LONDON — The cladding and insulation used in a London high rise where at least 79 people are believed to have died in a fire last week have failed safety tests conducted by investigators, the police said on Friday. Officials also confirmed that the blaze began with a faulty refrigerator, and that it was not started intentionally.

The high death toll at the 24-story Grenfell Tower in West London has prompted the authorities to consider charges of manslaughter, along with other criminal offenses, said Detective Superintendent Fiona McCormack, who is overseeing the investigation.

Detective Superintendent McCormack did not indicate who might face manslaughter charges, and a police spokeswoman declined to provide any additional details, as investigators sought to learn more about how and why the fire spread so quickly.

Much of the early focus has been on cladding and insulation that are thought to have allowed the blaze to race up the sides of the building after it broke out, leaving many people with no way to escape.

“Preliminary tests on the insulation samples from Grenfell Tower show that they combusted soon after the test started,” Detective Superintendent McCormack said in a televised statement. Cladding tiles had also failed initial tests, she said.

At least 11 buildings in Britain use combustible cladding material similar to that used on Grenfell Tower, officials said on Thursday, and safety checks are being carried out on cladding from at least 600 high-rise buildings across the country.

After Friday’s statement, Tony Rice, a shareholder of Omnis Exteriors, which manufactured materials for Grenfell’s cladding system, stepped down from the board of trustees of Shelter London, a charity that has been providing advice and support to the victims of the fire.

Derek Myers, who was the chief executive of the Royal Borough of Kensington and Chelsea in 2013, when Grenfell Tower underwent renovation, also resigned from the board.

Local activists in North Kensington, who for years had warned the authorities of fire risks at Grenfell Tower, reacted with outrage to the initial details emerging from the investigation.

“It’s obvious that the contractors took it upon themselves to use cheaper cladding and material, and I’m sure that’s the case in hundreds of other towers,” said Tony Glockner, a local activist and resident who lives in public housing owned by the Royal Borough of Kensington and Chelsea.

“None of this surprises me at all,” he added. “Social housing residents in North Kensington have been crying out about fire hazards and poor housing conditions for years, but they have been ignored.”

The appliance that started the fire was a Hotpoint FF175BP refrigerator and freezer, Detective Superintendent McCormack added. She said that the model had never been subject to a recall, and that tests were being carried out to determine if it now should be.

In a statement posted online, Hotpoint said it was aware of a “possible incident” involving one of its products, and it asked its customers to check if they had bought models FF175BP or FF175BG made from March 2006 to July 2009. Consumers who had were asked to contact the company.

Nine victims of the fire have now been formally identified, the authorities said, but the number of presumed dead remains at 79. The police said that every complete body had been recovered from the building, but that the authorities were still working to identify remains.

“Such is that devastation down at the scene, this may take at least until the end of the year,” Detective Superintendent McCormack said, adding, “There is the terrible reality that we may not find or identify all those that died during the fire.”

Over 600 calls were made to emergency services on the night of the fire, with some lasting more than an hour, which Detective Superintendent McCormack described as “harrowing.”

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