A 16-year-old boy has been named among the four victims of an explosion at a waste water treatment site near Bristol.
The four people who died have been named by police as Michael James, 64, Brian Vickery, 63, Raymond White, 57, and Luke Wheaton, 16.
Avon and Somerset Police said a fifth person was injured at the scene of the blast in Avonmouth.
They are recovering at home and investigators will speak with them when possible.
The explosion at Wessex Water’s Bristol water recycling centre happened at around 11.20am on Thursday.
The blast involved one of the chemical tanks and the workers were on top of the tank when it exploded, police had said.
Officers are working with the Health and Safety Executive and chemical and mechanical experts to determine the cause.
Supt Simon Brickwood said the investigation “is likely to be ongoing for some time”.
He added: “We appreciate the impact this incident has had on the local community and we thank those affected for their patience while our investigative work is carried out. The local neighbourhood policing team is available to address any concerns members of the public may have.
“I’d like to pay tribute to those involved in the emergency response, who have been at the scene throughout the night under very difficult and challenging circumstances.”
Wessex Water’s chief executive Colin Skellett said: “We are all absolutely devastated by what has happened.
“”Our hearts go out to the family, friends and colleagues of those who lost their lives during the tragic event on Thursday.
“I know from the thoughts and comments I have received from so many, that this has affected the whole Wessex Water family.
“I know Avonmouth, I worked there for many years, and I know the people, some of whom have lost their lives during this terrible incident.”