Reduce Heat Stress Research Articles

Design and performance evaluation of novel personal cooling garment

Personal cooling garments (PCGs) have been developed to reduce heat stress and improve human thermal comfort in hot environments. In this study, a new type of PCG, a PCM-liquid cooling vest (PLV), is developed to improve the ease of use of phase change material (PCM) garments. The PLV adopts the scheme of combining PCM with water pipes buried in the PCM. The PCM in the vest is used to cool the torso and the water pipe buried in the PCM circulates cold water from a microchiller to freeze the PCM. This PLV is designed and tested using mathematical modeling and human trial. Based on the simulation results, inorganic PCM with high density and conductivity, a high flow rate of cold water, and multiple parallel water pipes buried in PCM are recommended. Adjusting the tightness and wearing the insulation vest are effective methods to enhance the comfort and prolong the service time of the PLV, respectively. In the human trial, a PLV containing inorganic PCM and with a total mass of 1.8 kg is fabricated and used. The experimental results show that the fabricated PLV can provide effective cooling for at least two hours for users working indoors, without sacrificing the overall thermal comfort in the wearing mode. The cooling-storage can be finished within 40 min in the cooling-storage mode or within 60 min in the cooling-storage and wearing combined mode.

Air/CO2 cooling garment: Description and benefits of use for subjects exposed to a hot and humid climate during physical activities

The severity of the hot and humid conditions to which miners are exposed increases as the depth of the work site increases. This can cause heat stress that can greatly affect the health and safety of workers. To resolve this, a cooling garment has been developed that uses an atmospheric discharge of liquid CO2 to create a cool microclimate with an average temperature of 12.5 (±0.4) °C beneath the garment. To evaluate the garment’s cooling efficiency, 19 male subjects participated in an experimental procedure. The two modes, cooling on and off, were compared. Significant physiological differences were found between the two modes after minute 27 (p < 0.05) until the end of the recovery phase for the heart rate (maximum difference of 10 beats per minute) and the internal body temperature (maximum difference of 0.33 °C). It was found that the modes also affected the subjects’ perceptions. The ON-mode was associated with better well-being and thermal comfort, and reduced humidity sensation. Perceptions of exertion were lower in the ON-mode condition from minute 2. The findings provide strong evidence of the ability of this cooling garment to reduce heat stress in hot and humid conditions similar to those encountered in deep mines.

Forecasting the response to global warming in a heat-sensitive species

Avoiding hyperthermia entails considerable metabolic costs for endotherms. Such costs increase in warm conditions, when endotherms may trade food intake for cooler areas to avoid heat stress and maximize their energy balance. The need to reduce heat stress may involve the adoption of tactics affecting space use and foraging behaviour, which are important to understand and predict the effects of climate change and inform conservation. We used resource selection models to examine the behavioural response to heat stress in the Alpine ibex (Capra ibex), a cold-adapted endotherm particularly prone to overheating. Ibex avoided heat stress by selecting the space based on the maximum daily temperature rather than moving hourly to ‘surf the heat wave’, which minimised movement costs but prevented optimal foraging. By integrating these findings with new climate forecasts, we predict that rising temperatures will force mountain ungulates to move upward and overcrowd thermal refugia with reduced carrying capacity. Our approach helps in identifying priority areas for the conservation of mountain species.

Physical mechanisms influencing localized patterns of temperature variability and coral bleaching within a system of reef atolls

Interactions between oceanic and atmospheric processes within coral reefs can significantly alter local-scale (< km) water temperatures, and consequently drive variations in heat stress and bleaching severity. The Scott Reef atoll system was one of many reefs affected by the 2015–2016 mass coral bleaching event across tropical Australia, and specifically experienced sea surface temperature anomalies of 2 °C that caused severe mass bleaching (> 60%) over most of this system; however, the bleaching patterns were not uniform. Little is known about the processes governing thermodynamic variability within atolls, particularly those that are dominated by large amplitude tides. Here, we identify three mechanisms at Scott Reef that alleviated heat stress during the marine heatwave in 2016: (1) the cool wake of a tropical cyclone that induced temperature drops of 1.3 °C over a period of 8 days; (2) air–sea heat fluxes that interacted with the reef morphology during neap tides at one of the atolls to reduce water temperatures by up to 2.9 °C; (3) internal tidal processes that forced deeper and cooler water (up to 2.7 °C) into some sections of the shallow reefs. The latter two processes created localized areas of reduced temperatures that led to lower incidences of coral bleaching for parts of the reef. We predict these processes are likely to occur in other similar tide-dominated reef environments worldwide. Identifying locations where physical processes reduce heat stress will likely be critical for coral reefs in the future, by maintaining communities that can help facilitate local recovery of reefs following bleaching events that are expected to increase in frequency and severity in the coming decades.

Evaluation of the Effect of Urban Redevelopment on Surface Urban Heat Islands

Climate change is a global challenge with multiple consequences. One of its impacts is the increase in heatwave frequency and intensity. The risk is higher for populations living in urban areas, where the highest temperatures are generally identified, due to the urban heat island effect. This phenomenon has recently been taken into account by local elected officials. As a result, developers have decided to use solutions in redevelopment projects to combat high temperatures in urban areas. Consequently, the objective is to study the land-surface temperature evolution of six main urban redevelopments in Lyon, France, from 2000 to 2017. Three of them (the Confluence, Kaplan, and Museum sites) were composed of industrial areas that have undergone major transformations and are now tertiary or residential areas. Two sites have been more lightly transformed, particularly by increasing vegetation to reduce heat stress and urban flooding (Dock and Garibaldi Street). Finally, the Groupama Stadium has been built into agricultural and wooded areas. Changes in vegetation cover (NDVI), water (MNDWI), and moisture (NDMI) content, built areas (NDBI) and bare soil (NDBaI) are also monitored. The results show that the Confluence and Kaplan sites were accompanied by a decrease in surface temperature and an increase in vegetation and moisture, whereas the Groupama Stadium displayed a rise in surface temperature and a decrease in vegetation. On the other hand, the Museum, Dock, and Garibaldi sites did not exhibit clear and uniform trends, although an increase in surface temperature was shown in some statistical tests. The disparity of the results shows the necessity to include a significant amount of vegetation during redevelopment operations in order to reduce heat stress.

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.

Heat Waves Occurrence and Outdoor Workers' Self-assessment of Heat Stress in Slovenia and Greece.

Changing patterns of heat waves are part of the global warming effect and the importance of changes is reinforced by their negative impact on society. Firstly, heat waves were analyzed in Brnik (Slovenia) and Larisa (Greece) in the period 1981–2017 to reflect the environment which workers are exposed to. Secondly, outdoor workers (70 from Greece, 216 from Slovenia) provided a self-assessment of heat stress. The heat wave timeline is presented as an effective way of illustrating long-term changes in heat waves’ characteristics for various stakeholders. In both countries, workers assessed as significant the heat stress impact on productivity (Greece 69%, Slovenia 71%; p > 0.05), and in Slovenia also on well-being (74%; p < 0.01). The main experienced symptoms and diseases were thirst (Greece 70%, Slovenia 82%; p = 0.03), excessive sweating (67%, 85%; p = 0.01), exhaustion (51%, 62%; p > 0.05) and headache (44%, 53%; p > 0.05). The most common way to reduce heat stress was drinking more water (Greece 64%, Slovenia 82%; p = 0.001). Among the informed workers, the prevalent source of information was discussions. Therefore, educational campaigns are recommended, together with the testing of the efficiency of mitigation measures that will be proposed on the Heat-Shield project portal.

Effect of heat ameliorative measures on microclimate, physiological, blood biochemical parameters and milk production in lactating Surti buffaloes

The present investigation was carried out to evaluate the effect of heat ameliorative measures (fans, foggers, green agro shadenet) on physiological, haematological, biochemical and milk production parameters in Surti buffaloes. Lactating Surti buffaloes (36) were equally divided into two groups and kept in two sheds. Group I animals were housed in a shed without any modification while Group II animals housed in a shed fitted with fans and foggers inside the shed and roof top white washed with microfine lime and open paddock was covered with green shade net and foggers were fitted. There were significant differences in the THI values of both inside and outside of the sheds at majority of periods during the hot-dry season. The floor and roof temperature of control shed at almost all-time intervals was significantly higher than the floor temperature of treatment shed. Significant difference in rectal temperature was observed at 14 and 28 days while respiration rate was significantly lower in animals of treatment shed. In treatment group, total erythrocyte count and haematocrit was significantly low at day 21 and mean platelet volume was significantly high at day 42. Significantly high levels of cholesterol, chloride and sodium at day 21 and glucose, protein, triglyceride, GSH, TAS and sodium at day 42 were observed in treatment group. Weekly milk yield (kg) during hot-dry season was significantly higher for treatment group than control group at 3rd, 4th and 5th weeks of the experiment. Evening milk yield of treatment group was significantly higher than the control and the cumulative milk yield (for 42 days) was also significantly higher for treatment group than control group (180.08 vs.150.80 kg). It can be concluded that microclimate modifications help in reducing heat stress and has beneficial effect on physiological responses, blood biochemical parameters and total milk production in lactating Surti buffaloes during hot dry season.

Characterization of miRNA profiles in the mammary tissue of dairy cattle in response to heat stress

BackgroundMicroRNAs (miRNAs) are a class of small noncoding RNAs that play important roles in the regulation of gene expression. However, the role of miRNAs in bovine mammary gland responses to heat stress is not well understood.ResultsIn the present study, we performed a deep RNA sequencing analysis to identify miRNAs associated with the heat stress potential of the bovine mammary gland. We identified 27 miRNAs that were differentially expressed significantly between the mammary tissue of Holstein cattle heat stress and normal conditions. Twenty miRNAs had higher expression in the mammary tissue of heat-stressed Holstein cattle. The seven highest differentially expressed candidate miRNAs (bta-miR-21-5p, bta-miR-99a-5p, bta-miR-146b, bta-miR-145, bta-miR-2285 t, bta-miR-133a, and bta-miR-29c) identified by deep RNA sequencing were additionally evaluated by stem-loop qPCR. Enrichment analyses for targeted genes revealed that the major differences between miRNAs expression in the mammary gland of heat-stressed versus control were associated with the regulation of Wnt, TGF-β, MAPK, Notch, and JAK-STAT.ConclusionsThese data indicated that the differentially expressed miRNAs identified in this study may act as dominant regulators during heat stress. We might reduce heat stress damage of Holstein cows by up-regulating or down-regulating these differentially expressed miRNAs.

Assessment of thermally comfortable urban spaces in Amsterdam during hot summer days

Since it is insufficiently clear to urban planners in the Netherlands to what extent design measures can reduce heat stress and which urban spaces are most comfortable, this study evaluates the impact of shading, urban water, and urban green on the thermal comfort of urban spaces during hot summer afternoons. The methods used include field surveys, meteorological measurements, and assessment of the PET (physiological equivalent temperature). In total, 21 locations in Amsterdam (shaded and sunny locations in parks, streets, squares, and near water bodies) were investigated. Measurements show a reduction in PET of 12 to 22 °C in spaces shaded by trees and buildings compared to sunlit areas, while water bodies and grass reduce the PET up to 4 °C maximum compared to impervious areas. Differences in air temperature between the locations are generally small and it is concluded that shading, water and grass reduce the air temperature by roughly 1 °C. The surveys (n = 1928) indicate that especially shaded areas are perceived cooler and more comfortable than sunlit locations, whereas urban spaces near water or green spaces (grass) were not perceived as cooler or thermally more comfortable. The results of this study highlight the importance of shading in urban design to reduce heat stress. The paper also discusses the differences between meteorological observations and field surveys for planning and designing cool and comfortable urban spaces. Meteorological measurements provide measurable quantities which are especially useful for setting or meeting target values or guidelines in reducing urban heat in practice.

Research trends on prevention of heat stroke using clothing: Focusing on practical research in Japan

This study identifies Japanese study content on heat stroke prevention measures using clothes, provides basic data for quantitative wearing assessment studies, presents a developmental direction for those, and helps invigorate further research. Studies were collected concerning clothing-based heat stroke measures in order to analyze the following factors: current status of heat stroke by industry and working environment, heat stroke and body cooling method, clothing microclimate and air circulation in a hot environment, hot environments and wearable sensors, and heat stress reduction and skin exposure. The current WBGT standard does not consider the diversity of wearing clothes according to the working environment. Therefore, it is preferable to add a correction value in consideration of design, materials, and ventilation to prevent heat strokes. For the heat stroke and body cooling method, wearing water-perfused clothing is effective to reduce heat stress and maintain exercise ability. Changing the material and design of clothing or wearing air-conditioned clothing can improve ventilation and the clothing microclimate. However, further evaluation is needed on the effectiveness of air-conditioned clothing as a heat stroke prevention product. The measurement method using a wearable sensor can provide real-time data on the body response due to working in a hot environment. Therefore, it is an effective alarm for heat stroke. Skin exposure area and heat dissipation efficiency should be considered to prevent heat stroke. Reducing the covering area by exposing the head, neck, and limbs, and wearing breathable material can prevent heat stroke from increased body temperature.

Influence of urban green on human thermal bioclimate – application of thermal indices and micro-scale models

For the quantification of the atmospheric conditions and their impact on humans methods from human biometeorology can be applied. For the thermal component air temperature, humidity, wind and radiation fluxes are the factors which are required. Most significant for urban areas and urban green is the quantification of heat stress which can be estimated by thermal indices (e.g., the physiologically equivalent temperature (PET), the perceived temperature (PT), or the universal thermal climate index (UTCI)). For an overall assessment, different approaches can be applied based on measurements and models (e.g., RayMan, ENVI-met, SkyHelios) for single points (hotspots) within urban areas or neighbourhoods and city quarters. The most relevant reduction of heat stress can be obtained by increasing shade with specific trees and by improving wind conditions. These two factors (radiation and wind modification) can be extremely helpful in the creation of optimised thermal comfortable urban places and green areas. The application of models, which focus on long-term quantifications, can deliver valuable results and information for whole year assessment of the effect of urban green on human thermal bioclimate. In addition, models deliver additional basic parameters (sun paths, sunshine duration, roughness), which are important in the estimation of the effects of urban green on human thermal bioclimate.

Rapid and Nondestructive Methods to Capture the Flower Opening Time in Rice to Identify Donors for High Temperature Stress

The time of day of flowering or the early morning flowering (EMF) trait has been demonstrated to significantly reduce heat stress damage by employing an escaping mechanism. Early flower opening is being one of the important traits that aids in the escape of rice flowers from spikelet sterility due to the high temperature stress. This strategy, which is less explored, can be used to breed cultivars that escape heat at flowering because of their early morning flowering (EMF) trait. With the advancement of instrumentation, the study was proposed to screen the genotypes using rapid and non-destructive methods like use of interval shot cameras to identify EMF traits. Once the early morning flowering trait is identified and studied for heat tolerance, it can be used as a potential donor in rice breeding programs to develop an early morning flowering variety for high temperature prone areas. The already available diverse rice germplasm collections having wide genetic diversity for FOT based on First Spikelet Opening Time (FSOT) at PBS, TNAU was used in this study. Nearly twenty one rice germplasms (landraces) were grown under natural ambient conditions (field) and interval shot cameras were used to capture the time of flower opening (Start, peak and end of anthesis) to identify the early morning flowering trait. These lines with EMF trait will be suitable donors to high temperature stress tolerance. Among them two lines namely, Mattikar and Panamara samba showed early morning flowering trait.

Role of green roofs in reducing heat stress in vulnerable urban communities—a multidisciplinary approach

Green infrastructure, such as green roofs, is increasingly being used to reduce ‘heat stresses’ associated with urban heat island effects. This article discusses strategies to identify vulnerable neighborhoods in the City of Chicago, where green roofs could achieve multiple goals to mitigate urban heat-related challenges. Numerical simulations were performed using the urbanized version of the Advanced Research Weather Research and Forecasting model to predict rooftop temperatures, a representative variable for exposure in this study. The model was dynamically coupled with a physically-based green rooftop algorithm as a part of the urban parameterization within the model. Our approach integrates information from multiple sources: social vulnerability indices (a function of exposure, sensitivity, and adaptive capacity), high-resolution temperature simulations over the urban area, and observed electricity (air conditioning) consumption data. The social vulnerability indicators were used to develop a quantitative heat vulnerability index for Chicago. We found that an analysis of multiple drivers is needed to identify neighborhoods that will likely benefit from mitigation strategies like green roofs. Our case study identified a large number of census tracts in south and west Chicago, along with isolated tracts throughout the city that would strongly benefit from green roof implementation. The tools and methodology from this study can be easily adopted for other urban regions and would be informative for stakeholders and managers, in general, in making adaptation strategies for extreme heat management.

Effects of Landscape Design on Urban Microclimate and Thermal Comfort in Tropical Climate

A climate-responsive landscape design can create a more livable urban microclimate with adequate human comfortability. This paper aims to quantitatively investigate the effects of landscape design elements of pavement materials, greenery, and water bodies on urban microclimate and thermal comfort in a high-rise residential area in the tropic climate of Singapore. A comprehensive field measurement is undertaken to obtain real data on microclimate parameters for calibration of the microclimate-modeling software ENVI-met 4.0. With the calibrated ENVI-met, seven urban landscape scenarios are simulated and their effects on thermal comfort as measured by physiologically equivalent temperature (PET) are evaluated. It is found that the maximum improvement of PET reduction with suggested landscape designs is about 12°C, and high-albedo pavement materials and water bodies are not effective in reducing heat stress in hot and humid climate conditions. The combination of shade trees over grass is the most effective landscape strategy for cooling the microclimate. The findings from the paper can equip urban designers with knowledge and techniques to mitigate urban heat stress.

Heart rate, cardiac vagal tone, respiratory rate, and rectal temperature in dairy calves exposed to heat stress in a continental region.

Changes in non-invasive stress biomarkers were studied in shaded (n = 8) and non-shaded (n = 8) Holstein bull calves exposed to extreme heat load conditions in a continental region. Ambient temperature and humidity data were recorded for the S and NS hutch and exercise pen environments. Temperature-humidity-index (THI) was also calculated. Respiratory rate, rectal temperature, heart rate, and the root mean square of successive differences between R-R intervals (RMSSD) were recorded as animal-based indicators during three periods: (1) day 1, control day, during which all calves were shaded for 24h (shade removal from non-shaded calves at 2400h); (2) day 2, heat stress day, with shade over shaded calves; and (3) days 3-5, post-stress period, with shade over shaded calves. On the heat stress day, the maximum temperatures were 44.3 and 46.7°C for the non-shaded hutch and pen environments, respectively. The temperatures were with 6.2 and 6.9°C (P = 0.015 and P = 0.008) and the THIs were with 5.9 and 4.2units higher (P = 0.020 and P = 0.032) in the non-shaded than in the shaded environment for the hutch and exercise pen, respectively. Shaded calves had with 42.3 ± 3.2 breaths/min higher respiratory rate than non-shaded ones on the heat stress day at 1200h (P = 0.001), which was moderated to 20.1 ± 2.4 breaths/min at 1600h (P = 0.023). Significant differences in respiratory rate occurred earlier than in any other animal-based parameter between shaded and non-shaded calves on day 2. The only significant group difference in rectal temperature was found at 1200h on day 2 when THI exceeded 91units, with 0.59°C higher values for non-shaded calves (P = 0.045). The heart rate on days 2 and 3 was higher for non-shaded calves than for shaded ones. Group differences were also significant at 0800h (18.2 ± 1.2 beats/min, P = 0.008), 1200h (22.3 ± 1.4 beats/min, P = 0.003), 1600h (15.3 ± 0.8 beats/min, P = 0.012), and 2000h (19.0 ± 1.1 beats/min, P = 0.010) on day 2. Following a rapid daytime reduction, RMSSD showed a nighttime overcompensation in non-shaded calves on day 3 (between 0000 and 0600h) and day 4 (between 0000 and 0800h), exceeding the levels recorded on day 1 (control) and the levels for shaded calves, thus suggesting a recovery of the autonomic nervous system from heat stress. Based on our results, shading effectively reduced heat stress as evidenced by heart rate and RMSSD in addition to traditional measures of heat stress. Respiratory rate and heart rates exhibited by non-shaded calves support that the well-being of pre-weaned calves can be impaired in continental regions during following a heat stress day without providing shade.

The association between wet-bulb globe temperature and other thermal indices (DI, MDI, PMV, PPD, PHS, PSI and PSIhr): a field study

The current study aimed at comparing the correlation coefficients between wet-bulb globe temperature (WBGT) and a number of parameters, including the discomfort index (DI), modified discomfort index (MDI), predicted mean vote (PMV), predicted percentage of dissatisfaction (PPD), predicted heat strain (PHS), physiological strain index (PSI) and physiological strain index heart rate (PSIhr). In total, 30 workers of a pelletizing factory participated in this study. Environmental parameters and workers’ physiological parameters were measured in 10 working stations. The results showed that effective WBGT (WBGTeff) strongly correlates with DI, MDI, PMV, PPD, PHS, PSI and PSIhr. WBGTeff had the highest correlation coefficients with PMV, MDI, PHS and PSIhr. Based on the obtained results, it was concluded that heat stress exceeded the standard limit for a number of indices in some of the working stations. Thus, some controlling measures should be taken to reduce heat stress in these stations.

Evaluation of Occupational Exposure Limits for Heat Stress in Outdoor Workers - United States, 2011-2016.

Heat stress, an environmental and occupational hazard, is associated with a spectrum of heat-related illnesses, including heat stroke, which can lead to death. CDC's National Institute for Occupational Safety and Health (NIOSH) publishes recommended occupational exposure limits for heat stress (1). These limits, which are consistent with those of the American Conference of Governmental Industrial Hygienists (ACGIH) (2), specify the maximum combination of environmental heat (measured as wet bulb globe temperature [WBGT]) and metabolic heat (i.e., workload) to which workers should be exposed. Exposure limits are lower for workers who are unacclimatized to heat, who wear work clothing that inhibits heat dissipation, and who have predisposing personal risk factors (1,2). These limits have been validated in experimental settings but not at outdoor worksites. To determine whether the NIOSH and ACGIH exposure limits are protective of workers, CDC retrospectively reviewed 25 outdoor occupational heat-related illnesses (14 fatal and 11 nonfatal) investigated by the Occupational Safety and Health Administration (OSHA) from 2011 to 2016. For each incident, OSHA assessed personal risk factors and estimated WBGT, workload, and acclimatization status. Heat stress exceeded exposure limits in all 14 fatalities and in eight of 11 nonfatal illnesses. An analysis of Heat Index data for the same 25 cases suggests that when WBGT is unavailable, a Heat Index screening threshold of 85°F (29.4°C) could identify potentially hazardous levels of workplace environmental heat. Protective measures should be implemented whenever the exposure limits are exceeded. The comprehensive heat-related illness prevention program should include an acclimatization schedule for newly hired workers and unacclimatized long-term workers (e.g., during early-season heat waves), training for workers and supervisors about symptom recognition and first aid (e.g., aggressive cooling of presumed heat stroke victims before medical professionals arrive), engineering and administrative controls to reduce heat stress, medical surveillance, and provision of fluids and shady areas for rest breaks.

Thermal moderation of the intertidal zone by seaweed canopies in winter

Canopy-forming seaweeds are important foundation species or ecosystem engineers in intertidal habitats. By limiting a variety of abiotic stresses during low tides, algal canopies improve the performance of many understory organisms. The reduction of heat stress through substrate shading and moisture retention has received considerable attention in marine biology. However, the thermal influence of canopies during winter has not been empirically evaluated. Using intertidal fucoid canopies (Ascophyllum nodosum) from Atlantic Canada, we did a field experiment contrasting canopy-covered and no-canopy areas to test the hypothesis that canopies limit low temperatures during winter low tides. During 35 days between January and March, mid-intertidal temperature was often negative near the time of the lowest daily tides, on average more than 1 °C lower on bare substrate than under full canopy cover. The difference between both canopy treatments was higher around spring tides than around neap tides. Temperature on bare substrate was once even up to 10 °C lower than under a full canopy. Previous studies have shown that single occurrences of lethal negative temperatures and frequent occurrences of sublethal temperatures kill intertidal organisms every winter. Thus, our study suggests that, in addition to their bioprotective role during summer, canopy-forming seaweeds might also play a relevant facilitative role during winter.

Strategic application of convective cooling to maximize the thermal gradient and reduce heat stress response in dairy cows

This study determined the effectiveness of convective cooling at different times of day when air temperature (Ta) was cycled from day to night. Mid-lactation Holstein cows (n = 12) were placed in 3 environmental chambers (4 cows per chamber) and acclimated to Ta 19.9°C (thermoneutral; TN) for 7 d followed by an incremental increase over 3 d to a heat stress (HS) condition. Conditions were maintained for 11 d at high and low daily Ta of 33 and 23°C, respectively. To determine adaptive HS response, the HS period was divided into early (E: d 11 to 14) and late (L: d 17 to 20) periods. During HS, cows were exposed to continuous fan (convective) cooling (CC), 8-h day fan cooling (1100 to 1900 h; DC), or 8-h night fan cooling (2300 to 0700 h; NC). Compared with DC, the NC treatment maximized the thermal gradient during the convective cooling. Each animal received all treatments within 3 trials using a repeated 3 × 3 Latin square design. Cows were fed a total mixed ration and milked twice daily. Thermal status was assessed by using thermal conductance and average daily values for mean, minimum, and maximum rectal temperature (Tre), skin temperatures, and respiration rate. Percent reduction in dry matter intake from TN to HS was less for CC than DC and NC, with no change from E to L periods. The DC group exhibited the greatest trend for a percent reduction in total milk yield below CC due to the significantly lower morning milk production. All values for total daily milk production decreased from E to L periods, with E to L reductions in both morning and afternoon milk production. Minimum Tre for CC and NC cows was 0.4°C below DC. In contrast, maximum Tre was similar for NC and DC groups, at 0.5 to 0.6°C above the CC group. Skin temperature for CC cows was always less than DC cows. Skin temperature for NC cows was equal to CC for minimum skin temperature, but exceeded both CC and DC cows for maximum skin temperature. Average skin temperature decreased from E to L, which suggested heat adaptation. The thermal advantage of night (lowest Ta and greatest thermal gradient) versus day cooling (greatest Ta and lowest thermal gradient) was increased heat transfer via thermal conductance with NC. The higher thermal strain of DC cows caused a larger percent decrease in morning milk yield than for NC cows. In contrast, use of convective cooling at night in the absence of elevated humidity could sufficiently reduce heat strain beyond DC to maintain milk production at a level that is closer to that of CC cows.