Perceptual and physiological heat strain: Examination in firefighters in laboratory- and field-based studies

Firefighting demands performing heavy muscular work under adverse and potentially dangerous conditions. Although the physiological and psychological responses to simulated firefighting activities have been described, the heat strain has not been characterised using standardised indices of exercise–heat strain. The purpose of the study is to describe the physiological and perceptual strain associated with working in personal protective equipment and performing simulated firefighting activities in a hot environment using recently developed strain indices (Physiological Strain Index (PhSI); Perceptual Strain Index (PeSI)). Data from two previously published studies (Smith et al. 1995 Smith, D. L. 1995. Selected physiological and psychological responses to physical activity in different configurations of firefighting gear. Ergonomics, 38: 2065–2077. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar], 2001 Smith, D. L. 2001. Effect of strenuous live-fire fire fighting drills on hematological, blood chemistry and psychological measures. Journal of Thermal Biology, 26: 375–379. [Crossref], [Web of Science ®] , [Google Scholar]) – one a laboratory-based study and one a field-based study – were re-analysed incorporating the strain indices. The laboratory study involved walking on a treadmill for 15 min while wearing three different clothing and equipment configurations. The field study involved three trials of standardised firefighting tasks in a live-fire training structure (mean trial length = 5.76 min). Heart rate, rectal temperature, thermal sensations and ratings of perceived exertion were collected in each study. PhSI and PeSI values were calculated using the formulae developed by Moran et al. (1998b Moran, D. S., Shitzer, A. and Pandolf, K. B. 1998b. A physiological strain index to evaluate heat stress. American Journal of Physiology, 275: R129–R134. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) and Tikuisis et al. (2002 Tikuisis, P., McLellan, T. M. and Selkirk, G. 2002. Perceptual versus physiological heat strain during exercise-heat stress. Medicine & Science in Sports & Exercise, 34: 1454–1461. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]), respectively. PhSI and PeSI increased significantly over time in both studies. Even relatively brief bouts of exercise while wearing heavy impermeable clothing or simulated firefighting activity in the heat results in moderate to high levels of heat strain as assessed by PhSI and PeSI.     

Thermal and cardiovascular strain imposed by motorcycle protective clothing under Australian summer conditions

Motorcycle protective clothing can be uncomfortably hot during summer, and this experiment was designed to evaluate the physiological significance of that burden. Twelve males participated in four, 90-min trials (cycling 30 W) across three environments (25, 30, 35 °C [all 40% relative humidity]). Clothing was modified between full and minimal injury protection. Both ensembles were tested at 25 °C, with only the more protective ensemble investigated at 30 and 35 °C. At 35 °C, auditory canal temperature rose at 0.02 °C min^?1 (SD 0.005), deviating from all other trials (p < 0.05). The thresholds for moderate (>38.5 °C) and profound hyperthermia (>40.0 °C) were predicted to occur within 105 min (SD 20.6) and 180 min (SD 33.0), respectively. Profound hyperthermia might eventuate in ~10 h at 30 °C, but should not occur at 25 °C. These outcomes demonstrate a need to enhance the heat dissipation capabilities of motorcycle clothing designed for summer use in hot climates, but without compromising impact protection.

Practitioner’s Summary:

Motorcycle protective clothing can be uncomfortably hot during summer. This experiment was designed to evaluate the physiological significance of this burden across climatic states. In the heat, moderate (>38.5 °C) and profound hyperthermia (>40.0 °C) were predicted to occur within 105 and 180 min, respectively.     

Metabolic demands of law enforcement personal protective equipment during exercise tasks

Many occupations require the use of personal protective equipment (PPE) but the added metabolic demands are unknown for certain professions. The purpose of this study was to quantify metabolic and perceptual differences between activity with and without the PPE ensemble required for police officers. Twelve participants were asked to complete experimental and control exercise sessions consisting of three modes of exercise (walking, jogging and stepping). A significant main effect (p < 0.01) for gear was found for heart rate (beats per minute) and VO₂ (L/min) between conditions. Dependent t-tests revealed significant differences for perceived effort, discomfort and session rating of perceived exertion between trials. Medium to large effect sizes for all variables with significant main effects between modes (p < 0.01, η² = 0.51–0.96, 1–β = 0.98–1.0, d = 0.42–2.7) were observed. These findings help to increase awareness of how PPE affects metabolic demands and perception of discomfort during exercise.     

Comparison of firefighters and non-firefighters and the test methods used regarding the effects of personal protective equipment on individual mobility

The aims of this study were 1) to evaluate the current pilot test method and ascertain reliable measurements for a standard test method of mobility with personal protective equipment (PPE), such as physical performance and balance ability tests; 2) to compare two participant groups (firefighters versus non-firefighters) and to investigate whether non-firefighters are appropriate as a standard participant group in the field of PPE or not. Totally, 18 participants (nine professional firefighters and nine untrained males) performed the current pilot test method consisting of a balance test, completed prior to and after a performance test. Significant differences were found between PPE conditions and CON (the control clothing ensemble: T-shirt, shorts, and running shoes) for the functional balance test, physical performance test, heart rate, and subjective evaluations in firefighters group. Therefore, the present pilot test method is valid as a standard test method for assessing mobility while wearing PPE. Moreover, the present result shows that firefighters are more reliable than non-firefighters in testing of PPE with current test methods.     

Response to thermal and physical strain during flashover training in Croatian firefighters

Flashover training (FOT) for firefighters is a simulation of the flashover phenomenon under controlled conditions. This study assessed arterial blood pressure (BP) and its response to thermal and physical strain during FOT in 48 professional and 18 volunteer firefighters.     

Measuring the risk of sustaining injury in sport a novel approach to aid the re-design of personal protective equipment

Despite the possibilities offered by new approaches in design and advances in materials and manufacturing methods, few items of Personal Protective Equipment (PPE) used in sport have seen significant change for many decades. A major reason for this is the tradition and conservative attitudes associated with many sports, although the absence of appropriate tools and techniques to assist the design and development process has also played a large part. The aim of this study was to develop the first stage of a method of identifying specific regions of the human anatomy that are at the greatest risk of sustaining injury during participation in sports in which the player is subjected to multiple ballistic impacts. It is proposed that the findings could be used to confirm future designs of sports PPE. Previous studies have identified the amount and the location of the protection provided by current commercially available products but, until now, no evidence has been reported to determine what protection is required based on an understanding of the likely impact and the anatomy of the athlete.     

The effect of firefighter personal protective equipment on static and dynamic balance

Abstract

Firefighters work in unpredictable conditions, necessitating the use of personal protective equipment (PPE). However, the additional weight from the PPE and self-contained breathing apparatus (SCBA) alters their centre of mass (COM), restricts movement and limits vision (face mask) contributing to a firefighters’ challenge of maintaining balance. Thus, the purpose of this study was to quantify the effects of firefighter PPE on static and dynamic balance. Participants performed two sets of three functional balance tests: (1) Static Single Leg (SSL); (2) Dynamic Single Leg (DSL); (3) Limits of Stability (LOS). The balance tests were performed under one control and three randomised PPE conditions: (1) athletic clothing; (2) turnouts; (3) turnouts?+?SCBA; (4) turnouts?+?SCBA?+?face mask. Our study found turnouts?+?SCBA both with and without the face mask negatively affected dynamic balance. These findings identify factors in fall-related injuries and strategies to reduce occupational risk.

Practitioner summary: Slips, trips and falls are the most common cause of injury in firefighters. Our study investigated the effects of firefighter personal protective equipment (PPE) on static and dynamic balance utilising a computerised balance instrument. We found that turnouts with a self-contained breathing apparatus (SCBA) with or without face mask negatively affected balance.     

A review of heat transfer phenomena and the impact of moisture on firefighters' clothing and protection

Protective clothing with high insulation properties helps to keep the wearer safe from flames and other types of hazards. Such protection presents some drawbacks since it hinders movement and decreases comfort, in particular due to heat stress. In fact, sweating causes the accumulation of moisture which directly influences firefighters' performance, decreasing protection due to the increase in radiant heat flux. Vaporisation and condensation of hot moisture also induces skin burn. To evaluate the heat protection of protective clothing, Henrique's equation is used to predict the time leading to second-degree burn. The influence of moisture on protection is complex, i.e. at low radiant heat flux, an increase in moisture content increases protection, and also changes thermal properties. Better understanding of heat and mass transfer in protective clothing is required to develop enhanced protection and to prevent burn injuries.

Practitioner Summary: This paper aims to contribute to a better understanding of heat and mass transfer inside firefighters' protective clothing to enhance safety. The focus is on the influence of moisture content and the prevention of steam burn.     

Comparison of physiological and subjective strain in workers wearing two different protective coveralls for asbestos abatement tasks

The aim of this study was to compare the physiological and subjective strain in workers wearing a disposable “Tyvek” (TYV) and a ventilated “Mururoa” (MUR) coverall in a real working situation. Eleven men performing normal abatement tasks volunteered to participate. Physiological measurements included oral temperature, heart rate and sweat loss. Subjective evaluations of clothing comfort, cooling, robustness, cumbersomness, acceptable exposure duration and physical exertion were carried out at the end of the task. The ventilated MUR reduced heat strain. Indeed, it allowed significantly higher sweat loss than TYV and showed a tendency to reduce the increase in oral temperature. Subjective ratings reveal that MUR was considered better than TYV in terms of clothing comfort, coolness and robustness. On the other hand, MUR is more cumbersome to wear. In this study, where workload and heat stress were moderate, there were few differences between the two coveralls in terms of physiological strains, but far more significant differences in the subjective ratings.     

Work tolerance and subjective responses to wearing protective clothing and respirators during physical work

This study examined work tolerance and subjective responses while performing two levels of work and wearing four types of protective ensembles. Nine males (mean age = 24·8 years, weight = 75·3 kg, [Vdot]O₂ max = 44·6 ml/kg min) each performed a series of eight experimental tests in random order, each lasting up to 180 min in duration. Work was performed on a motor-driven treadmill at a set walking speed and elevation which produced work intensities of either 30% or 60% of each subject's maximum aerobic capacity. Work/rest intervals were established based on anticipated SCBA refill requirements. Environmental temperature averaged 22·6°C and average relative humidity was 55%. The four protective ensembles were: a control ensemble consisting of light work clothing (CONTROL); light work clothing with an open circuit self-contained breathing apparatus (SCBA); firefighter's turnout gear with SCBA (FF); and chemical protective clothing with SCBA (CHEM). Test duration (tolerance time) was determined by physiological responses reaching a predetermined indicator of high stress or by a 180-min limit. Physiological and subjective measurements obtained every 2·5 min included: heart rate, skin temperature, rectal temperature, and subjective ratings of perceived exertion, thermal sensation, and perspiration.

The mean tolerance times were 155, 130, 26, and 73 min, respectively, for the CONTROL, SCBA, FF, and CHEM conditions during low intensity work; and 91, 23, 4, and 13 min, respectively, during high intensity work. Differences between ensemble and work intensity were significant FF and CHEM heart rate responses did not reach a steady state, and rose rapidly compared to CONTROL and SCBA values. SCBA heart rates remained approximately 15 beats higher than the CONTROL ensemble during the tests. At the low work intensity, mean skin.     

Physical and thermal strain of firefighters according to the firefighting tactics used to suppress wildfires

The aim of this study was to analyse the physiological strain of firefighters, using heart rate (HR) and core temperature, during real wildfire suppression according to the type of attack performed (direct, indirect or mixed). Threeintensity zones were established according to the HR corresponding to the ventilatory threshold (VT) and respiratory compensation threshold (RCT): zone 1, <VT; zone 2 (Z2), between VT and RCT; zone 3 (Z3), >RCT. The exercise workload (training impulse (TRIMP)), the physiological strain index (PSI) and the cumulative heat strain index(CHSI) were calculated using the time spent in each zone, and the HR and core temperature, respectively. Significantly higher mean HR, time spent in Z2 and Z3 and TRIMP h^?1 were found in direct and mixed versus indirect attacks. The highest PSI and CHSI were observed in the direct attack. In conclusion, exercise strain and combined thermal strain, but not core temperature during wildfire suppression, are related to the type of attack performed.

Statement of relevance: Our findings demonstrated that wildfire firefighting is associated with high physiological demands, which vary significantly depending on the tactics chosen for performing the task. These results should be kept in mind when planning programmes to improve wildland firefighters' physical fitness, which will allow improvement in their performance.     

Effect of base layer materials on physiological and perceptual responses to exercise in personal protective equipment

Ten men (non-firefighters) completed a 110 min walking/recovery protocol (three 20-min exercise bouts, with recovery periods of 10, 20, and 20 min following successive bouts) in a thermoneutral laboratory while wearing firefighting personal protective equipment over one of four base layers: cotton, modacrylic, wool, and phase change material. There were no significant differences in changes in heart rate, core temperature, rating of perceived exertion, thermal discomfort, and thermal strain among base layers. Sticking to skin, coolness/hotness, and clothing humidity sensation were more favorable (p < 0.05) for wool compared with cotton; no significant differences were identified for the other 7 clothing sensations assessed. Separate materials performance testing of the individual base layers and firefighting ensembles (base layer + turnout gear) indicated differences in thermal protective performance and total heat loss among the base layers and among ensembles; however, differences in heat dissipation did not correspond with physiological responses during exercise or recovery.     

Measuring the effects of structural turnout suits on firefighter range of motion and comfort

Abstract

Range of motion (ROM) can be restricted by wearing stiff and bulky clothing. This is particularly true of firefighter suits that are constructed using fabric layers to provide thermal protection from fire. This study developed an evaluation technique to quantify the loss of mobility associated with wearing firefighters’ protective suits that were deliberately selected to represent similar ergonomic design features. The ROM of 10 firefighters was measured using electro-goniometers attached to their bodies while they wore uniforms and a reference outfit, and performed specific movements. The most restrictive uniform is the Bulky suit that contained additional layers of materials in sleeves and on the knees. The Traditional Suit was more ROM restrictive than Ergonomic. The subjective evaluation of suits supported the objective assessments provided by the electro-goniometers. A 3-D body scanning technique was employed to establish a correlation between the bulkiness of firefighter outfits and subject ROM.

Practitioner Summary: This study presents a methodology for measurements of range of motion (ROM) in firefighters wearing personal protective equipment (PPE). Even small differences in designs of PPE may impact firefighters’ ROM, which can be detected by electro-goniometers providing measurements if they are attached along the joint to measure limb angular movement.     

Comparison of physiological and subjective strains of two protective coveralls in two short physically simulated demanding tasks

A total of 15 physically active male students carried out a normalised task (T(N)) and a task of access by ladder and scaffolding (T(L)) in two impermeable protective coveralls and a reference sports wear to compare the physiological and subjective strains. Heart rate (HR) was recorded and sweat loss was checked. Subjective evaluations of comfort parameters, acceptable exposure durations and physical exhaustion were recorded at the end of the tasks. Results show that both protective clothing, compared to the sport wear, increase significantly HR, RPE and CR10 in both tasks. However the strains of both protective clothing are not significantly different except in sweat loss and cumbersomeness.     

Additional helmet and pack loading reduce situational awareness during the establishment of marksmanship posture

Abstract

The pickup of visual information is critical for controlling movement and maintaining situational awareness in dangerous situations. Altered coordination while wearing protective equipment may impact the likelihood of injury or death. This investigation examined the consequences of load magnitude and distribution on situational awareness, segmental coordination and head gaze in several protective equipment ensembles. Twelve soldiers stepped down onto force plates and were instructed to quickly and accurately identify visual information while establishing marksmanship posture in protective equipment. Time to discriminate visual information was extended when additional pack and helmet loads were added, with the small increase in helmet load having the largest effect. Greater head-leading and in-phase trunk–head coordination were found with lighter pack loads, while trunk-leading coordination increased and head gaze dynamics were more disrupted in heavier pack loads. Additional armour load in the vest had no consequences for Time to discriminate, coordination or head dynamics. This suggests that the addition of head borne load be carefully considered when integrating new technology and that up-armouring does not necessarily have negative consequences for marksmanship performance.

Practitioner Summary: Understanding the trade-space between protection and reductions in task performance continue to challenge those developing personal protective equipment. These methods provide an approach that can help optimise equipment design and loading techniques by quantifying changes in task performance and the emergent coordination dynamics that underlie that performance.     

A system to test the ground surface conditions of construction sites--for safe and efficient work without physical strain

Ground surface conditions on construction sites have an important influence on the health and safety of workers and their productivity. The development of an expert-based "working conditions evaluation" system is described, intended to assist site managers in recognising unsatisfactory ground conditions and remedying these. The system was evaluated in the period 2002-2003. The evaluation shows that companies recognize poor soil/ground conditions as problematic, but are not aware of the specific physical workload hazards. The developed methods allow assessment of the ground surface quality and selection of appropriate measures for improvement. However, barriers exist at present to wide implementation of the system across the industry. Most significant of these is that responsibility for a site's condition is not clearly located within contracting arrangements, nor is it a topic of serious negotiation.     

Duration of slip-resistant shoe usage and the rate of slipping in limited-service restaurants: results from a prospective and crossover study

Several studies have indicated that slip-resistant shoes may have a positive effect on reducing the risk of slips and falls, a leading cause of injury at work. Few studies, however, have examined how duration of shoe usage affects their slip-resistance properties. This study examined the association between the duration of slip-resistant shoes usage and the self-reported rate of slipping in limited-service restaurant workers. A total of 475 workers from 36 limited-service restaurants in the USA were recruited to participate in a 12-week prospective study of workplace slipping. Of the 475 participants, 83 reported changing to a new pair of shoes at least once during the 12-week follow-up. The results show that slip-resistant shoes worn for less than six months were moderately more effective than those worn for more than six months. Changing to a new pair of shoes among those wearing slip-resistant shoes at baseline was associated with a 55% reduction in the rate of slipping (RR = 0.45, 95% CI = 0.23–0.89). Further research is needed to develop criteria for the replacement of slip-resistant shoes.

Practitioner Summary: The duration of usage impacts the slip-resistance properties of slip-resistant shoes. Slip-resistant shoes worn for less than six months were moderately more effective in reducing slips than slip-resistant shoes worn for more than six months. Shoe use policies should not only encourage or require their use but also include guidance on replacing slip-resistant shoes at regular intervals.     

Effects of thermal,personal and behavioural factors on the physiological strain,thermal comfort and productivity of Australian shearers in hot weather

Abstract

Multiple-regression analyses were used to evaluate the separate and combined effects of factors that are commonly expected to influence strain and productivity in a hot workplace. Forty-three men were studied throughout 54 man-days of shearing sheep and pressing wool bales, in air temperatures 19-41°C and Wet-bulb Globe Temperature index (WBGT) 16-29°C; 43% of the observations of WBGT exceeded 26-7°C, the Threshold Limit Value (TLV) for the subjects&rsquo; work rate of 400 W. Subjects were men of age 18-59 years, fat-free mass 44–77 kg, and body fat content 11-26%, who had drunk an estimated 0-207 g alcohol the previous evening. Afternoon mean values of rectal temperature (T _re) exceeded 38-0°C (maximum 38-4°C) in 4 of the 15 observations made when WBGT > TLV. and in none of those made when WBGT < TLV. Over the 10 h work day the subjects sweated 24–9-9 kg, but they replaced their sweat losses so successfully that warmer weather and heavier sweating were not accompanied by significantly greater dehydration. Surprisingly, the fatter men felt cooler, and those who had drunk more alcohol the previous evening had lower T _re and tended to be more productive. Age was not associated with any measured response. All factors together explained barely half the observed variation in T _re and thermal comfort, and almost none of the variation in productivity. The findings highlight the uncertainty inherent in attempts to define safe limits for occupational heat stress; they show how such uncertainty could restrict the usefulness in the shearing industry of current heat-stress guidelines; and they demonstrate the effectiveness of the behavioural responses that permit shearers to perform sustained strenuous work in a hot environment without excessive physiological strain.     

Comparison of two different cooling systems in alleviating thermal and physiological strain during prolonged exercise in the heat

Abstract

This study compared the efficacy of an ice vest comprising of water (WATER) or a water-carbon (CARBON) emulsion on thermophysiological responses to strenuous exercise in the heat. Twelve male cyclists completed three 50-minute constant workload trials (55% of peak power output, ambient temperature 30.4?±?0.6°C) with WATER, CARBON, and without ice vest (CONTROL), respectively. The increase in core body temperature (Tcore) was lower in WATER at 40 (?0.49?±?0.34 °C) and 50?minutes (?0.48?±?0.48 °C) and in CARBON at 30 (?0.41?±?0.48 °C), 40 (?0.54?±?0.51 °C), and 50?minutes (?0.67?±?0.62 °C) as compared to CONTROL (p?<?0.05, ES > 0.8). While heart rate and blood lactate kinetics did not differ between the conditions, statistical main effects in favour of both WATER and CARBON were found for thermal sensation (condition p?<?0.001 and interaction p?<?0.01) and rating of perceived exertion (condition p?<?0.05). Per-cooling with CARBON and WATER similarly reduced Tcore but not physiological strain during prolonged exercise in the heat.

Practitioner Summary: Exercise in the heat is characterised by increases in thermophysiological strain. Both per-cooling with a novel carbon-based and a conventional water-based ice vest were shown to reduce core temperature significantly. However, due to its lower mass, the carbon-based system may be recommended especially for weight-bearing sports.