Physiological and Biophysical Properties of a Semipermeable Attached Hood to a Chemical Protective Garment

Abstract

An evaluation was done on a prototype 70-mil permeable hood integrated to a standard 90-mil chemical protective overgarment to verify its potential in reducing heat strain during continuous exercise. Each of 14 subjects (in two groups of seven) did treadmill exercise (heat production, M = 473 W) in six environments: at ambient air temperature (Ta) = 32°C/80 %rh/ V=l m·s-1 and 5m·s-1; T2 = 35°C / 50 %rh / V=1 m·s-1 and 5 m·s-1; and Ta = 43°C / 20 %rh / V=1 m·s-1 and 5 m·s-1. Rectal (Tre), heart rate, 3-site skin temperatures, and head temperature and dewpoint in the skin-air space underneath each hood were recorded continuously. Subjects exercised until Tre reached 39°C and/or heart rates were = 180 beats/min for 5 min. These end-points signified the endurance time limit for each subject. The 70-mil semipermeable hood integrated to a BDO gave no significant advantages compared to the standard BDO + butyl hood in reduction of heat strain, improvement in vapor permeation to a given thermal insulation, and overall extension of endurance times. Present use of a butyl hood with an appropriate respiratory mask is a preferable option because of the reduced thickness of the hood which offers augmented heat transfer at high wind speeds.

Heat strain models applicable for protective clothing systems: comparison of core temperature response

“…Thermal component evaluated from partitional calorimetry. The basic analytical form discussed may be easily calculated for coding in computers by analysis of heat-exchange properties (2,3,5) in which T re,f ϭ T re,0 ϩ 0.004 • H sk ϩ 0.0011 • Dry ϩ Evap (5) where T re,f (°C) refers to the final steady-state level at a given time interval (from an initial T re,0 ), predicted as a function of the following variables: skin heat transfer (H sk ; in W) composed of (M Ϫ W ex ) (in W), with M being a function of weight, walking velocity, grade, and terrain factors; W ex being rate of work done on an organism by a external system as a function of grade, terrain, body weight, and clothing plus equipment weight, the latter generally assessed at three wind speeds (2,5,6,17). Dry (in W) incorporates the sensible environmental heat load (R ϩ C) on the person, where 1018 HEAT STRAIN MODEL COMPARISONS Dry ϭ 6.45/I T • A D (T sk Ϫ T a ), in which total clothing thermal insulation (I T ) (assessed over a minimum of three wind speeds), body surface (A D ), and average skin-to-ambient temperature (T sk Ϫ T a ) are generally evaluated on a copper manikin in a specific garment (Table 1) (2,3).…”

“…in which LR is the Lewis relation ϭ 2.2°C/Torr (16.5 K/kPa) (2,5) that is used to evaluate, at sea level, evaporative heat transfer to radiative and convective heat transfer, respectively (LR ϭ h e /h c ); i m /I T describes the evaporative potential of a specific clothing system based on the Woodcock's factor i m to thermal insulation (I T ), and (P s,sk Ϫ P a ) is the body skin saturation vapor pressure (P s,sk ) to ambient water vapor pressure (P a ) gradient depending on an effective body surface area (A eff ) (2,3,5,6). Sweating rate and net water requirements.…”

“…Sweating rate and net water requirements. The change in T re from rest to a given time point during transients depending on metabolic activity can be determined by (3,5) and required evaporative heat loss from the heat balance equation (21) Eqs. A15-A16 in APPENDIX.…”

“…Metabolic heat production was calculated by open-circuit spirometry (5). Total body sweating rates were determined from body weight changes before and after exercise utilizing a Sauter balance (Ϯ0.005 kg).…”

“…A significant database has been collected by using human experimental studies and wide clothing systems from which predictive modeling equations can be developed for individuals working in temperate and hot environments (1,4,5,8,11,25). However, few comparisons of the results from various model outputs have ever been carried out.…”