Working in hot weather can lead to dehydration, rashes, fainting and increase the risk of skin cancer for outdoor workers, the union suggested.
In a statement on the TUC's website, general secretary Paul Nowak said: "Our buildings, infrastructure and laws were made for a different climate in a different century.
“Extreme heat is becoming the norm, and we’re struggling to cope. We need to adapt – and that means improving the law, investing in resilience and delivering climate action."
Outdoor workers are most at risk of injury or fatality due to working in the heat, explained Keith Whitehead, senior consultant at the British Safety Council.
Speaking to HR magazine, he said: “The International Labour Organisation estimates that at least 2.41 billion workers are exposed annually to excessive heat. Exposure to excessive heat at work leads to around 22.85 million occupational injuries and 18,970 work-related deaths every year.
“Outdoor workers such as farmers, foresters, landscapers, painters, roofers, pavers, roadworkers and construction workers are the most obviously at risk, but the knock-on consequences of higher temperatures and severe weather on public transport and other key infrastructure will continue to have a significant impact on an increasing number of workers, the general public and business operations.”
Read more: Working in a heat wave: health and safety guidance
There is currently no legal minimum or maximum temperature for working, according to Acas, but employers have a legal duty of care to ensure that temperatures are reasonable for their staff in the workplace, and when working from home.
However Whitehead added that employers have a legal obligation to protect employees from climate change-related weather changes.
He continued: “Since April 2022, some of the UK’s largest companies have been legally obliged to disclose their climate-related risks and opportunities. Two international standards have been produced to help businesses adapt and assess their vulnerability to climate change.
“These international standards provide guidance for businesses on how to look at vulnerability and adaptation to climate change.
“There are several key areas for businesses to adapt to climate change impacts such as changing marketplaces and customer needs, direct and indirect impacts on operational, logistical and supply chain processes, and the impact on the health, safety and wellbeing of staff and the general public from severe weather events such as storms, high winds, floods and heatwaves.”
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Cate Walter, a health and safety expert at consultancy Rhino Safety, suggested that employers could improve working conditions during the heat by offering flexibility and frequent breaks.
Speaking to HR magazine, she said: "Providing plenty of ventilation, plenty of cool water, more frequent breaks, and allowing staff to work from home are all reasonable protections employers should consider. They should also have specific risk assessments for vulnerable workers, assessing specific risks on an individual basis to ensure employees are not only comfortable but also safe at work."
Walter added that employers should encourage workers at high risk of sun exposure to wear protection.
She continued: "Employers whose workers are at particular risk, such as those in construction, should consider even more measures to protect their staff. They should encourage staff to use adequate sun protection such as wearing hats, sunglasses and sunscreens (as long as these measures don't create other risks associated with their work).
"They should ensure there are shaded areas for staff to take regular breaks in, and in extreme cases, may need to consider closing down sites temporarily if the heat risk is unreasonable."
