The Grenfell Fire, and the Logic of Plastics in Cladding

For me, the most depressing recent news was the London fire, in which a high-rise of flats (apartments for Americans) somehow caught fire, and once it did, it spread like crazy. There is a lot of blame to share around for the death toll. Apparently people were told to stay in their flats, but that advice was given by firemen who were unaware that the building had no useful fire doors, or the other usual means of containing and retarding fires. After all, if the building is concrete, and there is no easy way to spread the fire, it should be able to be kept local. So what went wrong? We don’t know about why the interior of the building seemed to burn very nicely, but it seemed that the outside burned furiously. The outside had an aluminium cladding, apparently to make it look more attractive. The aluminium tiles were backed by polyethylene, which is essentially a solid hydrocarbon of structure similar to diesel, but a much larger molecular weight. That burns very well, and if you saw video of it, you would see great globs of fire falling off the building.

We don’t know exactly why the polyethylene was there. Some say heat insulation, others say to give the cladding rigidity. Much has also been made of the fact that for about $3 a tile more, the backing could have been fire resistant. I am not sure what that backing is as the maker’s website does not say, but would guess it is some sort of polyamide or polyurethane with non-flammable filler. These certainly do not catch fire as easily, but there is another catch with some of them: in a fire they do burn, and while not as well, they tend to give off some rather poisonous gases. There is another catch. According to the manufacturer, the fire resistant tiles passed ASTM E 84 tests, which are the standard tests for surface burning characteristics, but so did the polyethylene backed tiles. That sort of lab test does not represent a real fire.

This brought back memories of my past, when I got involved with two structural foams that could be suitable for building cladding. One was a glass foam, originally intended to be made from waste glass. This would make quite a good wall cladding without the aluminium, except possibly on the bottom floor because it does not have very good impact resistance. Thin glass shatters on impact, but it does not burn or corrode. You can also have a wide range of colours. The other is a plastic foam, for which you do not even need fillers to make it fire resistant.

The story of my involvement with that goes back to the late 1970s. In the late 1960s, New Zealand discovered a large offshore natural gas field, and the government took it upon itself to enter a “take or pay” agreement so the field would be developed. It was not clear what their idea was, but presumably electricity generation was one of them. However, when the first energy crisis struck, about 1972 from memory, there was a sort of panic, and after a lot of deliberation they decided to construct a synthetic fuels plant at Motunui, which was to use a process developed by Mobil. I was on a committee to advise on the science, and I advised this was a bad idea because they could not build it for anything like the costs presented to them. As it turned out, my projected cost was out by $200 million, but no site had been chosen, and my estimate was “plus site development”. (In the end, the site development would have been about $130 million, so I was rather pleased with myself.) However, at the committee, I was about 4.5 times greater than the figure they were comfortable with (and note the government was going to pay) so I was never asked to be on such committees again. However, when that process was chosen, I knew that there was one byproduct they would not know what to do with: 1,2,4,5-tetramethylbenzene. The reason: it is a solid, which is not good in petrol for cars. The good news from my point of view was that it could be oxidized to pyromellitic dianhydride, which would be a precursor to stepladder and even ladder polymers, and in particular to polyimide plastics. The bad news was that the top public servants did not want their synfuels project upstaged, and the politicians were unenthused, probably because they were totally out of their depth.

So to get rid of the road blocks, I needed a stunt. As it happened, the fire hazard with plastic foams was to be the subject of a half-hour nationwide TV program, and I was invited to comment as a scientist. I agreed, provided I could have a few minutes for a demonstration of fire resistant foams. That was agreed, so I made myself some polyimide foam. This was rigid, and not much use for furniture, but you can’t really do much development work with one day’s notice. So I turned up, and at the end of the program, which had the dangers of fires, and of the poisonous gases drilled into everyone, I had the cameras turned on me. I put a bit of home-made foam in the palm of my hand and directed a gas torch at it. It glowed a nice yellow-hot under the flames, and I just sat there. Eventually they got bored of watching this, and they turned off the torch, then made the comment, “It still stinks, though.” So, with a bit of acting here, I held the plastic up to my face and sniffed deeply, and made no expression. Since there was no fire, while the plastic was ablating slowly, once the torch was taken away there was no more reaction. Unfortunately, my wife forgot to record this so I can’t actually prove it.

The whole point of this, of course, is it is possible to make very fire resistant foams. Without the type of chemical plant I was proposing, such foams would be expensive, but the question then is, is preventing x number of deaths worth spending a few extra dollars (or in this case, pounds)? In my opinion, there is no real excuse. Yes, the foam I made was rigid, but as building insulation, so what? While science can provide answers to many problems, there is not much point in it if nobody in power takes any notice.

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