The government has ordered more urgent fire safety tests in the wake of the Grenfell disaster to better understand the risks posed to tower block residents.
So far 190 towers in 51 local authority areas have tested positive for combustible cladding in national tests ordered days after the Grenfell disaster on 14 June.
The Department of Communities and Local Government asked every local authority with tall towers to send in a sample of the buildings' cladding – external tiles that protect buildings from rain and offer increased insulation.
But on Thursday the DCLG announced that, on the advice of an independent expert panel set up to advise on fire safety, six different combinations of common external cladding and insulation will be tested in a realistic tower fire test environment. None of the samples that have been tested so far will be retested.
"The results of these tests will help landlords make decisions on any further measures that may need to be put in place to make their buildings safe following the Grenfell Tower fire," the DCLG said in a statement.
The six combinations will include three kinds of aluminium composite material (ACM): with cores consisting of noncombustible mineral (e.g. zinc), fire-retardant polyethylene, and non-modified polyethylene. The last type, ACM PE, was used at Grenfell and has been implicated as a contributing factor to the spread of the fire.
The samples – which will be bought from commercial manufacturers – will be attached to a 9-metre structure and subjected to "a fire that replicates a severe fire in a flat breaking out of a window and whether it then spread up the outside wall", which can last up to 60 minutes.
This test is in accordance with British Standard 8414, which is recommended in the current building regulations as a way to gain fire safety assurance when using materials that are rated less than A1, the most fire-resistant rating.
As with previous tests, they will be carried out by the Building Research Establishment at its test centre in Watford.
The expert panel, which first met last week, will issue new fire safety advice for landlords, specifically regarding cladding and insulation, shortly.