The effect of appraisers in estimating metabolic rate with the Edholm scale

A study was made of the appraisers' effect on the estimation of metabolic rate with the Edholm scale and a table of the ISO 7243 heat stress standard. The appraisers, five experienced and five inexperienced persons, estimated the metabolic rate of three different work tasks from videotapes. Analysis of variance indicated significant ( [Formula: see text] ) differences in the appraisers' recordings of the activities. The appraisers were grouped according to the similarity of the estimated values they gave. The groups thus contained both experienced and inexperienced appraisers, and it was not possible to classify the appraisers into experienced and inexperienced groups according to their earlier experience. The metabolic rates according to the Edholm scale were higher than according to the ISO 7243 table. The differences in metabolic rates given by the individual observers varied from 38 to 118 W/m(2). The variations in the estimation of metabolic rates were greater when the Edholm scale was used. This variation caused considerable variation also in the predicted mean vote, PMV index. It is recommended that the appraisers be selected carefully, because it is not possible to know whether a randomly selected appraiser is an 'average' or an 'extreme' appraiser without a test. Before conducting extensive field surveys where several appraisers estimate the metabolic rates, it would be useful to arrange training in order to calibrate the levels of the Edholm scale as well as ISO method among the appraisers because training clearly unified the estimation.     

Comparison between required clothing insulation and that actually worn by workers exposed to artificial cold

Required Clothing Insulation (IREQ) is a new thermal index submitted to the International Organisation for Standardisation (ISO) for discussion. It is designed to prevent general body cooling and is based on an analysis of heat exchanges. The thermal clothing insulation actually worn (lcl) is estimated using a new method, also submitted to ISO.

IREQ of 54 workers exposed to artificial cold (air temperature between −30° C and +10° C) was compared with lcl actually worn by these workers. The results of the present study show that, on average, the workers choose accurately lcl they need if their IREQ is below and up to 1·5 clo. Moreover, these workers prefer to wear garments which provide them with thermal comfort. If IREQ of workers is higher than 1·5–2 clo (i e, workers exposed to −20° C), it is difficult for them to increase their thermal insulation with additional garments. Although their lcl is not sufficient, there is no risk of gradual body cooling because of their continuous time exposure (CTE) which is shorter than the calculated Duration Limited Exposure (DLE). On the other hand, Wind Chill Index (WCI), which is proposed to prevent local cooling, is better adapted to prevent cold injuries than physiological thermal strain; for example, impairment of manual dexterity cannot be prevented with this index.     

Limits of and possibilities to improve the IREQ cold stress model (ISO/TR 11079). A validation study in the field

Estimated insulation (Icl) of clothing worn by workers daily exposed to air temperatures between 0 and 15 degrees C was compared with the corresponding insulation calculated for thermal neutrality using the IREQ-model (IREQneutral, ISO/TR 11079). The goal was to determine possible limitations of the applicability of the IREQ-model and to stress to necessities and possibilities to improve the model. Sixteen female and 59 male workers (16-56 yr) were monitored during their work. According to their cold stress at the workplace they were allocated to three groups (33 persons were exposed to constant temperatures of more than 10 degrees C, 32 to less than 10 degrees C, and 10 persons experienced frequent temperature changes of 13 degrees C. Another categorization concerned workload (8 persons worked at metabolic rates of less than 100 W/m2, 50 persons worked at 101-164 W/m2, and 17 worked at more than 165 W/m2, respectively). The analysis of the differences between estimated worn insulation (Icl) and calculated IREQneutral revealed that the IREQ-model applies for air temperatures up to 15 degrees C and for temperature changes of 13 degrees C (at least) but needs to be improved with respect to gender. The IREQ model does not apply sufficiently for high and largely varying workloads (165 W/m2 and more). However, these situations are beyond the currently available possibilities to protect workers adequately with conventional clothing material. A suitable short-term measure is a more even work flow by avoiding activities with very high and low metabolic rates.     

A comparison of methods for assessing the thermal insulation value of children's schoolwear in Kuwait

In this study, three methods were used to determine the thermal insulation values of different school clothing worn by 6 to 17 year old girls and boys in Kuwait classrooms for both summer and winter seasons. The different clothing ensembles' insulations were determined by 1: measurement using adult-sized versions of the clothing on thermal manikins, 2: estimations from adult clothing data obtained from the standards tables in ISO 9920 and ASHRAE 55, and 3: calculations using a regression equation from McCullough et al. (1985) that was adapted to accommodate children's sizes for ages 6-17 years. Values for the clothing area factor, f(cl), were also determined by measurement and by using a prediction equation from ISO 9920. Results in this study suggested that the clothing insulation values found from the measured and adapted data were similar to the adult's data in standards tables for the same summer and winter seasons. Further, the effect of the insulation values on the different scholars' age groups were investigated using the clothing temperature rating technique and compared to the scholars' comfort temperature found in recent field studies. Results showed that the temperature ratings of the clothing using the three methods described above are close and in agreement with the scholars' comfort temperature. Though estimated and measured f(cl) data differed, the impact on the temperature ratings was limited. An observed secular change in the children's heights and weights in the last few decades implies that, for adolescents, the children's body surface areas are similar to those of adults, making the use of adult clothing tables even more acceptable. In conclusion, this study gives some evidence to support the applicability of using adults' data in ASHRAE 55 and ISO 9920 standards to assess the thermal insulation values of different children's clothing ensembles, provided that careful selection of the garments, ensembles material and design takes place.     

Determining temperature ratings for children's cold weather clothing

This study examined the physical and physiological differences between children and adults that affect body heat generation and losses and then developed a heat loss model for determining the temperature ratings of cold weather clothing designed for use by children of various ages. The thermal insulation values of selected jackets were measured using a heated manikin dressed in two base ensembles, and the temperature ratings were calculated using the model. The results indicated that the type of garments used in the base ensemble had a major effect on jacket ensemble insulation and the predicted comfort temperature. For a given level of insulation, the temperature rating decreased as the wearer's age and activity level increased. This is probably because children have a higher surface area per unit mass ratio than adults, and they lose heat faster. However, this effect is partially offset by their higher metabolic rates.     

Effect of physical activity and air velocity on the thermal insulation of clothing

Abstract

Intrinsic thermal clothing insulation and surface air insulation were measured on human subjects by the use of indirect calorimetry. Four male clothing ensembles (0-1-1 -8 clo) and three female clothing ensembles (0-2-1-2 clo) were investigated. Using the standing position as a reference, the influence of sitting, bicycling (40r.p.m., 20 W), walking (3-75 km hour^?1) and of light packing work on the thermal insulation was studied. The influence of an air velocity of 11ms^?1 on thermal insulation during the standing and walking conditions was investigated. The results showed that: (i) intrinsic clothing insulation was maximal in the standing position. It was reduced by 8-18% in the seated position and by 30-50% during bicycling and walking. An air velocity of 11ms^?1 did not influence the intrinsic clothing insulation during walking, but decreased it by 18% in the standing position; (ii) surface air insulation varied with activity and air velocity, but not with clothing. It was increased by up to 25% in the seated position, reduced by 7-26% during bicycling and by 30-50% during walking. An air velocity of 11 ms-1 reduced the surface air insulation by 50% in the standing position and 30% during walking.     

The effect of unevenly distributed thermal stimuli on the sensation of warmth and coolness

Combinations of clothing provide different degrees of thermal insulation for various parts of the body. The effect of this uneven thermal insulation on general comfort is examined by using experimental clothing which could provide varying degrees of thermal resistance. The relationship between skin temperature and sensation was found to be approximately linear when the exposed areas were not large, and that clothing of the same thermal resistance can yield different sensations depending on the parts of the body involved.     

Assessment of cold stress in terms of required clothing insulation—IREQ

A heat exchange model has been developed, by which the thermal stress associated with work in cold environments can be evaluated. Based on measurements of air temperature, mean radiant temperature, humidity and air velocity and measurements or estimates of activity level (energy metabolism) the model calculates a clothing insulation (IREQ) required to maintain body heat balance. IREQ may be regarded as an index of cold stress, and the value for IREQ specifies the insulation to be provided by clothing under given conditions, in addition to the insulation of the boundary air layer. IREQ, hence, may serve as a guideline for selection of appropriate clothing in cold environments. Basic insulation values of clothing (I_cI) measured with thermal manikins can be used for this purpose, but need to be corrected to account for the effect of body motion, posture, wind penetration and moisture absorption before a comparison is made with IREQ.     

Wearer related performance standards for conditioned clothing

Abstract

Estimates, based on American experience of work in the heat, indicate that in the UK, half a million workers or more may be working in thermally uncomfortable and stressfully hot environments. In addition, many will be experiencing cold working conditions and associated discomfort. The role of protective clothing as one of the factors involved in imposing thermal stress is emphasized.

One method of thermal stress control is to provide conditioned garments which warm or cool the wearer as required. The use of ‘air supplied’ garments for cooling is specifically dealt with and the methods of defining their performance reviewed. The application of the concept of ‘per cent wetted skin surface area’ is discussed as one method of defining the performance of air ventilated garments if thermal comfort cannot be achieved. The use of low pressure air for ventilating garments is proposed. The performance of such a system employing a small battery powered blower is defined in terms of the wearers work rate and supply air temperature and volume using the wetted surface area concept. The necessary steps to be taken by manufacturers if they are to develop the market for such conditioned garments are outlined.     

3D quantification of microclimate volume in layered clothing for the prediction of clothing insulation

Garment fit and resultant air volume is a crucial factor in thermal insulation, and yet, it has been difficult to quantify the air volume of clothing microclimate and relate it to the thermal insulation value just using the information on the size of clothing pattern without actual 3D volume measurement in wear condition. As earlier methods for the computation of air volume in clothing microclimate, vacuum over suit and circumference model have been used. However, these methods have inevitable disadvantages in terms of cost or accuracy due to the limitations of measurement equipment. In this paper, the phase-shifting moiré topography was introduced as one of the 3D scanning tools to measure the air volume of clothing microclimate quantitatively. The purpose of this research is to adopt a non-contact image scanning technology, phase-shifting moiré topography, to ascertain relationship between air volume and insulation value of layered clothing systems in wear situations where the 2D fabric creates new conditions in 3D spaces. The insulation of vests over shirts as a layered clothing system was measured with a thermal manikin in the environmental condition of 20 degrees C, 65% RH and air velocity of 0.79 m/s. As the pattern size increased, the insulation of the clothing system was increased. But beyond a certain limit, the insulation started to decrease due to convection and ventilation, which is more apparent when only the vest was worn over the torso of manikin. The relationship between clothing air volume and insulation was difficult to predict with a single vest due to the extreme openings which induced active ventilation. But when the vest was worn over the shirt, the effects of thickness of the fabrics on insulation were less pronounced compared with that of air volume. In conclusion, phase-shifting moiré topography was one of the efficient and accurate ways of quantifying air volume and its distribution across the clothing microclimate. It is also noted that air volume becomes more crucial factor in predicting thermal insulation when clothing is layered.     

Pumping effects on thermal insulation of clothing worn by human subjects

This study was undertaken in order to analyse the importance of the pumping effect on clothing's thermal insulation. To enhance differences in heat exchanges due to the pumping effect, two sets of condition were fixed, minimizing either the convective or the radiative heat transfers. The results showed that: (i) the clothing insulation determined on a manikin, even if he is moving, is larger than the resultant clothing insulation for living subjects; (ii) the insulation is not the same for radiant heat or cold as for convective heat or cold;(iii) the pumping effect can increase or decrease the resultant clothing insulation; (iv) the clothing insulation is smaller in warmer conditions thanin cooler ones; (v) it becomes necessary to make a definite distinction between several kinds of clothing insulation; intrinsic or basic insulation against radiation and convection; effective insulation against radiation and convection taking into account only the heat flowing through the clothing fabric; resultant insulation taking into account the magnitude of the pumping effect when clothing is worn by living subjects     

Clothing and thermal environments. Field studies on industrial work in cool conditions

Thermal environmental factors, heart rate, skin temperatures and thermal sensation votes were recorded in 19 workers in different types of cool environment industries. 45 workers from the same workplaces completed questionnaires. Transient thermal conditions were prevalent. After exercise chill, progressive cooling of the body during the working day, and cooling of hands and feet were general problems. Local cooling of certain body areas was found to be a trade-specific problem. Commonly used work clothing was insufficient for thermal comfort. Proposals for a more suitable choice of work clothing are given.     

Effect of posture positions on the evaporative resistance and thermal insulation of clothing

Evaporative resistance and thermal insulation of clothing are important parameters in the design and engineering of thermal environments and functional clothing. Past work on the measurement of evaporative resistance of clothing was, however, limited to the standing posture with or without body motion. Information on the evaporative resistance of clothing when the wearer is in a sedentary or supine posture and how it is related to that when the wearer is in a standing posture is lacking. This paper presents original data on the effect of postures on the evaporative resistance of clothing, thermal insulation and permeability index, based on the measurements under three postures, viz. standing, sedentary and supine, using the sweating fabric manikin-Walter. Regression models are also established to relate the evaporative resistance and thermal insulation of clothing under sedentary and supine postures to those under the standing posture. The study further shows that the apparent evaporated resistances of standing and sedentary postures measured in the non-isothermal condition are much lower than those in the isothermal condition. The apparent evaporative resistances measured using the mass loss method are generally lower than those measured using the heat loss method due to moisture absorption or condensation within clothing. STATEMENT OF RELEVANCE: The thermal insulation and evaporative resistance values of clothing ensembles under different postures are essential data for the ergonomics design of thermal environments (e.g. indoors or a vehicle's interior environment) and functional clothing. They are also necessary for the prediction of thermal comfort or duration of exposure in different environmental conditions.     

Design of functional work clothing for meat-cutters

The aim of this study was to design new functional work clothing for meat-cutters, paying particular attention to the metabolic requirements of the work and the thermal and general working conditions in slaughterhouses. On the basis of the results of the pilot study (review of the literature, questionnaires and interviews, work analysis, physiological measurements) different types of work clothing were designed for prolonged used during normal work in meat cutting. Physical material tests and measurements of thermal insulation values (l(cl)), and the follow-up of clothing maintenance were carried out. Further modifications and evaluations of work clothing were based on the opinions of meat-cutters and on the physiological trials in slaughterhouses. The final assembly of work clothing consists of three pieces (cotton/polyester): an apron, trousers with extra insulation in the lower back, and a work coat with extra insulation in the neck and shoulders, and at the wrists. The sleeves are protected against moisture by special textile material. The thermal insulation of this new set of work clothing together with long sleeved and legged underwear is 1.3 clo and it proved to be sufficient for thermal comfort in moderate work in an air temperature of 10 degrees C.     

Thermal responses at three low ambient temperatures: Validation of the duration limited exposure index

The objective of the study was to validate the DLE (duration limited exposure) index, which provides a method to determine acceptable time limits when, in a cold environment, clothing insulation is not sufficient to protect the wearer from body cooling. The thermal responses of ten male subjects dressed in winter clothing to −6, −14 and −22°C during very light exercise were studied. The individual variation of peripheral temperature responses was large. The majority of the subjects stated that they would accept the exposure once a day, but not continuously. DLE was on the ‘safe side' according to the body net heat debt and rectal temperature, but at the same time it allowed for low skin temperatures, especially of the extremities at low ambient temperatures. At predicted time limits, the mean skin temperature criteria of DLE suggested in the ISO document ISO/TR 11079 were not met at −14 and −22°C. Introduction of limit criteria for extremity cooling in prediction models would render a more complete assessment of cold stress.Relevance to industrySince the protective clothing worn by the worker is not always sufficient for the actual low ambient temperature there is a need for accurate predictions of exposure time.     

A quasi-physical model for predicting the thermal insulation and moisture vapour resistance of clothing

Based on the improved understanding of the effects of wind and walking motion on the thermal insulation and moisture vapour resistance of clothing induced by air ventilation in the clothing system, a new model has been derived based on fundamental mechanisms of heat and mass transfer, which include conduction, diffusion, radiation and natural convection, wind penetration and air ventilation. The model predicts thermal insulation of clothing under body movement and windy conditions from the thermal insulation of clothing measured when the person is standing in the still air. The effects of clothing characteristics such as fabric air permeability, garment style, garment fitting and construction have been considered in the model through the key prediction parameters. With the new model, an improved prediction accuracy is achieved with a percentage of fit being as high as 0.96.     

Performance enhancement of hybrid personal cooling clothing in a hot environment: PCM cooling energy management with additional insulation

A novel design of personal cooling clothing incorporating additional insulation sandwiched between phase change materials (PCMs) and clothing outer layer is proposed. Performance of four personal cooling systems including clothing with only PCMs, clothing with PCMs and insulation (PCM?+?INS), clothing with PCMs and ventilation fans (HYB), and clothing with PCMs, ventilation fans and insulation (HYB?+?INS) was investigated. Effect of additional insulation on clothing cooling performance in terms of human physiological and perceptual responses was also examined. Human trials were carried out in a hot environment (i.e. 36?°C, RH = 59%). Results showed that significantly lower mean skin/torso temperatures were registered in HYB?+?INS as compared to HYB. In contrast, no significant effect of the use of insulation on both skin and body temperatures between PCM and PCM?+?INS was observed. Also, no significant difference in thermal sensations, thermal comfort, and skin wetness sensation was registered between cooling systems with and without additional insulation.

Practitioner Summary: Hybrid personal cooling clothing has shown the ability to provide a relatively cool microclimate around the wearer’ body while working in hot environments. The present work addresses the importance of cooling energy saving for PCMs in a hot environment. This work contributes to optimising cooling performance of hybrid personal cooling systems.     

Layering garments during rest and exercise in the cold (8°C): wearer responses and comparability with selected fabric properties

How garments contribute to performance of the clothing system during wear is of interest, as is understanding the value of using fabric properties to inform end-use characteristics. To investigate the influences of layering upper-body garments, four fabrics were used to construct two first-layer garments (wool and polyester) and two outer-layer garments (wool and membrane laminate). Over six sessions, 10 moderately trained males wore each first-layer garment as a single layer and in combination with each outer-layer garment while resting, running and walking in cold environmental conditions (8 ± 1°C, 81 ± 4% RH). Here, the type of garment arrangement worn (fabric type or number of layers) had little influence on heart rate, core body temperature and change in body mass. Weighted mean covered skin temperature was warmer and weighted mean next-to-skin vapour pressure was typically higher (following the onset of exercise) with two layers versus one. Differences among fabrics for individual properties were typically overstated compared to differences among corresponding garments for physiological and psychophysical variables under the conditions of this study. These findings inform the interpretation of particular fabric properties and highlight issues to be acknowledged during development/refinement of fabric test methods.

Practitioner Summary: We examined the way in which selected fibre, fabric and garment (layering) characteristics contribute to performance of the clothing system during wear under cold conditions. Selected properties of the constituent fabrics were found to provide limited insight into how garments perform during wear under the conditions of this study.