Received date: August 15, 2013; Accepted date: September 08, 2013; Published date: September 10, 2013
Citation: Hur P, Hsiao-Wecksler ET, Rosengren KS, Horn GP, Smith DL (2013) Effect of Protective Clothing and Fatigue on Functional Balance of Firefighters. J Ergonomics S2:004. doi: 10.4172/2165-7556.S2-004
Copyright: © 2013 Hur P, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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We investigated the effects of wearing personal protective equipment (PPE), design of PPE (Standard vs. Enhanced), and fatigue during a simulated firefighting activity on the functional balance of firefighters. We defined functional balance as the ability to prevent a loss of balance and maintain body posture while performing functional tasks. A novel Functional Balance Test (FBT) was used to assess functional balance of firefighters while stepping up, stepping down, turning, walking along a beam, and passing under an obstacle. Data are presented from fifty-seven male firefighters, who were randomly divided into two groups: Standard PPE (n=28) and Enhanced PPE (n=29). The specially designed Enhanced PPE was lighter, more breathable, and capable of air circulation, compared to traditional Standard PPE. Each participant performed the FBT at three time periods (baseline with station uniform, pre-activity with PPE, and post-activity with PPE after a live-fire simulated firefighting activity). The firefighting activity involved alternating 2-minute rest- work cycles of four stations: stair climb, forcible entry, room search, and hose advancement. The FBT had four trials each with and without an overhead obstacle. Performance errors (major and minor), performance time, and a composite performance index were recorded. Wearing PPE significantly impaired functional balance, as noted by increases in all performance metrics. Following the firefighting activity, performance time increased by 3% but the number of minor and major errors decreased by 13% and 32%, respectively, suggesting that firefighters may trade-off between speed and accuracy depending on perceived threat to balance safety. There was no significant difference in functional balance between the Enhanced PPE and Standard PPE groups, suggesting that Enhanced PPE with a passive cooling system and an external circulating hose is not effective in improving functional balance of firefighters. A better designed PPE, with an improved cooling system and minimal (or no) protruding attachments may be of benefit in terms of firefighter functional balance.
Firefighting; Personal protective equipment; Functional balance; Obstacle crossing
Every year, more than 38,000 firefighters are injured on the fireground . Among causes of moderate or severe injuries of firefighters, slips, trips, and falls are the most significant cause (28%) of firefighting injuries . The medical cost per claim due to slips, trips, and falls was $8,662, which is 60% more than the average costs for all claims in a 2003 study . Firefighters regularly work in hot, smoky, and slippery fire ground conditions with many obstacles. To provide protection under these circumstances, firefighters are usually required to wear personal protective equipment (PPE) which includes bunker coat, pants, boots, helmet, face mask, gloves, and self-contained breathing apparatus (SCBA) . The primary design requirements for firefighting PPE is to provide protection from the by-products of combustion (heat, smoke, gasses), with minimal consideration for potential negative impacts on balance. Likewise on the fireground, firefighters may become tired and fatigued by the strenuous firefighting activity and heat stresses, which can be further detrimental to balance control. The goal of the current study was to investigate the impact of PPE and fatigue on the functional balance of firefighters. In spite of the obvious benefits of PPE in protecting firefighters from heat, smoke and fire, the use of PPE may negatively affect balance. Wearing PPE might impair the functional balance of firefighters due to the heavy weight of PPE and limited vision associated with wearing an SCBA face mask [4,5]. Wearing PPE may also change the firefighter’s center of gravity , increase fatigue , and impose physiological burdens [7-10]. The heavy, insulative aspect of PPE may also contribute to increased metabolic work done by the firefighter, potentially resulting in increased heat stress [11,12] that might impact on functional balance. During firefighting activity, heat stress and the resulting elevation of body temperature hastens muscular fatigue, promotes dehydration, increases cardiovascular strain, and interferes with cognitive function [13,14]. All of these may lead to problems with functional balance. Modifying the design of current bunker gear style firefighting PPE has potential to improve functional balance of firefighters. Researchers have found that reducing SCBA weight can enhance gait performance , and different PPE clothing configurations can reduce thermal and cardiovascular strain  and reduce time to complete firefighting tasks during live fire drills . Reducing the weight of PPE and introducing an air circulation system to reduce heat stress may serve to improve the functional balance of firefighters. For this purpose, an Enhanced PPE with relatively light-weight clothing and passive air circulation system within the bunker coat was designed and developed by project partners (Total Fire Group and International Personnel Protection Inc.). The Enhanced PPE met the US guidelines (NFPA 1971) for thermal protection of structural firefighting gear. In this study, the Enhanced PPE was compared to a Standard PPE ensemble that is currently used by US firefighters. The purpose of this study was to examine the effects of wearing of PPE, type of PPE and strenuous firefighting activity on the functional balance of firefighters. Specifically, functional balance was assessed: a) while wearing PPE (station blues vs. PPE), b) while wearing different PPE designs (Enhanced vs. Standard), and c) following an18-minute strenuous firefighting activity. Furthermore, to assess functional balance, a novel functional balance test was developed.
Sixty-one male firefighters (ages 18-47) were recruited from the Illinois Fire Service Institute (IFSI) training events and local fire companies. All participants reported no neurological or postural disorders. Informed consent was given by all participants and the study was approved by the Institutional Review Board at the University of Illinois. Participants were divided into two groups: 1) control group with Standard PPE (n=31), and 2) intervention group with Enhanced PPE (n=30). Data from four participants were excluded for the data analysis due to incomplete data collection. The final sample included 57 participants (control, n=28; intervention, n=29). Participants’ age, height, weight, body mass index (BMI), and months of firefighting experience were collected (Table 1). There were no significant differences between the two groups for any of these values.
|Standard PPE||Enhanced PPE||p-value|
|(n = 31)||(n = 30)|
|Age (years)||26.2 ± 6.5||28.2 ± 6.5||0.32|
|Height (m)||1.78 ± 0.07||1.78 ± 0.06||0.82|
|Weight (kg)||84.6 ± 13.7||87.9 ± 13.1||0.23|
|BMI (kg/m2)||26.5 ± 3.5||27.9 ± 4.0||0.12|
|Experience (months)||69.8 ± 69.6||68.8 ± 83.4||0.96|
Table 1: Demographics of two PPE groups (Mean ± SD).
The control group wore a Standard PPE ensemble typically used by firefighters in the United States. This PPE included 1) a traditional style helmet, 2) insulated hood, 3) bunker gear with relatively heavy insulation and low breathability, and 4) rubber boots (Figure 1a). On average, the full set of Standard PPE weighed 11.1 kg. The intervention group wore an Enhanced PPE ensemble designed with an industrial partner of IFSI that included: 1) a lighter, low profile helmet, 2) more breathable Nomax hood, 3) bunker gear with reduced insulation, improved breathability, and a passive cooling system to assist with heat transfer in the coat; and 4) lightweight leather/Kevlar boots (Figure 1b). The novel passive cooling system was intended to circulate exhaled air from the firefighter’s face piece to the coat’s inner lining. The idea behind this design was to create air movement inside the gear to assist with heat dissipation and thereby provide a means for evaporative cooling within the fully encapsulating PPE. On average, the full set of Enhanced PPE weighed 9.5 kg. Both PPE ensembles meet current NFPA 1971 standards for thermal protection and breathability. Both groups wore identical SCBA packs (50i SCBA, Scott) with a 4500 psi 30-minute carbon fiber bottle (DOT # E10951- 4500, Luxfer). The SCBA packs with a carbon fiber bottle weighed additional 9.5 kg.
Functional balance test (FBT)
In this study, a novel FBT was developed to assess the functional balance of firefighters. This test was designed to simulate movements typically performed by firefighters on the fireground including stepping up and down from a platform, walking along a narrow walkway, and ducking under an overhead obstacle. This new test was developed due to significant limitations with existing balance tests, particularly when studying firefighters who had just completed a strenuous bout of firefighting activities. In pilot testing, traditional balance assessments that use a force platform to measure the control of center pressure were found not to be feasible because the firefighters were unable to complete the necessary repeated trials of quiet standing in their PPE due to the accumulation of heat stress. Several firefighters reported feeling faint while attempting these protocols. Additionally, the FBT developed by Punakallio et al. [4,15] was judged to be too challenging and dangerous for firefighters after an 18-minute strenuous activity due to the required backward walking on a narrow plank. While these assessments are well characterized for rested subjects, they were not feasible in this study design. As a result, we developed a more tractable and applicable functional balance test similar to that proposed by Punakallio et al. [4,15], but that could be safely utilized after strenuous firefighting activity. The FBT involved walking from one raised platform (15 cm (H)), stepping down and walking along a narrow plank (3 m (L), 15 cm (W), 4 cm (H)), stepping up and turning around within a small defined space (61×61 cm2) on a second raised platform (10 cm (H)), and walking back to stop within a defined space (61×61 cm2) on the original platform. The task was made more challenging during some trials by placing an overhead obstacle (a lightweight rod) across the center of the pathway at 75% of the participant’s height (Figure 2). The rod was supported by vertical supports placed approximately 114 cm apart. The inclusion of the obstacle was to mimic the need to pass through a low confined enclosure without hitting the structure. For safety, the rod was designed to fall away if the rod or supports were hit, rather than being a rigid structure. For each testing period, participants performed eight trials: two trials with no obstacle, four with the obstacle, and finally two with no obstacle trials. Participants were instructed to perform the task as quickly and safely as possible without committing errors. Each trial was timed by two investigators. T?he number of errors that each participant made was recorded. A minor error was counted when: 1) a foot or hand contacted the ground, 2) a hand contacted a platform, 3) the turn was not completed within the defined space in the platform, 4) the participant could not stop within the defined space, and 5) the obstacle was touched but did not fall. A major error was counted when the obstacle was contacted and the rod fell. This event was considered to be a major error because had the firefighter hit a rigid obstacle then the impact could have caused a potentially dangerous and destabilizing effect to balance. Participants were instructed that their score would be penalized if they committed an error. If an error was committed, the investigator informed the participant of the error and reminded him to try to not do the error during the subsequent trials.
To assess the effects of wearing PPE, wearing different types of PPE, and strenuous firefighting activity on functional balance, participants were evaluated at three testing periods: baseline (BL) with station blues (typically t-shirts and jeans), pre-activity (PRE) with PPE on before firefighting activity, and post-activity (POST) with PPE on after firefighting activity. The firefighting activity was designed to simulate realistic firefighting scenarios and developed in consultation with firefighting program staff members at IFSI. The activity consisted of 18-minutes of alternating rest-work cycles. These cycles included four simulated firefighting activities: stair climb, forcible entry, room search, and hose advancement. The simulated firefighting activity took place on the second floor of the training building where temperatures at waist level (1.2 m above the ground) averaged between 71-82°C. Each activity took 2 minutes and was followed by a 2-minute break. For each testing period (i.e., BL, PRE and POST), the FBT was performed. The FBT for POST occurred within 1-2 minutes after completing the simulated firefighting activity (Figure 3). The effect of wearing PPE was examined by comparing BL and PRE. The effects of PPE type and strenuous firefighting activity were examined by comparing PRE and POST.
The number of major errors, minor errors, and performance time were recorded. A performance index was created from the weighted sum of major and minor errors and performance time. Greater weight was put on major errors than minor error since a major error was considered a critical and life-threatening error on the fireground. In this study, the performance index was defined as by the following equation. Performance Index 2 Major Error 1 Minor Error 1 Performance Time A three-way repeated measures multivariate analysis of variance (MANOVA) was performed to examine the effects of PPE ensemble (Standard vs. Enhanced), existence of obstacle, and firefighting activity (BL, PRE, and POST) on the number of major errors, number of minor errors, performance time, and performance index. The withingroup factors were existence of obstacle and firefighting activity. The between- group factor was type of PPE. Subsequent univariate repeated measures ANOVAs were used to examine significant effects. Post hoc tests used the LSD approach (Fisher’s least significant difference). The level of significance was set to α=0.05. Statistical analyses were run on SPSS (SPSS Inc., Chicago, IL; v17).
Overall, both major and minor errors increased after wearing PPE and decreased after firefighting activity (Figure 4). Performance time increased after wearing PPE and after firefighting activity. Performance index increased after wearing PPE, and decreased slightly after firefighting activity. The presence of an obstacle increased all variables. The Enhanced PPE group had a significant increase in performance index, and non- statistically significant trends in increased major errors and performance time than the Standard PPE group. The MANOVA revealed significant main effects of obstacle presence, and firefighting activity (BL, PRE, and POST). The presence of an obstacle significantly affected functional balance (p<0.001). Subsequent univariate repeated measures ANOVA revealed that the presence of an obstacle significantly increased major and minor errors (p<0.001), performance time (p<0.001), and performance index (p<0.001). Firefighting activity also significantly affected functional balance (p<0.001). Subsequent repeated measures univariate ANOVAs revealed that firefighting activity significantly affected major errors (p<0.001), minor errors (p=0.012), performance time (p<0.001), and performance index (p<0.001). Post hoc tests showed that major errors, minor errors, performance time, and performance index were significantly affected by wearing PPE (BL vs. PRE) and by the activity (BL vs. POST). All of these values increased significantly for PRE or POST compared to BL suggesting that wearing PPE significantly reduces functional balance. Furthermore, statistically significant differences were found in major error and performance time for PRE vs. POST. Major errors significantly decreased whereas performance time increased in POST compared to PRE. Obstacle and PPE were found to have significant interaction for performance index (p=0.036). Firefighters with Enhanced PPE had larger performance index values compared to firefighters with Standard PPE.
Figure 4: Plots of (a) Minor Errors, (b) Major Errors, (c) Performance Time, and (d) Performance Index as functions of type of PPE, obstacle conditions, and firefighting activity. Error bars represent standard error. Significant main effect for firefighting activity pairing is indicated with asterisk symbol (*).
The purpose of this study was to investigate the effects of PPE and fatigue due to strenuous firefighting activity on the functional balance of firefighters. It was hypothesized that wearing PPE and strenuous firefighting activity would worsen functional balance. It was further hypothesized that Enhanced PPE would improve the functional balance of the firefighters compared to Standard PPE. We found that wearing PPE significantly impaired all of our measures of functional balance of firefighters regardless of PPE type (Figure 4). Specifically, firefighters slowed down their movement speed when they wore PPE (Figure 4c). Even with reduced gait speed, firefighters made significantly more errors when they were wearing PPE compared to BL (Figure 4a and 4b). This result extends prior research [4,7,16] that showed that the weight of PPE is an important factor that impedes the functional balance and gait performance of the firefighters. After 18 minutes of strenuous firefighting activity (POST), firefighters further reduced their movement speed compared to PRE condition (Figure 4c, p=0.002). Interestingly, the number of major errors also significantly reduced for POST compared to PRE condition (Figure 4b, p=0.007). As a result of the reduction in major errors, the performance index was not affected by strenuous firefighting activity (Figure 4d, p>0.05). These findings suggest that firefighters were proceeding with greater caution following a strenuous bought of firefighting activity. The reduction of errors may not seem to be due to learning effect since the number of minor errors before obstacle condition was not significantly different from the number of minor errors after obstacle condition (p>0.05). Rather, it is possible that firefighters may have used a trade-off strategy to compromise between speed and accuracy. The instruction given to firefighters was to complete the task as safely and quickly as possible. Firefighters may have chosen their own weighting factors for both speed and accuracy for a given condition (PRE vs. POST). Before the strenuous firefighting activity, firefighters may have put more weight on speed over accuracy. After the firefighting activity, firefighters may become more careful and put more weight on accuracy over speed. Even though muscle fatigue might have some influence on the functional balance of firefighters, muscle fatigue and tiredness may have not affected visuo-spatial attention of the firefighters, as was the case for the elite karate athletes . This argument may be feasible because during firefighting, even though firefighting activity is fast paced on the fireground, firefighters try to be cautious and usually do not run unless it is an urgent and life-threatening situation. The Enhanced PPE, which was lighter, more breathable, and capable of air circulation, did not improve the functional balance of firefighters. Contrary to expectation, the Enhanced PPE group had significantly larger performance index values compared to Standard PPE for PRE and POST conditions when considering the obstacle condition (Figure 4d, p=0.036). This significant difference in performance index was driven by the tendency to have more major errors while wearing the Enhanced PPE (Figure 4b) and longer performance time post-activity (Figure 4c); although these differences were not statistically significant (p>0.05). Furthermore, we did not find any difference in the average core temperature or heart rate of the firefighters wearing Standard vs. Enhanced PPE, thus the intervention was not successful in reducing the heat stress or physiological strain of the firefighting activity. One reason for these results may be because the firefighters were not accustomed to the novel Enhanced PPE. The Enhanced bunker coat and pants were custom-made and available to firefighters for the first time during the experiment. Even though the PPE was lighter and less restrictive, a number of firefighters found the protruding circulation hose on the coat to be cumbersome and in some instances it was this aspect of the PPE that hit the obstacle when firefighters passed under the obstacle (Figure 1). Enhanced PPE may have not Enhanced functional balance, but may help enhance other aspects of performance (e.g., range of motion). Firefighters in the Enhanced PPE group anecdotally reported that their range of motion increased compared to when they would wear their usual Standard PPE. The cooling system adopted in the novel Enhanced PPE design was passive. The intent of the cooling system was to passively circulate exhaled air from the firefighter’s face piece to the coat’s inner lining so that the created air movement inside the gear may assist with heat dissipation by providing a means for evaporative cooling within the fully encapsulating PPE. An active cooling system may be more helpful reducing core temperature and heat stress of firefighters  and have a greater impact on mitigating the postfirefighting declines in functional balance. For future PPE design, any additional external attachment for the cooling system, such as the circulating hose in the Enhanced PPE in the present study, should be embedded inside the PPE and should not reduce the flexibility of the PPE .
In this study, the effects of wearing PPE (BL vs. PRE), type of PPE (Standard vs. Enhanced), and fatigue after a strenuous firefighting activity (PRE vs. POST) on the functional balance of firefighters were investigated. A novel functional balance test (FBT) protocol was developed to assess functional balance of firefighters. It was found that wearing PPE significantly impaired functional balance by slowing down movement speed and increasing errors. Strenuous firefighting activity resulted in slower performance speed and decreased number of errors, suggesting that firefighters may take a trade-off between speed and accuracy depending on the need for greater caution. The Enhanced PPE with a passive cooling system and an external circulating hose may not be effective for enhancing functional balance of firefighters. A better design of PPE with an active cooling system and no external circulating hose needs to be developed.
This research was funded by a grant from US Department of Homeland Security (#EMW-2006-FP-02459). Authors thank all test participants, research team, and especially over 20 graduate and undergraduate students for their assistance in data collection and coding.