A population-based dynamic model of human thermoregulation was expanded with control equations in... more A population-based dynamic model of human thermoregulation was expanded with control equations incorporating the individual person's characteristics (body surface area, mass, fat%, maximal O2 uptake, acclimation). These affect both the passive (heat capacity, insulation) and active systems (sweating and skin blood flow function). Model parameters were estimated from literature data. Other data, collected for the study of individual differences {working at relative or absolute workloads in hot-dry [45°C, 20% relative humidity (rh)], warm-humid [35°C, 80% rh], and cool [21°C, 50% rh] environments}, were used for validation. The individualized model provides an improved prediction [mean core temperature error, −0.21 → −0.07°C ( P< 0.001); mean squared error, 0.40 → 0.16°C, ( P < 0.001)]. The magnitude of improvement varies substantially with the climate and work type. Relative to an empirical multiple-regression model derived from these specific data sets, the analytical simu...
Journal of PHYSIOLOGICAL ANTHROPOLOGY and Applied Human Science, 2000
A model for foot skin temperature prediction was evaluated on the basis of 2 experiments on subje... more A model for foot skin temperature prediction was evaluated on the basis of 2 experiments on subjects at various environmental temperatures (light seated manual work at 10.7°C (Study 1), and a short walking period in combination with standing and sitting at +2.8°C, 11.8°C and 24.6°C (Study 2), with boots of 3 insulation levels. Insulation of the footwear was measured on a thermal foot model. Predicted and measured data showed a relatively good correlation (r=0.87) at the 2 colder conditions in Study 2. The environmental temperature of 2.8°C was not low enough at the chosen activity for a considerable foot skin temperature drop. In Study 1 the predicted temperature stayed higher for the whole exposure period and the difference between the predicted and the measured foot skin temperatures grew proportionally with time, while subsequent warmup curves at room temperature were almost parallel. In Study 1 the correlation was 0.95. However, the paired t-test showed usually significant differences between measured and predicted foot skin temperatures. The insulation values from thermal foot measurements can be used in the model calculations. Lotens' foot model is lacking activity as direct input parameter, however, the blood flow is used instead (effect through Tcore). The Lotens foot model can give reasonable foot skin temperature values if the model limitations are considered. Due to the lack of activity level input, it will be difficult to make any good estimation of foot skin temperature during intermittent exercise. The rate of the foot temperature recovery after cold exposure was somewhat overestimated in the model-the warmup of the feet of the subjects started later and was slower in the beginning of the warm-up than in the prediction. It could be useful to develop the model further by taking into consideration various wetness and activity levels.
The ability to thermoregulate typically decreases with age. This is strongly related to decreases... more The ability to thermoregulate typically decreases with age. This is strongly related to decreases in physical fitness and increases in the incidence of disabilities with ageing. The reduced thermoregulatory capacity leads to increased mortality and morbidity. Heat stroke, hypothermia, increased number of falls, and in home drowning are some of the problems that are identified to be associated with this reduced thermoregulatory capacity. As solution, using advanced technology in terms of full climate control is suggested as a short-term solution for the ill or infirm only. For longer-term solutions, limited climate control (taking away peak loads), improved housing design and proper use of modern clothing are proposed to alleviate the problems. For the clothing, better education of the elderly in the possible advantages of high tech clothing materials is proposed, as well as education to their proper way of use. Manufacturers should consider adjusting their marketing policies to include the elderly in their targeted groups.
Air layers trapped within a clothing microenvironment contribute to the thermal insulation afford... more Air layers trapped within a clothing microenvironment contribute to the thermal insulation afforded by the ensemble. Any exchange of air between the external environment and these trapped air layers results in a change in the ensemble's thermal insulation and water vapor resistance characteristics. These effects are seldom taken into account when considering the effects of clothing on human heat balance, the thermal characteristics usually being restricted to intrinsic insulation and intrinsic evaporative resistance measurements on static manikins. Environmental assessments based on these measurements alone may therefore lead to under-(or over-) estimation of thermal stress of the worker. The aim of this study was to quantify the relationship between clothing ventilation and thermal insulation properties. A one-layer, airimpermeable ensemble and a three-layer, air-permeable ensemble were tested using an articulated, thermal manikin in a controlled climate chamber (t a ϭ t r ϭ 10ЊC, P aH2O ϭ 0.73 kPa). The manikin, which was designed for thermal insulation measurements, was also equipped with a system to determine clothing ventilation. Baseline measurements of clothing ventilation (V T) and thermal insulation (total clothing insulation: I T-measured, intrinsic insulation: I cl-calculated) were made of the clothing with the manikin standing stationary in still air conditions. Increased clothing ventilation was induced when the manikin ''walked'' (walking speeds of 0.37 m/sec and 0.77 m/sec) and by increasing the environmental air speed (v a ϭ 1.0 m/sec). These increases in V T reduced I cl , this being ascribed to the increased heat transfer from the manikin skin surface to the cooler external environment due to the exchange of air between the clothing microenvironment and the external environment. Measured air exchanges were shown to have a potential heat exchange capacity of up to 17 and 161 W/m 2 for the one-and three-layer ensembles, respectively, emphasizing the need to take clothing ventilation characteristics into consideration during thermal audits and thermal risk assessments.
Human temperature regulation is based upon a physiological system 'designed' for a naked person. ... more Human temperature regulation is based upon a physiological system 'designed' for a naked person. Hence, the statement 'man is a tropical animal'. Human thermoregulation can be described as a feedback system with sensors in the body core and the skin, and effectors in the form of skin blood flow (vasoconstriction and dilation), metabolic activity (shivering), piloerection and sweating. This system on its own would provide some adjustment capabilities to various environments, but would nevertheless limit man to life in warm environments. It is the behavioural response that is the most powerful additional thermoregulatory effector in humans. People wear clothing, live in houses and have active heating and cooling systems to expand their habitat beyond the original physiological limits. Clothing is an important interface between the human and the environment. Apart from the cultural meaning of clothing it provides insulation against cold, protection against sun, wind or rain as well as protection from other environmental hazards (chemicals, mechanical). The effect of clothing on thermoregulation depends in the first place on the textile materials used. These provide thermal insulation as well as resistance against vapour (sweat) transfer. However, a garment is more than just the textile layer. Air layers included in the clothing provide additional insulation and the total thermal protection provided by a garment is for a large part based on these enclosed air layers and strongly influenced by the clothing design and fit. Clothing comfort is determined by a number of clothing properties that affect the thermal conditions at the skin. Skin temperatures and the tactile sensation of the skin (e.g. sticky moist clothing) are the main signals that are fed to the brain and lead to an overall sensation of comfort or discomfort.
Abstract Dry and evaporative heat losses of clothed people are highly affected by the air exchang... more Abstract Dry and evaporative heat losses of clothed people are highly affected by the air exchange between the clothing microclimate and the environment. This air exchange, or clothing ventilation, is highly affected by the air permeability of the fabric materials as well as the clothing design. To examine the effect of the air permeability of fabric on clothing ventilation, the ventilation rate of three suits with identical design but with different air permeability (air resistance: 0.3 and 20.5 kPa· s− 1· m− 1, and impermeable) was ...
Textile Bioengineering and Informatics Symposium Proceedings, Vols 1 and 2, 2008
This paper describes the relevance of knowledge of processes that happen at the skin for sports c... more This paper describes the relevance of knowledge of processes that happen at the skin for sports clothing design. It looks at skin temperature distribution while cooling, relevant e.g. to outdoor winter sports and mountaineering, at sweat distribution over the body while running, relevant e.g. to clothing designed for running in general and more particularly for exercise in warm and hot
Medicine & Science in Sports & Exercise, 1993
Clothing adds resistance to heat exchange between the wearer and the environment. If clothing-spe... more Clothing adds resistance to heat exchange between the wearer and the environment. If clothing-specific heat exchange coefficients are known, a combined rational/empirical approach can be used to describe thermal exchange between clothed humans and the environment. However, during exercise these coefficients--typically calculated using thermal manikins--change, primarily due to wetting of the fabric during intense sweating and body movement. A procedure is described that allows for the simultaneous determination of both total insulation (IT) and resistance to water vapor permeation (Re) on exercising clothed subjects without the need to directly measure skin water vapor pressure or continuously weigh the subjects. Two tests are performed by each subject in each clothing ensemble. In one test, ambient water vapor pressure (Pa) is systematically increased in stepwise fashion while dry-bulb temperature (Tdb) is held constant; in the second test protocol Pa is held constant while Tdb is increased. Heat exchange data are collected at the time at which core temperature is forced out of equilibrium by the environment (according to the assumption that heat production is balanced by heat loss immediately prior to this critical environmental limit). Previous studies using similar approaches have typically estimated IT a priori and used this value in the subsequent derivation of Re for each clothing ensemble or condition tested. In the proposed method, IT and Re are derived from the solution of two simultaneous equations based on heat balance data from both tests. This paper describes and critiques this methodology via an error analysis, and compares the coefficients obtained with those from similar trials using other physiological and nonphysiological approaches.
The ability to increase skin blood flow is an important mechanism for transferring heat from the ... more The ability to increase skin blood flow is an important mechanism for transferring heat from the body core to the skin for dissipation. 2. During exercise, skin blood flow is typically 20-40% lower in men and women aged 55 and over (compared with 20-30 years old) at a given body core temperature. Yet criterion measures of heat tolerance (changes in core temperature, heat storage) often show minimal or no age-related alterations. From a series of studies conducted in our laboratory over the past 5 years, the following conclusions can be drawn. 3. When fit healthy older subjects are matched with younger subjects of the same gender, size and body composition, Vo~m~, acclimation state, and hydration level, age-related differences in skin blood flow are evident. However, these differences often do not translate into "poorer" heat tolerance or higher core temperatures. 4. The larger core-to-skin thermal gradient maintained by the older individuals allows for effective heat transfer at lower skin blood flows. 5. Furthermore, there is an increased coefficient of variation for thermoregulatory response variables with increasing age. 6. Despite differences in the mechanisms underlying thermoregulation, true thermal tolerance is less a function of chronological age than of functional capacity and physiological health status. 7. While this conclusion is based primarily on cross-sectional studies, it is supported by the results of more recent studies using multiple regression analyses. 8. Implicit in this conclusion is the notion that thermal tolerance, at any age, is a modifiable individual characteristic.
Investigating claims that a clothed person's mass loss does not always represent their evapor... more 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°C in ambient temperatures of 10, 20, and 34°C with constant vapor pressure (1 kPa), additional heat losses from wet skin compared with dry skin were analyzed. EVAP based on mass loss ( Emass) measurement and direct measurement of the extra heat loss by the manikin due to wet skin ( Eapp) were compared. A clear discrepancy was observed. Emass overestimated Eapp in warm environments, and both under and overestimations were observed in cool environments, depending on the clothing vapor permeability. At 34°C, apparent latent heat (λapp) of pure evaporative cooling was lower than the physical value (λ; 2,430 J/g) and reduced with increasing ...
International Journal of Clothing Science and Technology, 2006
PurposeThe aim of this study is to explore the influence of the clothing ventilation in three bod... more PurposeThe aim of this study is to explore the influence of the clothing ventilation in three body regions on the humidity of the local clothing microclimates under five work‐shirts immediately after the onset of sweating in light exercise.Design/methodology/approachThe clothing microclimate ventilations were measured at chest, back and upper arm using a manikin. Separate wear trials were performed to determine the sweat production and the humidity of the clothing microclimate at the same locations as where the ventilation was measured during light exercise.FindingsEvery shirt shows the greatest value of ventilation index (VI) for the chest and the smallest one for the upper arm. The values of VI differ remarkably at the chest among the five shirts. Comfort sensation became gradually worse as the time passed after starting exercise. There was no significant difference among the clothing conditions in mean values of rectal temperature, local skin temperatures, microclimate temperatur...
The important requirement that COST Action 730 demanded of the physiological model to be used for... more The important requirement that COST Action 730 demanded of the physiological model to be used for the Universal Thermal Climate Index was its capability of accurate simulation of the human thermophysiological responses across a wide range of relevant environmental conditions, such as conditions corresponding to the selection of all habitable climates and their seasonal changes, and transient conditions representing temporal variation of outdoor conditions. In the first part of this study available heat budget/two-node models and multi-node thermophysiological models were evaluated by direct comparison over the wide spectrum of climatic conditions. The UTCI-Fiala model predicted most reliably the average human thermal response which was showed by least deviations from physiologically plausible responses when compared to other models. In the second part of the study, this model was, therefore, subjected to extensive validation using results of human subject experiments for a range of relevant (steady-state and transient) environmental conditions. The UTCI-Fiala multi-node model proved its ability to predict adequately the human physiological response for a variety of moderate and extreme conditions represented in the COST 730 database. The mean skin and core temperatures were predicted with average root-meansquare deviations of 1.35 ± 1.00 °C and 0.32 ± 0.20 °C, respectively.
The UTCI-Fiala mathematical model of human temperature regulation forms the basis of the new UTC ... more The UTCI-Fiala mathematical model of human temperature regulation forms the basis of the new UTC Index. Following extensive validation tests, adaptations and extensions such as the inclusion of an adaptive clothing model, the model was used to predict human temperature and regulatory responses for combinations of the prevailing outdoor climate conditions. This paper provides an overview of the underlying algorithms and methods that constitute the multi-node dynamic UTCI-Fiala model of human thermal physiology and comfort. Treated topics include modelling heat and mass transfer within the body, numerical techniques, modelling environmental heat exchanges, thermoregulatory reactions of the central nervous system and perceptual responses. Other contributions of this special issue describe the validation of the UTCI-Fiala model against measured data and the development of the adaptive clothing model for outdoor climates.
The Universal Thermal Climate Index (UTCI) aimed for a one-dimensional quantity adequately reflec... more The Universal Thermal Climate Index (UTCI) aimed for a one-dimensional quantity adequately reflecting the human physiological reaction to the multi-dimensionally defined actual outdoor thermal environment. The human reaction was simulated by the UTIC-Fiala multi-node model of human thermoregulation, which was integrated with an adaptive clothing model. Following the concept of an equivalent temperature, UTCI for a given combination of wind speed, radiation, humidity and air temperature was defined as the air temperature of the reference environment, which according to the model produces an equivalent dynamic physiological response. Operationalising this concept involved (i) the definition of a reference environment with 50% relative humidity (but vapour pressure capped at 20 hPa), with calm air and radiant temperature equalling air temperature and (ii) the development of a one-dimensional representation of the *Manuscript Click here to download Manuscript: IJBM-UTCI-Broede-revised.doc Click here to view linked References 2 multivariate model output at different exposure times. The latter was achieved by principal component analyses showing that the linear combination of 7 parameters of thermophysiological strain (core, mean and facial skin temperatures, sweat production, skin wettedness, skin blood flow, shivering) after 30 min and 120 min exposure time accounted for two thirds of the total variation in the multi-dimensional dynamic physiological response. The operational procedure was completed by a scale categorising UTCI equivalent temperature values in terms of thermal stress, and by providing simplified routines for fast but sufficiently accurate calculation, which included look-up tables of pre-calculated UTCI values for a grid of all relevant combinations of climate parameters and polynomial regression equations predicting UTCI over the same grid. The analyses of the sensitivity of UTCI to humidity, radiation and wind speed showed plausible reactions as well in the heat as in the cold, and indicate that UTCI may in this regard be universally useable in the major areas of research and application in human biometeorology.
The Universal Thermal Climate Index (UTCI) was conceived as a thermal index covering the whole cl... more The Universal Thermal Climate Index (UTCI) was conceived as a thermal index covering the whole climate range from heat to cold. This would be impossible without considering clothing as the interface between the person (here the physiological model of thermoregulation) and the environment. It was decided to develop a clothing model for this application in which the following three factors were considered: 1: typical dressing behaviour in different temperatures, as observed in the field, resulting in a model of the distribution of clothing over the different body segments in relation to the ambient temperature, 2: the changes in clothing insulation and vapour resistance caused by wind and body movement, and 3: the change in wind speed in relation to the height above ground. The outcome was a clothing model that defines in detail the effective clothing insulation and vapour resistance for each of the thermo-physiological model's body segments over a wide range of climatic conditions. This paper details this model's conception and documents its definitions.
International Archives of Occupational and Environmental Health, 2002
To coordinate the work of the main European research teams in the field of thermal factors in ord... more To coordinate the work of the main European research teams in the field of thermal factors in order to develop and improve significantly the methods presently available for assessing the risks of heat disorders encountered during work in hot conditions. Method: Each item from the required sweat rate model was reviewed on the basis of the most recent literature. A database with 1,113 laboratory and field experiments, covering the whole range of hot working conditions, was assembled and used for the validation. Results: Influence of clothing ensemble on heat exchange: methods and formulas were developed that take into account the dynamic effects associated with forced convection and the pumping effect associated with body movements and exercise. Prediction of the average skin temperature: the model used in the required sweat rate standard ISO 7933 was extended to cover more severe conditions with high radiation and high humidity and different clothing and take into account the rectal temperature for the prediction of the skin temperature. Criteria for estimating acceptable exposure times in hot work environments: criteria were reviewed and updated concerning the maximum increase in core temperature and the acceptable water loss, for acclimatised and nonacclimatised subjects. These limits are intended to protect 95% of the population. Measuring strategy: a strategy was developed to assess the risks in any working situation with varying conditions of climate, metabolic rate or clothing. A detailed methodology was developed in three stages: an ''observation'' method for the recognition of the conditions that might lead to thermal stress; an ''analysis'' method for evaluating the problem and optimising the solutions; and an ''expert'' method for in-depth analysis of the working situation when needed. Validation: the different results were used to prepare a revision of the interpretation procedure proposed in the ISO standard 7933. We validated the modified approaches using the database. This involved the whole range of conditions for which the model was extended, namely conditions with high and low radiation, humidity and air velocity as well as fluctuating conditions. Based on these results, the predicted heat strain model was developed: it is presently proposed as an ISO and CEN standard.
International Archives of Occupational and Environmental Health, 2000
Objectives: To revise the criteria used in the present``Required Sweat Rate'' standard ISO 7933 (... more Objectives: To revise the criteria used in the present``Required Sweat Rate'' standard ISO 7933 (1989) for the prediction of the maximum duration of work in hot environments. Methods: Review of the literature and in particular, of the bases for the present criteria. Results: A new method is proposed, to take into account the increase in core temperature associated with activity in neutral environments. The prediction of maximum wetness and maximum sweat rates are revised, as well as the limits for maximum water loss and core temperature. Conclusion: An improved set of maximum values and limits is described, to be used in the revised version of the ISO 7933 standard. Due to the major modi®cations to the``Required Sweat Rate'' index and in order to avoid any confusion, it is suggested that the revised model be renamed the``Predicted Heat Strain'' (PHS) model.
European Journal of Applied Physiology and Occupational Physiology, 1990
An experiment was set up to quantify the relative influence of fitness, acclimatization, gender a... more An experiment was set up to quantify the relative influence of fitness, acclimatization, gender and anthropometric measures on physiological responses to heat stress. For this purpose, 12 male and 12 female subjects were exposed to a neutral [ambient temperature (Ta) 21 ° C, relative humidity (r.h. 50%)], a warm, humid (T, 34 ° C, r.h. 80%) and a hot, dry (Ta 45 ° C, r.h. 20%) climate at rest and at two exercise intensities [25%, and 45% maximal 0 2 intake (VO2max)], seated seminude in a net chair behind a cycle ergometer. Their physiological responses were recorded and the data submitted to a multiple regression analysis. It was shown that for the variance in heat storage, the percentage of body fat and the surface to mass ratio had relatively the largest influence of all the individual parameters, followed by l?O2m,x and the sweat rate versus increase in core temperature (total r2= 92%). For the skin temperature variation, the relative influence of individual parameters (sweat gain, 1102m,x) was small. For body core temperatures, individual parameters had a large influence. The largest effect was due to the percentage of fat and the surface to mass ratio, followed by the sweating setpoint and, finally, I?O2m~x (total r.2=54%-70%). For the variance in heart rate the VO2m~x was the most relevant parameter, followed by the setpoint of the sweat rate:rectal temperature relationship (total r2= 88%). Blood pressure and skin blood flow predictions were also shown to improve by the addition of individual characteristics to the model. Body surface area, l?O2m~x and the sweating setpoint were shown to have a large influence but the proportion of the variance explained by these variables was too small (r 2 < 70%) to use them as strain predictors, however. For all the predicted variables, it was shown that gender lost its influence, once l?O2m~ or anthropometric data were introduced into the prediction equation.
A population-based dynamic model of human thermoregulation was expanded with control equations in... more A population-based dynamic model of human thermoregulation was expanded with control equations incorporating the individual person's characteristics (body surface area, mass, fat%, maximal O2 uptake, acclimation). These affect both the passive (heat capacity, insulation) and active systems (sweating and skin blood flow function). Model parameters were estimated from literature data. Other data, collected for the study of individual differences {working at relative or absolute workloads in hot-dry [45°C, 20% relative humidity (rh)], warm-humid [35°C, 80% rh], and cool [21°C, 50% rh] environments}, were used for validation. The individualized model provides an improved prediction [mean core temperature error, −0.21 → −0.07°C ( P< 0.001); mean squared error, 0.40 → 0.16°C, ( P < 0.001)]. The magnitude of improvement varies substantially with the climate and work type. Relative to an empirical multiple-regression model derived from these specific data sets, the analytical simu...
Journal of PHYSIOLOGICAL ANTHROPOLOGY and Applied Human Science, 2000
A model for foot skin temperature prediction was evaluated on the basis of 2 experiments on subje... more A model for foot skin temperature prediction was evaluated on the basis of 2 experiments on subjects at various environmental temperatures (light seated manual work at 10.7°C (Study 1), and a short walking period in combination with standing and sitting at +2.8°C, 11.8°C and 24.6°C (Study 2), with boots of 3 insulation levels. Insulation of the footwear was measured on a thermal foot model. Predicted and measured data showed a relatively good correlation (r=0.87) at the 2 colder conditions in Study 2. The environmental temperature of 2.8°C was not low enough at the chosen activity for a considerable foot skin temperature drop. In Study 1 the predicted temperature stayed higher for the whole exposure period and the difference between the predicted and the measured foot skin temperatures grew proportionally with time, while subsequent warmup curves at room temperature were almost parallel. In Study 1 the correlation was 0.95. However, the paired t-test showed usually significant differences between measured and predicted foot skin temperatures. The insulation values from thermal foot measurements can be used in the model calculations. Lotens' foot model is lacking activity as direct input parameter, however, the blood flow is used instead (effect through Tcore). The Lotens foot model can give reasonable foot skin temperature values if the model limitations are considered. Due to the lack of activity level input, it will be difficult to make any good estimation of foot skin temperature during intermittent exercise. The rate of the foot temperature recovery after cold exposure was somewhat overestimated in the model-the warmup of the feet of the subjects started later and was slower in the beginning of the warm-up than in the prediction. It could be useful to develop the model further by taking into consideration various wetness and activity levels.
The ability to thermoregulate typically decreases with age. This is strongly related to decreases... more The ability to thermoregulate typically decreases with age. This is strongly related to decreases in physical fitness and increases in the incidence of disabilities with ageing. The reduced thermoregulatory capacity leads to increased mortality and morbidity. Heat stroke, hypothermia, increased number of falls, and in home drowning are some of the problems that are identified to be associated with this reduced thermoregulatory capacity. As solution, using advanced technology in terms of full climate control is suggested as a short-term solution for the ill or infirm only. For longer-term solutions, limited climate control (taking away peak loads), improved housing design and proper use of modern clothing are proposed to alleviate the problems. For the clothing, better education of the elderly in the possible advantages of high tech clothing materials is proposed, as well as education to their proper way of use. Manufacturers should consider adjusting their marketing policies to include the elderly in their targeted groups.
Air layers trapped within a clothing microenvironment contribute to the thermal insulation afford... more Air layers trapped within a clothing microenvironment contribute to the thermal insulation afforded by the ensemble. Any exchange of air between the external environment and these trapped air layers results in a change in the ensemble's thermal insulation and water vapor resistance characteristics. These effects are seldom taken into account when considering the effects of clothing on human heat balance, the thermal characteristics usually being restricted to intrinsic insulation and intrinsic evaporative resistance measurements on static manikins. Environmental assessments based on these measurements alone may therefore lead to under-(or over-) estimation of thermal stress of the worker. The aim of this study was to quantify the relationship between clothing ventilation and thermal insulation properties. A one-layer, airimpermeable ensemble and a three-layer, air-permeable ensemble were tested using an articulated, thermal manikin in a controlled climate chamber (t a ϭ t r ϭ 10ЊC, P aH2O ϭ 0.73 kPa). The manikin, which was designed for thermal insulation measurements, was also equipped with a system to determine clothing ventilation. Baseline measurements of clothing ventilation (V T) and thermal insulation (total clothing insulation: I T-measured, intrinsic insulation: I cl-calculated) were made of the clothing with the manikin standing stationary in still air conditions. Increased clothing ventilation was induced when the manikin ''walked'' (walking speeds of 0.37 m/sec and 0.77 m/sec) and by increasing the environmental air speed (v a ϭ 1.0 m/sec). These increases in V T reduced I cl , this being ascribed to the increased heat transfer from the manikin skin surface to the cooler external environment due to the exchange of air between the clothing microenvironment and the external environment. Measured air exchanges were shown to have a potential heat exchange capacity of up to 17 and 161 W/m 2 for the one-and three-layer ensembles, respectively, emphasizing the need to take clothing ventilation characteristics into consideration during thermal audits and thermal risk assessments.
Human temperature regulation is based upon a physiological system 'designed' for a naked person. ... more Human temperature regulation is based upon a physiological system 'designed' for a naked person. Hence, the statement 'man is a tropical animal'. Human thermoregulation can be described as a feedback system with sensors in the body core and the skin, and effectors in the form of skin blood flow (vasoconstriction and dilation), metabolic activity (shivering), piloerection and sweating. This system on its own would provide some adjustment capabilities to various environments, but would nevertheless limit man to life in warm environments. It is the behavioural response that is the most powerful additional thermoregulatory effector in humans. People wear clothing, live in houses and have active heating and cooling systems to expand their habitat beyond the original physiological limits. Clothing is an important interface between the human and the environment. Apart from the cultural meaning of clothing it provides insulation against cold, protection against sun, wind or rain as well as protection from other environmental hazards (chemicals, mechanical). The effect of clothing on thermoregulation depends in the first place on the textile materials used. These provide thermal insulation as well as resistance against vapour (sweat) transfer. However, a garment is more than just the textile layer. Air layers included in the clothing provide additional insulation and the total thermal protection provided by a garment is for a large part based on these enclosed air layers and strongly influenced by the clothing design and fit. Clothing comfort is determined by a number of clothing properties that affect the thermal conditions at the skin. Skin temperatures and the tactile sensation of the skin (e.g. sticky moist clothing) are the main signals that are fed to the brain and lead to an overall sensation of comfort or discomfort.
Abstract Dry and evaporative heat losses of clothed people are highly affected by the air exchang... more Abstract Dry and evaporative heat losses of clothed people are highly affected by the air exchange between the clothing microclimate and the environment. This air exchange, or clothing ventilation, is highly affected by the air permeability of the fabric materials as well as the clothing design. To examine the effect of the air permeability of fabric on clothing ventilation, the ventilation rate of three suits with identical design but with different air permeability (air resistance: 0.3 and 20.5 kPa· s− 1· m− 1, and impermeable) was ...
Textile Bioengineering and Informatics Symposium Proceedings, Vols 1 and 2, 2008
This paper describes the relevance of knowledge of processes that happen at the skin for sports c... more This paper describes the relevance of knowledge of processes that happen at the skin for sports clothing design. It looks at skin temperature distribution while cooling, relevant e.g. to outdoor winter sports and mountaineering, at sweat distribution over the body while running, relevant e.g. to clothing designed for running in general and more particularly for exercise in warm and hot
Medicine & Science in Sports & Exercise, 1993
Clothing adds resistance to heat exchange between the wearer and the environment. If clothing-spe... more Clothing adds resistance to heat exchange between the wearer and the environment. If clothing-specific heat exchange coefficients are known, a combined rational/empirical approach can be used to describe thermal exchange between clothed humans and the environment. However, during exercise these coefficients--typically calculated using thermal manikins--change, primarily due to wetting of the fabric during intense sweating and body movement. A procedure is described that allows for the simultaneous determination of both total insulation (IT) and resistance to water vapor permeation (Re) on exercising clothed subjects without the need to directly measure skin water vapor pressure or continuously weigh the subjects. Two tests are performed by each subject in each clothing ensemble. In one test, ambient water vapor pressure (Pa) is systematically increased in stepwise fashion while dry-bulb temperature (Tdb) is held constant; in the second test protocol Pa is held constant while Tdb is increased. Heat exchange data are collected at the time at which core temperature is forced out of equilibrium by the environment (according to the assumption that heat production is balanced by heat loss immediately prior to this critical environmental limit). Previous studies using similar approaches have typically estimated IT a priori and used this value in the subsequent derivation of Re for each clothing ensemble or condition tested. In the proposed method, IT and Re are derived from the solution of two simultaneous equations based on heat balance data from both tests. This paper describes and critiques this methodology via an error analysis, and compares the coefficients obtained with those from similar trials using other physiological and nonphysiological approaches.
The ability to increase skin blood flow is an important mechanism for transferring heat from the ... more The ability to increase skin blood flow is an important mechanism for transferring heat from the body core to the skin for dissipation. 2. During exercise, skin blood flow is typically 20-40% lower in men and women aged 55 and over (compared with 20-30 years old) at a given body core temperature. Yet criterion measures of heat tolerance (changes in core temperature, heat storage) often show minimal or no age-related alterations. From a series of studies conducted in our laboratory over the past 5 years, the following conclusions can be drawn. 3. When fit healthy older subjects are matched with younger subjects of the same gender, size and body composition, Vo~m~, acclimation state, and hydration level, age-related differences in skin blood flow are evident. However, these differences often do not translate into "poorer" heat tolerance or higher core temperatures. 4. The larger core-to-skin thermal gradient maintained by the older individuals allows for effective heat transfer at lower skin blood flows. 5. Furthermore, there is an increased coefficient of variation for thermoregulatory response variables with increasing age. 6. Despite differences in the mechanisms underlying thermoregulation, true thermal tolerance is less a function of chronological age than of functional capacity and physiological health status. 7. While this conclusion is based primarily on cross-sectional studies, it is supported by the results of more recent studies using multiple regression analyses. 8. Implicit in this conclusion is the notion that thermal tolerance, at any age, is a modifiable individual characteristic.
Investigating claims that a clothed person's mass loss does not always represent their evapor... more 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°C in ambient temperatures of 10, 20, and 34°C with constant vapor pressure (1 kPa), additional heat losses from wet skin compared with dry skin were analyzed. EVAP based on mass loss ( Emass) measurement and direct measurement of the extra heat loss by the manikin due to wet skin ( Eapp) were compared. A clear discrepancy was observed. Emass overestimated Eapp in warm environments, and both under and overestimations were observed in cool environments, depending on the clothing vapor permeability. At 34°C, apparent latent heat (λapp) of pure evaporative cooling was lower than the physical value (λ; 2,430 J/g) and reduced with increasing ...
International Journal of Clothing Science and Technology, 2006
PurposeThe aim of this study is to explore the influence of the clothing ventilation in three bod... more PurposeThe aim of this study is to explore the influence of the clothing ventilation in three body regions on the humidity of the local clothing microclimates under five work‐shirts immediately after the onset of sweating in light exercise.Design/methodology/approachThe clothing microclimate ventilations were measured at chest, back and upper arm using a manikin. Separate wear trials were performed to determine the sweat production and the humidity of the clothing microclimate at the same locations as where the ventilation was measured during light exercise.FindingsEvery shirt shows the greatest value of ventilation index (VI) for the chest and the smallest one for the upper arm. The values of VI differ remarkably at the chest among the five shirts. Comfort sensation became gradually worse as the time passed after starting exercise. There was no significant difference among the clothing conditions in mean values of rectal temperature, local skin temperatures, microclimate temperatur...
The important requirement that COST Action 730 demanded of the physiological model to be used for... more The important requirement that COST Action 730 demanded of the physiological model to be used for the Universal Thermal Climate Index was its capability of accurate simulation of the human thermophysiological responses across a wide range of relevant environmental conditions, such as conditions corresponding to the selection of all habitable climates and their seasonal changes, and transient conditions representing temporal variation of outdoor conditions. In the first part of this study available heat budget/two-node models and multi-node thermophysiological models were evaluated by direct comparison over the wide spectrum of climatic conditions. The UTCI-Fiala model predicted most reliably the average human thermal response which was showed by least deviations from physiologically plausible responses when compared to other models. In the second part of the study, this model was, therefore, subjected to extensive validation using results of human subject experiments for a range of relevant (steady-state and transient) environmental conditions. The UTCI-Fiala multi-node model proved its ability to predict adequately the human physiological response for a variety of moderate and extreme conditions represented in the COST 730 database. The mean skin and core temperatures were predicted with average root-meansquare deviations of 1.35 ± 1.00 °C and 0.32 ± 0.20 °C, respectively.
The UTCI-Fiala mathematical model of human temperature regulation forms the basis of the new UTC ... more The UTCI-Fiala mathematical model of human temperature regulation forms the basis of the new UTC Index. Following extensive validation tests, adaptations and extensions such as the inclusion of an adaptive clothing model, the model was used to predict human temperature and regulatory responses for combinations of the prevailing outdoor climate conditions. This paper provides an overview of the underlying algorithms and methods that constitute the multi-node dynamic UTCI-Fiala model of human thermal physiology and comfort. Treated topics include modelling heat and mass transfer within the body, numerical techniques, modelling environmental heat exchanges, thermoregulatory reactions of the central nervous system and perceptual responses. Other contributions of this special issue describe the validation of the UTCI-Fiala model against measured data and the development of the adaptive clothing model for outdoor climates.
The Universal Thermal Climate Index (UTCI) aimed for a one-dimensional quantity adequately reflec... more The Universal Thermal Climate Index (UTCI) aimed for a one-dimensional quantity adequately reflecting the human physiological reaction to the multi-dimensionally defined actual outdoor thermal environment. The human reaction was simulated by the UTIC-Fiala multi-node model of human thermoregulation, which was integrated with an adaptive clothing model. Following the concept of an equivalent temperature, UTCI for a given combination of wind speed, radiation, humidity and air temperature was defined as the air temperature of the reference environment, which according to the model produces an equivalent dynamic physiological response. Operationalising this concept involved (i) the definition of a reference environment with 50% relative humidity (but vapour pressure capped at 20 hPa), with calm air and radiant temperature equalling air temperature and (ii) the development of a one-dimensional representation of the *Manuscript Click here to download Manuscript: IJBM-UTCI-Broede-revised.doc Click here to view linked References 2 multivariate model output at different exposure times. The latter was achieved by principal component analyses showing that the linear combination of 7 parameters of thermophysiological strain (core, mean and facial skin temperatures, sweat production, skin wettedness, skin blood flow, shivering) after 30 min and 120 min exposure time accounted for two thirds of the total variation in the multi-dimensional dynamic physiological response. The operational procedure was completed by a scale categorising UTCI equivalent temperature values in terms of thermal stress, and by providing simplified routines for fast but sufficiently accurate calculation, which included look-up tables of pre-calculated UTCI values for a grid of all relevant combinations of climate parameters and polynomial regression equations predicting UTCI over the same grid. The analyses of the sensitivity of UTCI to humidity, radiation and wind speed showed plausible reactions as well in the heat as in the cold, and indicate that UTCI may in this regard be universally useable in the major areas of research and application in human biometeorology.
The Universal Thermal Climate Index (UTCI) was conceived as a thermal index covering the whole cl... more The Universal Thermal Climate Index (UTCI) was conceived as a thermal index covering the whole climate range from heat to cold. This would be impossible without considering clothing as the interface between the person (here the physiological model of thermoregulation) and the environment. It was decided to develop a clothing model for this application in which the following three factors were considered: 1: typical dressing behaviour in different temperatures, as observed in the field, resulting in a model of the distribution of clothing over the different body segments in relation to the ambient temperature, 2: the changes in clothing insulation and vapour resistance caused by wind and body movement, and 3: the change in wind speed in relation to the height above ground. The outcome was a clothing model that defines in detail the effective clothing insulation and vapour resistance for each of the thermo-physiological model's body segments over a wide range of climatic conditions. This paper details this model's conception and documents its definitions.
International Archives of Occupational and Environmental Health, 2002
To coordinate the work of the main European research teams in the field of thermal factors in ord... more To coordinate the work of the main European research teams in the field of thermal factors in order to develop and improve significantly the methods presently available for assessing the risks of heat disorders encountered during work in hot conditions. Method: Each item from the required sweat rate model was reviewed on the basis of the most recent literature. A database with 1,113 laboratory and field experiments, covering the whole range of hot working conditions, was assembled and used for the validation. Results: Influence of clothing ensemble on heat exchange: methods and formulas were developed that take into account the dynamic effects associated with forced convection and the pumping effect associated with body movements and exercise. Prediction of the average skin temperature: the model used in the required sweat rate standard ISO 7933 was extended to cover more severe conditions with high radiation and high humidity and different clothing and take into account the rectal temperature for the prediction of the skin temperature. Criteria for estimating acceptable exposure times in hot work environments: criteria were reviewed and updated concerning the maximum increase in core temperature and the acceptable water loss, for acclimatised and nonacclimatised subjects. These limits are intended to protect 95% of the population. Measuring strategy: a strategy was developed to assess the risks in any working situation with varying conditions of climate, metabolic rate or clothing. A detailed methodology was developed in three stages: an ''observation'' method for the recognition of the conditions that might lead to thermal stress; an ''analysis'' method for evaluating the problem and optimising the solutions; and an ''expert'' method for in-depth analysis of the working situation when needed. Validation: the different results were used to prepare a revision of the interpretation procedure proposed in the ISO standard 7933. We validated the modified approaches using the database. This involved the whole range of conditions for which the model was extended, namely conditions with high and low radiation, humidity and air velocity as well as fluctuating conditions. Based on these results, the predicted heat strain model was developed: it is presently proposed as an ISO and CEN standard.
International Archives of Occupational and Environmental Health, 2000
Objectives: To revise the criteria used in the present``Required Sweat Rate'' standard ISO 7933 (... more Objectives: To revise the criteria used in the present``Required Sweat Rate'' standard ISO 7933 (1989) for the prediction of the maximum duration of work in hot environments. Methods: Review of the literature and in particular, of the bases for the present criteria. Results: A new method is proposed, to take into account the increase in core temperature associated with activity in neutral environments. The prediction of maximum wetness and maximum sweat rates are revised, as well as the limits for maximum water loss and core temperature. Conclusion: An improved set of maximum values and limits is described, to be used in the revised version of the ISO 7933 standard. Due to the major modi®cations to the``Required Sweat Rate'' index and in order to avoid any confusion, it is suggested that the revised model be renamed the``Predicted Heat Strain'' (PHS) model.
European Journal of Applied Physiology and Occupational Physiology, 1990
An experiment was set up to quantify the relative influence of fitness, acclimatization, gender a... more An experiment was set up to quantify the relative influence of fitness, acclimatization, gender and anthropometric measures on physiological responses to heat stress. For this purpose, 12 male and 12 female subjects were exposed to a neutral [ambient temperature (Ta) 21 ° C, relative humidity (r.h. 50%)], a warm, humid (T, 34 ° C, r.h. 80%) and a hot, dry (Ta 45 ° C, r.h. 20%) climate at rest and at two exercise intensities [25%, and 45% maximal 0 2 intake (VO2max)], seated seminude in a net chair behind a cycle ergometer. Their physiological responses were recorded and the data submitted to a multiple regression analysis. It was shown that for the variance in heat storage, the percentage of body fat and the surface to mass ratio had relatively the largest influence of all the individual parameters, followed by l?O2m,x and the sweat rate versus increase in core temperature (total r2= 92%). For the skin temperature variation, the relative influence of individual parameters (sweat gain, 1102m,x) was small. For body core temperatures, individual parameters had a large influence. The largest effect was due to the percentage of fat and the surface to mass ratio, followed by the sweating setpoint and, finally, I?O2m~x (total r.2=54%-70%). For the variance in heart rate the VO2m~x was the most relevant parameter, followed by the setpoint of the sweat rate:rectal temperature relationship (total r2= 88%). Blood pressure and skin blood flow predictions were also shown to improve by the addition of individual characteristics to the model. Body surface area, l?O2m~x and the sweating setpoint were shown to have a large influence but the proportion of the variance explained by these variables was too small (r 2 < 70%) to use them as strain predictors, however. For all the predicted variables, it was shown that gender lost its influence, once l?O2m~ or anthropometric data were introduced into the prediction equation.
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