Taking action on workplace heat

In January this year the World Meteorological Organization confirmed that 2025, 2024 and 2023 were the hottest years in the 176-year record. Average global surface temperatures across these three years were 1.48˚C above pre-industrial levels (+/- 0.13˚C). On the basis of these years, the planet is dangerously close to breeching the 1.5˚C limit set by the Paris Agreement – “a red line for humanity” in the words of António Guterres. 

This will come as no great surprise to workers. The ILO estimates 2.4 billion workers are exposed to excessive heat whilst at work. Numerous reports from apparel and textile factories in South Asia describe unbearably hot working conditions, with profound impacts on workers’ health and safety.  

Against this backdrop, the development of a heat stress protocol by the International Accord is both timely and welcome. Coordinated, binding action is essential. But businesses do not need to wait for new global frameworks before acting. Recent collaborative work shows that brands and suppliers can act now, at low cost, with measurable health and productivity gains. 

A collaborative approach

In September 2025, a research team specialising on the impacts of climate change on workers from University of Sussex and Royal Holloway, University of London met with workers and management at an apparel manufacturing factory in Noida, India. The manufacturer is a key supplier to an ETI company member committed to working with its supply chain partners to ensure workers are safe during periods of extreme heat. Over two weeks, using a methodology applied extensively in Cambodia’s garment sector, the team developed a detailed picture of how factory workers are impacted by heat, and then tested interventions to reduce this.

Many studies focus on workplace ambient air temperature; the methodology used here is different. Via a lightweight wearable sensor, the internal core body temperature of each worker is measured throughout the working day. Internal body temperatures between 36.5 to 37.62˚C are considered normal for working adults. Once internal temperature reaches 38˚C the body is overheating and can enter a state of heat stress, which brings significant health implications – from nausea and dizziness to kidney and heart disease – if temperature are not promptly reduced. The benefit of this methodology is that it combines ambient temperatures with heat generated by work itself. This is crucial because as muscles burn energy they generate heat in our bodies which is stored even after activity reduces. This means that workers doing different tasks within the same workplace can be exposed to different levels of risk.

Findings – understanding heat risk levels

During the first phase of the work, a sample of 160 workers from across departments wore sensors for five days whilst undertaking normal work. Results revealed that workers at the factory spend an average of 1.5% of working time at unsafe core body temperatures above 38˚C. This is broadly comparable to findings from apparel factories in Cambodia during the hot season. 

However, a powerful aspect of the methodology is that it enables analysts to zoom in and examine how results vary by department. The study shows that actually the proportion of working time spent at unsafe core body temperatures is close to zero for the majority of factory departments, with the bulk of the risk experienced in just five teams, the worst affected – thread-cutting – spends 2.1% of working time at unsafe temperatures. 

Digging deeper into the data reveals that workers overall are spending a much higher proportion of working time, 6.2%, at elevated core body temperatures above 37.62˚C. However, once again the factory average disguises a range, with the most affected department – again thread-cutting – spending 23.2% of working time at above 37.62˚C. The study was undertaken in September as the hot and humid season was drawing to a close, suggesting a higher vulnerability to heat stress in these higher risk departments during peak months.

The factory is spread across four floors and a partially covered roof terrace. Disaggregating results by floor shows those working in the basement and on the first floor experience the highest risk, with 0.5% and 0.4% of their working time at unsafe core body temperatures. This coheres with the departmental analysis, for example the thread-cutting team is located in the basement, and further supports the need for targeted action in those areas experiencing the highest risk.

Testing mitigation actions

In the second phase of the work, the team tested three different low-cost mitigation actions with the sample of 160 workers. These were: 1) providing additional floor standing fans to workers; 2) adjusting the working routine to a heat optimised daily schedule, where work is broken up by four 15 minute breaks during the hottest part of the day and within which workers sat in a cooler area and drank cold water; 3) target based work where workers self-pace against a specified daily target, choosing when and when not to work.

Results show all three interventions are effective in reducing the time workers spend at unsafe core body temperatures. The implementation of a heat optimised working schedule generated the largest decrease, down to 0.6% of time at the lower 37.62˚C threshold – and close to 4% in the highest risk department, thread-cutting.  In addition, gender disaggregation shows women workers spend a higher proportion of normal working time at elevated core body temperatures – 7.7% compared with men’s 4.9% – but both fans and the heat optimised work schedule reduced this time by more than half for both women and men.

Crucially, the three mitigation actions were tested against workers’ self-reported productivity targets. All three resulted in improvements in productivity, with the provision of fans generating the largest increase at 16%.  Target based worked increased productivity by 14% and the heat optimised work schedule by 12%.

Developing a workplace heat action plan

This work has been instrumental in informing the development of the factory’s heat action plan. It has enabled the business to prioritise those parts of the factory and those departments where the risk of working at or near unsafe core body temperatures is highest. The business has chosen to prioritise the provision of fans over the other two tested interventions. Target based work was deemed difficult to manage in a production line set-up where one worker’s work depends on timely completion of tasks by the previous worker, and the extended breaks of the heat optimised working schedule were deemed too significant a disruption to afternoon working patterns for such a large workforce. 

As a result, additional fans are being provided at work stations. These are effective in temperatures up to 39˚C – which account for around 77% of days during Delhi NCR’s hottest months. An additional exhaust fan is being installed in the thread-cutting area, which is effective in reducing temperatures throughout the year. All workers are being trained on heat risks and heat stress, with an additional chapter included in the factory’s occupational safety and health training module. Royal Holloway and Sussex University specialists have provided invaluable advice on the content of training and awareness raising material. The factory’s medical facilities are being upgraded to be better equipped to respond to heat related illness. Meanwhile the ETI company member participating in the work has provided training and guidance on heat risks to all its South Asian suppliers and is supporting with implementation. 

Wider lessons for supply chain partners

Some key lessons from this work for brands and manufacturers to consider.

• Heat risk is not uniform across a factory environment, some workers and some departments are more at risk than others – in part due to the nature of their work (level of physicality) but also due to the location.  Identify where the high risk locations are and prioritise actions here.
• Effective actions need not be high cost, and crucially, the productivity gains from reducing the time workers spend at or near unsafe core body temperatures are considerable.
• That said, not all potential interventions will be appropriate or feasible in all contexts.  Management need to feel comfortable that recommended solutions will work for their industry and organisation.
• There is a very strong correlation between when workers feel they are working at unsafe body temperatures and when they actually are. This is why self-paced work is a highly effective solution.  The lesson here is to trust workers and their representatives: freedom of association and collective bargaining are enabling rights.
• Collaboration between supply chain partners is key. Lead firms can catalyse, enable and support action to keep workers in their supply chains safe.  Further vertical and horizontal collaboration in high risk supply chains and sectors is needed.
• Our planet is warming rapidly, with dangerous, potentially life-threatening, impacts for workers. Extreme heat is a salient risk for businesses across multiple sectors. Preventative action is always preferable to reacting in the aftermath of a tragedy. The time to act is now.