Research by tradesman insurance provider Protectivity, based on weather data across UK cities, found tradespeople face the highest risk on August 12, with certain locations significantly more hazardous than others as temperatures rise. The findings come as the Met Office warns of an increased likelihood of heatwaves this summer, while the UK continues to have no legal maximum working temperature or enforceable right for outdoor workers to stop work during extreme heat.

When heat becomes a health hazard

Despite more than 100 million working hours estimated to be lost to heat stress across the British labour force, there is currently no legal maximum working temperature in the UK. While other European countries enforce upper limits beyond which outdoor work must pause, UK employers are only required to maintain a ‘reasonable’ temperature, with no legal definition and no enforceable upper limit. 

To reveal both the locations and the dates carrying the greatest risk, Protectivity analysed historical weather data where temperatures hit 27°C or above for at least two hours during the working day (6am–6pm). The same data was then broken down by individual calendar date to reveal which days of summer are statistically most likely to see dangerous temperatures for outdoor workers, using the 27°C threshold that the TUC recommends strenuous outdoor work should stop at. 

St Albans in Hertfordshire tops the table as the most dangerous city for tradespeople working outdoors in summer, recording an average of 47 days where temperatures reach dangerous levels during working hours.

Urban areas also face a compounded risk due to the ‘heat island effect’, where concrete, tarmac and traffic push temperatures up several degrees, as London City comes in second place with 45 days of dangerous temperatures recorded, followed by Oxford (37) and Cambridge (37).

But it isn’t just where tradespeople work that increases their risk this summer, it’s also when. Across the full study period, August 12th stands out as the single most dangerous working day of the summer, registering a total of 61 days where the temperature reached 27°C over the last three years. 

Chris Trotman, underwriting manager at Protectivity comments on the research: “What makes this research particularly striking is that the risk isn’t concentrated in one place or one month and it’s actually spread across cities many wouldn’t necessarily flag as heat hotspots, and it also starts earlier in the summer than most people would assume.

“Self-employed tradespeople in particular, who make up the largest self-employed workforce of any sector in the UK, have no employer to mandate rest breaks or enforce a heat policy on their behalf. The data makes clear this isn’t a niche risk and for tradespeople working outdoors right now, this is a very present and very real danger.”