Ham Concert Marquee at Sidmouth Folk Week - bad design, overheating and risk of death. (letter sent to Sidmouth Herald, July 2025, during a heat wave!)

Sirs

Heat waves should concern the organisers of Sidmouth Folk Festival.

For many years, there were complaints about overheating and inadequate ventilation in the dance marquee when this was located in a sheltered corner of Blackmore Gardens. The location used in the last few years is far better.

However, the Ham concert marquee is potentially dangerous. Recent unhelpful changes have included increasing the number of seats, installing tiered seating, and restricting the inherently poor ventilation. The latter was centred on a fervent desire to stop anyone viewing the performers from any public vantage point.

One issue has been lack of understanding of single-sided ventilation, a topic well-known to designers of large industrial buildings, for example.

The design of the Ham marquee is arguably unsuitable for over 1000 people even if both long sides were to be kept fully open. The reasons centre around solar gain, internal heat generation (100 watts per person, plus electrical usage) and ventilation rate under low wind conditions. These can be calculated. Outdoor temperature could be 35C in a severe heat wave, and with inside temperatures well above 40C.

A recent high-profile prosecution for gross negligence manslaughter centred upon a woman who organized a paddle boarding expedition. Four people died. She was jailed for 10 years for failing adequately to foresee and act upon avoidable severe danger.

Attendees at the Ham have suffered from heat exhaustion - which is one stage removed from potentially fatal heat stroke. Festival organisers owe a duty of care to attendees. Do they keep adequate records of temperatures and humidity levels at representative points in this venue? Measurement of wet bulb temperature would be important.

Whilst humans can tolerate an air temperature of 40C or higher at moderate humidity levels, sustained exposure to a wet bulb temperature above 35C can prove fatal. This is because core body temperature can no longer adequately be regulated via sweating. With over 1000 people in the Ham marquee, humidity may increase rapidly. At 100% humidity, wet bulb and dry bulb temperatures are the same.

Already, areas of the world are losing their favoured status as holiday destinations owing to heat waves. Even in the UK, building designers now need to consider summer cooling as much as they do winter heating. Global warming is a reality, and there are both health and legal consequences.



Dr Stephen J Wozniak