Non-evaporative effects of a wet mid layer on heat transfer through protective clothing

Bröde, Peter; Havenith, George; Wang, Xingmei; Candas, Victor; Hartog, E.A. den; Griefahn, Barbara; Holmér, Ingvar; Kuklane, Kalev; Meinander, Harriet; Nocker, Wolfgang; Richards, Maryse H.

doi:10.1007/s00421-007-0629-y

Cited by 31 publications

(39 citation statements)

References 12 publications

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“…This was in the range reported by Brode et al (2008) (up to 9%). Kenney et al (1993) used two critical conditions at warm, humid and hot, dry environments to solve for the two unknowns in Eq.…”

Section: Discussionsupporting

confidence: 75%

“…For instance, walking at a brisk pace can nearly halve the insulation of moderately thick clothes because body movements pump air in and out of the clothing (Lotens 1989;Havenith et al 1990;Holmer et al 1999). The insulation is further reduced if the clothing becomes wet (Kenney et al 1993;Holmer and Nilsson 1995;Brode et al 2008;Havenith et al 2008). Another way to examine the thermal effects of clothing during exposures to heat stress was first proposed by Woodcock (1962).…”

Section: Introductionmentioning

confidence: 99%

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Apparent evaporative resistance at critical conditions for five clothing ensembles

et al. 2008

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A limiting factor for clothing ensembles inherent during heat stress exposures is the evaporative resistance, which can be used to compare candidate ensembles and in rational models of heat exchange. In this study, the apparent total evaporative resistance of five clothing ensembles (cotton work clothes, cotton coveralls, and coveralls made of Tyvek 1424 and 1427, NexGen and Tychem QC was estimated empirically from wear trials using a progressive heat stress protocol and from clothing insulation adjustments based on ISO 9920 (2007) and wetness. The metabolic rate was moderate at 165 W m(-2) and relative humidity was held at 50%. Twenty-nine heat-acclimated participants (20 men and 9 women) completed trials for all clothing ensembles. A general linear mixed effects model (ensemble and participants as a random effect) was used to analyze the data. Significant differences (p < 0.0001) among ensembles were observed for apparent total evaporative resistance. As expected, Tychem QC had the highest apparent total evaporative resistance at 0.033 kPa m(2) W(-1). NexGen was next at 0.017 kPa m(2) W(-1). These were followed by Tyvek 1424 at 0.015 kPa m(2) W(-1), and Tyvek 1427, Cotton Coveralls and Work Clothes all at 0.013 kPa m(2) W(-1). This wear test method improves on past methods using the progressive protocol to determine evaporative resistance by including the effects of movement, air motion and wetness on the estimate of clothing insulation. The pattern of evaporative resistance is the same as that for critical WBGTs and a linear relationship between apparent total evaporative resistance and WBGT clothing adjustment factor is suggested. With the large sample size, a good estimate of sample variance associated with progressive method can be made, where the standard error is 0.0044 kPa m(2) W(-1) with a 95% confidence interval of 0.0040-0.0050 kPa m(2) W(-1).

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Section: Discussionsupporting

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Apparent evaporative resistance at critical conditions for five clothing ensembles

et al. 2008

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“…The various effects of moisture in protective clothing have been studied more extensively in recent years [79][80][81] . Moist layers (not fully saturated) may increase the heat loss by about 5%, while increased heat loss due to the "heat pipe" effect may reach up to 40%.…”

Section: Moisture In Footwearmentioning

confidence: 99%

Protection of Feet in Cold Exposure

Kuklane

2009

Ind Health

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Safety shoes worn in cold climates need to protect the wearer from work hazards while at the same time offering thermal comfort 1) . Ordinary street shoes can do a good job of keeping feet warm and comfortable within a wide temperature range of -5 to +25˚C under normal activities and with the body's own thermal reaction and heat redistribution. However, added moisture at +15 to +20˚C in combination with low activity may easily cause local cold discomfort. Total foot comfort is determined by the interaction of socks, soles and shoes. In order to choose correct footwear for cold weather it is necessary to define what is meant by cold in various user conditions. Such an approach may also eliminate some of the conflicting requirements from the footwear properties "wish list", including mobility, protection, insulation, waterproofing, vapour permeability, durability, weight, fit, etc. 2) .Based on this approach and footwear thermal properties, cold may be divided into the three ranges: cool (above +5˚C); around the freezing point of water (+5 to -10˚C); and cold (below -10˚C). For temperatures above +5˚C no specific consideration of footwear insulation is required. Most ordinary shoes and occupational footwear have a total insulation around and above 0.20 m 2˚C /W. This insulation should be enough to keep feet warm with medium-heavy activity at temperatures down to +5˚C. The use of somewhat thicker socks (e.g. sports socks in terry cloth) does affect the situation by maintaining warmth. For this range, footwear should be chosen to keep external moisture from entering and/or to allow internal moisture to leave the footwear.The temperature range of +5 to -10˚C is the most complicated due to changing weather conditions around the freezing point of water (0˚C). In this range, considerations for footwear choice should include both protection from external moisture and the need for greater insulation.At temperatures below -10˚C there is less external moisture available to penetrate the footwear, while moisture from sweating does not easily leave footwear due to low temperatures (condensation) in the outer layers of the footwear material package. In these conditions high footwear insulation and internal moisture management properties of the materials increase in importance. Abstract: The paper summarizes the research on cold protection of feet. There exist several conflicting requirements for the choice of the best suited footwear for cold exposure. These conflicts are related to various environmental factors, protection needs and user comfort issues. In order to reduce such conflicts and simplify the choice of proper footwear the paper suggests dividing the cold into specific ranges that are related to properties and state of water and its possibility to penetrate into, evaporate from or condensate in footwear. The thermo-physiological background and reactions in foot are briefly explained, and main problems and risks related to cold injuries, mechanical injuries and slipping discussed. Footwear thermal insulation is the m...

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“…Most of the clothing was the same as used by Havenith et al (18) and Broede et al (4). Four custom-made outer garments were used, identical in design and production but of either impermeable (IMP), semipermeable (SEMI), permeable (PERM) material, or a highly permeable material (OPEN), providing four levels of vapor permeability (Table 1).…”

Section: Clothingmentioning

confidence: 99%

Evaporative cooling: effective latent heat of evaporation in relation to evaporation distance from the skin

Havenith

Bröde²,

Hartog

et al. 2013

Journal of Applied Physiology

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111

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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.

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Non-evaporative effects of a wet mid layer on heat transfer through protective clothing

Cited by 31 publications

References 12 publications

Apparent evaporative resistance at critical conditions for five clothing ensembles

Apparent evaporative resistance at critical conditions for five clothing ensembles

Protection of Feet in Cold Exposure

Evaporative cooling: effective latent heat of evaporation in relation to evaporation distance from the skin

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