Unconditioned air ventilation inside an aircrew NBC …cradpdf.drdc-rddc.gc.ca/PDFS/unc81/p530876.pdf · Unconditioned air ventilation inside an aircrew NBC suit during exposure to

Unconditioned air ventilation inside an

aircrew NBC suit during exposure to

warm environments

Michel B. DuCharmeDRDC Valcartier

Defence R&D Canada – ValcartierTechnical Report

DRDC Valcartier TR 2007-066August 2008

Unconditioned air ventilation inside an aircrew NBC suit during exposure to warm environments

Michel B. DuCharme DRDC Valcartier

Defence R&D Canada –Valcartier Technical Report DRDC Valcartier TR 2007-066 August 2008

Principal Author

Michel B. DuCharme, PhD

Approved by

Guy Turcotte

Section Head, System of Systems Section

Approved for release by

Christian Carrier, Ph.D. Chief Scientist

In conducting the research described in this report, the investigators adhered to the policies and procedures set out in the Tri-Council Policy Statement: Ethical conduct for research involving humans, National Council on Ethics in Human Research, Ottawa, 1998 as issued jointly by the Canadian Institutes of Health Research, the Natural Sciences and Engineering Research Council of Canada and the Social Sciences and Humanities Research Council of Canada.

© Her Majesty the Queen in Right of Canada, as represented by the Minister of National Defence, 2008

© Sa Majesté la Reine (en droit du Canada), telle que représentée par le ministre de la Défense nationale, 2008

DRDC Valcartier TR 2007-066 i

Abstract ……..

The heat tolerance and thermal responses of aircrew were evaluated during their exposure to warm ambient conditions while dressed in two different NBC ensembles: the current Canadian Air Forces (CF) NBC charcoal coveralls and the LASA ventilated-NBC suit, with unconditioned ambient air circulated inside the suit and the helmet at 220 L/min. Six subjects were randomly exposed to five 6-hr periods of experimental conditions involving a 1-hr pre-flight simulation at room temperature, followed by a 4-hr flight simulation in 35 or 45ºC and 40% relative humidity (RH) ambient conditions, with a 1-hr post-flight simulation at room temperature. During the 4-hr flight simulation, the subjects simulated helicopter backender activities (cabin check, hoisting rescue, loading sonar buoys) in a climatic chamber. The five tested conditions were: LASA suit with air flow on at 35ºC (35FI); LASA suit with no air flow at 35ºC (35FO); LASA suit with air flow on at 45ºC (45FI); LASA suit with no air flow at 45ºC (45FO); and current NBC coveralls at 45ºC (45CU). During the test, heart rate (HR), rectal temperature (Tre), rate of increase in rectal temperature, mean skin temperature (Tsk), sweating rate, thermal comfort, rate of perceived exertion (RPE), relative humidity inside the clothing and tolerance time were measured. Tolerance time in the chamber, sweating rate and rate of increase in rectal temperature were similar for all conditions (average ± SE: 1.1 ± 0.2 hr; 0.65 ± 0.02 kg/hr; 1.44 ± 0.05ºC/hr, respectively), except for condition 35FI, where tolerance time was longer (3.5 ± 0.4 hr) and sweat rate (0.46 ± 0.29 kg/hr) and rate of increase in rectal temperature (0.40 ± 0.11ºC/hr) were lower than for the other conditions. In general, increases in Tre and Tsk were larger at 45ºC than 35ºC and when the flow inside the LASA suit was “off” than when it was “on.” Increases in Tre and Tsk were larger for conditions 45FO than 45CU, and no difference was observed between conditions 45FI and 45CU. The lowest thermal comfort ratings were observed for condition 35FI. It was concluded that the ventilation inside the LASA suit and helmet increases the tolerance time during simulated aircrew operations at an ambient temperature of 35ºC, but not at 45ºC.

Key words: Hyperthermia; heat stress; thermal comfort; helicopter aircrew; protective clothing

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DRDC Valcartier TR 2007-066 iii

Résumé ….....

On a évalué la tolérance à la chaleur et les réponses thermiques des membres d’équipage d’aéronef exposés à la chaleur ambiante et revêtus de deux sortes de combinaisons de protection NBC: la combinaison NBC actuellement utilisée par les Forces canadiennes (FC) et la combinaison pressurisée LASA, de même que le casque à l’intérieur desquels circule l’air ambiant à 220 L/min. On a exposé six sujets choisis au hasard à des conditions expérimentales ; cinq périodes de six heures, dont une heure de simulation avant le vol à la température ambiante, suivie d’une simulation de vol de quatre heures à 35 ou 45ºC, 40 % d’humidité relative (RH) et une heure de simulation après le vol à la température ambiante. Durant la simulation de vol de quatre heures, les sujets ont procédé à la simulation d’activités à l’intérieur d’un hélicoptère (vérification de l’habitacle, hissage, chargement de balises de localisation) dans une chambre climatique. Les cinq conditions expérimentales étaient : la combinaison LASA avec circulation d’air à 35ºC (35FI); la combinaison LASA sans circulation d’air à 35ºC (35FO); la combinaison LASA avec circulation d’air à 45ºC (45FI); la combinaison LASA sans circulation d’air à 45ºC (45FO); et la combinaison NBC actuelle à 45ºC (45CU). Au cours de cet essai, on a mesuré le rythme cardiaque (HR), la température rectale (Tre), le taux d’accroissement de la température rectale, la température cutanée moyenne (Tsk), le rythme de la transpiration, le confort thermique, le rythme d’effort perçu (RPE), l’humidité relative à l’intérieur de la combinaison et la durée de tolérance. La durée de tolérance dans la chambre, le rythme de la transpiration et le taux d’accroissement de la température rectale étaient semblables dans toutes les conditions (moyenne ± SE: 1,1 ± 0,2 h; 0,65 ± 0,02 kg/h; 1,44 ± 0,05ºC/r, respectivement), sauf dans les conditions 35FI, où la durée de tolérance était plus longue (3,5 ± 0,4 h) ; le taux la transpiration (0,46 ± 0,29 kg/h) et le taux d’accroissement de la température rectale (0,40 ± 0,11ºC/h) étaient plus faibles que dans les autres conditions. En général, l’augmentation de la Tre et de la Tsk était plus considérable à 45ºC qu’à 35ºC et encore davantage sans circulation d’air à l’intérieur de la combinaison LASA qu’avec circulation d’air. L’augmentation de la Tre et de la Tsk était plus considérable dans les conditions 45FO que dans les 45CU et on n’a constaté aucune différence entre les conditions 45FI et 45CU. On a observé les mesures du confort thermique les plus faibles dans les conditions 35FI. On en a conclu que la pressurisation à l’intérieur de la combinaison LASA et du casque augmentait la durée de tolérance lors des simulations à une température ambiante de 35ºC, mais pas à 45ºC.

iv DRDC Valcartier TR 2007-066


DRDC Valcartier TR 2007-066 v

Executive summary


Michel B. DuCharme; DRDC Valcartier TR 2007-066; Defence R&D Canada – Valcartier; August 2008.

The Canadian Air Forces is in the process of acquiring NBC immersion protection for its helicopter aircrew to replace the current NBC protection suit. The LASA suit, a newly developed German product, was identified as the potential NBC protection system to replace the current one. The Directorate of Aerospace Engineering Support (DAES) tasked DRDC with evaluating the LASA suit on human subjects during exposure to warm environments. The heat tolerance and thermal responses of aircrew were evaluated during their exposure to warm ambient conditions while dressed in two different NBC ensembles: the current Canadian Air Forces (CF) NBC charcoal coveralls and the LASA ventilated-NBC suit, with unconditioned ambient air circulated inside the suit and the helmet at 220 L/min. Six subjects were randomly exposed to five 6-hr periods of experimental conditions involving a 1-hr pre-flight simulation at room temperature, followed by a 4-hr flight simulation in 35 or 45ºC and 40% RH ambient conditions, with a 1-hr post-flight simulation at room temperature. During the 4-hr flight simulation, the subjects simulated helicopter backender activities (cabin check, hoisting rescue, loading sonar buoys) in a climatic chamber. The five tested conditions were: LASA suit with air flow on at 35ºC (35FI); LASA suit with no air flow at 35ºC (35FO); LASA suit with air flow on at 45ºC (45FI); LASA suit with no air flow at 45ºC (45FO); and current NBC coveralls at 45ºC (45CU). During the test, heart rate (HR), rectal temperature (Tre), rate of increase in rectal temperature, mean skin temperature (Tsk), sweating rate, thermal comfort, rate of perceived exertion, relative humidity inside the clothing and tolerance time were measured. Tolerance time in the chamber, sweating rate and rate of increase in rectal temperature were similar for all conditions (average ± SE: 1.1 ± 0.2 hr; 0.65 ± 0.02 kg/hr; 1.44 ± 0.05ºC/hr, respectively), except for condition 35FI, where tolerance time was longer (3.5 ± 0.4 hr) and sweat rate (0.46 ± 0.29 kg/hr) and rate of increase in rectal temperature (0.40 ± 0.11ºC/hr) were lower than for the other conditions. In general, increases in Tre and Tsk were larger at 45ºC than 35ºC and when the flow inside the LASA suit was “off” than when it was “on.” Increases in Tre and Tsk were larger for conditions 45FO than 45CU, and no difference was observed between conditions 45FI and 45CU. The lowest thermal comfort ratings were observed for condition 35FI. It was concluded that the ventilation inside the LASA suit and helmet increases the tolerance time during simulated aircrew operations at an ambient temperature of 35ºC, but not at 45ºC.

vi DRDC Valcartier TR 2007-066


DRDC Valcartier TR 2007-066 vii

Sommaire .....


Michel B. DuCharme; DRDC Valcartier TR 2007-066; R et D pour la défense Canada – Valcartier; août 2008.

Les Forces canadiennes procèdent à l’acquisition de nouvelles combinaisons NBC pour la protection des membres d’équipage d’hélicoptères en condition d’immersion afin de remplacer les combinaisons actuelles. La combinaison LASA, récemment mise au point par les Allemands, pourrait remplacer la combinaison de protection NBC actuelle. Le Directorat du soutien en génie aérospatial (DSGA) a chargé la RDDC d’évaluer la combinaison LASA lors d’essais sur des sujets humains exposés à la chaleur. On a ainsi évalué la tolérance à la chaleur et les réponses thermiques des membres d’équipage exposés à la chaleur ambiante et revêtus de deux sortes de combinaisons de protection NBC: la combinaison NBC actuellement utilisée par les Forces canadiennes (FC) et la combinaison pressurisée LASA, de même que le casque à l’intérieur desquels circule l’air ambiant à 220 L/min. On a exposé six sujets choisis au hasard à des conditions expérimentales : cinq périodes de six heures, dont une heure de simulation avant le vol à la température ambiante, suivie d’une simulation de vol de quatre heures à 35 ou 45ºC, 40 % d’humidité relative (RH) et une heure de simulation après le vol à la température ambiante. Durant la simulation de vol de quatre heures, les sujets ont procédé à la simulation d’activités à l’intérieur d’un hélicoptère (vérification de l’habitacle, hissage, chargement de balises de localisation) dans une chambre climatique. Les cinq conditions expérimentales étaient : la combinaison LASA avec circulation d’air à 35ºC (35FI); la combinaison LASA sans circulation d’air à 35ºC (35FO); la combinaison LASA avec circulation d’air à 45ºC (45FI); la combinaison LASA sans circulation d’air à 45ºC (45FO); et la combinaison NBC actuelle à 45ºC (45CU). Au cours de cet essai, on a mesuré le rythme cardiaque (HR), la température rectale (Tre), le taux d’accroissement de la température rectale, la température cutanée moyenne (Tsk), le rythme de la transpiration, le confort thermique, le rythme d’effort perçu (RPE), l’humidité relative à l’intérieur de la combinaison et la durée de tolérance. La durée de tolérance dans la chambre, le rythme de la transpiration et le taux d’accroissement de la température rectale étaient semblables dans toutes les conditions (moyenne ± SE: 1,1 ± 0,2 h; 0,65 ± 0,02 kg/h; 1,44 ± 0,05ºC/r, respectivement), sauf dans les conditions 35FI, où la durée de tolérance était plus longue (3,5 ± 0,4 h) ; le taux la transpiration (0,46 ± 0,29 kg/h) et le taux d’accroissement de la température rectale (0,40 ± 0,11ºC/h) étaient plus faibles que dans les autres conditions. En général, l’augmentation de la Tre et de la Tsk était plus considérable à 45ºC qu’à 35ºC et encore davantage sans circulation d’air à l’intérieur de la combinaison LASA qu’avec circulation. L’augmentation de la Tre et de la Tsk était plus considérable dans les conditions 45FO que dans les 45CU et on n’a constaté aucune différence entre les conditions 45FI et 45CU. On a observé les mesures du confort thermique les plus faibles dans les conditions 35FI. On en a conclu que la pressurisation à l’intérieur de la combinaison LASA et du casque augmentait la durée de tolérance lors des simulations à une température ambiante de 35ºC, mais pas à 45ºC.

,

viii DRDC Valcartier TR 2007-066


DRDC Valcartier TR 2007-066 ix

Table of contents

Abstract …….. ................................................................................................................................. i Résumé …..... ................................................................................................................................. iii Executive summary ......................................................................................................................... v Sommaire ...................................................................................................................................... vii Table of contents ............................................................................................................................ ix List of figures .................................................................................................................................. x List of tables .................................................................................................................................... x Acknowledgements ........................................................................................................................ xi Introduction ..................................................................................................................................... 1 Materials and Methods .................................................................................................................... 2 Results……. .................................................................................................................................... 6 Discussion and Conclusions .......................................................................................................... 11 References ..... ............................................................................................................................... 12 Distribution list.............................................................................................................................. 13

x DRDC Valcartier TR 2007-066

List of figures

Figure 1. LASA NBC suit with air ventilation and filtration systems............................................. 4 Figure 2. Mean skin temperature (± SE) from 12 skin sites on the subjects (n=6 at time 0 min)

during the 60-min pre-flight and 240-min heat tests in the climatic chamber. ............. 7 Figure 3. Mean rectal temperature (± SE) of the subjects (n=6 at time 0 min) during the 60-

min pre-flight and 240-min heat tests in the climatic chamber. .................................... 8 Figure 4. Mean heart rate (± SE) of the subjects (n=6 at time 0 min) during the 60-min pre-

flight and 240-min heat tests in the climatic chamber................................................... 9 Figure 5. Mean vapour pressure inside the clothing (± SE; n=6 at time 0 min) during the 60-

min pre-flight and 240-min heat tests in the climatic chamber. .................................. 10

List of tables

Table 1. Subject Information and Physical Characteristics ............................................................. 2

DRDC Valcartier TR 2007-066 xi

Acknowledgements

The author would like to acknowledge the technical support of Robert Limmer and Debbie Kerrigan-Brown from DRDC Toronto.

xii DRDC Valcartier TR 2007-066


DRDC Valcartier TR 2007-066 1

Introduction

Aircrew wearing NBC protective clothing and exposed to a warm environment during military operations are often subjected to heat stress that can lead to dehydration and heat exhaustion resulting in a decrease in performance (Faerevik and Reinertsen, 2003). Under such conditions, a cooling system is required to minimize the heat strain experienced by the aircrew. Current cooling systems used by aircrew have limitations. They can be heavy, cumbersome, tethered to the aircraft (causing limitation of movement), may require frequent re-supply of ice and often need too much power to operate over a long period.

The LASA suit is an integrated protective garment that was developed to protect helicopter aircrew from exposure to NBC and extreme environments, including cold water immersion. The suit comprises a ventilated, one-piece dry immersion suit with a biological/chemical barrier and a ventilated helmet. The suit and helmet ventilation is provided by two blowers that send filtered but unconditioned air around the skin of the body and head at a rate of 220 L/min to remove excess humidity and body heat. This cooling approach requires a minimum of power to operate, optimizes freedom of movement and does not require re-supply of material.

The objective of the present investigation was to evaluate the heat tolerance and thermal responses of aircrew during exposure to warm ambient conditions when dressed is two different NBC protective ensembles: the current Canadian Air Forces NBC charcoal coveralls with no cooling system and the LASA ventilated-NBC suit with unconditioned ambient air circulated inside the suit and helmet.

2 DRDC Valcartier TR 2007-066

Materials and Methods

Subjects. Six male subjects were selected to participate in this trial. The subjects were (mean ± SD) 37.8 ± 8.5 years old, 1.73 ± 0.05 m tall, weighed 84.6 ± 9.8 kg, had a surface body area of 1.98 ± 0.13 m2 and 21.2 ± 3.7% body fat (see Table 1 for details). The body surface area was estimated according to the Dubois and Dubois equation (1916). Percentage body fat was estimated from skin-fold measurements at five body sites (triceps, scapula, suprailiac, abdomen and front thigh) and calculated according to Forsyth et al. (1984). All subjects were healthy and had a medical screening before signing their volunteer consent form. The protocol was approved by the DRDC Human Research Ethics Committee (HREC).

Before each experimental session, the subjects were asked to follow a routine similar to the one used before a flight operation, e.g., observe a 12-hour restriction on alcohol consumption, take no over-the-counter medication, get a good night’s sleep and be well hydrated and fed on the morning of the test. The routine was consistent between the different days of the laboratory testing in order to control for physiological status. All sessions for each subject were scheduled at the same time of the day. No other restrictions were imposed on the subjects.

Table 1. Subject Information and Physical Characteristics

Subject Age(yr) Ht(m) Mass(kg) %BF SA (m2) 1 31 1.76 81.5 17.52 1.98 2 41 1.64 68.8 22.60 1.75 3 41 1.76 95.1 19.90 2.11 4 25 1.71 84.5 26.13 1.96 5 49 1.73 87.2 21.94 2.01 6 40 1.75 90.5 19.03 2.06

Average 37.8 1.73 84.6 21.2 1.98 Std. Dev. 8.5 0.05 9.8 3.7 0.13

Experimental conditions. Each subject was exposed to 5 experimental sessions over a 2-month period, in addition to an initial familiarization session. Each experimental session was conducted in a climatic chamber at DRDC Toronto and involved a different test condition as follows: Session 1: LASA suit with internal air flow during exposure to 45ºC with low humidity (40%) (FI45); Session 2: LASA suit with no internal air flow during exposure to 45ºC with low humidity (40%) (FO45); Session 3: LASA suit with internal air flow during exposure to 35ºC with low humidity (40%) (FI35); Session 4: LASA suit with no internal air flow during exposure to 35ºC with low humidity (40%) (FO35); Session 5: current aircrew NBC suit during exposure to 45ºC with low humidity (40%) (CU45). The thermal conditions were defined on the basis of the highest average temperatures reported in the Gulf Region (45ºC) and Canada (35ºC). The no internal flow conditions simulated failure of the blower during an operation―a worst case scenario.


Clothing. Under the first four conditions, the subjects wore the following items in addition to the LASA suit system (Fig. 1): top and bottom long underwear, socks, aircrew boots and gloves, life vest and flight pack. This clothing configuration represents the proposed new CF standard clothing to be worn by aircrew during normal flight operations over water on missions with NBC threat. Under the fifth condition, the current CF aircrew NBC coveralls were worn over long underwear, in addition to the AC4 mask and aircrew helmet, rubber boots over the aircrew leather boots, rubber gloves over the aircrew leather gloves, life vest and flight pack. The current aircrew NBC coveralls are a one-piece suit comprising a charcoal and a Nomex® shell layer. The current aircrew NBC coveralls do not include protection against cold water immersion.

Procedures. The sessions were assigned in a counter-balanced fashion. Each session lasted 6 hours during which period the subjects were wearing either suit, as described above. All experimental sessions started in the morning and consisted of the following activities: 1 hour pre-flight at room temperature (~21ºC); 4 hours of backender simulation activity (activity done by the aircrew located at the back of the aircraft, e.g., the navigators and sensor operators); 1 hour post-flight at room temperature. All except pre- and post-flight activities were performed in a climatic chamber where the temperature was maintained at either 35ºC or 45°C, with a relative humidity of 40%. During the 6-hour sessions, the subjects were allowed to drink water ad libitum.


Figure 1. LASA NBC suit with air ventilation and filtration systems.

The 1-hour pre-flight and post-flight activities simulated a flight briefing and debriefing and consisted of having the subject sitting in the climatic chamber while listening to TV. The energy expenditure of the subject was around 100 W (resting level). The backender simulations consisted of four different activities of the following durations and levels of energy expenditure: sensor operation (12 x 11 min; ~100 W), cabin check (10 x 5 min; ~200 W), loading of sonar buoys (2 x 15 min; ~400 W) and hoisting rescue (2 x 14 min; ~300 W). The different activities were alternated during the 4-hour simulation. The sensor operation activity consisted of having the subject seated in front of a monitor and playing a computer simulation. The cabin check


activity consisted of having the subject walking around a simulated helicopter cabin and checking instruments. The loading of sonar buoys activity consisted of having the subject loading five muck-up buoys inside hollow cylinders using a special gripping tool. The hoisting rescue activity consisted of having the subject simulating the hoisting inside the helicopter of three victims (weighing 70 kg) in a stoke litter using a portable electric hoist. An experimental session was terminated if one of the following criteria was achieved: elapsed time of 6 hrs, a core temperature of 39.5°C, or 95% of the maximum estimated heart rate for three minutes. Following the session, the subjects were undressed and were cooled in a cool water bath set at 20°C until their core temperature started to decline.

Upon arrival at the testing facilities, the subjects were weighed nude, instrumented with sensors and dressed with the appropriate garment. The weights of the fully dressed subjects were then obtained before the subjects moved to the chamber. Following the session, the dressed and nude weights were again obtained to estimate the sweating and evaporation rates.

Measured parameters. The following parameters were continuously measured on the subjects during the sessions using portable data loggers: rectal temperature, with a thermistor probe inserted by the subject 15 cm into the rectum; skin temperature, with thermistors at 12 locations (forehead, scapula, chest, shoulder, upper arm, lower arm, abdomen, back, front and back thigh, shin, and calf) (Hardy and Dubois, 1938); heart rate, with a Polar heart rate monitor; and relative humidity inside the clothing at 3 locations (chest, lower back and front thigh), with small humidity sensors located between the long underwear and the liner of the suit. Every 20 min during the tests, the subjects were asked to rate their thermal comfort according to the Gagge Thermal Comfort Scale (Gagge et al., 1967) and their perceived exertion according to the Borg Perceived Exertion Scale (Borg, 1982).

Calculated variables. The sweating rate was calculated by subtracting the post nude weight from the pre-nude weight of the subjects and correcting for fluid intake and urine loss. The rate of increase in rectal temperature (in ºC/hr) was calculated from the change in rectal temperature observed over the duration of the sessions inside the chamber. The tolerance time was defined as the time inside the chamber until a terminating criteria was observed and the session ended.

Statistical analysis. The data were analyzed by repeated measures ANOVA to test for differences over time in the measured variables depending on clothing configuration and ambient conditions. Significant differences were tested using a Neuman-Keuls post-hoc procedure. Significance was accepted at the p < 0.05 level.


Results

Mean skin temperature. Figure 2 presents the mean skin temperature for all conditions tested with the 6 subjects over the 60-min pre-flight and 240-min heat exposure. During the pre-flight exposure, the increase in skin temperature was about 1 to 1.2ºC and similar for all conditions. Mean skin temperature increased significantly faster and by a larger amount (6.2ºC) for condition 45FO than for the other conditions. Conditions 35FO, 45FI and 45CU showed similar increases in mean skin temperature (5.1ºC), while condition 35FI had the smallest increase in mean skin temperature (about 3ºC). Mean skin temperature reached a steady-state only for condition 35FI, while for the other conditions the mean skin temperature never reached a plateau.

Mean rectal temperature and rate of increase in rectal temperature. Figure 3 presents the mean rectal temperature for all conditions tested with the six subjects over the 60-min pre-flight and 240-min heat exposure. During the pre-flight exposure, a minor decrease in rectal temperature of about 0.2ºC was observed and the decrease was similar for all conditions. During the heat exposure in the chamber, the increase in rectal temperature was similar for all conditions (~1.5ºC) except FI35, under which the increase was significantly smaller at about 0.4ºC. Similarly, the rate of increase in rectal temperature did not differ among the various conditions, averaging 1.44 ± 0.05ºC/hr, again with the exception of FI35, under which the rate of increase in rectal temperature was significantly smaller, at 0.40 ± 0.11ºC/hr. The rectal temperature did not reach a plateau during the exposure period in the heat for any condition except condition FI35, under which a steady-state was almost achieved.

Heart rate. Figure 4 presents the mean heat rate for all conditions tested with the six subjects over the 60-min pre-flight and 240-min heat exposure. During the pre-flight exposure, the heart rate was at its minimum, averaging 67.5 ± 3.6 beats/min, with no difference between conditions. During the backenders activities, the mean heart rate increased significantly for all conditions. The lowest increase in heart rate was observed for the sensor operation activity, with an average of 107 ± 4 beats/min, while the other activities registered similar heart rates, averaging 131 ± 6 beats/min. On average, the heart rate was significantly higher during the heat exposures in the chamber at 45ºC than during those at 35ºC, and was the lowest for condition 35FI. No difference was observed between all conditions at 45ºC.

Vapour pressure inside the clothing. Figure 5 presents the mean vapour pressure at the three sites inside the clothing for all conditions tested with the six subjects over the 60-min pre-flight and 240-min heat exposure. During the pre-flight exposure, the vapour pressure stabilized at about 10 mmHg for all conditions except condition 45CU, under which the vapour pressure increased to ~22 mmHg. During the exposure to the heat, the mean vapour pressure inside the clothing increased to about 50 mmHg by the end of the exposure for all conditions, except for condition 35FI, under which the vapour pressure was significantly lower, at ~40 mmHg. The vapour pressure stabilized only for condition 35FI, after about 120 min of exposure.


Tolerance time in the heat. The tolerance time of the subjects in the hot chamber was similar for all conditions tested, averaging 1.1 ± 0.2 hr, except for condition 35FI, under which the tolerance time was significantly longer, averaging 3.5 ± 0.4 hr.

Sweating rate. The mean sweating rate was similar for the various conditions, averaging 0.65 ± 0.02 kg/hr, except for condition 35FI, under which the sweating rate was significantly lower, averaging 0.46 ± 0.29 kg/hr.

Thermal comfort and perceived exertion. In general, the thermal comfort rating was lower for the 35ºC (8.9 ± 0.4) than the 45ºC conditions (9.6 ± 0.5), and was not affected by the air flow inside the suit. Similarly, the perceived exertion rating was generally lower for the 35ºC (10.8 ± 0.9) than the 45ºC conditions (12.2 ± 0.8) and was not affected by the air flow inside the suit. The exception was provided by condition 45CU, under which the perceived exertion rating did not differ from the rating under the other conditions.

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Figure 2. Mean skin temperature (± SE) from 12 skin sites on the subjects (n=6 at time 0 min)

during the 60-min pre-flight and 240-min heat tests in the climatic chamber.


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Figure 3. Mean rectal temperature (± SE) of the subjects (n=6 at time 0 min) during the 60-min

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Figure 4. Mean heart rate (± SE) of the subjects (n=6 at time 0 min) during the 60-min pre-flight

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Figure 5. Mean vapour pressure inside the clothing (± SE; n=6 at time 0 min) during the 60-min pre-flight and 240-min heat tests in the climatic chamber.


Discussion and Conclusions

One objective of this study was to evaluate the thermal and physiological benefits of ventilating the inside of an NBC protective garment with unconditioned air during simulated helicopter operation in two warm environments: 35 and 45ºC. The results of the present study show that a significant benefit is to be gained from ventilating the suit with unconditioned air during exposure to an ambient temperature of 35ºC, but not during exposure to 45ºC. Ventilation of the NBC suit during exposure to 35ºC produced a lower increase in mean skin temperature, mean rectal temperature and mean heart rate, and caused a lower rate of increase in rectal temperature and a lower sweating rate during the exposure to the heat. All those factors are indications of a lower heat strain for the subjects with ventilation of the suit at 35ºC than with no ventilation. Consequently, ventilation of the suit during exposure to 35ºC dramatically increased the tolerance time in the chamber, i.e., by a factor of 3, from 1.1 to 3.5 hrs, while the tolerance time and the thermal strain were not significantly affected by air ventilation during exposure to 45 ºC.

A second objective of the study was to quantify the thermal and physiological differences between the ventilated NBC LASA suit and the current CF charcoal NBC coveralls during simulated helicopter operations at 45ºC. The results of the present study do not show evidence of any thermal or physiological advantages associated with using the ventilated LASA suit over using the current CF NBC coveralls. Under the condition in which the LASA suit was used without air ventilation (FO45), the thermal strain tended to be higher than under the CF NBC coveralls condition (CU45), as reflected by a higher increase in rectal and skin temperatures and a tendency towards a higher RPE and HR. This tendency for a higher thermal strain under condition FO45 did not significantly affect the tolerance time in the chamber when compared with condition CU45.

It was concluded from the present study that ventilating the inside of an NBC protective suit with unconditioned air could be thermally beneficial as long as the ambient air temperature is lower than the skin temperature, as was the case for the condition at 35ºC, but not for an ambient temperature of 45ºC.


References .....

[1] Borg GAV. Psychological bases of perceived exertion. Med. Sci. Sports Exerc 14: 377-381, 1982.

[2] DuBois D. and DuBois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Int Med, 17: 863-71, 1916.

[3] Faerevik H, Reinertsen RE. Effects of wearing aircrew protective clothing on physiological and cognitive responses under various ambient conditions. Ergonomics (England), 46, 780-99.

[4] Forsyth RD, Plyley MJ, and Shephard RJ. Estimation of body fatness of Canadian Forces. Can J Appl Sport Sci 9: 5, 1984.

[5] Gagge AP, Stolwijk JAJ, Hardy JD. Comfort and thermal sensations and associated physiological responses at various ambient temperatures. Environ Res, 1, 1-20, 1967.

[6] Hardy J.D., DuBois E.F. The technic of measuring radiation and convection. J. Nutr. 15: 461-475, 1938.


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The heat tolerance and thermal responses of aircrew were evaluated during their exposure towarm ambient conditions while dressed in two different NBC ensembles: the current CanadianAir Forces (CF) NBC charcoal coveralls and the LASA ventilated-NBC suit, withunconditioned ambient air circulated inside the suit and the helmet at 220 L/min. Six subjectswere randomly exposed to five 6-hr periods of experimental conditions involving a 1-hr pre-flight simulation at room temperature, followed by a 4-hr flight simulation in 35 or 45ºC and40% relative humidity (RH) ambient conditions, with a 1-hr post-flight simulation at roomtemperature. During the 4-hr flight simulation, the subjects simulated helicopter backenderactivities (cabin check, hoisting rescue, loading sonar buoys) in a climatic chamber. The fivetested conditions were: LASA suit with air flow on at 35ºC (35FI); LASA suit with no air flowat 35ºC (35FO); LASA suit with air flow on at 45ºC (45FI); LASA suit with no air flow at 45ºC(45FO); and current NBC coveralls at 45ºC (45CU). During the test, heart rate (HR), rectaltemperature (Tre), rate of increase in rectal temperature, mean skin temperature (Tsk), sweatingrate, thermal comfort, rate of perceived exertion (RPE), relative humidity inside the clothing andtolerance time were measured. Tolerance time in the chamber, sweating rate and rate ofincrease in rectal temperature were similar for all conditions (average ± SE: 1.1 ± 0.2 hr;0.65 ± 0.02 kg/hr; 1.44 ± 0.05ºC/hr, respectively), except for condition 35FI, where tolerancetime was longer (3.5 ± 0.4 hr) and sweat rate (0.46 ± 0.29 kg/hr) and rate of increase in rectaltemperature (0.40 ± 0.11ºC/hr) were lower than for the other conditions. In general, increases inTre and Tsk were larger at 45ºC than 35ºC and when the flow inside the LASA suit was “off”than when it was “on.” Increases in Tre and Tsk were larger for conditions 45FO than 45CU,and no difference was observed between conditions 45FI and 45CU. The lowest thermalcomfort ratings were observed for condition 35FI. It was concluded that the ventilation insidethe LASA suit and helmet increases the tolerance time during simulated aircrew operations at anambient temperature of 35ºC, but not at 45ºC.

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Hyperthermia; heat stress; thermal comfort; helicopter aircrew; protective clothing

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