Active Versus Passive Cooling During Work in Warm Environments While Wearing Firefighting Protective Clothing

Abstract

This study examined whether active or passive cooling during intermittent work reduced the heat strain associated with wearing firefighting protective clothing (FPC) and self-contained breathing apparatus (SCBA) in the heat (35 degrees Celsius, 50% relative humidity). Fifteen male Toronto firefighters participated in the heat-stress trials. Subjects walked at 4.5 km.h(-1) with 0% elevation on an intermittent work (50 min) and rest (30 min) schedule. Work continued until rectal temperature (T(re)) reached 39.5 degrees Celsius, or heart rate (HR) reached 95% of maximum or exhaustion. One of three cooling strategies, forearm submersion (FS), mister (M), and passive cooling (PC) were employed during the rest phases. Tolerance time (TT) and total work time (WT) (min) were significantly increased during FS (178.7 +/- 13.0 and 124.7 +/- 7.94, respectively) and M (139.1 +/- 8.28 and 95.1 +/- 4.96, respectively), compared with PC (108.0 +/- 3.59 and 78.0 +/- 3.59). Furthermore, TT and WT were significantly greater in FS compared with M. Rates of T(re) increase, HR and T-(sk) were significantly lower during active compared with passive cooling. In addition, HR and T(re) values in FS were significantly lower compared with M after the first rest phase. During the first rest phase, T(re) dropped significantly during FS (approximately 0.4 degree Celsius) compared with M (approximately 0.08 degree Celsius) while PC increased (approximately 0.2 degree Celsius). By the end of the second rest period T(re) was 0.9 degree Celsius lower in FS compared with M. The current findings suggest that there is a definite advantage when utilizing forearm submersion compared with other methods of active or passive cooling while wearing FPC and SCBA in the heat.

Extremity cooling for heat stress mitigation in military and occupational settings

“…While some investigations have reported that heart rate was 10-25 bpm less than during non-cooling control (Khomenok et al, 2008;Selkirk et al, 2004) others have reported no difference in heart rate between conditions (Giesbrecht et al, 2007). Postural differences may explain the discrepancy, as subjects were seated or leaning over the cooling apparatus in the former studies (Khomenok et al, 2008;Selkirk et al, 2004) but remained standing in the latter (Giesbrecht et al, 2007). It should be noted, however, that heart rate differences persisted into subsequent work bouts in the aforementioned studies (Khomenok et al, 2008;Selkirk et al, 2004), suggesting that more than postural differences are involved.…”

“…When ice and/or water supply and resupply in a field environment are taken into consideration, water as 'warm' as 20 1C still provides significant cooling power (House, 1998;Livingstone et al, 1989;Selkirk et al, 2004); therefore it may not be necessary to maintain water temperature in the 10 1C range, which would have the benefit of extending the useful time of a given volume of cold water and reducing the logistical burden of keeping the water at 10 1C. However, repeated use by multiple individuals and ambient environment conditions may increase water bath temperature such that immersion cooling is no longer beneficial, requiring periodic ice and/or water resupply.…”

“…In addition to being impractical in a military training environment (Khomenok et al, 2008;Selkirk et al, 2004), data suggest that the rate of core temperature cooling during foot immersion is inferior compared to hand or hand and forearm immersion (House, 1998;Livingstone et al, 1995). Similar to hand or combined hand and forearm immersion, when immersing the feet, heat loss was greatest in the 10 1C water condition, such that heat loss was $3 times greater at that temperature compared to 30 1C (Livingstone et al, 1995).…”

“…Again using participants wearing firefighter protective clothing, Selkirk and colleagues had participants repeat a 50 min work: 30 min rest cycle until exhaustion or core temperature reached 39.6 1C (Selkirk et al, 2004). During the rest period the participants remained in the heat and either immersed their hands and forearms in 17 1C water or passively recovered (non-cooling control).…”

“…Postural differences may explain the discrepancy, as subjects were seated or leaning over the cooling apparatus in the former studies (Khomenok et al, 2008;Selkirk et al, 2004) but remained standing in the latter (Giesbrecht et al, 2007). It should be noted, however, that heart rate differences persisted into subsequent work bouts in the aforementioned studies (Khomenok et al, 2008;Selkirk et al, 2004), suggesting that more than postural differences are involved. No previous studies have reported changes in skin blood flow or stroke volume changes during extremity immersion cooling; however using cold air exposure or water-perfused suit models, it is well-established that skin temperature and skin blood flow are directly related (DeGroot and Kenney, 2006;Stephens et al, 2001).…”