Imagine you are standing next to a boiler plant in a dark factory with insufficient ventilation. You are near the furnace, which is generating 350-450 degrees Celsius of heat. Your job is to feed wood into it for at least 10 hours each day.

To deal with the “hellfire” coming out of the furnace, you keep a cloth over your shoulder to wipe away the river of sweat running down your forehead.

The temperature near the furnace fluctuates between 44 and 46°C, with a wet bulb (WB) temperature (a measure of both heat and humidity) of 32°C. There is no option to cool down your body, not even the relief of an occasional cool breeze that may help during outside work.

Only after 30 minutes do you get to go outside, where the ambient temperature, which ranges between 40 and 42°C, is not much help either. But you must return inside quickly because another stack of wood awaits you to be fed into the furnace, among other tasks…

…External heat combined with internal heat generated in the body puts additional strain on the workers. So, someone who works continuously near a furnace and shovels wood inside it has a physical intensity of 400 watts, which is equivalent to someone working in agriculture or construction in the sun, says Luke Parsons, climate scientist, global science division, The Nature Conservancy.

Physical intensity of 400 watts is categorised as ‘heavy work’ as per International Labour Organization’s 2019 report Working on a Warmer Planet.

This heat gets even more extreme as many factories lack proper ventilation. For example, where Singh works, apart from the main entrance, there is no other ventilation. Most of the factories have fans, but workers describe them as “useless” as these blow hot air, due to a lack of ventilation.

“Aadat” (habit) and “majboori” (compulsion or helplessness) are common refrains heard when a conversation is steered towards rising temperatures.

Research shows that on average, acclimatisation may protect from an additional 2.5-3°C WB globe temperature (wbgt) of exposure.

WBGT considers humidity, wind speed and sun exposure in addition to temperature and is sometimes referred to as ‘feels like’ temperature because it indicates how hot one feels rather than how hot it is.

The International Organization for Standardization (ISO 7243) recommends resting for part of an hour, above 26°C WBGT, if an acclimatised worker has ‘heavy’ work. Above 32-33°C WBGT, ‘heavy’ work should stop.

Heat acclimatisation is important, but it has its limits and there is individual variability. The magnitude of acclimatisation depends on the intensity, duration and frequency of physical activity in the heat and environmental conditions, says Parsons.

He was part of a team of researchers investigating the effects of global warming on the health of tropical workers. According to the findings, at 1°C of global warming, heavy work for acclimatised workers wearing light work clothes should be limited to a fraction of an hour for at least half of all hours in the year.

Although the study focused on outdoor workers, the findings can also apply to ‘heavy’ work done indoors.

Aside from the high ambient temperature, indoor workers in factories must contend with radiant heat from machines or equipment that emit their own heat. This exacerbates the already hot conditions. Rajan Rawal, a professor at CEPT University in Ahmedabad, calls it “waste heat.”

“Machines use fuel or electricity in an inefficient manner and emit or reject heat in the process and people around those machines are the recipient of this heat,” says Rawal, who is also a senior advisor at the Centre for Advanced Research in Building Science and Energy at CEPT Research and Development Foundation.

Dangerous heat indoors

Some 260 kilometres away from the boiler plant, a weaver in Surat’s Udhana works robotically on the ground floor of a power loom unit without even a ceiling fan. The room is cramped: 10 shuttle machines are producing polyester fabric in an 18×30 foot space with barely two feet between the looms. The worker must constantly shift between the 10 machines he manages.

On the first floor, nine more machines are managed by another employee. In larger power looms, one worker manages 15-16 machines on average.

The room is not only cramped, but also deafening: The machines run at a dangerously frenetic speed, around 115-125 decibels, around the clock. The only ventilation on the first floor is the main door, whereas the second and third floors have windows to compensate for the lack of fans or other sources of air circulation.

A power loom is a mechanised loom that produces different fabrics like synthetic, polyester, denim and cotton from yarns and serves as the starting point for many textile industry processes.

Workers spend more than 12 hours per day inside this heated environment, constantly moving between machines that may be on different floors of the building. Fans are not used because the air they produce interferes with the fabric work. Furthermore, there is no room to sit anywhere inside the unit. As a result, even brief periods of rest are not permitted and workers can only do so during breaks.

For 49-year-old Prakash Chandra Pradhan, indoor heat is as real as working outside in the sun. He has witnessed the dangers of extreme indoor heat firsthand. Around five years ago, a loom operator at Pradhan’s workplace died from heat exhaustion after working all night inside the unit.

“He felt dizzy at around 4 am in the morning, went outside and lied down near the gate and never got up again,” Pradhan recounted with a stoical gloom.

The worker was in his early forties and had been working in the power loom unit for 15 years.

According to Pradhan, heat-related deaths have increased over the last few years but not all are reported to the authorities. Another power loom worker who was operating 12 machines died in a similar manner in the second week of June 2024, but the cause is unknown at this time.

Power looms have a higher revolutions per minute (RPM) at night, which increases the rate at which the machines work, making the atmosphere inside the factory extremely hot on days when nighttime temperatures are above normal.

“Both temperature and humidity were high that day and he had worked through the night continuously. I got a phone call after workers realised that he had fainted. We took him to the nearby hospital, but he had passed away by then. We later found out he died because of a heat stroke,” says Pradhan, who now works as a ‘master’ in the unit, overseeing the workers.

High humidity, even at lower temperatures, can be life threatening.

“If it is very humid, then it can be very uncomfortable and difficult to function even at lower temperatures. So, 30°C temperature with very high humidity will be far worse than 35°C temperature with low humidity,” says Anant Sudarshan, associate professor at department of economics, University of Warwick and senior fellow at the Energy Policy Institute at the University of Chicago.

A 35°C WBGT is roughly equivalent to a 40°C main temperature and 75% humidity and it is potentially fatal. “At that temperature, a human can only survive for six hours,” Sudarshan says.