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Encapsulated Environment

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Abstract

In many occupational settings, clothing must be worn to protect individuals from hazards in their work environment. However, personal protective clothing (PPC) restricts heat exchange with the environment due to high thermal resistance and low water vapor permeability. As a consequence, individuals who wear PPC often work in uncompensable heat stress conditions where body heat storage continues to rise and the risk of heat injury is greatly enhanced. Tolerance time while wearing PPC is influenced by three factors: (i) initial core temperature (Tc), affected by heat acclimation, precooling, hydration, aerobic fitness, circadian rhythm, and menstrual cycle (ii) Tc tolerated at exhaustion, influenced by state of encapsulation, hydration, and aerobic fitness; and (iii) the rate of increase in Tc from beginning to end of the heat‐stress exposure, which is dependent on the clothing characteristics, thermal environment, work rate, and individual factors like body composition and economy of movement. Methods to reduce heat strain in PPC include increasing clothing permeability for air, adjusting pacing strategy, including work/rest schedules, physical training, and cooling interventions, although the additional weight and bulk of some personal cooling systems offset their intended advantage. Individuals with low body fatness who perform regular aerobic exercise have tolerance times in PPC that exceed those of their sedentary counterparts by as much as 100% due to lower resting Tc, the higher Tc tolerated at exhaustion and a slower increase in Tc during exercise. However, questions remain about the importance of activity levels, exercise intensity, cold water ingestion, and plasma volume expansion for thermotolerance. Published 2013. Compr Physiol 3:1363‐1391, 2013.

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Figure 1. Figure 1.

The energy cost of movement while wearing a multilayered Arctic clothing ensemble or carrying equivalent weight as a single‐layer uniform with weighted belt. Adapted from Teitlebaum and Goldman (239).

Figure 2. Figure 2.

A schematic representation of sweat production and its vaporization through clothing together with sweat lost through dripping off the skin surface and condensation in the clothing layers. Reproduced, with permission, from Cheung (32).

Figure 3. Figure 3.

The relationship between tolerance time and metabolic rate when wearing Canadian Forces nuclear, biological, and chemical protective clothing in different environmental conditions. Solid and dotted lines represent data from various environmental conditions derived from McLellan (153) and McLellan et al. (162,163,164).

Figure 4. Figure 4.

The effects of 12 days of heat acclimation to a hot and humid environment on tolerance time during cycling at a constant power output. Note that the increase in tolerance time following the heat acclimation is due to the decrease in resting core temperature. The figure is derived from data in Nielsen et al. (181).

Figure 5. Figure 5.

Rectal temperature in the morning during 12 days of heat acclimation (HA) with minimal recovery and 3, 7, and 18 days later. Please note that the reduction in core temperature is not seen during, but after HA. Reproduced, with permission, from Daanen et al. (54).

Figure 6. Figure 6.

Rectal temperature after 60 min exercise during heat acclimation for 10 days followed by reacclimation 26 days later for 7 days. Note that even after 26 days the core temperature is the same as the end of the initial heat acclimation period. Reproduced, with permission, from Weller et al. (253).

Figure 7. Figure 7.

The change in core temperature while wearing either the current personal protective ensemble consisting of the combat uniform and overgarment concept or new stand‐alone chemical and biological (CB) uniforms. During the low dress state minimal protection is required and only the combat uniform is worn. However, during the high dress state full encapsulation and maximum protection is required, necessitating the use of the overgarment. The use of the new CB uniforms does not require an overgarment since the CB protection is already included within the clothing material. Notice after 60 min at the beginning of the transition from the low to high dress state core temperature is higher for the new CB uniform.

Figure 8. Figure 8.

Heart rate and rectal temperature tolerated at exhaustion during low exercise intensity of 165 W·m2 with a tolerance time of 105 min versus high exercise intensity of 260 W·m2 and tolerance time of 60 min. The asterisk indicates a significant difference between the low and high exercise intensities.

Figure 9. Figure 9.

Sample size of participants from each training status throughout a passive heating protocol. The highly fit (circles), moderately fit (squares), and lower fit (triangles) groups began with similar sample sizes, although the majority of the lower fit participants were unable to complete the protocol. Reproduced, with permission, from Morrison et al. (176).

Figure 10. Figure 10.

The theoretical effect of cooling on tolerance time in protective equipment based on modeling studies. Reproduced, with permission, from Pandolf et al. (194).

Figure 11. Figure 11.

The effects of hand and forearm submersion in 18°C water for 20 min on the increase in rectal temperature (expressed as delta Tre) following 50 min of exercise at 35°C while wearing full firefighting PPC. The asterisk indicates a significant difference between the hand and forearm immersion trial compared with the condition that involved passive cooling when some of the firefighting PPC was removed during the 20‐min rest periods. Tolerance time was increased significantly from 108 ± 14 min with passive cooling to 179 ± 50 min with hand and forearm submersion. Adapted from Selkirk et al. (218).

Figure 12. Figure 12.

A schematic representation of the tolerance time during uncompensable heat stress for a sedentary untrained individual (A) and the influence of raising the initial resting core temperature due to circadian rhythm, menstrual phase or minor (B) or severe (C) hypohydration, lowering resting core temperature through heat acclimation or precooling strategies (D) and a decrease in body fatness, an increase in gross movement efficiency or providing cooling during encapsulation (E). Also depicted is the improvement in heat tolerance for an endurance trained individual (F) who can tolerate much higher core temperatures at exhaustion. The values depicted on the x‐axis represent mean changes that would be expected from the average response observed during light exercise. Individual effects could be much greater or less.



Figure 1.

The energy cost of movement while wearing a multilayered Arctic clothing ensemble or carrying equivalent weight as a single‐layer uniform with weighted belt. Adapted from Teitlebaum and Goldman (239).



Figure 2.

A schematic representation of sweat production and its vaporization through clothing together with sweat lost through dripping off the skin surface and condensation in the clothing layers. Reproduced, with permission, from Cheung (32).



Figure 3.

The relationship between tolerance time and metabolic rate when wearing Canadian Forces nuclear, biological, and chemical protective clothing in different environmental conditions. Solid and dotted lines represent data from various environmental conditions derived from McLellan (153) and McLellan et al. (162,163,164).



Figure 4.

The effects of 12 days of heat acclimation to a hot and humid environment on tolerance time during cycling at a constant power output. Note that the increase in tolerance time following the heat acclimation is due to the decrease in resting core temperature. The figure is derived from data in Nielsen et al. (181).



Figure 5.

Rectal temperature in the morning during 12 days of heat acclimation (HA) with minimal recovery and 3, 7, and 18 days later. Please note that the reduction in core temperature is not seen during, but after HA. Reproduced, with permission, from Daanen et al. (54).



Figure 6.

Rectal temperature after 60 min exercise during heat acclimation for 10 days followed by reacclimation 26 days later for 7 days. Note that even after 26 days the core temperature is the same as the end of the initial heat acclimation period. Reproduced, with permission, from Weller et al. (253).



Figure 7.

The change in core temperature while wearing either the current personal protective ensemble consisting of the combat uniform and overgarment concept or new stand‐alone chemical and biological (CB) uniforms. During the low dress state minimal protection is required and only the combat uniform is worn. However, during the high dress state full encapsulation and maximum protection is required, necessitating the use of the overgarment. The use of the new CB uniforms does not require an overgarment since the CB protection is already included within the clothing material. Notice after 60 min at the beginning of the transition from the low to high dress state core temperature is higher for the new CB uniform.



Figure 8.

Heart rate and rectal temperature tolerated at exhaustion during low exercise intensity of 165 W·m2 with a tolerance time of 105 min versus high exercise intensity of 260 W·m2 and tolerance time of 60 min. The asterisk indicates a significant difference between the low and high exercise intensities.



Figure 9.

Sample size of participants from each training status throughout a passive heating protocol. The highly fit (circles), moderately fit (squares), and lower fit (triangles) groups began with similar sample sizes, although the majority of the lower fit participants were unable to complete the protocol. Reproduced, with permission, from Morrison et al. (176).



Figure 10.

The theoretical effect of cooling on tolerance time in protective equipment based on modeling studies. Reproduced, with permission, from Pandolf et al. (194).



Figure 11.

The effects of hand and forearm submersion in 18°C water for 20 min on the increase in rectal temperature (expressed as delta Tre) following 50 min of exercise at 35°C while wearing full firefighting PPC. The asterisk indicates a significant difference between the hand and forearm immersion trial compared with the condition that involved passive cooling when some of the firefighting PPC was removed during the 20‐min rest periods. Tolerance time was increased significantly from 108 ± 14 min with passive cooling to 179 ± 50 min with hand and forearm submersion. Adapted from Selkirk et al. (218).



Figure 12.

A schematic representation of the tolerance time during uncompensable heat stress for a sedentary untrained individual (A) and the influence of raising the initial resting core temperature due to circadian rhythm, menstrual phase or minor (B) or severe (C) hypohydration, lowering resting core temperature through heat acclimation or precooling strategies (D) and a decrease in body fatness, an increase in gross movement efficiency or providing cooling during encapsulation (E). Also depicted is the improvement in heat tolerance for an endurance trained individual (F) who can tolerate much higher core temperatures at exhaustion. The values depicted on the x‐axis represent mean changes that would be expected from the average response observed during light exercise. Individual effects could be much greater or less.

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Tom M. McLellan, Hein A. M. Daanen, Stephen S. Cheung. Encapsulated Environment. Compr Physiol 2013, 3: 1363-1391. doi: 10.1002/cphy.c130002