An investigation has started into the explosion yesterday at an Avonmouth wastewater treatment plant that killed four people.
A fifth person was injured in the incident at Wessex Water’s Bristol Wastewater Recycling Centre at Avonmouth but is not thought to be in a life-threatening condition. 
Three of those killed in the blast, which happened in a silo that held treated biosolids, were employees of Bath-headquartered Wessex Water with the fourth a contractor.
Wessex Water chief executive Colin Skellett, pictured, said: “We are absolutely devastated that the tragic incident at our site has resulted in four fatalities.
“Our thoughts are with the families, friends and colleagues of those involved. We are working with the Health and Safety Executive to understand what happened and why.”
Biosolids are treated sludge recovered as a by-product of the sewage treatment process. It is treated in anaerobic digesters to produce agricultural fertiliser and renewable energy.
Avon and Somerset Police Chief Insp Mark Runacres said: “Emergency services were called at approximately 11.20am to reports of a large explosion involving one of the chemical tanks at the site off Kings Weston Lane.
“The fire service led the rescue operation but sadly, despite the best efforts of all those involved, we can confirm there have been four fatalities.
“A thorough investigation will be carried out into what happened, involving a number of agencies and the Health and Safety Executive in due course, and we will not be speculating on the cause of the explosion while such work is being undertaken. 
“I can confirm, though, that this is not being treated as a terror-related incident. The explosion happened in a silo that holds treated biosolids before it is recycled to land as an organic soil conditioner. I can reassure people in the nearby area there is not believed to be any ongoing public safety concerns.”
Avon Fire and Rescue service said it believed the silo also contained lime, which can be used in the stabilisation process of waste treatment.
Wessex Water is owned by YTL Power International, part of the Malaysian conglomerate YTL which redeveloping Filton Airfield and building the Bristol Arena.
It serves 2.8m customers across the South West including Bath, Bristol and most of Wiltshire. It treats 480m litres of wastewater every day.
It recently announced it was increasing treatment capacity at the wastewater recycling centres by around 35%.
John Phillips, regional secretary of GMB – the union representing many Wessex Water workers – said: “This is another stark reminder of the absolute need to ensure people are able to work in environments where risks to their health and safety are properly controlled.
“Whilst the cause of this tragedy is not yet known, it is essential that a full and thorough investigation takes place at the appropriate time.”
Mayor of Bristol Marvin Rees added: “The thoughts of our city are with their families at this heartbreaking time. This has already been such a challenging year, and this news of further loss of life is another terrible blow.
“As a city we will mourn for them. Local residents may be concerned about safety in the area. Wessex Water, police and fire have assured us the incident is contained, and there is no risk to your safety.”
