 men, 12 women) reached 40 min of the assessment, 10 men and 11 women sustained 50 min, and four men and six women completed 60 min. All subjects reached rectal temperatures of 38.5 °C by the end of the trial, with an average time to 38.5 °C of 45±8 min for males and 46±7 min for females. Baseline rectal temperature, aerobic capacity, and body fat percentage did not impact time to increase rectal temperature by 1.5 °C (p>0.05), nor were there sex-related differences (males: 44.5±7.1 min; females: 49.9±5.6 min; p=0.051).

No statistical difference in rectal temperature at 40 min was observed between males and females (38.3±0.3 °C and 38.2±0.3 °C, respectively, p=0.63); however, lower baseline rectal temperature was associated with lower rectal temperature at 40 min (r=0.60, p=0.002). There were no sex-related differences in perceptual responses at 40 min of heat exposure for the rating of perceived exertion, thermal sensation, or thermal comfort. Males experienced greater absolute sweat loss than females (1.4±0.5 L/hr vs. 1.0±0.2 L/hr; p=0.018), yet there were no sex-related differences in the percent of body mass lost following the trial (males: 1.5±0.5%; females: 1.4±0.3%; p=0.480) due to differences in body mass. Interestingly, females perceived that they were sweating more as the median report was "heavy sweating" from females and "moderate sweating" from males (p<0.05). While heat production, V02max, relative intensity (%V02max), and walking speed were not different between the sexes (p>0.05), the trial required a greater mechanical power among the females (430±33 W) than the males (551±85 W; mean difference: 121 W; p<0.001).

RELEVANCE FOR THE TACTICAL FACILITATOR

Males and females demonstrate similar heat tolerance when thermal regulation is impaired by PPE. It is important for fire department stakeholders to understand the diverse physiological needs of personnel to enhance firefighters' safety and readiness. This may include educating firefighters of smaller stature and/or females regarding the importance of fitness to compensate for the higher relative work rate required to complete tasks compared to larger and/or male firefighters (13).

Effective heat stress management can improve safety, performance, and long-term health outcomes for firefighters. Tactical facilitators should incorporate science-based heat acclimatization techniques to reduce the risks of heat stress among firefighters, including controlled heat exposure throughout the year. Specifically, heat acclimatization (or "heat acclimation" in indoor environments) should include multiple controlled exercise­heat exposures over 1 - 2 weeks (12). Departments should monitor heat exposure during training and live emergencies, especially on days with high ambient temperatures and relative humidity. Firefighters may consider adopting preventative techniques before heat exposure such as pre-cooling by holding cold water bottles or palm-cooling devices, consuming cold fluids, and staying in a climate-controlled environment for as long as possible prior to heat exposure (4). Additionally, post-heat exposure caution should be exercised such as quickly removing PPE to allow for heat dissipation, limb immersion in circulating 10 - 14°C cool water for 5 - 12 min, or sternum or neck-depth immersion in circulating 15 - 26°C cool water for 15 min (2.12). Less demanding logistical options may include utilizing portable misting fans in shaded or climate­controlled areas and cool fluid consumption, ideally with electrolytes to minimize risk of hyponatremia.

THE PHYSICAL COMPETENCE OF THE DUTCH NATIONAL POLICE: THE EFFECTS OF WEARING A POLICE UNIFORM ON TESTER PERFORMANCE. POLICE PRACTICE AND RESEARCH 21(3): 264-278, 2020.

KOEDIJK, M, STUURMAN, HF, RENDEN, PG, HUTTER, RI, STRATING, M, AND OUDEJANS, RRD.

BLUF: PPE reduces occupational performance among LEOs.

Law enforcement requires physical fitness to perform many occupational tasks, such as chasing a subject, combating an assailant, and rescuing unconscious individuals while wearing PPE (11). The majority of an 8 - 10 hr shift is performed in agency-specific PPE that often includes reinforced clothing, a protective vest, and a duty belt with various tools (e.g., sidearm, pepper spray, radio, handcuffs, etc.) (6). However, LEO physical fitness assessments tend to be performed in athletic clothes, which may not most accurately simulate occupational demands considering 6.5 kg of LEO PPE has been shown to increase the metabolic demand of performing steady-state treadmill exercise by approximately 7% (rJ2=0.79, p<0.01) (6). Therefore, this study investigated the effect of LEO PPE on occupational performance as assessed by the timed completion of the Dutch National Police Force's Physical Competence Test (PCT).  Twenty-seven Dutch LEOs (age: 38.3±8.9 yr; 21 males, 6 females) completed an annual fitness test which included the PCT. The PCT is a timed obstacle course consisting of five rounds that include eight total sub-parts. There are four sub-parts per round, including two that require traversing over obstacles (e.g., 150-cm box), two that involve moving heavy objects (e.g., moving three 5-kg medicine balls) and running between sub-part tasks for a combined total distance of 226.5 m (Table 1).

The LEOs completed the PCT twice on the same day, once in PPE, and once in athletic clothing, with a two-hour inter-test recovery period. The test order was counterbalanced. Athletic clothing consisted of a t-shirt, shorts, and tennis shoes, while PPE included strengthened pants, armored shoes, safety vest, and a duty belt with handcuffs. The Borg 6 - 20 scale was used to assess the rating of perceived exertion (RPE). Physiological intensity was calculated as %HRmax converted to a O - 10 scale, with "O" being s 50% HRmax, and "10" being 100% HRmax and reported in arbitrary units (AU).

Results indicated that LEOs completed the PCT 7.2% (14 s) slower while wearing PPE (195.2±20.3 s; p<0.001) compared to athletic clothing (181.2±19.1 s). The PPE condition elicited greater perceived exertion than the athletic clothing condition (14.4±1.7 vs. 12.3±1.1, respectively; p<0.001) but heart rate data indicated similar cardiovascular intensities (8.65±0.68 AU vs. 8.70±0.88 AU; p=0.815). Furthermore, the effect of PPE on fatigue increased with work time, as shown by the increased difference in round completion times (performance decrement: rounds 1 and 2: 2.0%, round 3: 3.4%, round 4: 2.7%, round 5: 3.7%; p<0.01). Specifically, running time between sub-part tasks was five seconds greater in PPE (71.0±6.0 s) compared to athletic clothing (66.0±6.2 s), and timed completion of sub-part tasks increased by nine seconds in PPE (124.1±15.3 s) versus athletic clothing (115.2 ±13.8 s; p<0.001).

RELEVANCE FOR THE TACTICAL FACILITATOR

PPE may increase the perceived intensity and decrease task efficiency due to the additional load carriage and reduced mobility (5,15,16). Interestingly, research indicates that despite these deleterious outcomes, marksmanship is not affected when performing occupational tasks in PPE (15). To address these PPE-induced work rate deficiencies, tactical facilitators should prioritize the development of aerobic endurance, anaerobic fatigue tolerance, and muscular strength outcomes (15).

This article originally appeared in TSAC Report, the NSCA’s quarterly, online-only publication geared toward the training of tactical athletes, operators, and facilitators. It provides research-based articles, performance drills, and conditioning techniques for operational, tactical athletes. The TSAC Report is only available for NSCA Members. Read more articles from TSAC Report 

Related Reading

Lesniak, AV, Bergstrom, HC, Clasey, JL, Stromberg, AJ, and Abel, MG. The effect of personal protective equipment on firefighter occupational performance. Journal of Strength and Conditioning Research 34(8): 2165-2172, 2020.

Thomas, M, Pohl, MB, Shapiro, R, Keeler, J, and Abel, MG. Effect of load carriage on tactical performance in special weapons and tactics operators. Journal of Strength and Conditioning Research 32(2): 554-564, 2018.