Background: Global climate change is already increasing the average temperature and direct heat exposure in many places around the world. Objectives: To assess the potential impact on occupational health and work capacity for people exposed at work to increasing heat due to climate change. Design: A brief review of basic thermal physiology mechanisms, occupational heat exposure guidelines and heat exposure changes in selected cities. Results: In countries with very hot seasons, workers are already affected by working environments hotter than that with which human physiological mechanisms can cope. To protect workers from excessive heat, a number of heat exposure indices have been developed. One that is commonly used in occupational health is the Wet Bulb Globe Temperature (WBGT). We use WBGT to illustrate assessing the proportion of a working hour during which a worker can sustain work and the proportion of that same working hour that (s)he needs to rest to cool the body down and maintain core body temperature below 38°C. Using this proportion a ‘work capacity’ estimate was calculated for selected heat exposure levels and work intensity levels. The work capacity rapidly reduces as the WBGT exceeds 26-30°C and this can be used to estimate the impact of increasing heat exposure as a result of climate change in tropical countries. Conclusions: One result of climate change is a reduced work capacity in heat-exposed jobs and greater difficulty in achieving economic and social development in the countries affected by this somewhat neglected impact of climate change. Keywords: climate change; work; heat; occupational health; productivity (Published: 11 November 2009) Citation: Global Health Action 2009. DOI: 10.3402/gha.v2i0.2047

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Workplace heat stress, health and productivity - an increasing challenge for low and middle-income countries during climate change.

Global climate change will increase outdoor and indoor heat loads, and may impair health and productivity for millions of working people. This study applies physiological evidence about effects of heat, climate guidelines for safe work environments, climate modeling, and global distributions of working populations to estimate the impact of 2 climate scenarios on future labor productivity. In most regions, climate change will decrease labor productivity, under the simple assumption of no specific adaptation. By the 2080s, the greatest absolute losses of population-based labor work capacity (in the range 11% to 27%) are seen under the A2 scenario in Southeast Asia, Andean and Central America, and the Caribbean. Increased occupational heat exposure due to climate change may significantly impact on labor productivity and costs unless preventive measures are implemented. Workers may need to work longer hours, or more workers may be required, to achieve the same output and there will be economic costs of lost production and/or occupational health interventions against heat exposures.

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The direct impact of climate change on regional labor productivity.

Heat balance in humans is maintained at near constant levels through the adjustment of physiological mechanisms that attain a balance between the heat produced within the body and the heat lost to the environment. Heat balance is easily disturbed during changes in metabolic heat production due to physical activity and/or exposure to a warmer environment. Under such conditions, elevations of skin blood flow and sweating occur via a hypothalamic negative feedback loop to maintain an enhanced rate of dry and evaporative heat loss. Body heat storage and changes in core temperature are a direct result of a thermal imbalance between the rate of heat production and the rate of total heat dissipation to the surrounding environment. The derivation of the change in body heat content is of fundamental importance to the physiologist assessing the exposure of the human body to environmental conditions that result in thermal imbalance. It is generally accepted that the concurrent measurement of the total heat generated by the body and the total heat dissipated to the ambient environment is the most accurate means whereby the change in body heat content can be attained. However, in the absence of calorimetric methods, thermometry is often used to estimate the change in body heat content. This review examines heat exchange during challenges to heat balance associated with progressive elevations in environmental heat load and metabolic rate during exercise. Further, we evaluate the physiological responses associated with heat stress and discuss the thermal and nonthermal influences on the body's ability to dissipate heat from a heat balance perspective.

Thermometry, calorimetry, and mean body temperature during heat stress.

The very large number of human thermal climate indices that have been proposed over the past 100 years or so is a manifestation of the perceived importance within the scientific community of the thermal environment and the desire to quantify it. Schemes used differ in approach according to the number of variables taken into account, the rationale employed, the relative sophistication of the underlying body-atmosphere heat exchange theory and the particular design for application. They also vary considerably in type and quality, as well as in several other aspects. Reviews appear in the literature, but they cover a limited number of indices. A project that produces a comprehensive documentation, classification and overall evaluation of the full range of existing human thermal climate indices has never been attempted. This paper deals with documentation and classification. A subsequent report will focus on evaluation. Here a comprehensive register of 162 thermal indices is assembled and a sorting scheme devised that groups them according to eight primary classification classes. It is the first stage in a project to organise and evaluate the full range of all human thermal climate indices. The work, when completed, will make it easier for users to reflect on the merits of all available thermal indices. It will be simpler to locate and compare indices and decide which is most appropriate for a particular application or investigation.

A comprehensive catalogue and classification of human thermal climate indices

Heat stress and strain in exercise and sport

Eight laboratories participated in a concerted research project on the assessment of hot working conditions. The objectives were, among others, to co-ordinate the work of the main European research teams in the field of thermal factors and to improve the methods available to assess the risks of heat disorders at the workplace, and in particular the "Required Sweat Rate" model as presented in International Standard ISO 7933 Standard (1989). The scientific bases of this standard were thoroughly reviewed and a revised model, called "Predicted Heat Strain" (PHS), was developed. This model was then used to predict the minute by minute sweat rates and rectal temperatures during 909 laboratory and field experiments collected from the partners. The Pearson correlation coefficients between observed and predicted values were equal to 0.76 and 0.66 for laboratory experiments and 0.74 and 0.59 for field experiments, respectively, for the sweat rates and the rectal temperatures. The change in sweat rate with time was predicted more accurately by the PHS model than by the required sweat rate model. This suggests that the PHS model would provide an improved basis upon which to determine allowable exposure times from the predicted heat strain in terms of dehydration and increased core temperature.

Development and validation of the predicted heat strain model

Objective: To co-ordinate the work of the main European research teams in the field of thermal factors in order to develop and improve significantly the methods presently available for assessing the risks of heat disorders encountered during work in hot conditions. Method: Each item from the required sweat rate model was reviewed on the basis of the most recent literature. A database with 1,113 laboratory and field experiments, covering the whole range of hot working conditions, was assembled and used for the validation. Results: Influence of clothing ensemble on heat exchange: methods and formulas were developed that take into account the dynamic effects associated with forced convection and the pumping effect associated with body movements and exercise. Prediction of the average skin temperature: the model used in the required sweat rate standard ISO 7933 was extended to cover more severe conditions with high radiation and high humidity and different clothing and take into account the rectal temperature for the prediction of the skin temperature. Criteria for estimating acceptable exposure times in hot work environments: criteria were reviewed and updated concerning the maximum increase in core temperature and the acceptable water loss, for acclimatised and non-acclimatised subjects. These limits are intended to protect 95% of the population. Measuring strategy: a strategy was developed to assess the risks in any working situation with varying conditions of climate, metabolic rate or clothing. A detailed methodology was developed in three stages: an "observation" method for the recognition of the conditions that might lead to thermal stress; an "analysis" method for evaluating the problem and optimising the solutions; and an "expert" method for in-depth analysis of the working situation when needed. Validation: the different results were used to prepare a revision of the interpretation procedure proposed in the ISO standard 7933. We validated the modified approaches using the database. This involved the whole range of conditions for which the model was extended, namely conditions with high and low radiation, humidity and air velocity as well as fluctuating conditions. Based on these results, the predicted heat strain model was developed: it is presently proposed as an ISO and CEN standard.

Assessment of the risk of heat disorders encountered during work in hot conditions

Objectif: L'objectif de la recherche a ete de coordonner le travail des principales equipes de recherche europeennes dans le domaine des facteurs thermiques afin d'ameliorer et de developper de maniere significative les methodes actuellement disponibles pour evaluer le risque d'astreintes thermiques lors du travail en ambiances chaudes. Resultats: - Influence des vetements sur les echanges thermiques Les effets dynamiques lies a la vitesse de l'air et l'effet de pompage lie aux mouvements et au travail sont pris en compte. - Prediction de la temperature cutanee moyenne Le modele a ete etendu a des conditions climatiques plus severes (rayonnement et humidite eleves, differents vetements...) et tient compte de la temperature centrale (rectale) pour la prediction de la temperature cutanee. - Criteres pour estimer des durees d'exposition acceptables dans les environnements chauds de travail Les criteres d'augmentation maximale de la temperature centrale et de perte hydrique acceptable ont ete revus pour des sujets acclimates et non acclimates. Ces limites protegent 95% de la population. - Strategie de mesure Une strategie a ete developpee pour evaluer les risques dans n'importe quelle situation de travail, avec des conditions variables de climat, de metabolisme ou de vetement. Des outils ont ete decrits en details pour les trois niveaux superieurs de la strategie SOBANE: ○ Une demarche d'Observation, pour l'identification des conditions qui pourraient mener a la contrainte thermique; ○ Une demarche d'Analyse, pour l'evaluation du probleme et l'optimisation des solutions quand la demarche d'Observation n'a pas abouti; ○ Une demarche d'Expertise lorsque l'etude specialisee de la situation de travail est indispensable. - Le Modele de prediction de la contrainte thermique (PHS: Predicted Heat Strain) Un nouveau modele de prediction de l'astreinte thermique a ete developpe et une revision de la norme ISO 7933 relative a la contrainte thermique en ambiances chaudes a ete preparee, en remplacement de l'indice de Sudation Requise qui devient ainsi obsolete. - Validation Le nouveau modele a ete valide a partir des donnees d'un ensemble d'experiences menees en laboratoire et sur le terrain et couvrant la gamme entiere des conditions pour lesquelles le modele a ete etendu, a savoir les conditions avec rayonnement, humidite ou vitesse d'air eleves et faibles, ainsi que pour des conditions fluctuantes au cours du temps.

G. Alfano

Papers

Development and validation of the predicted heat strain model

Assessment of the risk of heat disorders encountered during work in hot conditions

Évaluation du risque de contrainte thermique lors du travail en ambiances chaudes

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