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Tawatsupa B, Yiengprugsawan V, Kjellstrom T, Berecki-Gisolf J, Seubsman S, Sleigh A.

Industrial Health. 2013;51(1):34-46.

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Heat lossCooling by Evaporation

Na+Cl-

H2OH2O

H

Heat gainFrom internal heat source

(Physical activity)

Heat gainFrom external heat source

(Environment)

"Heat stress" (ACGIH, 2008)

Overall heat burden on the body from the combination of:

Body heat generated

Environmental sources Air temperature Humidity Air movement Radiation from the sun or hot

surfaces/sources

Clothing requirements

Background

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Conceptual Framework

Climate Change

Human exposure

HealthImpacts

Heat Stress

Individual/ behaviour factors

(Age/sex/ BMI/ Drinking alcohol)

Socioeconomic status- Income/Education- Air conditioning- Type of job- Location of job

Air pollution:(SO2, NO2, PM10,

O3, CO)

Related weather variables- Relative humidity- Dew point temperature,- Precipitation- Wind speed

Well-beingLife dissatisfaction

(Paper 3)

Physical health

Kidney disease(Paper 2)

Occupational Injury(Paper 5)

Mental HealthPsychological

distress (Paper 1)

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IntroductionGlobal warming will increase heat stressRapid urbanization cause workers to do heavy labour for

long periodsWorkers are exposed to heat and are at risk of heat-

related illness and increased occupational injury

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Heat stress in Thailand Tropical developing country Large working population High temperature and high humidity

Mean temp. increased 0.74°C over the last century Extreme temperature events will become more prevalent

Mean temp.

Source : Limjirakan et al., 2008

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Public health concern in ThailandHeat is “extreme caution” or “danger” in a wide array of work

settings in Thailand (Langkulsen et al 2010)

Current warming trends are expected to exacerbate problem However, information on occupational injury related to heat

stress in Thailand is still quite limited

Paddy fieldSteel-making plant

Aim: To examine association between heat stress and injury in the Thai workplace

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Data and study population A large national Thai Cohort Study (TCS) in 2005 Researching the health-risk transition in the Thai population 87,134 respondents aged 15-87 years enrolled as distance

learning students at Sukhothai Thammathirat Open University Further details about the questionnaire data collection are

given in Sleigh et al (2008)

8Fig. 1 Selection of the analysed population from TCS, 2005

Working for income N= 76,748 “Do you work for income? (in 2005)” - "Yes"

Reported workplace heat stress N= 75,287“During the last 12 months, how often did you experience

high temperatures at work that made you uncomfortable?”

– “often”, “sometimes”, “rarely”, and “never”

- 1,461 do not know and missing responses

Answered first injury question N=75,287“In the last 12 months how many injuries have you had

that were serious enough to interfere with daily activities and/or required medical treatment”

•Yes – 16,388 (21.7%) • No serious injury – 58,899 (78.2%)

•10,386 did not work

Thai Cohort Study (TCS) baseline (2005)N = 87,134 (100%)

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Measures of occupational injury

- 3,581 any missing valuesGroup analysed for heat stress-related injury at

work N=58,495•25,908 men (44%) and 32,587 women (56%)

•Mean age of men (34 yrs) and women (31 yrs)

Answered question on injury at workplace N=62,076

“Workplace injury in last 12 months” - Yes for non-agricultural workplace = 2,373 (3.8%)

- Yes for agricultural workplace = 804 (1.3%)

- 13,211 reported non-workplace injures

Analysis of heat stress-related occupational injury at agricultural workplaces

restricted to physical workers in rural areas (N=11,634)•5,892 men (51%) and 5,742 women (49%)

- 2,221 reported injury at non-agricultural workplace- 31,811 office workers- 12,829 work in non-rural areas

Fig. 1 Selection of the analysed population from TCS, 2005

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Management of confounding

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Data processing and statistical analysis

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Heat stress at work & Occupational injury

Heat stress and occupational injury

Males Females TotalN % N % N %

Total 25,908 44.3 32,587 55.7 58,495 100

Heat stress Rarely /Never 11,260 43.5 18,125 55.6 29,385 50.2

Sometimes 8,899 34.4 9,427 28.9 18,326 31.3Often 5,749 22.2 5,035 15.5 10,784 18.4

Serious injury at work No serious injury 24,236 93.6 31,299 96.1 55,535 94.9

Occupational injury 1,672 6.5 1,288 4.0 2,960 5.1

Table 2 Reported heat stress at work and occupational injury in a national cohort of 58,495 workers in Thailand

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Association of cohort attributes with heat stress

Age group; <35>=35

Education; University

DiplomaHigh school

Income; 20001+

10001-200007001-10000

<7000

Alcohol consumption; NeverEx/Social drinkerRegular drinking

Smoking; Never smoked

Ex-smokerCurrent smoker

BMI; Normal weight

UnderweightOverweight

Obese

Job location; BangkokUrbanRural

Job type; Office job

Physical job

Sleep 6-8 hrsSleep >8hrsSleep <6hrs

No disease

Existing disease

work very fast; RarelySometimes

Often

0.50 1.00 1.50 2.00 2.50

MalesAge group; <35

>=35

Education; UniversityDiploma

High school

Income; 20001+10001-200007001-10000

<7000

Alcohol consumption; NeverEx/Social drinkerRegular drinking

Smoking; Never smoked

Ex-smokerCurrent smoker

BMI; Normal weight

UnderweightOverweight

Obese

Job location; BangkokUrbanRural

Job type; Office job

Physical job

Sleep 6-8 hrsSleep >8hrsSleep <6hrs

No disease

Existing disease

work very fast; RarelySometimes

Often

0.50 1.00 1.50 2.00 2.50

Females

Fig. 2 Association of cohort covariates with heat stress

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Association of cohort attributes with occupational injury

Age group; <35>=35

Education; University

DiplomaHigh school

Income; 20001+

10001-200007001-10000

Alcohol consumption; Never

Ex/Social drinkerRegular drinking

Smoking; Never smoked

Ex-smokerCurrent smoker

BMI; Normal weight

UnderweightOverweight

Obese

Job location; BangkokUrbanRural

Job type; Office job

Physical job

Sleep 6-8 hrsSleep >8hrsSleep <6hrs

No disease

Existing disease

work very fast; RarelySometimes

Often

<=7000

0.50 1.00 1.50 2.00 2.50 3.00

MalesAge group; <35

>=35

Education; UniversityDiploma

High school

Income; 20001+10001-200007001-10000

Alcohol consumption; Never

Ex/Social drinkerRegular drinking

Smoking; Never smoked

Ex-smokerCurrent smoker

BMI; Normal weight

UnderweightOverweight

Obese

Job location; BangkokUrbanRural

Job type; Office job

Physical job

Sleep 6-8 hrsSleep >8hrsSleep <6hrs

No disease

Existing disease

work very fast; RarelySometimes

Often

<=7000

0.50 1.00 1.50 2.00 2.50 3.00

Females

Fig. 3 Association of cohort covariates with occupational injury

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Effects of heat stress on occupational injury

Heat stress 2005

Occupational injury

ORs

N % Crude Adj. (95% CI) p-trend

Males N= 25,908 1,672 6.5Never/Rarely 473 4.2 1 1 <0.001

Sometimes 616 6.9 1.70*** 1.54*** (1.36-1.74)Often 583 10.1 2.57*** 2.12*** (1.87-2.42)

Females N = 32,587 1,288 4.0

Never/Rarely 578 3.2 1 1 <0.001Sometimes 384 4.1 1.29*** 1.24*** (1.08-1.42)

Often 326 6.5 2.10*** 1.90*** (1.64-2.18)

Table 3 Associations between heat stress and occupational injury among male and female workers (N=58,495)

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Effects of heat stress on occupational injury in agricultural workplaces

Heat stress 2005

Occupational injury

ORs

N % Crude Adj.b (95% CI)p-

trend

Males N= 5,892 228 3.9

Never/Rarely 59 2.8 1 1 <0.001

Sometimes 81 3.7 1.35 1.31 (0.93-1.85)

Often 88 5.6 2.09*** 1.99*** (1.41-2.81)

Females N = 5,742 84 1.5

Never/Rarely 25 0.9 1 1 0.001

Sometimes 31 1.6 1.78* 1.64 (0.96-2.80)

Often 28 2.5 2.80*** 2.58*** (1.49-4.47)

Table 4 Associations between heat stress and occupational injury at agricultural workplaces among male and female workers in rural areas with physical jobs (N=11,634)

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Principal findings

Heat stress at work has a significant association with occupational injury

Occupational heat stress affected 18% of Thai workersAssociation between heat stress and occupational injury

remained substantial and significant after accounting for effects of covariates

For rural physical workers at agriculture workplaces showed a similar association.

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Strengths of this studyA large national cohort of 58,495 workers who represent

well working age Thais A wide range of values for variables of interest, revealing

relationship between heat stress & occupational injuryThe restricted analysis of 11,634 workers with physical

jobs in rural areas were similar to the overall analysis of 58,459 workers

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Limitation of this studyCould not directly establish that the

occupational injury arose as a result of heat stress.

Unknown source or nature of the heat stress at work

Not able to make direct measurements of work environments or occupational injuryWe classify this study as

preliminary in nature.

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Compare with other studies

Occupational heat stress is a problem in Thailand, especially in agriculture workplaces (Langkulsen et al 2010, Jakreng 2010)

The younger age group reported more occupational injury (Curtis et al 2007)

A higher risk of serious occupational injury among males (Fan et al 2012)

The risk of injury related to job type, rural job location (Dembe et al 2004), and frequency of alcohol consumption (Dawson 1994)

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Significance of this studyHeat stress increases the risk of serious injury among

workers who are exposed to hot and humid work environments

Hot and humidity together with workers’ physical exertion and dehydration can cause potentially heat-related illness or heat exhaustion (fainting or collapse) Increase occupational injury & associated costs Reduce work performance and productivity

The existing heat stress problem will worsen if global warming continues and workplaces become even more thermally stressful

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Need to strengthen policy and guidelines on prevention and management of heat stress and occupational injury

Thai workers must take safety precautions while working under heat stress

policymakers should develop the interventions to prevent occupational injury, especially new young workers.

Prevention of heat stress-related injury through education, training and procedures is needed

Significance of this study for Thailand

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Future research

Validation the self-reported measurement of heat exposure

Direct observations of heat stress and its effects in informative work settings

Investigate heat-related injury in different regions of Thailand because the geography and heat stress are different

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Conclusion

Association between heat stress & occupational injury reported here is a great concern.

Continued urbanisation & global warming will make these trends worse for workers in tropical developing countries: Thailand.

Injury interventions need to include strategies that mitigate occupational heat stress

We need to develop and test interventions that reduce the number & severity of occupational injuries

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Acknowledgments The International Collaborative Research Grants Scheme

The Wellcome Trust UK The Australian National Health And Medical Research Council

The Thai Cohort Study team Sukhothai Thammathirat Open University (STOU) the STOU students The Australian National University (ANU) Department of health, Ministry of Public Health, Thailand

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Any questions/ suggestions?