Four killed in explosion at UK water treatment site

Article by Adam Duckett

FOUR people have died and another has been injured in an explosion at a UK water treatment works.

The incident occurred yesterday at Wessex Water’s Bristol water recycling centre in Avonmouth. The explosion killed three employees and one contractor. One other person was hurt but their injuries are not thought to be life-threatening, Avon and Somerset Police said.

Chief Inspector Mark Runacre said: “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 living in the nearby area that there is not believed to be any ongoing public safety concerns”.

The police said the incident is not being treated as a terror-related incident.

“A thorough investigation will be carried out into what happened today, 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,” Runacre said.

Safety experts have commented on the possible cause of the incident, which photos showed has resulted in the top of the storage vessel being ruptured. The material will have passed from an anaerobic digester to the storage silo, where it can continue to generate a small amount of methane.

Tony Ennis, Director of HAZTECH Consultants, a firm that helps industry manage risk, said: “The spent waste can be used as soil improver in agriculture, and the methane is often used to drive a gas engine to generate electricity. Methane is flammable and explosive between 5–15% by volume in air.

“It is possible that personnel were carrying out hot work, eg drilling or other work, which caused a spark and ignition of the methane gas in the top of the tank.

Clifford Jones, a combustion expert and visiting Professor at the University of Chester, UK, said: "The substance responsible for the explosion might well have been methane which, as is well known, is formed in sewage treatment. Sewage at an advanced state of treatment can form sewage sludge dust, which is capable of a dust explosion. The HSE have previously put out a document on this.”

Wessex Water CEO Colin Skellett said: “We are absolutely devastated that the tragic incident at our site earlier today 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.”

IChemE said in a statement: “IChemE would like to send our condolences to the families, friends and colleagues of those involved following the tragic incident at Wessex Water’s works in Avonmouth. It is hoped that we can quickly investigate, understand and share lessons from this tragedy.”

Runacre said: “I would finally like to pay tribute to all the emergency services who have assisted with today’s operation in incredibly difficult and challenging circumstances.”

Correction: The original version of this article incorrectly stated that the explosion occurred in an ‘aerobic digester’. The explosion took place in a storage silo. We have edited the article to remove reference to a ‘digester’.

Article by Adam Duckett

Editor, The Chemical Engineer

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