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Thermal Environments in the Construction Industry: A Critical Review of Heat Stress Assessment and Control Strategies

  • Ruwini Edirisinghe
  • Mary Myla Andamon
Chapter
Part of the Green Energy and Technology book series (GREEN)

Abstract

In the light of climate change predictions, the increasing number of hot days will cause a significant impact on public health, mortality rates, energy demand and economy of Australia. Heat is also an occupation hazard, which is a growing concern in many industries. Heat stress hazards can be categorized as clinical, human performance diminishing and accident causing. The risk can be exaggerated in certain industries, including the construction industry, due to specific environmental conditions, work characteristics and occupational settings. This chapter discusses the main problems and risks associated with heat stress, with a particular emphasis on the construction industry. Various heat stress indices and advances in the assessment of heat stress in recent years are discussed. Finally, this chapter discusses the strategies and controls that can be implemented to mitigate the impact of heat stress in the construction industry. Various acclimatization protocols, hydration, self-pacing and exposure time limits or temperature risk control regimes are discussed by analysing standards, guidelines and policies and practices. This chapter contributes to resolving a timely and strategic occupational hazard through a holistic view of the thermal environment in construction industry settings.

1 Introduction

Australia is the world’s driest inhabited continent, and there is an extensive body of climatological evidence that the landscape and environments of the country differ significantly from those of other continents [32]. As discussed in Chapter “ Urban Climates in the Transformation of Australian Cities”, extreme heat events are projected to occur more frequently across the country and with increased severity, including in all capital city locations [52] in Australia. This alerts us to the potential for exaggerated climatic heat stress in the future with potentially significant impact on public health, mortality rates, energy demand and economy [78, 82].

1.1 Heat Stress

Rowlinson et al. [77: p. 188] define heat stress as the ‘heat load imposed on the human body, including environmental heat, metabolic heat and the thermal effect of clothing’. A dynamic heat balance between the body and its environment is required by the laws of thermodynamics; that is, heat transferred into the body and generated within the body must be balanced by heat outputs from the body in a dynamic manner [71 #7: p. 9, 72: p. 33, #125]. When the total of the heat transferred to the body and the heat generated within the body is greater than the heat output, body temperature rises.

The human thermal environment was originally fundamentally defined as consisting of four basic environmental factors (air temperature, humidity, radiant heat and wind speed) and two personal parameters of clothing and the amount of metabolic heat generated by physical activity [34] as discussed below. However, the literature suggests that other environmental factors such as barometric pressure are also influential [7, 13]. To present the environmental heat stress more accurately, it is important to go down to a microlevel. Urban microclimate (atmospheric) as well as clothing microclimate are crucial in this regard. Local microclimates can vary greatly based on such factors as topography, elevation, moisture, wind, soil and vegetation. Climatic heat stress ultimately occurs in the microclimate between the body and the clothing covering it, and thus the properties of the clothing are significant [34]. The insulation, permeability and water vapour resistance of the clothing [30] worn by the person significantly affect the heat exchange between the body and the environment. Metabolic heat is generated by activity. Posture, too, affects the heat exchange between the body and the environment. Hence, an understanding of the relevant activities and postures is crucial in analysing metabolic heat production. In addition to the fundamental factors needed to represent the minimum requirements for a conceptualization of heat stress conditions, a number of personal and external factors can influence the ability of an individual to dissipate excess heat [90].

1.2 Heat Stress Hazard

From a medical perspective, heat-induced illness covers a spectrum of disorders [53], ranging from minor to catastrophic based on the duration, severity and consequences of the risk. The spectrum of disorders covered by ‘heat stress’ includes physical fatigue, mental fatigue, heat-related chronic conditions and heat illnesses (where some are symptoms of heat stroke [10, 49]) in which the risk of heat stroke is catastrophic on the basis of its severe consequences.

Physical fatigue elevated by exposure to heat causes significant physical performance decrements [10]. Miller and Bates [57] flag the fact that physiological heat stress increases worker vulnerability to heat-related illness and decreases physical and cognitive performance and physical alertness [71]. Heat stress not only threatens survival, but also harms morale [13] and leads to deterioration of work efficiency and productivity [33] among workers.

Workplace accidents are more common in hot environments and are often associated with heat stress and dehydration [48]. Fatigue, which includes the deterioration of both physical and cognitive ability, is identified as one of the most important causes of construction accidents [20, 38]. In this regard, Edwards and Bowen [31] argue that heat stress presents a legal risk to organizations when accidents subsequently occur.

1.3 Construction Environments and Conditions

Conditions in construction sites vary with the geographic locations, types of construction and the stages of a project life cycle, particularly with the construction phases and stages of procurement of the projects. Depending on the site characteristics and construction work, the environmental parameters will amplify the effects of the ambient thermal conditions. In outdoor works such as civil works, concrete pouring and roofing [87], workers are more vulnerable to radiant heat from site characteristics, handling of construction materials and external building surfaces. For building works that offer shaded areas or enclosed conditions, environments will mostly be characterized as with high humidity with poor ventilation. The requirement of the use of construction personal protection equipment (PPE) also contributes to and exacerbates the construction workers’ heat strain [58, 89].

While studies have addressed heat stress problem in general and among other vulnerable population, heat stress in the construction industry is emerging. The exposure and susceptibility of construction workers to heat stress have always been a challenge to the construction industry [88]. Various strategies and policies within the building industry sector have been implemented [14, 15, 16, 40, 64]. However, despite the existence of these guidelines and regulatory requirements, increased heat stress-related morbidity and mortality are widely reported [21, 50, 60, 73, 74, 77, 83, 84].

In this vacuum, Sect. 2 of this chapter discusses the heat stress risk in the construction industry. Risk assessment mechanisms used in the industry are also analysed. Section 4 presents the control regimes adopted by the industry. Section 5 presents the discussion, where gaps and recommendations are highlighted, and Sect. 6 concludes the chapter.

2 Heat Stress Risk in the Construction Industry

The construction industry has complex processes, and managing work health and safety in construction remains a wicked problem [29]. Globally, the construction industry records high accident rates and thus has been a priority industry for occupational health and safety improvements for decades [28, 42]. The construction industry is found to be more susceptible to heat stress than other industries due to its occupations’ settings [84, 90]. Construction workers are vulnerable to heat stress factors (as set out above). These include: (i) direct exposure to climatic conditions (tropical/hot and humid or extreme environmental conditions, high radian heat loads or direct sun light); (ii) confined work environments and work environments near radiant heat sources; (iii) heat stress exacerbated by heavy industrial clothing and personal protective equipment (PPE); (iv) physically demanding work at a high metabolic rate; and (v) types of construction site (e.g. roads, buildings), project life cycles (indoor vs. outdoor) and construction activities which have a significant impact on climatic heat stress. The inherently dangerous construction industry is also inherently vulnerable to heat stress hazards.

3 Assessing Heat Stress

Physiological strain in the heat can be expressed in terms of the magnitude of core body temperature elevations, the volume of sweat lost (and the subsequent degree of dehydration if fluids are not fully replaced) [47] or loss of body mass through sweating [46], as well as, to a lesser extent, elevation in mean skin temperature [47]. Physical fatigue resulting from heat strain can be indicated by heart rate, oxygen uptake, blood pressure, respiration rate and/or perceived fatigue [10].

In the measurement and ‘prediction’ of the human response to thermal environments, thermal indices have proven useful in describing and assessing human thermal environments. Many studies have explored heat risk identification mechanisms [33] in general including the comfort literature reviews on indices [37, 39, 79, 86] Generally, these are categorized in three types [70]: those derived from heat balance equations and mathematical models that describe the behaviour of the human body in thermal environments (rational indices); those which are derived from experiments (empirical indices) and those based on measurements taken on simple instruments that respond to thermal environmental factors which also affect people (direct indices). An extensive discussion of these categories can be found in the ASHRAE Handbook Fundamentals [6]—application of heat stress indices and assessment methods in the construction industry.

The aim of this section is to review those mechanisms and indices that have been tried and tested in the construction industry or in equivalent industrial configurations. The industry sector is demarcated for the purposes of this section according to the definition of the Australian Construction and Mining Equipment Industry Group [14].

Some of these indices used in construction only look at one environmental parameter to assess heat stress [14], while others use more [67] (ISO 7243 1989 43]). Some indices assess or predict the heat stress, taking physiological [62] and/or perceptual [23] personal differences into account, including metabolic rates [12, 13]. Predictive models have been introduced that are based on multiple regression analysis of specific indices in conjunction with other factors. These indices and their application in the construction industry are discussed below. The indices are summarized in Table 1.
Table 1

Heat stress assessment methods used in the construction industry

Index

Parameters

Positives

Limitations

CFMEU single-parameter index

Ambient temperature

Simple, easy to use

Inaccurate, negative impact on productivity or health

NOAA heat index

Air temperature, relative humidity

More reliable than single parameter

Not represent heat stress with a sufficient accuracy

Natural WBGT index

Dry-bulb temperature, wet-bulb temperature, black globe temperature

Standardized, widely used, better representation of heat stress

Insensitive to wind speed, overestimation, weak correlation with strain parameters, effects of protective behaviours(self-pacing), age and BMI not covered, metabolic rate and clothing effects are ignored

PSI

Heat strain parameters

Accounts for protective behaviour, individual differences (age, BMI)

Difficult to measure on site, practical issues, calibration needed to individual factors for better accuracy

Perceptual heat stress

Human perception

High correlation with strain indices, generalization to climatic and working conditions is under-researched

Subjective measurements, not reliable scales of temperature

PHS model index

Temperature, humidity, globe temperature, air velocity, metabolic rate, clothing effect, body size, posture and wind direction

Best representation of related factors, model validated with a large sample

Not reliable with thick clothing, validated reliability in occupation setting is unavailable, complexities of use and taking measurements, negative impact on productivity

TWL

Dry-bulb, wet-bulb and globe temperatures, wind speed and atmospheric pressure

Works well with air movement

Assumption is clothing factor, only for self-paced workers

Regression model

VO2, minute ventilation (MV), respiratory exchange ratio (RER), metabolic equivalent (MET), energy expenditure (EE) heart rate, perceived exertion (RPE), WBGT

A model with a wide range of parameters

Practical issues in collecting parameters, small sample, not validated, regression models are less accurate, generalizability is an issue

3.1 Single-Parameter Index

Some heat stress management protocols in the construction industry use a single environmental parameter, usually the ambient temperature, as the indicator of heat stress. For example, the Enterprise Bargaining Agreement (EBA) of the Australian Construction, Forestry, Mining and Energy Union (CFMEU) states that 35 °C is the limit for work [14]. The use of a single environmental condition as a heat stress indicator has been widely criticized in the literature [9, 35, 61]. A single environmental condition is an unreliable indicator upon which to base a decision to terminate work or reduce shift length. Bates [9] highlights the negative impact of such strategies on productivity and protection of workers’ health.

3.2 Heat Index (NOAA)

The heat index system was developed by the US National Oceanographic and Atmospheric Administration (NOAA) [67]. It combines air temperature and relative humidity into a single value to indicate apparent hotness. Because this index factors in the evaporation of sweat from the skin through humidity, it is more reliable than using a single parameter. The US heat stress guidelines propose risk levels based on the ‘heat index’ and suggest protective measures based on several thresholds [68]. The heat stress guidelines also serve as the regulatory guidelines for the construction industry. However, the heat index does not take the effect of solar radiation into account when calculating the hotness of an environment and thus does not represent the environmental heat stress with sufficient accuracy.

Chan et al. [20] trialed heat index in the construction industry in Hong Kong with a sample of rebar workers. The model reported that many factors would affect human physiological response to heat stress triggering that the heat index as a function of temperature and relative humidity is only a rough indicator.

3.3 Wet-Bulb Globe Temperature (WBGT) Index

The wet-bulb globe temperature (WBGT) index was originally developed based on the weighting of three environmental parameters: dry-bulb temperature, wet-bulb temperature and black globe temperature [85]. A shielded dry-bulb thermometer, a natural wet-bulb thermometer and a globe thermometer (a black globe heated by solar radiation) are used to capture these environmental parameters. The WBGT index was later standardized (ISO 7243 1989 43]) and is now widely used as a heat stress index throughout the world, with the guidelines and permissible threshold limits [2] in many industries, including construction and underground mining operations [9], being based on this measure.

Even though natural WBGT is a better index than the NOAA ‘heat index’ as a way of representing environmental hotness, its shortcomings have been widely recognized in the literature. Among the critiques are that: (i) it is insensitive to wind speed [13] and underestimates the effect of wind speed [58]; (ii) the WBGT index has overestimated the heat stress faced by subjects exposed to heat in many developing countries, such as China, India, Thailand and Dubai [10, 41]; (iii) there is weak correlation between WBGT and physiological strain parameters [23, 24, 56], and thus the index is unable to indicate the physiological responses in the body for a true representation of heat stress; (iv) it is unable to represent the effects of self-pacing, age and BMI [24]; and (v) it is unable to measure the effect of the other non-environmental heat stress factors, namely metabolic rate and the clothing effect [71].

As widely recognized by the literature, the environmental indices on their own have limitations in reliably assessing/predicting heat stress due to the individual differences and complexity of the variables associated with the differences.

3.4 Physiological Strain Index (PSI)

The physiological strain index considers the individual heat strain parameters in contrast to the environmental parameters discussed above. PSI is based on heart rate and core temperature measurements and is represented on a scale from zero to 10 [62]. PSI can take into account parameters such as age and BMI and can also account for protective behaviour (e.g. self-pacing) [58].

3.5 Perceptual Heat Stress

The thermal sensation of hot or cold is psychological phenomena, and although there are physiological mechanisms in the body which respond to temperature, thermal sensation depends upon such things as previous experience, individual differences and rates of change of temperature. Humans are therefore not good temperature-measuring instruments and cannot provide reliable scales of temperature [71].

However, Dehghan et al. [23] argue that the body response to heat stress is known as the strain by which physiological and psychological parameters are measuring. They further argue that the physiological strain index together with observational–perceptual method shows a higher correlation with PSI than WBGT [8, 23]. Supportively, Chan and Yang [19] recently validated perceptual strain index (PeSI) developed by Tikuisis et al. [80] in the construction industry and found that PeSI is sensitive to the variants of WBGT and RHR and changes in the same general manner as PSI. Generalizability of the PeSI in various climatic and working environments is yet to be reported.

3.6 Predictable Heat Strain Model Index (ISO 7933:2004)

The predictable heat strain model [55] was developed and validated as a collaboration between eight major European laboratories, to ground the originally defined ‘required sweat rate’ model in ISO 7933:1989 [44] in a practical manner. For example, ISO 7933 is able to predict the sweat rate for constant climatic and working conditions. The PHI model was standardized as ISO 7933:2004 [45].

The PHS model takes air temperature, humidity, globe temperature, air velocity, metabolic rate, clothing effect, body size, posture and wind direction as inputs and provides a detailed analysis of the working conditions with predicted and required parameters such as the sweat rate, evaporative heat flow, the skin wettedness and the rectal temperatures. Despite the fact that which temperature more accurately describes the body thermal state is still an open question, in occupational terms rectal temperature is often assumed as being representative of the thermal state of an individual and is used in ISO 7933:2004 [75]. ISO 7933:2004 [45] suggests maximum allowable exposure duration. Rowlinson and Jia [76] applied the PHS model in the Hong Kong construction industry. This study was replicated by Lundgren et al. [54] in their Indian sample. Rowlinson and Jia [76] estimated metabolic rates based on heart rates which might have overestimated the metabolic rate. Even though it is protective of workers, can introduce unintended productivity issues. In addition, the study used tympanic temperature at the start instead of rectal temperature which has affected the accuracy defined in the ISO 7993:2004. Moreover, Rowlinson and Jia [76] assumed typical summer clothing ensemble and the effect of safety helmet was ignored which has a significant influence on body thermal state. Wang et al. [81] proved the lack of reliability of PHS index when it is used with thick protective clothing. It is paramount to evaluate the accuracy of the model with the actual parameters of clothing assembly. Hence, validated evidence on reliability of this method in various local settings is yet to be reported.

ISO 7933:2004 is often criticized when introduced into a workplace where large number of workers are involved, for complexities of use [58] and potential interruptions to the working environment and activities [76] which can have a negative consequence on productivity rather than a positive one.

3.7 Thermal Work Limit (TWL)

Brake and Bates [13] propose a heat index combined with data on environmental, metabolic and clothing factors called the ‘thermal work limit’ for workers who are well educated about working in heat, have control over their work rate, are healthy and are well hydrated. TWL uses five environmental variables: dry-bulb, wet-bulb, and globe temperatures, wind speed and atmospheric pressure and accommodates for clothing factors. As the equations used to derive heat transfer rate through clothing are not valid for subjects in encapsulating protective clothing (EPC), TWL cannot be assumed to be valid where impermeable clothing is used. TWL is particularly suitable when there is significant cooling related to air movement.

TWL model was validated in the Australian mining industry [58] and subsequently included in heat stress management guidelines and standards in Australia [5, 11, 25] and Abu Dhabi [27].

Dehydration status of construction workers was assessed using urine specific gravity (USG) measurements to indicate the absolute hydration status of the body in Australia [57], UAE [10] and Iran [9, 61]. All the studies found that the USG could be used as an indicator of thermal heat stress. While Bates and Schneider [10] found that use of WBGT as a thermal index is inappropriate for the study sample of 22 participants studies over 3 days, however, TWL was found to be a valuable index. In contrast, Farshad et al. [35] concluded that both GBWT and TWL were good indicators of heat stress in Iran climate but TWL has merit due to its based-on-required-intervention classifications.

3.8 Multiple Regression Analysis-Based Heat Stress Models

Chan et al. [17] conducted a study in Hong Kong construction industry. Prior to the experiments, they collected demographic data including age, behavioural habits (smoking, drinking) and other personal information together with body weight, percentage of body fat (PBF), resting heart rate and blood pressure. During the experiments, physiological data such as VO2, minute ventilation (MV), respiratory exchange ratio (RER), metabolic equivalent (MET), energy expenditure (EE) heart rate were monitored every five second. Rating of perceived exertion (RPE) was also recorded every five minutes. Environmental data on ambient dry-bulb temperature, natural wet-bulb temperature, globe temperature and relative humidity were also collected to calculate WBGT.

A similar study was conducted with a sample of rebar workers by Chan et al. [18] using TWL. These heat stress models were derived to predict workers’ physiological responses, different metrological factors, work-related factors and personal factors based on multiple regression analyses. As Rowlinson et al. [77] argue complexity of the factors affecting heat stress is beyond the predictive power of multiple regression models. Hence, generalizability of the model to varying trades with in construction industry and to climatic conditions is yet to be reported.

4 Heat Stress Control Regimes

The National Institute for Occupational Safety and Health [63] provides standards of working practices to address hot environments. The three categories of standard are based on the recommendations and control methods NIOSH published in 1986, and the categories are (i) engineering controls; (ii) administrative controls; and (iii) personal protective clothing and auxiliary body cooling. When applying engineering controls for heat stress is not practical or sufficient, administrative strategies can be implemented to control heat risk. A significant number of research studies on heat stress control in construction using such administrative controls have been reported in the literature.

The NIOSH standard [63] recommends education and training on heat stress, for both workers and management. Training programmes at both levels should include recognition of heat stress (i) signs and symptoms, (ii) causes, (iii) the impact of PPE, (iv) the effect of non-occupational factors (drugs, alcohol and obesity), (v) the importance of acclimatizing, (vi) procedures for responding to symptoms and (vii) the importance of hydration. In addition to self-awareness, the NIOSH standard also emphasizes the importance of enhancing heat tolerance. Regular medical programmes and health screening methods are also recommended to capture workers’ histories of heat illness and to monitor heat tolerance. Other control measures are discussed below.

4.1 Acclimatization Protocols

Human populations are acclimatized to their local climates, in physiological, behavioural and cultural terms. Stimulation of human heat-adaptive mechanisms can increase the capacity to tolerate work in heat [13, 63]. Even though a simple and practical measure of acclimatization is not available, some robust protocols have been designed to increase the ability of workers to work in hot environments. Heat acclimatization can usually be induced in 7 to 14 days of exposure at a hot job [3, 22, 66].

4.2 Hydration

Miller and Bates [57] studied fluid balance by monitoring fluid intake and hydration levels through urine specific gravity of Australian mining workers. They argue that the creation of a culture of hydration awareness in a workforce is an important component of a heat stress risk management strategy for workers. Supportively, Montazer et al. [61] argue that heat stress management without considering the real hydration status of workers is inadequate. However, self-hydration without an active campaign of the kind recommended by Miller and Bates [57] was challenged by the findings of Montazer et al. [61], in which they reported that the USG level of workers increased during midday work because the workers were asked to drink a specific volume of water during their work.

4.3 Self-pacing

Self-paced workers are defined as those who can and do regulate their own work rate, are not subject to excessive peer or supervisor pressure or monetary incentives and are well educated about the issues of working in heat and the importance of self-pacing [13: p. 176]. Brake and Bates [13] argue that for heat stress risk management to be effective, self-pacing should be formally incorporated in a protocol mandating workers to self-pace and supported by supervisors and management. In addition, the study of Australian mining workers [12] found that self-pacing occurs among well-informed workers. Supportively, Bates and Schneider [10], with a sample of UAE construction workers, found that people can work, without adverse physiological effects, in hot conditions if they are provided with the appropriate fluids and are allowed to self-pace. A further study in the UAE found that uneducated workers also regulate their workload in thermally stressful conditions [59].

Combining all three control strategies, Miller et al. [59] argue that well-hydrated, acclimatized workers who are permitted to self-pace may safely continue working under fluctuating harsh environmental conditions.

4.4 Limiting Exposure Time or Temperature

Guidelines for work–rest schedules and practical intervention levels and protocols are discussed below.

4.5 Construction, Forestry, Mining and Energy Union (CFMEU)

The CFMEU hot weather policy [14] recommends stopping work and leaving the site when air temperature reaches 35 °C. The agreement also states that at temperatures below 35 °C, workers are to be relocated out of direct sunlight where the work environment creates a serious risk to their health and safety. These serious risks include: (i) radiant heat from particular surfaces like bondeck, roofing; (ii) sun glare; and (iii) the type of work being performed.

4.6 ACGIH Threshold Limit Values (TLV) and Action Limit (AL) for Thermal Stress

The ACGIH [3] suggests threshold limit values (TLVs) for thermal stress. The objective of the TLV system is to maintain core body temperature within +1oC of the normal value (37 °C). TLV for heat-acclimatized, hydrated, un-medicated, healthy workers and action limit (AL) for un-acclimatized workers are expressed as time-weighted average (TWA) exposure for an eight-hour workday and 40-h (five-day) workweek. The effective wet-bulb globe temperature (WBGT) is derived based on the measured WBGT (then environmental index), plus the clothing adjustment factor (where clothing adjustment factor cannot be added for multiple layers). Empirical data are used to estimate metabolic rate. The time-weighted average of the effective WBGT accounts for the metabolic rate based on the work–rest regimen.

4.7 NIOSH Recommended Alert Limits (RALs) and Recommended Exposure Limits (RELs)

NIOSH is the US federal agency responsible for promoting occupational safety and health and recommends limiting the level of health risk associated with the total heat load imposed on a worker in a hot environment [63]. Recommended alert limits (RALs) are for un-acclimatized workers, whereas recommended exposure limits (RELs) are for acclimatized healthy workers, where the workers should be able to tolerate the heat stress without incurring adverse effects. Estimates of both environmental and metabolic heat are expressed as one-hour time-weighted averages (TWAs), as described by the ACGIH [4]. However, these limits are applicable to workers wearing the conventional one-layer work clothing ensemble. RAL and REL estimations are based on empirical data [26, 51, 63].

4.8 TWL-Based Interventions

The thermal work limit [13] gives a limiting (or maximum) sustainable metabolic rate (LMR) that acclimatized individuals can maintain in a specific thermal environment, in the form of a safe deep body core temperature (<38.2 °C or 100.8 °F) and a sweat rate (<1.2 kg or 2.6 lb/h). TWL predicts the limiting work rates under given environmental conditions, and interventions are recommended accordingly, such as withdrawal (if TWL value <115 W/m2), buffer (115–140 W/m2), acclimatization (141–220 W/m2) and unrestricted work (>220 W/m2).

Montazer et al. [61] found a strong correlation between TWL and USG, and a significant difference between the control group and the group exposed to heat. The maximum TWL levels were observed in the middle of the work shift. Bates and Schneider [10] indicated that with interventions to encourage fluid intake, self-paced construction workers were able to work in extreme temperatures, often in excess of 45 °C, with no evidence of physiological strain as assessed from working heart rates and aural temperature readings.

4.9 PHS Model (ISO 7933 2004)

The PHS model [45] predicts the maximum allowable exposure duration and provides a sensitivity analysis for testing the impact of specific parameters, including environmental heat, clothing effect and metabolic heat. Rowlinson and Jia [76] found that environmental thresholds computed by the PHS model, based on their sample, are 2–3 °C WBGT higher than the equivalent TLVs and thus argue that these thresholds can be used for initial screening but not as action-triggering thresholds.

Rowlinson and Jia [76] developed localized threshold-based guidelines for practical implementation using a number of the guidelines discussed above. They used the PHS model to develop a tool to facilitate managerial decision-making on an optimized work–rest regimen for paced work. Further, they used a TWL model-based limiting metabolic rate (LMR) to develop a tool to enable workers’ self-regulation during self-paced work. The recovery time following a period of paced work was calculated using TWA [2].

5 Discussion

A preventive measure called the heat alert programme by NIOSH recommends establishing a heat alert committee during hot seasons to declare heat alerts and execute appropriate actions accordingly. Note that maintaining an effective heat alert committee is quite a resource-intensive administrative process. In construction settings, stakeholder groups come together for a short period of time [36] to complete a job and disband upon project completion, often without forming long-term working relationships beyond the scope of the project [65]. Due to the dynamic nature of the industry and this project-based group cohesiveness, the practical aspects of ensuring regular medical screenings and setting up heat alert committees are challenging compared to industries with regular permanent workforces.

In addition to self-awareness, the NIOSH standard also emphasizes the importance of enhancing heat tolerance, which has been trialed in other industries such as defence [22, 66]. Acclimatization protocols are practical for the construction industry to adopt. We recommend embedding them in ongoing heat stress training or occupational health and safety programmes.

Intervention strategies, such as those developed by the American Conference of Governmental Industrial Hygienists [3], and the thermal work limit (TWL) [13], specify threshold values for acclimatized and non-acclimatized workers. According to the ACGIH [3], a worker is considered acclimatized when they have a recent history of heat stress exposure of at least two continuous hours over between 5 of the last 7 days and 10 of the last 14 days. Nevertheless, evidence as to whether workers exposed intermittently to various lengths and amounts of heat stress during their jobs develop heat acclimatization similar to that achieved by continuously exposed workers is yet to be reported.

Similarly to acclimatization, the electrolyte and water balance problems of intermittently heat-exposed workers in comparison with continuously heat-exposed workers are still unknown.

Regardless of the practical implications, the standards also recommend decreasing work time and increasing workforce size to reduce metabolic heat load, in addition to introducing mechanization. Productivity remains a subject of debate in the Australian construction industry, which is a serial productivity under-performer [1, 69]. Because of this, the implementation of strategies that consume more resources can be challenging. Nevertheless, in financial year 2013, an annual loss of $6 billion worth of labour productivity due to climatic heat stress was reported in Australia [91], which amounts to between 0.33 and 0.47% of GDP. This would seem to be sufficient to justify extra investment in heat stress mitigation.

6 Conclusions

This chapter has discussed the human thermal environment in a significant occupational setting. It presented an assessment of the heat stress hazards in construction, as well as risk assessment and risk control regimes. Research and practice gaps and recommendations were derived. It is of paramount importance that urban microclimates are measured in order to assess the degree of environmental heat stress in construction, and Chapter “ Urban Climate in the Transformation of Australian Cities” provides more detail about these microclimates in the context of climate change. It is vital to consider the requirements of vulnerable populations, such as construction workers, given their specific occupational settings, which can exacerbate heat stress. The importance of addressing the requirements of other vulnerable population such as low-income population and school children is discussed in Chapters “ Low-Energy Housing as a Means of Improved Social Housing: Benefits, Challenges and Opportunities” and “ Indoor Environmental Quality of Preparatory to Year 12 (P-12) Educational Facilities in Australia: Challenges and Prospects”, respectively.

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© Springer Nature Singapore Pte Ltd. 2019

Authors and Affiliations

  1. 1.Sustainable Building Innovation Laboratory, School of Property Construction and Project ManagementRMIT UniversityMelbourneAustralia

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