The UK Health Security Agency today (22 June) raised heat-health alerts to red – the highest – for much of England this week as temperatures are forecast to reach the high 30s and 40ºC in London.

The red alerts apply to London, the East Midlands, West Midlands, south east, south west and East of England.

They start at 1am Wednesday, forecast to be the hottest day of the week, and end at 11pm Thursday.

Amber warnings apply to the north east, north west and Yorkshire and Humber.

Red is more serious than amber on the alert scale. It means the impacts are expected to be both most severe and most likely to happen.

Legal duty to protect

The Health and Safety Executive (HSE) is reminding construction employers to protect their workers from heat exhaustion and the more serious heatstroke, which is a medical emergency.

There is no legal maximum temperature for workplaces, but heat is classed as a hazard and, by law, employers must assess risks to the health and safety of their workers, including risks from extreme heat.

“Last summer should have been a wake-up call for all employers,” said HSE’s John Rowe, deputy director for technical support and engagement.

“If we continue to experience hotter summers, this could have a big impact on the workforce of this country, affecting everything from health of workers to productivity on construction sites.”

Practical steps can include providing adequate ventilation and shade, allowing enough breaks for workers to cool down, providing free access to drinking water, relaxing dress codes if possible and letting workers start and finish earlier. HSE provides more detailed guidance here.

Symptoms to watch for

Workers and supervisors should be alert to the symptoms of heat exhaustion and heatstroke. Heat exhaustion causes tiredness, weakness, a feeling of faintness, headaches, muscle cramps, nausea, heavy sweating and intense thirst.

The more serious heatstroke is where the body can no longer cool itself down and its temperature becomes dangerously high. Symptoms include confusion, lack of coordination, fast heartbeat, fast breathing or shortness of breath, hot skin that is not sweating and seizures.

Heatstroke is a medical emergency. If you think someone has heatstroke, you should dial 999 and then try to cool them down.