Sustainable cooling strategies for workers in the ready-made garment factory industry in Bangladesh under simulated extreme heat: a randomised crossover trial

BACKGROUND: Bangladesh frequently experiences extreme heat and humidity, which threatens the health, wellbeing, and productivity of ready-made garment workers. Scalable, sustainable, and low-cost cooling strategies are urgently needed to protect this workforce in low-income and middle-income countries. Therefore, we examined the effects of building-level and personal-level cooling alternatives to air conditioning on worker heat strain in a simulated Bangladesh ready-made garment factory. METHODS: In a randomised cross over trial (ACTRN12622000457741), healthy participants (aged 18-40 years) recruited from a convenience sample of volunteers from diverse ethnic backgrounds completed six 3-h gender-specific ready-made garment work simulations (males ironed and females sewed) in a climate chamber at the University of Sydney: (1) current factory (control CON=40°C, 38% relative humidity); (2) CON with fan (FAN); (3) FAN with drinking water (FAN+HYD); (4) modified rooftop (ROOF=37·5°C, 38% relative humidity); (5) ROOF with fan (ROOF+FAN); and (6) air conditioning (AC=24°C, 40% relative humidity). Primary outcomes were end-trial core temperature, heart rate, and sweat loss fluid deficit. Linear mixed models with fixed effects of intervention and sex and random effects of participant were used for analysis. Pre-planned contrasts compared each intervention to CON, with Dunnett's correction for multiple testing. FINDINGS: Between March 16, 2022, and Nov 25, 2023, 42 participants (20 identifying as females, 22 as males) completed 247 trials. Compared to CON, male core temperature decreased with FAN+HYD (-0·27°C 99% CI -0·44 to -0·09), ROOF (-0·35°C -0·53 to -0·17), ROOF+FAN (-0·28°C -0·45 to -0·10), and AC (-0·71°C -0·89 to -0·53), but in females, core temperature decreased only with AC (-0·42°C -0·60 to -0·24). Male heart rate was lower with FAN (-6 beats per minute -12 to 0), FAN+HYD (-13 beats per minute -19 to -7), ROOF (-8 beats per minute -14 to -2), ROOF+FAN (-11 beats per minute -17 to -5), and AC (-34 beats per minute -41 to -28), and female heart rate was lower with FAN+HYD (-7 beats per minute -13 to 0), ROOF (-8 beats per minute -15 to -2), ROOF+FAN (-10 beats per minute -16 to -4), and AC (-25 beats per minute -31 to -18). Male sweat loss fluid deficit was reduced with FAN+HYD (-704 g -817 to -591), ROOF (-205 g -317 to -93), and AC (-853 g -966 to -741), and in females with FAN+HYD (-439 g -554 to -324), ROOF (-131g -246 to -16), and AC (-513g -628 to -398). INTERPRETATION: Sustainable cooling interventions can reduce physiological heat strain under peak heat stress conditions in a typical non-airconditioned Bangladeshi ready-made garment factory. Cooling benefits were greater in males, highlighting potential gender-based workplace heat stress inequalities. FUNDING: Wellcome Trust.