Investigating claims that a clothed person's mass loss does not always represent their evaporative heat loss (EVAP), a thermal manikin study was performed measuring heat balance components in more detail than human studies would permit. Using clothing with different levels of vapor permeability and measuring heat losses from skin controlled at 34 degrees C in ambient temperatures of 10, 20, and 34 degrees C with constant vapor pressure (1 kPa), additional heat losses from wet skin compared with dry skin were analyzed. EVAP based on mass loss (E(mass)) measurement and direct measurement of the extra heat loss by the manikin due to wet skin (E(app)) were compared. A clear discrepancy was observed. E(mass) overestimated E(app) in warm environments, and both under and overestimations were observed in cool environments, depending on the clothing vapor permeability. At 34 degrees C, apparent latent heat (lambda(app)) of pure evaporative cooling was lower than the physical value (lambda; 2,430 J/g) and reduced with increasing vapor resistance up to 45%. At lower temperatures, lambda(app) increases due to additional skin heat loss via evaporation of moisture that condenses inside the clothing, analogous to a heat pipe. For impermeable clothing, lambda(app) even exceeds lambda by four times that value at 10 degrees C. These findings demonstrate that the traditional way of calculating evaporative heat loss of a clothed person can lead to substantial errors, especially for clothing with low permeability, which can be positive or negative, depending on the climate and clothing type. The model presented explains human subject data on EVAP that previously seemed contradictive.

Havenith G, Bröde P, den Hartog E, Kuklane K, Holmer I, Rossi RM, Richards M, Farnworth B, Wang X. Evaporative cooling: effective latent heat of evaporation in relation to evaporation distance from the skin. J Appl Physiol 114: 778 -785, 2013. First published January 17, 2013 doi:10.1152/japplphysiol.01271.2012.-Calculation of evaporative heat loss is essential to heat balance calculations. Despite recognition that the value for latent heat of evaporation, used in these calculations, may not always reflect the real cooling benefit to the body, only limited quantitative data on this is available, which has found little use in recent literature. In this experiment a thermal manikin, (MTNW, Seattle, WA) was used to determine the effective cooling power of moisture evaporation. The manikin measures both heat loss and mass loss independently, allowing a direct calculation of an effective latent heat of evaporation (eff). The location of the evaporation was varied: from the skin or from the underwear or from the outerwear. Outerwear of different permeabilities was used, and different numbers of layers were used. Tests took place in 20°C, 0.5 m/s at different humidities and were performed both dry and with a wet layer, allowing the breakdown of heat loss in dry and evaporative components. For evaporation from the skin, eff is close to the theoretical value (2,430 J/g) but starts to drop when more clothing is worn, e.g., by 11% for underwear and permeable coverall. When evaporation is from the underwear, eff reduction is 28% wearing a permeable outer. When evaporation is from the outermost layer only, the reduction exceeds 62% (no base layer), increasing toward 80% with more layers between skin and wet outerwear. In semi-and impermeable outerwear, the added effect of condensation in the clothing opposes this effect. A general formula for the calculation of eff was developed.

The SensorTouch thermometer performs an infrared measurement of the skin temperature above the Superficial Temporal Artery (STA). This study evaluates the validity and the accuracy of the SensorTouch thermometer. Two experiments were performed in which the body temperature was measured with a rectal sensor, with an oesophageal sensor and with the SensorTouch. After entering a warm chamber the SensorTouch underestimated the core temperature during the first 10 minutes. After that, the SensorTouch was not significantly different from the core temperature, with an average difference of 0.5 degrees C (SD 0.5 degrees C) in the first study and 0.3 degrees C (SD 0.2 degrees C) in the second study. The largest differences between the SensorTouch and the core temperature existed 15 minutes after the start of the exercise. During this period the SensorTouch was significantly higher than the core temperature. The SensorTouch did not provide reliable values of the body temperature during periods of increasing body temperature, but the SensorTouch might work under stable conditions.

The heat transferred through protective clothing under long wave radiation compared to a reference condition without radiant stress was determined in thermal manikin experiments. The influence of clothing insulation and reflectivity, and the interaction with wind and wet underclothing were considered. Garments with different outer materials and colours and additionally an aluminised reflective suit were combined with different number and types of dry and pre-wetted underwear layers. Under radiant stress, whole body heat loss decreased, i.e., heat gain occurred compared to the reference. This heat gain increased with radiation intensity, and decreased with air velocity and clothing insulation. Except for the reflective outer layer that showed only minimal heat gain over the whole range of radiation intensities, the influence of the outer garments' material and colour was small with dry clothing. Wetting the underclothing for simulating sweat accumulation, however, caused differing effects with higher heat gain in less permeable garments.

Heat strain in chemical protective clothing is an important factor in industrial and military practice. Various improvements to the clothing to alleviate strain while maintaining protection have been attempted. More recently, selectively permeable membranes have been introduced to improve protection, but questions are raised regarding their effect on heat strain. In this paper the use of selectively permeable membranes with low vapour resistance was compared to textile-based outer layers with similar ensemble vapour resistance. For textile-based outer layers, the effect of increasing air permeability was investigated. When comparing ensembles with a textile vs. a membrane outer layer that have similar heat and vapour resistances measured for the sum of fabric samples, a higher heat strain is observed in the membrane ensemble, as in actual wear, and the air permeability of the textile version improves ventilation and allows better cooling by sweat evaporation. For garments with identical thickness and static dry heat resistance, but differing levels of air permeability, a strong correlation of microclimate ventilation due to wind and movement with air permeability was observed. This was reflected in lower values of core and skin temperatures and heart rate for garments with higher air permeability. For heart rate and core temperature the two lowest and the two highest air permeabilities formed two distinct groups, but they did not differ within these groups. Based on protection requirements, it is concluded that air permeability increases can reduce heat strain levels allowing optimisation of chemical protective clothing. STATEMENT OF RELEVANCE: In this study on chemical, biological, radiological and nuclear (CBRN) protective clothing, heat strain is shown to be significantly higher with selectively permeable membranes compared to air permeable ensembles. Optimisation of CBRN personal protective equipment needs to balance sufficient protection with reduced heat strain. Using selectively permeable membranes may optimise protection but requires thorough consideration of the wearer's heat strain.