Exterior foam and fires
MALCOLM TAYLOR
| Posted in General Questions on
There has been a fire that gutted a high rise apartment building in London. It appears to have spread through the foam-filled exterior cladding panels. Similar fires have occurred in tall buildings in Dubai.
While the situations aren’t directly analogous, I wonder if there are any lesson here for builders contemplating the use of exterior foam?
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Replies
Malcolm,
We should really wait for the investigators to make a report before drawing conclusions, but when I read yesterday that the London building had been recently rehabbed with exterior insulation panels, I immediately thought of the possibility that exterior rigid foam contributed to the fire's spread.
That's pure speculation, but I must admit that it was the first thing I thought of.
I just read that the 24-story building did not have a sprinkler system.
I found a news story that described the cladding panels as "colourful plastic and foam insulation panels."
That said, other news reports have stated that the composition of the cladding panels is unknown.
Another newspaper (the Sun) reports that the exterior insulation was "foam insulation."
Here are the relevant sentences: “Panels designed to improve energy efficiency were fitted to the block in a £9 million refurb completed in May last year, ordered by the firm who manages the tower. But they were filled with foam insulation that 'went up like matchsticks' in the blaze.”
Rock wool is fire proof.
If investigators conclude that exterior rigid foam played a role in this fire, there is no doubt that manufacturers of mineral wool insulation will see a significant increase of interest in their products. And they should.
There are all sorts of aspects to this, some political that are probably not useful to pursue here, but I'll ask my fire chief at this month's meeting what advice he is getting about exterior foam. I know when we have spoken in the past, except for the toxicity of the smoke, they weren't particularly concerned with foam filled exterior walls, mainly because they are encapsulated.
Malcolm,
I suspect that exterior rigid foam is more dangerous in high-rises than ranch homes because of the chimney effect. Once the fire is hot enough for the foam to burn, imagine what happens next, as the fire rises from floor to floor.
For commercial buildings in areas that have adopted IBC, there are already requirements for acceptable rigid foam in exterior wall assemblies as part of IBC Chapter 26. These requirements are not generally applicable to wood framed walls as the size of the building is already restricted based on this construction type. https://www.pacerepresentatives.com/uploads/NFPA%20285_What%20you%20Need%20to%20Know.pdf
Aaron,
Thanks for the link. We don't know, of course, whether the building in London complied with the requirements of NFPA 285 (Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components) -- probably not, since this is a U.S. standard.
Nor can I evaluate whether NFPA 285 is stringent enough to prevent the type of fire that occurred in London.
Martin,
Thank you for the clarification. You are correct and I didn't mean to imply that this was applicable to the building in the London fire. I was just responding to the initial question about whether there are any lessons to be learned when using exterior foam. My assumption was that Malcolm was referencing residential construction and the IRC doesn't have as much about foam plastic in exterior applications, so I referenced the applicable IBC chapter test reference. Your assertion about one-story versus multi-story is also supported by the fact that IBC does not require this testing on one-story structures.
I doubt many of the factors that lead to this tragedy apply to single family residences, but it seems like something worth thinking about.
As to Martin's point, this was part of a more recent Guardian article:
"One architect, who has used similar systems, said cladding panels are also available with mineral wool insulation, which are less flammable but more expensive.
“I only use the mineral wool ones because your gut tells you it is not right to wrap a building in plastic,” he told the Guardian.
As far back as 2000, Gordon Cooke – a leading fire safety consultant – warned in a report commissioned by the mineral wool industry “the use of plastic foam cored sandwich panels ... is difficult to justify when considering life safety”.
He said the panels “can contribute to the severity and speed of fire development” and said this has led to “massive fire loses” in the past."
The latest reports say that the exterior insulation installed on the London building were polyisocyanurate panels manufactured by Celotex.
Here's the link: "Ipswich firm Celotex confirmed it provided insulation materials for the refurbishment. The material has the most stringent fire rating in building standards regulations but independent tests on the material used to make it, polyisocyanurate, show that in intense fires it can release lethal hydrogen cyanide fumes and can be rapidly fatal."
P.S. A tweet by a company named ByggHouse says that it wasn't the insulation that caught fire -- it was the cladding itself. According to the tweet, the cladding, called Reynobond, is made of polyethylene. I don't know if this report is accurate.
One of the articles on the London fire reported, "Three versions of the Reynobond aluminium panels are produced. Two have fire resistant cores — the third has a flammable plastic core. It is thought the cheaper version, with the plastic sandwiched between metal panels, was used in the Grenfell building. A salesman for US-based Reynobond told The Times that the panels with the polyethylene (PE) core had been banned in the US for buildings higher than 12 metres. It’s because of the fire and smoke spread. The FR [variant] is fire resistant, the PE [is just plastic].”
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As I noted in Comment #2, the high-rise building in London did not have a sprinkler system. Other details: the building did not have a central fire alarm system, and the building had only one stairway.
Polyethylene is basically EPS insulation right? It's also a major component of Napalm.
No. EPS is polystyrene, which has many characteristic that differ from polyethylene. But both will melt and drip burning liquids once it's fully burning, unlike polyisocyanurate & polyurethane which char in place without melting.
Polyethylene's ignition temperature is about 350° C, whereas polystyrene ignites at about 490° C, which is a relevant (140° C) difference for how easy it is to get it started. But once ablaze it doesn't matter too much- they both turn into burning liquids.
Seeing how the stack effect in the cavity behind the cladding contributed to the fire, I wonder if it might be worth the small diminution in performance to not vent rain-screen gaps at the top?
Not just the rain screen gap. “Even a drill hole of four inches in diameter can be enough.”
http://www.scmp.com/news/world/europe/article/2098605/cladding-used-make-grenfell-tower-green-building-may-have
if these barriers are breached by a vent or a pipe, “a chimney effect may quickly develop that will cause the very rapid consumption of the insulation and expansion of the damage area”.
The latest news reports make no mention of any polyisocyanurate. Instead, the reports all focus on the Reynobond cladding.
The New York Times reports: "But experts on British fire safety rules say that the material, used as exterior cladding, in fact complied with regulations. Other countries, including the United States, have placed stricter restrictions on how such materials can be used, but Britain had not yet done so, they said. ...
"The material in the exterior cladding consisted of insulation sandwiched between two sheets of aluminum. The type used at Grenfell Tower is made under the Reynobond name by Arconic, a company spun off from the aluminum giant Alcoa last year. It was installed around the tower, which was built in 1974, in a renovation completed last year....
"Critics of the material have warned for years that aluminum surface sheets can melt in a fire, after which flames could race through flammable insulation....
"The use of the material is a sensitive issue for the British government because the United States and other countries years ago banned its application in tall buildings on the grounds that it was a fire hazard. ...
"But several British experts on fire safety said that the existing rules had not, in fact, banned use of the cladding, even in high-rise buildings like Grenfell Tower. The critical building regulation — Clause 13 of Appendix A of Document B — requires only that the exterior 'surface of a composite product' used as exterior cladding must be 'composed throughout of materials of limited combustibility.'
"The sheets of aluminum believed to have been the 'surface' around flammable insulation at Grenfell Tower would pass this test, even though the surfaces could, and did, melt in a fire.
“'This is where it all falls down,' Arnold E. Tarling, a chartered surveyor and expert on fire prevention who is a member of the Association for Specialist Fire Protection, said in an interview. 'The surface melts and it burns like a furnace.' But the cladding nonetheless 'complied with the regulations,' he said....
"The United States and other countries allow only low buildings to use such cladding because of the fire hazard. ...
"Along with the cladding, investigators are looking, among much else, at the absence of sprinklers and a centralized alarm system in the building, which is not uncommon for British apartment blocks as old as Grenfell Tower, and guidance that urged residents to 'stay put' and await instructions if a fire broke out in someone else’s unit."
Scott Gibson recently reported on the Grenfell Tower fire for GBA. Here is the link: Officials Investigate Role of Cladding in London Tower Fire.
Ah, extruded polyethylene is XPS insulation.
Anon3,
You're wrong. XPS is extruded polystyrene.
Extruded polyethylene is different. It's flexible foam, rarely used as insulation in the U.S. -- except for pipe insulation.
Last night the Guardian had an article with a drawing that showed the Grenfell Tower had the following exterior wall system. From outside:
Cladding, comprising aluminum sheets sandwiching polyethylene insulation
50 mm air gap
Foil faced Celotex polyisocyanurate insulation
Concrete wall
The fire apparently started in a refrigerator.
Here is the image.
More recent NY Times article which has quite a lot of detail about the cladding.
It doesn't mention polyiso but instead polyethylene. I don't know if that is correct or not.
"The facade, installed last year at Grenfell Tower, in panels known as cladding and sold as Reynobond PE, consisted of two sheets of aluminum that sandwich a combustible core of polyethylene. It was produced by the American manufacturing giant Alcoa, which was renamed Arconic after a reorganization last year."
"...a thin “sandwich” design: Two sheets of aluminum around a core made of flammable plastics like polyethylene."
"No aluminum cladding made with pure polyethylene — the type used at Grenfell Tower — has ever passed the [fire safety] test..."
https://www.nytimes.com/2017/06/24/world/europe/grenfell-tower-london-fire.html
David: the cladding has polyethylene in between the aluminum skins. Inside that is an air gap and then foil faced polyiso.
The latest NY Times article emphasizes the role of the rainscreen gap. Different reports (depending on which article you read) emphasize the role of either the polyisocyanurate, the polyethylene core of the cladding, or the rainscreen gap.
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The New York Times recently published a photo showing the thickness of the controversial Grenfell Tower cladding. See the photo below.
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