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.     

Using computer-based models for predicting human thermal responses to hot and cold environments

Four influential models, capable of predicting human responses to hot and cold environments and potentially suitable for use in practical applications, were evaluated by comparing their predictions with human data published previously. The models were versions of the Pierce Lab 2-node and Stolwijk and Hardy 25-node models of human thermoregulation, the Givoni and Goldman model of rectal temperature response, and ISO/DIS 7933. Experimental data were available for a wide range of environmental conditions, with air temperatures ranging from ?10 to 50°C, and with different levels of air movement, humidity, clothing and work. The experimental data were grouped into environment categories to allow examination of the effects of variables, such as wind or clothing, on the accuracy of the models' predictions. This categorization also enables advice to be given regarding which model is likely to provide the most accurate predictions for a particular combination of environmental conditions. Usually at least one of the models was able to give predictions with an accuracy comparable with the degree of variation that occurred within the data from the human subjects. The evaluation suggests that it is possible to make useful predictions of deep-body and mean skin temperature responses to cool, neutral, warm and hot environmental conditions. The models' predictions of deep-body temperature in the cold were poor. Overall, the 25-node model provided the most consistently accurate predictions. The 2-node model was often accurate but could be poor for exercise conditions. The rectal-temperature model usually overestimated deep-body temperature, although its predictions for very hot or heavy exercise conditions could be useful. The ISO model's allowable exposure times would not have protected subjects for some exercise conditions.     

Differences in wearer response to garments for outdoor activity

The performance of garments for outdoor activity was compared. Three fabrics, each in garments for the upper body, matched garment/wearer dimensions, were worn by 10 athletically 'well-trained' males under controlled conditions (hot 32 +/- 2 degrees C, 20 +/- 2% relative humidity (RH); cold 8 +/- 2 degrees C, 40 +/- 2% RH) with physical (instrumental) and sensory responses obtained during the trials. Differences in human responses to the fabrics/garments included heart rate, core temperature during run (hot, cold), rest (hot) and walk (cold), heat content of the body, humidity under garments during rest and run and time to onset of sweating. No such differences were identified for change in body mass, core temperature during walk (hot) and rest (cold), skin temperature, temperature of skin covered by the garment, humidity under the garments during walk or for any perceptions (thermal sensations, thermal comfort of torso, exertion, wetness). The garment in single jersey wool fabric performed best in both hot and cold conditions. Effects of garments on wearers are often related to properties of the fabrics from which the garments are made. This study shows that only some differences in fabric properties result in measurable thermophysiological and perceptual responses of the garment wearers and underlines the difficulty in predicting performance of garments/persons from laboratory tests on fabrics.     

Differences in wearer response to garments for outdoor activity

The performance of garments for outdoor activity was compared. Three fabrics, each in garments for the upper body, matched garment/wearer dimensions, were worn by 10 athletically ‘well-trained’ males under controlled conditions (hot 32 ± 2°C, 20 ± 2% relative humidity (RH); cold 8 ± 2°C, 40 ± 2% RH) with physical (instrumental) and sensory responses obtained during the trials. Differences in human responses to the fabrics/garments included heart rate, core temperature during run (hot, cold), rest (hot) and walk (cold), heat content of the body, humidity under garments during rest and run and time to onset of sweating. No such differences were identified for change in body mass, core temperature during walk (hot) and rest (cold), skin temperature, temperature of skin covered by the garment, humidity under the garments during walk or for any perceptions (thermal sensations, thermal comfort of torso, exertion, wetness). The garment in single jersey wool fabric performed best in both hot and cold conditions. Effects of garments on wearers are often related to properties of the fabrics from which the garments are made. This study shows that only some differences in fabric properties result in measurable thermophysiological and perceptual responses of the garment wearers and underlines the difficulty in predicting performance of garments/persons from laboratory tests on fabrics.     

A comparison of models for predicting human response to hot and cold environments

Four influential models which make predictions of human response to hot or cold environments have been described and their predictions compared. The models considered were the Givoni and Goldman prediction equations. ISO/DIS 7933, the J. B. Pierce Lab. 2-node and the Stolwijk and Hardy 25-node models of human thermoregulation. The models integrate the important environmental variables, (air temperature, mean radiant temperature, air speed and relative humidity) with subject variables (insulation of clothing worn and metabolic heal production), in order to make predictions such as core and skin temperature response and allowable exposure times. The models' predictions have been compared for a range of hot and cold environments. This comparison has shown that while for some environments the models' predictions are similar, for other environments they are very different. These differences would result in different practical decisions being made. The models should be used with caution until further evaluation for. a wide range of subjects and environmental conditions has determined the accuracy of the models and for which environments they are most appropriate.     

The effect of two kinds of T-shirts on physiological and psychological thermal responses during exercise and recovery

The aim of this study was to investigate the physiological and psychological responses during and after high-intensity exercise in a warm and humid environment in subjects wearing shirts of different fabrics. Eight healthy men exercised on two separate occasions, in random order, wearing two types of long-sleeve T-shirt: one made of polyester (PES) and the other of cotton fabric (CT). They performed three 20 min exercise bouts, with 5 min rest between each, and then rested in a chair for 60 min to recover. The ambient temperature was 25 °C and relative humidity was 60%. The exercise comprised of treadmill running at 8 km/h at 1° grade. Rectal temperature, skin temperatures at eight sites, heart rate, T-shirt mass and ratings of thermal, clothing wettedness, and shivering/sweating sensation were measured before the experiment, during the 5 min rest period after each exercise bout, and during recovery. Nude body mass was measured before the experiment and during recovery. The physiological stress index showed that the exercise produced a state of very high heat stress. Compared with exercise wearing the CT shirt, exercise wearing the PES fabric produced a greater sweating efficiency and less clothing regain (i.e., less sweat retention), but thermophysiological and subjective sensations during the intermittent high-intensity exercise were similar for both fabrics. However, skin temperature returned to the pre-exercise level faster, and the thermal and rating of shivering/sweating sensation were lower after exercise in the warm and humid environment in subjects wearing PES than when wearing the more traditional CT fabric.     

The effect of two kinds of T-shirts on physiological and psychological thermal responses during exercise and recovery

The aim of this study was to investigate the physiological and psychological responses during and after high-intensity exercise in a warm and humid environment in subjects wearing shirts of different fabrics. Eight healthy men exercised on two separate occasions, in random order, wearing two types of long-sleeve T-shirt: one made of polyester (PES) and the other of cotton fabric (CT). They performed three 20 min exercise bouts, with 5 min rest between each, and then rested in a chair for 60 min to recover. The ambient temperature was 25 °C and relative humidity was 60%. The exercise comprised of treadmill running at 8 km/h at 1° grade. Rectal temperature, skin temperatures at eight sites, heart rate, T-shirt mass and ratings of thermal, clothing wettedness, and shivering/sweating sensation were measured before the experiment, during the 5 min rest period after each exercise bout, and during recovery. Nude body mass was measured before the experiment and during recovery. The physiological stress index showed that the exercise produced a state of very high heat stress. Compared with exercise wearing the CT shirt, exercise wearing the PES fabric produced a greater sweating efficiency and less clothing regain (i.e., less sweat retention), but thermophysiological and subjective sensations during the intermittent high-intensity exercise were similar for both fabrics. However, skin temperature returned to the pre-exercise level faster, and the thermal and rating of shivering/sweating sensation were lower after exercise in the warm and humid environment in subjects wearing PES than when wearing the more traditional CT fabric.     

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.     

Evaluating functional clothing in climatic chamber tests versus field tests: a comparison of quantitative and qualitative methods in product development

For the evaluation of clothing by human beings, two different approaches can be identified- laboratory tests (i.e. climatic chamber tests) or field trials/wear trials. It has been suggested that the performance of clothing can be adequately predicted on the basis of the data obtained from climatic chamber tests and that field trials may be expendable altogether. From a product development perspective, this paper discusses the information provided by standard data collection methods and tools for the assessment of thermal comfort used in laboratory settings and compares this information with that acquired in field trials. When assessing the information provided in the laboratory test against those questions posed in a development process, the results highlight the insufficiency of objectively measurable criteria. Therefore, objective measurements alone cannot verify the adequacy of stated requirements for thermal comfort. The use of appropriate and sensitive tools for collecting subjective votes should also be noted, since small differences in thermal sensation affected the individual's preference for clothing. Exposed differences between subjects, in terms of thermophysiological as well as subjective responses, illustrate the importance of studying individual values and deviations as opposed to strict mean values for large populations in order to satisfy a potential user group. It is argued that complementary interviews form a basis for further understanding of ratings and preferences and that they should also be included in the climatic chamber evaluation 'tool box'. User satisfaction is based on a simultaneous assessment of partly opposing properties into a satisfying use value. Although laboratory test procedures can be developed and improved in relation to design issues, field evaluations must be regarded as an integrated part of an iterative development process. Only the actual use situation can provide the total spectrum of conditions on which basis requirements and/or properties can be prioritized or downgraded. This information forms the prerequisite for successful product development.     

Localized temperatures and water vapour pressures within clothing during alternate exercise/rest in the cold.

The purpose of this study was to determine the variation of localized skin temperatures, clothing surface temperatures and water vapour pressures within a clothing system when worn during alternating work/rest cycles in a cold environment. A two-layer prototype clothing system comprising underwear and a uniform was studied on eight subjects (Ta = Tr = 5 degrees C; Tdp = -3.5 degrees C; va = 0.32 m s-1; Itot = 0.24 m2 K W-1). The 2 h experiment comprised a twice-repeated bout of 40 min cycle exercise (W = 56 W m-2; M = 313 W m-2) followed by 20 min of rest (M = 62 W m-2). Esophageal, skin, clothing, and ambient temperatures, as well as dew-point temperatures near the skin, in the clothing and in the environment were monitored. In addition, evaporation of sweat and sweat accumulated in the clothing were determined. The temperatures and water vapour pressures in all clothing layers varied significantly with the human thermoregulatory responses (skin temperature, sweating) to alternating work/rest cycles. Different courses of localized corresponding temperatures and water vapour pressures indicated that various forms of heat transport and heat exchange in the skin-clothing-environment system are of significance in different body areas.     

Standards for moderate thermal environments

Recently two Draft International Standards dealing with specifications of the conditions for thermal comfort (ISO DIS 7730) and measurement procedures (ISO DIS 7726) have been approved by the International Stadardisation Organisation (ISO). The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has made a standard with similar requirements for the thermal environment (ASHRAE, 1981). To verify the requirements, measurements of different thermal parameters have to be performed. Guidelines as to how and where to measure are also given in the standards. The present paper deals mainly with the requirements and measurements that are relevant for moderate thermal environments in places of residence, offices, hospitals and light industry. For evaluation of very hot or very cold surroundings, other methods are required. Only measurements of parameters that influence the perception of the thermal surroundings are included.     

HealthSit: Designing Posture-Based Interaction to Promote Exercise during Fitness Breaks

This research was motivated by a desire to help office workers change their sedentary behavior because a prolonged sedentary posture increases the risks of developing musculoskeletal injuries and chronic diseases, thus threatening their physical and psychological well-being. Regular breaks involving low-effort physical activities are effective in reducing the adverse impacts of inactive behaviors. In this article, we present the design of a posture-based interactive system called HealthSit, which was developed to promote a short lower-back stretching exercise during work breaks. Through a within-subject study involving 30 office workers, the effectiveness of HealthSit in facilitating the stretching exercise was examined by making comparisons between an interaction-aided, a guided, and a self-directed exercise mode. We also used HealthSit as a research probe to investigate the interactivity of the system in enhancing user experience and the psychological benefits of the fitness breaks. Compared with the other two modes, the interaction-aided exercise mode significantly improved the quality of the stretching exercise and enhanced motivation and emotional state. These results confirm the effectiveness of HealthSit in supporting fitness breaks as a new workplace technology. Based on our study, a set of design implications have been derived for technology-assisted fitness work breaks.     

Physiological strains in hot-humid conditions while wearing disposable protective clothing commonly used by the asbestos removal industry

Abstract

The purpose of this study is to investigate workers' responses to work in hot-humid conditions while wearing protective clothing commonly used by the asbestos removal industry, and to evaluate the effects of resting between work bouts in a cool environment on the physiological strain. Seven male students wearing impermeable protective clothing and air masks were exposed to the following conditions for 100 min on separate days: (1) hot conditions (35°C/85%RH), (2) cool conditions (20°C/85%RH), and (3) hot/cool conditions (working in hot conditions and resting in cool conditions). After 12 min rest, the subjects worked on an ergometer (70 Watts) for 18 min. This experimental schedule was repeated three times under each environmental condition. Rectal temperature (T_π), heart rate (HR), sweat rate (SR) and discomfort sensation were recorded. Two of the subjects were not able to complete the experiment in hot conditions. The increases in T_π and HR with time were not found in cool conditions. Although T_π increased in hot/cool conditions, it was almost half of that in hot conditions. Since HR did not return to the pre-work level during recovery in hot conditions, HR during work was accompanied by increases in HR at pre-work. HR during work in hot/cool conditions was higher than that in cool conditions, HR at pre-work, however, was almost the same as that in cool conditions because of rapid recovery. The means of SR in hot and hot/cool conditions were five and four times greater than that in cool conditions, respectively. Discomfort sensation was improved by resting in cool conditions either at rest in cool conditions or during work in hot conditions. The rate of body heat storage that was calculated at the end of each work and recovery period showed that it was positive even in recovery under the hot conditions. It also presented a significant negative phase in recovery under the hot/cool conditions. Thermal stress was linked to work in protective clothing in hot-humid environments. However, the physiological strains were dramatically ameliorated by resting between work periods in a cool environment. The idea of a ‘cool room’ inside the workplace, so to reduce thermal stress, is proposed.     

Prevalence and work-related risk factors for reduced activities and absenteeism due to low back symptoms

Although quite a lot is known about the risk factors for low back symptoms (LBS), less is known about the risk factors for the consequences of LBS. A sample of 3003 men and women randomly selected from the New Zealand Electoral Roll, were interviewed by telephone about self reported physical, psychosocial, organizational, environmental factors and the consequences of LBS (i.e. self-reported reduced activities and absenteeism). The 12-month period prevalence of reduced activities and absenteeism were 18% and 9%, respectively. Lifting (OR 1.79 95% CI 1.16-2.77) increased the risk of reduced activities. Working in awkward/tiring positions (OR 2.11 95% CI 1.20-3.70) and in a cold/damp environment (OR 2.18 95% CI 1.11-4.28) increased the risk of absenteeism. Among those with LBS, reduced activities increased with working in a hot/warm environment (OR 2.14 95% CI 1.22-3.76) and absenteeism was increased with work in awkward/tiring positions (OR 2.06 95% CI 1.13-3.77), tight deadlines (OR 1.89 95% CI 1.02-3.50), and a hot/warm environment (OR 3.35 95% CI 1.68-6.68). Interventions to reduce the consequences of LBS should aim to reduce awkward/tiring positions, lifting and work in a cold/damp environment. For individuals with LBS, additional focus should be to reduce tight deadlines, and work in hot/warm environments.     

Congestion Control for Interactive Video-on-Demand over ATM

An interactive video-on-demand (IVoD) system consists of a video server and a client connected together through a high speed network. Use of interactive video-on-demand in an educational environment is very interactive because students frequently pause, fast-forward, skip and view frame-by-frame. Designing a network able to support interactivity and make efficient use of bandwidth is challenging. In this paper we evaluate the suitability of a number of congestion control schemes (based on the service categories of ATM) for carrying interactive video on demand. We have developed analytical models to evaluate and compare the various schemes. Data on interactive behaviour of students obtained from IVoD trails carried out in our laboratory have been used in the models. We show that the renegotiated constant bit rate service category has considerable potential for carrying IVoD over a high speed network, such as the asynchronous transfer mode (ATM). We also show the use of an application layer, (such as Winsock 2), by the server to limit congestion within the network.     

Comfort evaluation of maternity support garments in a wear trial

This study aims to evaluate the wear comfort of eight commercially available maternity support garments. The thermophysiological, sensory/tactile and movement comfort were assessed in a wear trial using a 19-item questionnaire. Fourteen pregnant Chinese women aged 32.3 +/- 4.2 years were recruited from a local obstetric clinic. The results show that the tested garments generally provided greater sensory comfort than thermophysiological comfort. The thermophysiological comfort was mainly influenced by the fibre contents and breathability. Significant linear relationships were found between material appearance and hand feel (r = 0.86, p < 0.001), and between non-itchiness and no red mark (r = 0.78, p < 0.001). Movement comfort was influenced by the garment type and style features. Overall, the soft, good-fit, cotton/elastane maternity brief was perceived as the best product. The findings of comfort needs in pregnant women and the effects of various garment attributes would be helpful for the development of maternity support garment design criteria that are required to satisfy critical ergonomic needs. Low back pain during pregnancy is a common and significant health problem. A maternity support garment is regarded as a convenient and safe device to stabilise the lumbar spine so as to relieve pain. However, patient compliance is likely to be affected by discomfort and inconvenience. The results of this study provide guidance for the optimal design of maternity support clothing.     

A shirt containing multistage phase change material and active cooling components was associated with increased exercise capacity in a hot,humid environment

Recent advances in clothing design include the incorporation of phase change materials (PCM) and other active cooling components (ACC) to provide better body heat dissipation. The purpose of this study was to determine the effect of wearing a shirt containing multistage PCM/ACC on exercise capacity at low (5.0), moderate–high (7.5) and extreme (9.0) levels of the physiological strain index (PSI). Fourteen individuals tested two shirts (control vs. cooling) during 45-min of interval running in a hot, humid (35 ± 1 °C; 55 ± 6% RH) environment. The cooling shirt resulted in an 8% improvement in exercise capacity at a PSI of 7.5 (p < 0.05). The observed increase in exercise capacity would likely translate to a significant improvement in exercise performance. More research is needed to determine a best practice approach for the use of cooling clothing as a counter to exercise-induced heat exposure.

Practitioner Summary: In this report, we demonstrate that when forced to exercise in a hot, humid environment, an individual’s exercise capacity may increase by as much as 8% when wearing a shirt composed of multistage phase change material and active cooling components.     

The effects of short‐term and long‐term exposure to extreme cold environment on the body’s physiological responses: An experimental study

There is little epidemiological data to make reliable conclusions about the effects of exposure to cold on the body’s physiological responses. The current study aimed to address this lacuna in the available research. The study sample consisted of 50 outdoor mechanic workers as a case group and 15 staff members as a control group used in the outdoor automechanic workshops. Air environmental factors, including dry‐bulb temperature and air velocity, were measured by the portable hot wire thermo anemometer in the workstation of each subject. The body’s physiological responses were also measured during daily activities in accordance with ISO 9886. Using Semmes–Weinstein monofilament, touch sensory tests were conducted for determining hands’ sensorineural functions. The baseline measurements showed the mechanic workers had lower finger sensation levels and finger skin temperatures than the control group (p < 0.05). This may be attributed to long‐term exposure to acute cold air during cold seasons. However, after short‐term exposure to extreme cold environment, the mechanic workers showed lower losses in finger skin temperatures and finger sensation levels than the control group ( p < 0.05). The findings confirmed that prolonged localized cold exposure among mechanic workers can result in localized habituation of vasoconstrictor responses.