Extending work tolerance time in the heat in protective ensembles with pre- and per-cooling methods

OBJECTIVES

Investigate whether a range of cooling methods can extend tolerance time and/or reduce physiological strain in those working in the heat dressed in a Class 2 chemical, biological, radiological, nuclear (CBRN) protective ensemble.

METHODS

Eight males wore a Class 2 CBRN ensemble and walked for a maximum of 120 min at 35 °C, 50% relative humidity. In a randomised order, participants completed the trial with no cooling and four cooling protocols: 1) ice-based cooling vest (IV), 2) a non-ice-based cooling vest (PCM), 3) ice slushy consumed before work, combined with IV (SLIV) and 4) a portable battery-operated water-perfused suit (WPS). Mean with 95% confidence intervals are presented.

RESULTS

Tolerance time was extended in PCM (46 [36, 56] min, P = 0.018), SLIV (56 [46, 67] min, P < 0.001) and WPS (62 [53, 70] min, P < 0.001), compared with control (39 [30, 48] min). Tolerance time was longer in SLIV and WPS compared with both IV (48 [39, 58 min]) and PCM (P ≤ 0.011). After 20 min of work, HR was lower in SLIV (121 [105, 136] beats·min^-1), WPS (117 [101, 133] beats·min^-1) and IV (130 [116, 143] beats·min^-1) compared with control (137 [120, 155] beats·min^-1) (all P < 0.001). PCM (133 [116, 151] beats·min^-1) did not differ from control.

CONCLUSION

All cooling methods, except PCM, utilised in the present study reduced cardiovascular strain, while SLIV and WPS are most likely to extend tolerance time for those working in the heat dressed in a Class 2 CBRN ensemble.

The acute effect of training fire exercises on fire service instructors

Fire service instructors (FSI) regularly experience different types of fire exercises, however the strain experienced from these scenarios is not well understood. This study aims to identify the physiological and perceptual strain of Fire Service Instructors (FSI) to three training exercises: DEMO, ATTACK, COMPARTMENT, and the different roles performed: SETTER, INSTRUCTOR. The study also aims to assess the effect that different exercise patterns over a day (BOX, MULTI, COMBINATION) have on immunological responses. Sixteen FSI (age: 41 ± 8 years, body mass: 83.7 ± 6.7 kg, height: 177.0 ± 6.7 cm) were recruited, with 10 FSI completing the three exercises. Physiological and perceptual measures were collected prior to and immediately post each exercise. Venous blood samples were collected at the beginning and end of each day. One-way analysis of variance (ANOVA) were conducted to assess differences in physiological variables between exercise types, independent samples t-tests were conducted between roles. Day changes in hematological variables were assessed by paired sample t-tests and analyzed by one-way ANOVAs to identify differences between exercise patterns. The COMPARTMENT exercise resulted in a greater change in rectal temperature (ΔT_re) (0.49 ± 0.28 °C) than both the DEMO (0.23 ± 0.19 °C, p = 0.045) and ATTACK (0.27 ± 0.22 °C, p = 0.016). Within the COMPARTMENT exercise, the SETTER resulted in a greater ΔT_re and rating of perceived exertion than the INSTRUCTOR (0.67 ± 0.29 °C vs. 0.43 ± 0.18 °C, p = 0.027 and 14 ± 2 vs. 11 ± 2, p = 0.001, respectively). Following a day of fire exercises white blood cells (WBC), neutrophils, lymphocytes (LYMPH), monocytes (MONO), platelets (PLT), mean platelet volume (MPV), Interleukin (IL)-6, and cardiac troponin T (cTnT) all increased (p < 0.05). Exercise patterns containing a COMPARTMENT exercise resulted in greater PLT, MPV, and IL-6. Total daily variation in ΔT_re was correlated with post-exercise WBC, MONO, and LYMPH. COMPARTMENT exercises produce the greatest physiological strain, with the SETTER role within this exercise causing the greatest ΔT_re. Although predominately physiological responses remain within safe limits. Exercise patterns that include a COMPARTMENT exercise also generate a greater inflammatory response.

A new occupational heat tolerance test: A feasibility study

Heat tolerance tests identify those susceptible to heat illnesses and monitor heat adaptations. Currently, tolerance tests do not replicate the uncompensable heat strain environments experienced in some occupations. In addition, tests can take up to 2 h to complete, and cannot offer intra and inter individual comparisons, due to the use of a fixed exercise intensity. This study aimed to assess the validity and reliability of a new heat occupational tolerance test (HOTT: 40 min at 6 W kg^-1 metabolic heat production, 50 °C 10% RH, in protective clothing) to the standard heat tolerance test (HTT: 2 h walk at 5 km h^-1 1% gradient, 40 °C 40% RH, in shorts and t-shirt). Eighteen participants (age: 21 ± 3 yrs, body mass: 81.3 ± 5.9 kg) completed trials to assess the validity and/or reliability of the HOTT. Peak rectal temperature (T_re) displayed strong agreement and low measurement error (0.19 °C) between HTT (38.7 ± 0.4 °C) and HOTT (38.6 ± 0.4 °C). Strong agreement was also displayed for physiological and perceptual measures between the two HOTT trials, including peak T_re (38.5 ± 0.4 °C vs. 38.5 ± 0.4 °C) and peak heart rate (182 ± 20 b min^-1 vs. 182 ± 21 b min^-1). The HOTT is the first tolerance test that assesses individuals' responses whilst wearing protective clothing in high temperatures. It can consistently identify individuals' levels of heat tolerance within a reduced time frame. In addition, it allows for participant monitoring over time and comparisons between individuals to be made. A continuum based approach is recommended when assessing individuals' responses to the HOTT.

Practical pre-cooling methods for occupational heat exposure

This study aimed to identify a pre-cooling method to reduce the physiological and perceptual strain, and the inflammatory response, experienced by individuals who wear personal protective equipment. Eleven males (age 20 ± 2 years, weight 75.8 ± 9.3 kg, height 177.1 ± 5.0 cm) completed 15min pre-cooling (phase change vest [PCV], forearm cooling [ARM], ice slurry consumption [ICE], or a no cooling control [CON]) and 45min intermittent walk (4  km h^-1, 1% gradient) in 49.5 ± 0.6 °C and 15.4 ± 1.0% RH, whilst wearing firefighter ensemble. ICE reduced rectal temperature (T_re) before heat exposure compared to CON (ΔT_re: 0.24 ± 0.09 °C, p < 0.001, d = 0.38) and during exercise compared to CON, ARM, and PCV (p = 0.026, η_p² = 0.145). Thermal sensation was reduced in ICE and ARM vs. CON (p = 0.018, η_p² = 0.150). Interleukin-6 was not affected by pre-cooling (p = 0.648, η_p² = 0.032). It is recommended that those wearing protective equipment consume 500 ml of ice slurry 15min prior to work to reduce physiological and perceptual strain.

Impact of error self-perception of aerobic capacity in the safety and efficacy of the lifeguards

INTRODUCTION

The strong physical demands that are required of lifeguards during rescues also require an accurate self-perception of one's fitness level to be able to regulate the intensity of effort.

OBJECTIVES

The aim of this study was to determine the real aerobic capacity (RAC) and to compare it with two self-reported measurements: subjective appraisal of aerobic capacity (SAAC) and appraisal of physical exercise (APE).

METHODS

Fifty-two professional lifeguards were included in the study. For an objective assessment of RAC, the lifeguards' maximum oxygen uptake (VO2max) values were measured during treadmill stress tests. A fitness assessment questionnaire was used to obtain the SAAC and APE values.

RESULTS

We found a statistically significant association between the APE and RAC variables in the contingency analysis (p < 0.001). In total, 93.7% of the lifeguards who obtained a VO2max value below 43 ml kg(-1) min(-1) considered their aerobic capacity to be high or very high.

CONCLUSION

This self-perception error of true aerobic capacity could lead to premature fatigue during a rescue, endangering both the lifeguard's life and the life of the victim. These data may help lifeguards and beach managers to become aware of the need to know lifeguards' true physical conditions through testing and structured training programs.

Repeat work bouts increase thermal strain for Australian firefighters working in the heat

BACKGROUND

Firefighters regularly re-enter fire scenes during long duration emergency events with limited rest between work bouts. It is unclear whether this practice is impacting on the safety of firefighters.

OBJECTIVES

To evaluate the effects of multiple work bouts on firefighter physiology, strength, and cognitive performance when working in the heat.

METHODS

Seventy-seven urban firefighters completed two 20-minute simulated search and rescue tasks in a heat chamber (105 ± 5°C), separated by a 10-minute passive recovery. Core and skin temperature, rate of perceived exertion (RPE), thermal sensation (TS), grip strength, and cognitive changes between simulations were evaluated.

RESULTS

Significant increases in core temperature and perceptual responses along with declines in strength were observed following the second simulation. No differences for other measures were observed.

CONCLUSIONS

A significant increase in thermal strain was observed when firefighters re-entered a hot working environment. We recommend that longer recovery periods or active cooling methods be employed prior to re-entry.

Cold-water immersion and iced-slush ingestion are effective at cooling firefighters following a simulated search and rescue task in a hot environment

Firefighters are exposed to hot environments, which results in elevated core temperatures. Rapidly reducing core temperatures will likely increase safety as firefighters are redeployed to subsequent operational tasks. This study investigated the effectiveness of cold-water immersion (CWI) and iced-slush ingestion (SLUSH) to cool firefighters post-incident. Seventy-four Australian firefighters (mean ± SD age: 38.9 ± 9.0 years) undertook a simulated search and rescue task in a heat chamber (105 ± 5 °C). Testing involved two 20-min work cycles separated by a 10-min rest period. Ambient temperature during recovery periods was 19.3 ± 2.7 °C. Participants were randomly assigned one of three 15-min cooling protocols: (i) CWI, 15 °C to umbilicus; (ii) SLUSH, 7 g·kg−1 body weight; or (iii) seated rest (CONT). Core temperature and strength were measured pre- and postsimulation and directly after cooling. Mean temperatures for all groups reached 38.9 ± 0.9 °C at the conclusion of the second work task. Both CWI and SLUSH delivered cooling rates in excess of CONT (0.093 and 0.092 compared with 0.058 °C·min−1) and reduced temperatures to baseline measurements within the 15-min cooling period. Grip strength was not negatively impacted by either SLUSH or CONT. CWI and SLUSH provide evidence-based alternatives to passive recovery and forearm immersion protocols currently adopted by many fire services. To maximise the likelihood of adoption, we recommend SLUSH ingestion as a practical and effective cooling strategy for post-incident cooling of firefighters in temperate regions.

The influence of short-term firefighting activity on information processing performance

This study examined the following: effects of simulated firefighting (FF) activities under heat stress on sustained attention; whether incident rehabilitation (IR) influences performance; and relationships between performance, affect and personality. Firefighters performed ~18 min of FF. Attention, physiological, perceptual and psychological assessments were made before and after FF, IR and recovery. IR had no effects. Self-rated Energy increased, Tiredness decreased and Anxiety increased immediately post-FF; all returned to baseline 120 min post. The immediate effect of FF was faster reaction time (RT) followed by slowing after recovery. Perceived Energy at baseline was associated (p-values < 0.05) with faster and Tiredness with slower post-FF RTs; Accuracy was unaffected. Conscientiousness was negatively associated with RT before and 120 min following FF. RTs were faster following FF, accuracy was unchanged. Higher baseline Energy/lower Tiredness were associated with faster, less variable RTs at baseline and post-FF. Those with higher Conscientiousness had faster RTs. Research should further investigate higher-level cognitive processing following, or ideally during, FF.