An experimental apparatus was developed to measure the response time of very ne thermocouples in air. Thermocouple wire size of 0.005 cm in diameter was used. The experiment was performed for air velocities ranging from 0 to 4.11 m/s and small changes in temperature ranging from 24 to 38 C. These experimental conditions were selected to simulate human respiratory conditions. The apparatus produced repeatable square waves and allowed change in direction of temperature gradient without dif culty. The experiment was carried out for both cooling (going from hot to cold) and heating (going from cold to hot) of the thermocouple. Thermocouple response times 54 3 ms when the thermocouple moved from hot to cold and 56 4 ms when moving from cold to hot. Conduction along thermocouple wire and radiation effects were shown to negligibly affect response times. The effects of the temperature change for small increments and direction of the gradient were also found to be insigni cant. There was a positive correlation between air velocity and the time response of a thermocouple. This technique allows investigators a means of assessing data acquisition system response times in a repeatable fashion.Characterizing temperature changes in small conduits (e.g., human nasal and oral cavities) requires highly accurate and rapidly responding temperature sensors. Previously, response times for ne thermocouples used to measure airway temperatures were either not measured, see Webb [1], or the techniques used in characterizing response times were unreliable, see Ray et al. [2]. In addition, thermocouples were limited to accuracy no greater than 6 0.5 C, signi cantly less accurate than thermistors. Present availability of high-purity copper and constantan wire permit fabrication of extremely ne thermocouples capable of high-accuracy measurement rivaling that of thermistors while achieving much faster responses.The most common techniques in characterizing thermocouple response times involve submersion of the thermocouple in a liquid bath. This conventional "lag" test is usually conducted by plunging a thermocouple into a heated liquid bath. The time required to reach 63.2% of the steady-state bath temperature is considered the response
Protection afforded by a respirator filter depends on many factors, among them chemical or biological agent and flow rate. Filtration mechanisms, such as chemical adsorption, depend on sufficient residence time for the filter media to extract noxious agents from the airstream. Consequently, filter efficiency depends on inspiratory air velocities, among other factors. Filter designs account for this by adjusting bed depth and cross-sectional area to anticipated flow rates. Many military and commercial filters are designed and tested at 32-40 L/min. The present study investigated respiratory demand while U.S. Marines (n=32) completed operationally relevant tasks in chemical protective ensembles, including M-40 masks and C2A1 filters. Respiratory demand greatly exceeded current test conditions during the most arduous tasks: minute ventilation=96.4+/-18.9 L/min (mean+/-SD) with a maximum of 131.7 L/min observed in one subject. Mean peak inspiratory flow rate (PIF) reached 238.7+/-34.0 L/min with maximum PIF often exceeding 300 L/min (maximum observed value=356.3 L/min). The observed respiratory demand was consistent with data reported in previous laboratory studies of very heavy workloads. This study is among the few to report on respiratory demand while subjects perform operationally relevant tasking in chemical protective ensembles. The results indicate that military and industrial filters will probably encounter higher flow rates than previously anticipated during heavy exertion.
A methodology to characterize particle penetration characteristics of individual protective equipment (IPE) under elevated wind conditions was developed. Performance of a complete IPE system can be determined from the knowledge of the performance characteristics of the IPE subsystems, or components. Here, particle penetration characteristics of a cylindrical-shaped component, consisting of an outer fabric sleeve enclosing an inner appendage, were studied as a function of particle size and ambient wind conditions. A component particle penetration model was developed by combining a potential flow model to calculate flow through and around a component with a filtration model. The filtration model combines classical filtration theory with simple bench-top experiments to determine net particle penetration. The component model predictions of particle penetration through a cylindrical component suggest that its filtration performance is strongly dependent on particle size and ambient wind velocities. To test model predictions, wind-tunnel experiments were conducted over an ambient wind velocity range of 10-80 mph (5-40 m s −1 ) and particle diameter range of 10 nm to 2 µm. The experimental results validated model predictions of particle penetration through a cylindrical component. The component model can be extended to model the integrated IPE system considering it to be composed of a combination of cylindrical components.
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