Characterization of human extreme heat exposure using an outdoor thermal manikin.

Extreme heat is a current and growing global health concern. Current heat exposure models include meteorological and human factors that dictate heat stress, comfort, and risk of illness. However, radiation models simplify the human body to a cylinder, while convection ones provide conflicting predictions. To address these issues, we introduce a new method to characterize human exposure to extreme heat with unprecedented detail. We measure heat loads on 35 body surface zones using an outdoor thermal manikin ("ANDI") alongside an ultrasonic anemometer array and integral radiation measurements (IRM). We show that regardless of body orientation, IRM and ANDI agree even under high solar conditions. Further, body parts can be treated as cylinders, even in highly turbulent flow. This geometry-rooted insight yields a whole-body convection correlation that resolves prior conflicts and is valid for diverse indoor and outdoor wind flows. Results will inform decision-making around heat protection, adaptation, and mitigation.

A simple three-cylinder radiometer and low-speed anemometer to characterize human extreme heat exposure.

As populations and temperatures of urban areas swell, more people face extreme heat and are at increasing risk of adverse health outcomes. Radiation accounts for much of human heat exposure but is rarely used as heat metric due to a lack of cost-effective and accurate sensors. To this end, we fuse the concepts of a three-globe radiometer-anemometer with a cylindrical human body shape representation, which is more realistic than a spherical representation. Using cost-effective and readily available materials, we fabricated two combinations of three cylinders with varying surface properties. These simple devices measure the convection coefficient and the shortwave and longwave radiative fluxes. We tested the devices in a wind tunnel and at fourteen outdoor sites during July 2023's record-setting heat wave in Tempe, Arizona. The average difference between pedestrian-level mean radiant temperature (MRT) measured using research-grade 3-way net radiometers and the three-cylinder setup was 0.4 ± 3.0 °C ( ±  1 SD). At most, we observed a 10 °C MRT difference on a white roof site with extreme MRT values (70 °C to 80 °C), which will be addressed through discussed design changes to the system. The measured heat transfer coefficient can be used to calculate wind speed below 2 m·s-1; thus, the three cylinders combined also serve as a low-speed anemometer. The novel setup could be used in affordable biometeorological stations and deployed across urban landscapes to build human-relevant heat sensing networks.

Concurrent Heat and Air Pollution Exposures among People Experiencing Homelessness.

BACKGROUND: Extreme heat and air pollution are important human health concerns; exposure can affect mental and physical well-being, particularly during periods of co-occurrence. Yet, the impacts on people are largely determined by underlying health conditions, coupled with the length and intensity of exposure. Preexisting adverse health conditions and prolonged exposure times are more common for people experiencing homelessness, particularly those with intersectional identity characteristics (e.g., disease, ability, age, etc.). Partially due to methodological limitations, such as data scarcity, there is a lack of research at the intersection of this at-risk population within the climate-health domain. OBJECTIVES: We have three distinct objectives throughout this article: a) to advance critical discussions around the state of concurrent high heat and air pollution exposure research as it relates to people experiencing homelessness; b) to assert the importance of heat and air pollution exposure research among a highly vulnerable, too-often homogenized population-people experiencing homelessness; and c) to underline challenges in this area of study while presenting potential ways to address such shortcomings. DISCUSSION: The health insights from concurrent air pollution and heat exposure studies are consequential when studying unhoused communities who are already overexposed to harmful environmental conditions. Without holistic data sets and more advanced methods to study concurrent exposures, appropriate and targeted prevention and intervention strategies cannot be developed to protect this at-risk population. We highlight that a) concurrent high heat and air pollution exposure research among people experiencing homelessness is significantly underdeveloped considering the pressing human health implications; b) the severity of physiological responses elicited by high heat and air pollution are predicated on exposure intensity and time, and thus people without means of seeking climate-controlled shelter are most at risk; and c) collaboration among transdisciplinary teams is needed to resolve data resolution issues and enable targeted prevention and intervention strategies. https://doi.org/10.1289/EHP13402.

Humidity's Role in Heat-Related Health Outcomes: A Heated Debate.

BACKGROUND: As atmospheric greenhouse gas concentrations continue to rise, temperature and humidity will increase further, causing potentially dire increases in human heat stress. On physiological and biophysical grounds, exposure to higher levels of humidity should worsen heat stress by decreasing sweat evaporation. However, population-scale epidemiological studies of heat exposure and response often do not detect associations between high levels of humidity and heat-related mortality or morbidity. These divergent, disciplinary views regarding the role of humidity in heat-related health risks limit confidence in selecting which interventions are effective in reducing health impacts and in projecting future heat-related health risks. OBJECTIVES: Via our multidisciplinary perspective we seek to a) reconcile the competing realities concerning the role of humidity in heat-related health impacts and b) help ensure robust projections of heat-related health risks with climate change. These objectives are critical pathways to identify and communicate effective approaches to cope with present and future heat challenges. DISCUSSION: We hypothesize six key reasons epidemiological studies have found little impact of humidity on heat-health outcomes: a) At high temperatures, there may be limited influence of humidity on the health conditions that cause most heat-related deaths (i.e., cardiovascular collapse); b) epidemiological data sets have limited spatial extent, a bias toward extratropical (i.e., cooler and less humid), high-income nations, and tend to exist in places where temporal variations in temperature and humidity are positively correlated; c) analyses focus on older, vulnerable populations with sweating, and thus evaporative, impairments that may be further aggravated by dehydration; d) extremely high levels of temperature and humidity (seldom seen in the historical record) are necessary for humidity to substantially impact heat strain of sedentary individuals; e) relationships between temperature and humidity are improperly considered when interpreting epidemiological model results; and f) sub-daily meteorological phenomena, such as rain, occur at high temperatures and humidity, and may bias epidemiological studies based on daily data. Future research must robustly test these hypotheses to advance methods for more accurate incorporation of humidity in estimating heat-related health outcomes under present and projected future climates. https://doi.org/10.1289/EHP11807.

Evidence-based guidance on reflective pavement for urban heat mitigation in Arizona.

Urban overheating is an increasing threat to people, infrastructure, and the environment. Common heat mitigation strategies, such as green infrastructure, confront space limitations in current car-centric cities. In 2020, the City of Phoenix, Arizona, piloted a "cool pavement" program using a solar reflective pavement seal on 58 km of residential streets. Comprehensive micrometeorological observations are used to evaluate the cooling potential of the reflective pavement based on three heat exposure metrics-surface, air, and mean radiant temperatures-across three residential reflective pavement-treated and untreated neighborhoods. In addition, the solar reflectivity of reflective pavement is observed over 7 months across eight residential neighborhoods. Results are synthesized with the literature to provide context-based reflective pavement implementation guidelines to mitigate urban overheating where common strategies cannot be applied. The three most important contextual factors to consider for effective implementation include urban location, background climate type, and heat exposure metric of interest.

Short hydration education video and hiker fluid selection and consumption at trails, a non-randomized quasi-experimental field study.

Background: Education may improve hiker safety on trails. Aim: To investigate the impact of an educational video on hiker fluid selection and fluid consumption in a hot environment. Methods: Quasi-experimental field study at hiking trails in which the intervention group (INT) viewed a three-minute hydration education video, whereas the control group (CON) did not. Before the hike, all hikers were asked if they wanted to select extra fluid, which was provided by the research team. Results: A total of n = 97 hikers participated in the study, with n = 56 in INT (32 male) and n = 41 in CON (25 male). Despite absolute differences in environmental conditions, the differences fell within the same WBGT category. The total amount of fluid brought to the trails by participants was different between INT: 904 (503-1758) mL and CON: 1509 (880-2176) mL (P = 0.006), but participants in the INT group selected extra fluid (41%; n = 23) significantly more often when compared with participants in the CON group (7%; n = 3; P < 0.001). As a result, there was no difference in the amount of fluid brought on the trail between INT: 1047 (611-1936) mL and CON: 1509 (932-2176) mL (P = 0.069), nor for fluid consumption between INT: 433 (289-615) mL/h and CON: 489 (374-719) mL/h (P = 0.18). Conclusions and Implications: A 3-min educational video may encourage hikers to select additional fluid before the start of their hike but does not appear to increase fluid intake.

Analysis of potential hydration opportunities during future football tournaments based on data from the 2018 FIFA World Cup.

The World Cup is traditionally held oppressive thermal conditions. Therefore, teams should follow heat strain mitigation strategies, including optimal fluid ingestion. The objective of this analysis was to assess and visually communicate match-based World Cup player hydration opportunities and behaviors. Broadcast recordings of the 2018 World Cup (June-July) were analyzed. Descriptive data were reported for match duration, the number, type, and duration of breaks, and player-initiated hydration moments, as well as environmental conditions categorized as 'no thermal stress' and 'thermal heat stress.' The median number and interquartile range of total match breaks were 7 [5-8] during official breaks, with a duration of 42 [23-72] seconds. There were 2 [1-3] player-initiated hydration moments per game, with a duration of 77 [55-100] seconds. On top of the 29% (#126) of breaks in which drinking occurred, an additional 26% (#33) of self-initiated drinking was registered with a duration of 7 [4-28] seconds without an official break. There was no significant difference (P = 0.22) in self-initiated hydration between thermal conditions. Relative percentages showed suboptimal use of substitution (14%) and VAR (38%) breaks vs. injury breaks (75%). In conclusion, football players did not sufficiently use available breaks to hydrate.

Evaporative misters for urban cooling and comfort: effectiveness and motivations for use.

Thermal comfort is an important determinant of quality of life and economic vitality in cities. Strategies to improve thermal comfort may become a more critical part of urban sustainability efforts with projections of continued urban growth and climate change. A case study was performed in the hot, dry summertime climate of Tempe, Arizona to quantify the influence of evaporative misters on the thermal environment in outdoor restaurants and to understand business managers' motivations to use misters. Microclimate measurements (air temperature (Ta), wind speed, relative humidity, globe temperature) were taken at five restaurants midday within four exposures: misted sun, misted shade, sun only, and shade only. We assessed Ta, mean radiant temperature (MRT), universal thermal climate index (UTCI), and physiological equivalent temperature (PET) between these four conditions within each location. Misters improved thermal comfort across all days, sites, and exposure conditions. MRT was on average 7.6 °C lower in misted locations, which significantly lowered average PET (- 6.5 °C) and UTCI (- 4.4 °C) (p < 0.05). Thermal comfort was most improved using mist in combination with shade. Under such conditions, PET and UTCI were reduced by 15.5 °C and 9.7 °C (p < 0.05), respectively. Business managers identified customer comfort and increased seating capacity as the principal factors for mister use. Esthetics of misters further encouraged use, while cost and environmental concerns were perceived to be less important. While this case study demonstrates value in outdoor misting in a hot, dry climate, additional work is needed to more fully evaluate tradeoffs between cost, water use, and comfort with continuing urban growth.

Wearable ultraviolet radiation sensors for research and personal use.

Skin cancers are strongly linked to personal exposure to ultraviolet (UV) radiation, yet UV exposure is also the most preventable risk factor. People are exposed to UV rays when they engage in outdoor activities, particularly exercise, which is an important health behavior. Thus, researchers and the general public have shown increasing interest in measuring UV exposure using wearable sensors during outdoor physical activity. However, minimal research exists at the intersection of UV sensors, personal exposure, adaptive behavior due to exposures, and risk of skin damage. Recent years have seen an influx of new consumer-based and research-based UV-sensing technologies with wide-ranging form factors and purposes to fill this research gap, yet a thorough review of available sensors for specific purposes does not exist. Hence, the overall goal of this state-of-the-art review is to synthesize the current academic and gray literature surrounding personal UV-sensing technologies. Peer-reviewed journal articles and "gray literature," such as working papers, manuals, and UV sensor websites, were reviewed, assessing attributes of UV wearables marketed for research use, personal use, or both. Overall, 13 wearable UV sensors are available for personal use and/or research applications. These sensors vary from electronic to photochromic, with large differences in price, data outputs, accuracy, and precision. Recommendations are provided for which sensors are most suitable for various types of research or public use. Notably, the review findings will help guide researchers in future studies assessing UV exposure during physical activity.

Enhanced intestinal permeability and intestinal co-morbidities in heat strain: A review and case for autodigestion.

Enhanced intestinal permeability is a pervasive issue in modern medicine, with implications demonstrably associated with significant health consequences such as sepsis, multiorgan failure, and death. Key issues involve the trigger mechanisms that could compromise intestinal integrity and increase local permeability allowing the passage of larger, potentially dangerous molecules. Heat stress, whether exertional or environmental, may modulate intestinal permeability and begs interesting questions in the context of global climate change, increasing population vulnerabilities, and public health. Emerging evidence indicates that intestinal leakage of digestive enzymes and associated cell dysfunctions--a process referred to as autodigestion--may play a critical role in systemic physiological damage within the body. This increased permeability is exacerbated in the presence of elevated core temperatures. We employed Latent Dirichlet Allocation (LDA) topic modeling methods to analyze the relationship between heat stress and the nascent theory of autodigestion in a systematic, quantifiable, and unbiased manner. From a corpus of 11,233 scientific articles across four relevant scientific journals (Gut, Shock, Temperature, Gastroenterology), it was found that over 1,000 documents expressed a relationship between intestine, enhanced permeability, core temperature, and heat stress. The association has grown stronger in recent years, as heat stress and potential autodigestion are investigated in tandem, yet still by a limited number of specific research studies. Such findings justify the design of future studies to critically test novel interventions against digestive enzymes permeating the intestinal tract, especially the small intestine.

Heat Safety in the Workplace: Modified Delphi Consensus to Establish Strategies and Resources to Protect the US Workers.

The purpose of this consensus document was to develop feasible, evidence-based occupational heat safety recommendations to protect the US workers that experience heat stress. Heat safety recommendations were created to protect worker health and to avoid productivity losses associated with occupational heat stress. Recommendations were tailored to be utilized by safety managers, industrial hygienists, and the employers who bear responsibility for implementing heat safety plans. An interdisciplinary roundtable comprised of 51 experts was assembled to create a narrative review summarizing current data and gaps in knowledge within eight heat safety topics: (a) heat hygiene, (b) hydration, (c) heat acclimatization, (d) environmental monitoring, (e) physiological monitoring, (f) body cooling, (g) textiles and personal protective gear, and (h) emergency action plan implementation. The consensus-based recommendations for each topic were created using the Delphi method and evaluated based on scientific evidence, feasibility, and clarity. The current document presents 40 occupational heat safety recommendations across all eight topics. Establishing these recommendations will help organizations and employers create effective heat safety plans for their workplaces, address factors that limit the implementation of heat safety best-practices and protect worker health and productivity.

Improved methods for estimating mean radiant temperature in hot and sunny outdoor settings.

Thermal comfort research has utilized various sensors and models to estimate the mean radiant temperature (MRT) experienced by a human, including the standard black globe thermometer (SGT), acrylic globe thermometers (AGT), and cylindrical radiation thermometers (CRT). Rather than directly measuring radiation, a temperature is measured in the center of these low-cost sensors that can be related to MRT after theoretically accounting for convection. However, these sensors have not been systematically tested under long-term hot and clear conditions. Further, under variable weather conditions, many issues can arise due to slow response times, shape, inaccuracies in material properties and assumptions, and color (albedo, emissivity) inconsistencies. Here, we assess the performance of MRT produced by various heat transfer models, with and without new average surface temperature ([Formula: see text]) correction factors, using five instruments-the SGT (15 cm, black), tan and black CRTs, gray and black 38 mm AGTs-compared to 3D integral radiation measurements. Measurements were taken on an unobscured roof throughout summer-to-early-fall months in Tempe, Arizona, examining 58 full-sun days. Deviations without correcting for asymmetrical surface heating-found to be the main cause of errors-reached ± 15-20 °C MRT. By accounting for asymmetric heating through [Formula: see text] calculations, new corrective algorithms were derived for the low-cost sensor models. Results show significant improvements in the estimated MRT error for each sensor (i.e., ∆MRTmodel - IRM) when applying the [Formula: see text] corrections. The tan MRTCRT improved from 1.9 ± 6.2 to -0.1 ± 4.4 °C, while the gray AGT and SGT showed improvements from -1.6 ± 7.2 to -0.4 ± 6.3 °C and - 6.6 ± 6.4 to - 0.03 ± 5.7 °C, respectively. The new corrections also eliminated dependence on other meteorological factors (zenith, wind speed). From these results, we provide three simple equations for CRT, AGT, and SGT correction for future research use under warm-hot and clear conditions. This study is the most comprehensive empirical assessment of various low-cost instruments with broad applicability in urban climate and biometeorological research.

Roundtable on Preseason Heat Safety in Secondary School Athletics: Environmental Monitoring During Activities in the Heat.

OBJECTIVE: To develop best-practice recommendations using thermal indices to determine work-to-rest ratios and facilitate further implementation of environmental monitoring for heat safety in secondary school athletics in the United States. DATA SOURCES: A narrative review of the current literature on environmental monitoring for heat safety during athletics was conducted by content experts. A list of action-oriented recommendations was established from the narrative review and further refined using the Delphi method. CONCLUSIONS: Assessment of wet bulb globe temperature at the site of activity and throughout the duration of the event is recommended to assist clinicians and administrators in making appropriate decisions regarding the duration and frequency of activity and rest periods. Activity-modification guidelines should be predetermined and approved by stakeholders and should outline specific actions to be followed, such as the work-to-rest ratio, frequency and timing of hydration breaks, and adjustment of total exercise duration, equipment, and clothing. Furthermore, integration of exertional heat illness injury data with environmental condition characteristics is critical for the development of evidence-based heat safety guidelines for secondary school athletics. Athletic trainers play an essential role in conducting prospective injury data collection, recording onsite wet bulb globe temperature levels, and implementing recommendations to protect the health and safety of athletes.

Community-based maternal health workers' perspectives on heat risk and safety: a pilot qualitative study.

In this study the authors examined how maternal health workers (MHWs) perceive the health risks of extreme heat exposure to pregnant women and fetuses. The authors conducted interviews with 12 MHWs (including midwives and doulas) in El Paso, Texas. Using qualitative analysis, the researchers identified numerous themes. Although heat was not communicated as a major health risk, participants expressed some concern with growing heat exposure and communicated standard protective measures. While all participants were familiar with some heat illness symptoms, they were generally unaware of their clients' vulnerability. MHWs' minimal heat-risk knowledge leaves pregnant women and developing fetuses at risk of preventable harm.

A multi-scalar climatological analysis in preparation for extreme heat at the Tokyo 2020 Olympic and Paralympic Games.

Extreme heat can be harmful to human health and negatively affect athletic performance. The Tokyo Olympic and Paralympic Games are predicted to be the most oppressively hot Olympics on record. An interdisciplinary multi-scale perspective is provided concerning extreme heat in Tokyo-from planetary atmospheric dynamics, including El Niño Southern Oscillation (ENSO), to fine-scale urban temperatures-as relevant for heat preparedness efforts by sport, time of day, and venue. We utilize stochastic methods to link daytime average wet bulb globe temperature (WBGT) levels in Tokyo in August (from meteorological reanalysis data) with large-scale atmospheric dynamics and regional flows from 1981 to 2016. Further, we employ a mesonet of Tokyo weather stations (2009-2018) to interpolate the spatiotemporal variability in near-surface air temperatures at outdoor venues. Using principal component analysis, two planetary (ENSO) regions in the Pacific Ocean explain 70% of the variance in Tokyo's August daytime WBGT across 35 years, varying by 3.95°C WGBT from the coolest to warmest quartile. The 10-year average daytime and maximum intra-urban air temperatures vary minimally across Tokyo (<1.2°C and 1.7°C, respectively), and less between venues (0.6-0.7°C), with numerous events planned for the hottest daytime period (1200-1500 hr). For instance, 45% and 38% of the Olympic and Paralympic road cycling events (long duration and intense) occur midday. Climatologically, Tokyo will present oppressive weather conditions, and March-May 2020 is the critical observation period to predict potential anomalous late-summer WBGT in Tokyo. Proactive climate assessment of expected conditions can be leveraged for heat preparedness across the Game's period.