A modelling framework for local thermal comfort assessment related to bicycle helmet use.

Thermal discomfort due to accumulated sweat increasing head skin wettedness may contribute to low wearing rates of bicycle helmets. Using curated data on human head sweating and helmet thermal properties, a modelling framework for the thermal comfort assessment of bicycle helmet use is proposed. Local sweat rates (LSR) at the head were predicted as the ratio to the gross sweat rate (GSR) of the whole body or by sudomotor sensitivity (SUD), the change in LSR per change in body core temperature (Δtre). Combining those local models with Δtre and GSR output from thermoregulation models, we simulated head sweating depending on the characteristics of the thermal environment, clothing, activity, and exposure duration. Local thermal comfort thresholds for head skin wettedness were derived in relation to thermal properties of bicycle helmets. The modelling framework was supplemented by regression equations predicting the wind-related reductions in thermal insulation and evaporative resistance of the headgear and boundary air layer, respectively. Comparing the predictions of local models coupled with different thermoregulation models to LSR measured at the frontal, lateral and medial head under bicycle helmet use revealed a large spread in LSR predictions predominantly determined by the local models and the considered head region. SUD tended to overestimate frontal LSR but performed better for lateral and medial head regions, whereas predictions by LSR/GSR ratios were lower and agreed better with measured frontal LSR. However, even for the best models root mean squared prediction errors exceeded experimental SD by 18-30%. From the high correlation (R > 0.9) of skin wettedness comfort thresholds with local sweating sensitivity reported for different body regions, we derived a threshold value of 0.37 for head skin wettedness. We illustrate the application of the modelling framework using a commuter-cycling scenario, and discuss its potential as well as the needs for further research.

Local effects of printed logos and reflective striping fixed to firefighter clothing material packages under low radiation exposure.

Notifications that related 1st degree burns to reflective striping and impermeable clothing elements did reach the investigators, while the mechanisms behind this phenomenon are still unclear. Material tests for thermal and evaporative resistance, and for heat transmission under dry and wet conditions at low radiation levels were done to evaluate the performance of protective clothing with and without printed logos or reflective striping. The results under the specified conditions showed reduction of heat loss capacity under impermeable elements from dry to wet conditions. Reflective surfaces, even when more impermeable, showed still lower heat transmission through the textile package than materials without striping under tested moisture and radiation combinations. It can be expected that the reported 1st degree burns were related to clothing design and tightness/fit rather than to reflective striping. However, due to the fine balance between clothing thermal and evaporative resistance, outer material emissivity, moisture quantity and location in clothing and applied radiation level, a different setup could lead to different results.

A Database of Static Thermal Insulation and Evaporative Resistance Values of Dutch Firefighter Clothing Items and Ensembles.

The rescue operations' environment can impair firefighters' performance and increase the risk of injuries, e.g., burns and hyperthermia. The bulk and carried weight of heavy protection contributes to lower physical performance, higher metabolic load and internal body heat production. For recommending optimal protection for the tasks and incident scenarios, knowledge of clothing thermal properties is needed. However, detailed data on firefighter protective clothing systems are not available. The aim of the study was to provide scientific background and a dataset that would allow for validation of thermo-physiological models for task-specific conditions of rescue work. Thermal insulation of 37 single items and their variations and 25 realistic protective clothing ensembles were measured on a thermal manikin. Twelve (12) ensembles that evenly covered the whole insulation range were selected for evaporative resistance testing. The equations for summing up individual item's insulation to ensemble insulation and calculating clothing area factor were derived from the dataset. The database of a firefighter clothing system was created. In addition, the local and regional thermal properties of the clothing ensembles were provided for use in future validation of advanced thermo-physiological models for rescue worker exposure predictions and for designing decision aid tools.

The Protective Performance of Process Operators' Protective Clothing and Exposure Limits under Low Thermal Radiation Conditions.

During the early stage of a fire, a process operator often acts as the first responder and may be exposed to high heat radiation levels. The present limit values of long- (>15 min) and short-term exposure (<5 min), 1.0 and 1.5 kW/m2, respectively, have been set using physiological models and manikin measurements. Since human validation is essentially lacking, this study investigated whether operators' protective clothing offers sufficient protection during a short-term deployment. Twelve professional firefighters were exposed to three radiation levels (1.5, 2.0, and 2.5 kW/m2) when wearing certified protective clothing in front of a heat radiation panel in a climatic chamber (20 °C; 50% RH). The participants wore only briefs (male) or panties and a bra (female) and a T-shirt under the operators' clothing. Skin temperatures were continuously measured at the chest, belly, forearm, thigh, and knee. The test persons had to stop if any skin temperature reached 43 °C, at their own request, or when 5 min of exposure was reached. The experiments showed that people in operators' clothing can be safely exposed for 5 min to 1.5 kW/m2, up to 3 min to 2.0 kW/m2, and exposure to 2.5 kW/m2 or above must be avoided unless the clothing can maintain an air gap.

Common clothing area factor estimation equations are inaccurate for highly insulating (Icl>2 clo) and non-western loose-fitting clothing ensembles.

The aim of this study was to evaluate the equations for calculating the clothing area factor (fcl) used in the standards based on data sets of clothing ensembles, that are meant to provide thermal comfort over a wide range of climatic conditions from hot summer days to extremely cold winter. Over 10 equations for fcl calculations were selected from the international standards and the literature. At first a theoretical comparison based on a range of insulation values was performed. Then the data sets were used to compare the equations and measurements on real clothing systems. Most of the fcl calculation equations do give reasonably good results for western type and industrial clothing with basic insulation (Icl) up to 1.5 clo. Above the Icl of 2 clo, the error in the calculations based on traditional equations increases considerably and they overestimate fcl. Some new equations were suggested for modern clothing systems. Oppositely, for non-western clothing (for hot climate), the available equations did give good match only for very light clothing sets and commonly underestimated the real fcl. For such sets and and fashion clothes their own equations maybe needed, that count for various design aspects, e.g. fit, draping etc.

Validation of ISO 9920 clothing item insulation summation method based on an ambulance personnel clothing system.

This study aimed to validate the summation methods suggested by ISO 9920. Twenty seven items from an ambulance personnel clothing system were selected for testing. The basic insulation of each garment item (Iclu) was calculated based on the thermal manikin tests. More than 100 realistic clothing combinations were compiled and basic insulation (Icl) of these ensembles was calculated according to ISO 9920. These were ranked after the calculated insulation, and 14 sets covering insulation from 0.63 to 3.33 clo were measured on the thermal manikin for acquiring the basic clothing insulation (Icl). Regression analysis was used to compare the summed and measured Icl values. The difference between values varied from -18 to 12%. The highest percentual difference was for the lightest clothing sets, while the absolute differences were similar over the whole insulation range ranging between -0.17 to 0.18 clo with an average difference of 0.02 clo (-0.16%). All basic insulation values stayed very close to the line of identity (R2=0.98). The summation equation gave, in the case of this ambulance clothing system, very close results to the measured values. This encourages evaluating and selecting protective clothing combinations for thermal comfort based on individual item measurements.

Insulation and Evaporative Resistance of Clothing for Sugarcane Harvesters and Chemical Sprayers, and Their Application in PHS Model-Based Exposure Predictions.

Many workers are exposed to heat stress that can be exacerbated by the type of clothing they wear. The resulted heat strain can lead to short or long-term heat-related disorders. This study aimed to measure clothing properties of sugarcane field workers and evaluate the heat strain by an international standard, predicted heat strain model (PHS). The clothing thermal insulation and evaporative resistance values of sugarcane cutter and chemical sprayer outfits were acquired for the whole body, body regions and specific body parts via thermal manikin measurements. The detailed clothing insulation values of body parts can be utilized in advanced thermo-physiological models, while in this study, the values for the whole body together with weather data were used in PHS. Estimated duration limited exposure times (DLE) for an hour-by-hour prediction over a workday and for a range of high humidity scenarios were calculated. Such evaluation tools can be used for risk assessment and management to support organizational measures and prepare equipment and materials in the case of hot weather events in order to avoid dehydration and other heat-related disorders.

Is There a Need to Integrate Human Thermal Models with Weather Forecasts to Predict Thermal Stress?

More and more people will experience thermal stress in the future as the global temperature is increasing at an alarming rate and the risk for extreme weather events is growing. The increased exposure to extreme weather events poses a challenge for societies around the world. This literature review investigates the feasibility of making advanced human thermal models in connection with meteorological data publicly available for more versatile practices and a wider population. By providing society and individuals with personalized heat and cold stress warnings, coping advice and educational purposes, the risks of thermal stress can effectively be reduced. One interesting approach is to use weather station data as input for the wet bulb globe temperature heat stress index, human heat balance models, and wind chill index to assess heat and cold stress. This review explores the advantages and challenges of this approach for the ongoing EU project ClimApp where more advanced models may provide society with warnings on an individual basis for different thermal environments such as tropical heat or polar cold. The biggest challenges identified are properly assessing mean radiant temperature, microclimate weather data availability, integration and continuity of different thermal models, and further model validation for vulnerable groups.

Heat Stress in Indoor Environments of Scandinavian Urban Areas: A Literature Review.

Climate change increases the risks of heat stress, especially in urban areas where urban heat islands can develop. This literature review aims to describe how severe heat can occur and be identified in urban indoor environments, and what actions can be taken on the local scale. There is a connection between the outdoor and the indoor climate in buildings without air conditioning, but the pathways leading to the development of severe heat levels indoors are complex. These depend, for example, on the type of building, window placement, the residential area's thermal outdoor conditions, and the residents' influence and behavior. This review shows that only few studies have focused on the thermal environment indoors during heat waves, despite the fact that people commonly spend most of their time indoors and are likely to experience increased heat stress indoors in the future. Among reviewed studies, it was found that the indoor temperature can reach levels 50% higher in °C than the outdoor temperature, which highlights the importance of assessment and remediation of heat indoors. Further, most Heat-Health Warning Systems (HHWS) are based on the outdoor climate only, which can lead to a misleading interpretation of the health effects and associated solutions. In order to identify severe heat, six factors need to be taken into account, including air temperature, heat radiation, humidity, and air movement as well as the physical activity and the clothes worn by the individual. Heat stress can be identified using a heat index that includes these six factors. This paper presents some examples of practical and easy to use heat indices that are relevant for indoor environments as well as models that can be applied in indoor environments at the city level. However, existing indexes are developed for healthy workers and do not account for vulnerable groups, different uses, and daily variations. As a result, this paper highlights the need for the development of a heat index or the adjustment of current thresholds to apply specifically to indoor environments, its different uses, and vulnerable groups. There are several actions that can be taken to reduce heat indoors and thus improve the health and well-being of the population in urban areas. Examples of effective measures to reduce heat stress indoors include the use of shading devices such as blinds and vegetation as well as personal cooling techniques such as the use of fans and cooling vests. Additionally, the integration of innovative Phase Change Materials (PCM) into facades, roofs, floors, and windows can be a promising alternative once no negative health and environmental effects of PCM can be ensured.

Surveillance of work environment and heat stress assessment using meteorological data.

Health surveillance and workplace surveillance are two related but different aspects of occupational health services. The assessment of heat stress using heat indices and thermal models in connection with meteorological data is an important part of surveillance of workplace heat. The assessment of heat exposure provides the basis for occupational health services. Workers should have health surveillance if the high heat stress cannot be reduced.

Oxygen uptake and muscle activity limitations during stepping on a stair machine at three different climbing speeds.

This laboratory study examined human stair ascending capacity and constraining factors including legs' local muscle fatigue (LMF) and cardiorespiratory capacity. Twenty-five healthy volunteers, with mean age 35.3 years, maximal oxygen uptake (VO2max) of 46.7 mL·min-1·kg-1 and maximal heart rate (HR) of 190 bpm, ascended on a stair machine at 60 and 75% (3 min each) and 90% of VO2max (5 min or until exhaustion). The VO2, maximal heart rate (HRmax) and electromyography (EMG) of the leg muscles were measured. The average VO2highest reached 43.9 mL·min-1·kg-1, and HRhighest peaked at 185 bpm at 90% of VO2max step rate (SR). EMG amplitudes significantly increased at all three levels, p < .05, and median frequencies decreased mostly at 90% of VO2max SR evidencing leg LMF. Muscle activity interpretation squares were developed and effectively used to observe changes over time, confirming LMF. The combined effects of LMF and cardiorespiratory constraints reduced ascending tolerance and constrained the duration to 4.32 min. Practitioner Summary: To expedite ascending evacuation from high-rise buildings and deep underground structures, it is necessary to consider human physical load. This study investigated the limiting physiological factors and muscle activity rate changes (MARC) used in the muscle activity interpretation squares (MAIS) to evaluate leg local muscle fatigue (LMF). LMF and cardiorespiratory capacity significantly constrain human stair ascending capacities at high, constant step rates.

Occupational heat stress assessment and protective strategies in the context of climate change.

Global warming will unquestionably increase the impact of heat on individuals who work in already hot workplaces in hot climate areas. The increasing prevalence of this environmental health risk requires the improvement of assessment methods linked to meteorological data. Such new methods will help to reveal the size of the problem and design appropriate interventions at individual, workplace and societal level. The evaluation of occupational heat stress requires measurement of four thermal climate factors (air temperature, humidity, air velocity and heat radiation); available weather station data may serve this purpose. However, the use of meteorological data for occupational heat stress assessment is limited because weather stations do not traditionally and directly measure some important climate factors, e.g. solar radiation. In addition, local workplace environmental conditions such as local heat sources, metabolic heat production within the human body, and clothing properties, all affect the exchange of heat between the body and the environment. A robust occupational heat stress index should properly address all these factors. This article reviews and highlights a number of selected heat stress indices, indicating their advantages and disadvantages in relation to meteorological data, local workplace environments, body heat production and the use of protective clothing. These heat stress and heat strain indices include Wet Bulb Globe Temperature, Discomfort Index, Predicted Heat Strain index, and Universal Thermal Climate Index. In some cases, individuals may be monitored for heat strain through physiological measurements and medical supervision prior to and during exposure. Relevant protective and preventive strategies for alleviating heat strain are also reviewed and proposed.

Limitations of oxygen uptake and leg muscle activity during ascending evacuation in stairways.

Stair ascending performance is critical during evacuation from buildings and underground infrastructures. Healthy subjects performed self-paced ascent in three settings: 13 floor building, 31 floor building, 33 m stationary subway escalator. To investigate leg muscle and cardiorespiratory capacities and how they constrain performance, oxygen uptake (VO2), heart rate (HR) and ascending speed were measured in all three; electromyography (EMG) in the first two. The VO2 and HR ranged from 89 to 96% of the maximum capacity reported in the literature. The average highest VO2 and HR ranged from 39 to 41 mL·kg-1·min-1 and 162 to 174 b·min-1, respectively. The subjects were able to sustain their initial preferred maximum pace for a short duration, while the average step rate was 92-95 steps·min-1. In average, VO2 reached relatively stable values at ≈37 mL·kg-1·min-1. EMG amplitudes decreased significantly and frequencies were unchanged. Speed reductions indicate that climbing capacity declined in the process of fatigue development. In the two buildings, the reduction of muscle power allowed the subjects to extend their tolerance and complete ascents in the 48 m and 109 m high stairways in 2.9 and 7.8 min, respectively. Muscle activity interpretation squares were developed and proved advantageous to observe fatigue and recovery over time.

Exploring how a traditional diluted yoghurt drink may mitigate heat strain during medium-intensity intermittent work: a multidisciplinary study of occupational heat strain.

It is common practice in India to consume the dairy drink buttermilk as a way of mitigating occupational heat strain. This paper explores the thermoregulatory and hydration benefits of drinking buttermilk but also the impacts of work in a hot environment on the gut microbiota, renal and cognitive function. Twelve healthy participants were subjected to a 3-h period of medium load physical intermittent work in a climatic chamber (34°C, 60% RH). The subjects were given water, buttermilk (700 ml) or no rehydration at random. Mean body temperatures when no rehydration was given were significantly higher (p≤0.001). When subjects drank water or buttermilk they had a lower sweat rate than with no rehydration (p≤0.05) and the perception of feeling hot, uncomfortable, thirsty and physically exerted was significantly reduced (p≤0.05). A hormonal stress response at the end of the exposure was seen when not drinking (p≤0.05). No differences in cognitive abilities and gut microbiota were found. The exposure lowered the renal blood flow suggesting an acute impact of short term heat exposure. It was also found that buttermilk has a protective effect on this impact. Our results demonstrated that keeping hydrated by water/buttermilk consumption mitigates heat strain in well-nourished subjects.

Human responses in heat - comparison of the Predicted Heat Strain and the Fiala multi-node model for a case of intermittent work.

Two mathematical models of human thermal regulation include the rational Predicted Heat Strain (PHS) and the thermophysiological model by Fiala. The approaches of the models are different, however, they both aim at providing predictions of the thermophysiological responses to thermal environments of an average person. The aim of this study was to compare and analyze predictions of the two models against experimental data. The analysis also includes a gender comparison. The experimental data comprised of ten participants (5 males, 5 females, average anthropometric values were used as input) conducting an intermittent protocol of rotating tasks (cycling, stacking, stepping and arm crank) of moderate metabolic activities (134-291W/m2) with breaks in-between in a controlled environmental condition (34°C, 60% RH). The validation consisted of the predictions' comparison against experimental data from 2.5h of data of rectal temperature and mean skin temperature based on contact thermometry from four body locations. The PHS model over-predicted rectal temperatures during the first activity for males and the cooling effectiveness of sweat in the recovery periods, for both males and females. As a result, the PHS simulation underestimated the thermal strain in this context. The Fiala model accurately predicted the rectal temperature throughout the exposure. The fluctuation of the experimental mean skin temperature was not reflected in any of the models. However, the PHS simulation model showed better agreement than the Fiala model. As both models predicted responses more accurately for males than females, we suggest that in future development of the models it is important to take this result into account. The paper further discusses possible sources of the observed discrepancies and concludes with some suggestions for modifications.

Validation of the thermophysiological model by Fiala for prediction of local skin temperatures.

The most complete and realistic physiological data are derived from direct measurements during human experiments; however, they present some limitations such as ethical concerns, time and cost burden. Thermophysiological models are able to predict human thermal response in a wide range of environmental conditions, but their use is limited due to lack of validation. The aim of this work was to validate the thermophysiological model by Fiala for prediction of local skin temperatures against a dedicated database containing 43 different human experiments representing a wide range of conditions. The validation was conducted based on root-mean-square deviation (rmsd) and bias. The thermophysiological model by Fiala showed a good precision when predicting core and mean skin temperature (rmsd 0.26 and 0.92 °C, respectively) and also local skin temperatures for most body sites (average rmsd for local skin temperatures 1.32 °C). However, an increased deviation of the predictions was observed for the forehead skin temperature (rmsd of 1.63 °C) and for the thigh during exercising exposures (rmsd of 1.41 °C). Possible reasons for the observed deviations are lack of information on measurement circumstances (hair, head coverage interference) or an overestimation of the sweat evaporative cooling capacity for the head and thigh, respectively. This work has highlighted the importance of collecting details about the clothing worn and how and where the sensors were attached to the skin for achieving more precise results in the simulations.

Opportunities and constraints of presently used thermal manikins for thermo-physiological simulation of the human body.

Combining the strengths of an advanced mathematical model of human physiology and a thermal manikin is a new paradigm for simulating thermal behaviour of humans. However, the forerunners of such adaptive manikins showed some substantial limitations. This project aimed to determine the opportunities and constraints of the existing thermal manikins when dynamically controlled by a mathematical model of human thermal physiology. Four thermal manikins were selected and evaluated for their heat flux measurement uncertainty including lateral heat flows between manikin body parts and the response of each sector to the frequent change of the set-point temperature typical when using a physiological model for control. In general, all evaluated manikins are suitable for coupling with a physiological model with some recommendations for further improvement of manikin dynamic performance. The proposed methodology is useful to improve the performance of the adaptive manikins and help to provide a reliable and versatile tool for the broad research and development domain of clothing, automotive and building engineering.

A ventilation cooling shirt worn during office work in a hot climate: cool or not?

The aim of the study was to identify whether a ventilation cooling shirt was effective in reducing heat strain in a hot climate. Eight female volunteers were exposed to heat (38 °C, 45% relative humidity) for 2 h with simulated office work. In the first hour they were in normal summer clothes (total thermal insulation 0.8 clo); in the second hour a ventilation cooling shirt was worn on top. After the shirt was introduced for 1 h, the skin temperatures at the scapula and the chest were significantly reduced (p < 0.05). The mean skin and core temperatures were not reduced. The subjects felt cooler and more comfortable by wearing the shirt, but the cooling effect was most conspicuous only during the initial 10 min. The cooling efficiency of the ventilation shirt was not very effective under the low physical activity in this hot climate.