[SystemSafety] Electrical Safety, Fire Safety

[Peter Bernard Ladkin]

Some facts are emerging which paint an uncomfortable picture of the situation with cladding on
higher buildings in the UK.

I suppose what apparently happened with the cladding is the most visible of the effects. Surely also
building-escape mechanisms/routes and firefighting access are major factors. But I'll just address
cladding here. It may be the easiest of the apparently-major factors to deal with.

It is also interesting how quickly apparently-reliable information about the event is accumulating.
Some of it is the speed of the WWW. But it is interesting how quickly organisations such as the FPA
and RMS are coming out with considered, contentful comments. I find that relatively unusual. I
wonder whether this technical issue has been building for some time?

First, apparently the polyethylene panels Reynobond PE from the manufacturer Reynobond cost only £2
less than the fire-resistant mineral-wool ones Reynobond FR (third paragraph of
https://www.theguardian.com/uk-news/2017/jun/16/experts-urge-ban-on-use-of-combustible-materials-in-tower-blocks
, also
https://www.theguardian.com/uk-news/2017/jun/16/manufacturer-of-cladding-on-grenfell-tower-identified-as-omnis-exteriors
). The commentator Jonathan Freeland says this saved £4,750 (paragraph 11 of
https://www.theguardian.com/commentisfree/2017/jun/16/grenfell-tower-rebuke-right-rampant-inequality
, an article that is largely about the politics emerging from the event).

That suggests that 2,375 m^2 of cladding were used. Grenfell Tower is 67.4m high
http://www.skyscrapernews.com/buildings.php?id=2016

This picture, https://en.wikipedia.org/wiki/File:Grenfell_Tower_fire_(wider_view).jpg , taken from
square on, measures about 7.5 cm projected height to 2.5 cm, resp. 1.2 cm projected width of the two
visible exterior walls. If that 7.5 is accurate, that gives a scale of almost exactly 9,000:1 in the
picture (1cm represents about 9m). Some eyeball-trigonometry suggests the angle of view is about 40°
to the longer facade. That suggests its relative extension is 2.5cm/(cos 40°) = 3.26cm which times
9000 suggests the facade is about 29.3m wide. Similarly, the shorter side is then 1.2cm/(cos 50°) x
9000 = 16.8m. Hence the vertical outside walls have a surface area of about 2 x 1975 m^2 + 2 x 1132
m^2 = (3950 + 2262) m^2 = 6212 m^2. Put together with the cladding figure, this suggests that around
38% of the exterior wall was cladded. If I am out by 5% on the linear estimation, then I am out by
10% on the square measure and the percentage of cladding goes down some 3° to 34.8%. So I think it's
fair to say that around a third of the outside vertical surface area was cladding, if Freedland's
cost estimate is accurate and if my arithmetic isn't egregiously erroneous.

I have difficulty reconciling that estimate with evidence directly in the photos, though. It looks
to me as if the apartment windows take up about half the horizontal dimension of the facade and half
the vertical, which would make them one-quarter of the surface area, suggesting that 75% is wall,
which would be cladded. The estimate via Freedland's figure is half of what this suggests.

However, even if we take this second figure, almost double the first, the extra cost of using the FR
cladding would have been less than £9,000. That doesn't seem like a huge lot of money.

So I'll make one prediction. I imagine building-insurance costs on a polyethelene-cladded UK
high-rise will rise. The difference in initial outlay between PE and FR cladding could well be saved
in the lower cost of insurance within the first year and certainly within the first five. However
British building regulations may change as a consequence of this event, as a practical matter people
thus won't be cladding medium-to-high buildings in PE any more in the UK.

(There is a possible flaw in this reasoning in that the people who pay for cladding and the people
who pay the building insurance might not be financially connected in any substantial way, so that
the expense of the first is not passed on to savings for the second.)

Of course, this also doesn't say what's going to be done with the up to 4,000 buildings that may
already be so cladded.

Second, I wrote that there didn't seem to be precedent in the UK. However, there does seem to be a
fair amount of precedent in China, according to RMS's technical director Robert Muir-Brown in this
blog post:  http://www.rms.com/blog/2017/06/16/how-does-an-apartment-fire-turn-into-a-catastrophe/
Apparently the 2014 Melbourne Docklands fire also involved Chinese-produced PE cladding.

Third, the Fire Protection Association has also highlighted the "chimney effect" mentioned by Peter
and Mike, although not in quite the terms in which Peter expressed it. Apparently the PE cladding
performs appropriately in lab tests, but, when the integrity is compromised in an actual
installation by the accommodation of vents and pipes and devices which build air paths between the
panels, then there is potential for rapid spread of a conflagration. This came out of a study they
performed in 2014-5:
http://www.thefpa.co.uk/about/news/news_detail.grenfell-tower-block-fire-statement-from-the-fire-protection-association.html
The extended statement in this post came from FPA Technical Director Jim Glockling, who is also
cited in
https://www.theguardian.com/uk-news/2017/jun/16/experts-urge-ban-on-use-of-combustible-materials-in-tower-blocks


Fourth, the article just cited also says that

[begin quote
https://www.theguardian.com/uk-news/2017/jun/16/experts-urge-ban-on-use-of-combustible-materials-in-tower-blocks
]

At least seven countries – Germany, Denmark, Croatia, Poland, Slovakia, Serbia and the Czech
Republic – have recently changed their building regulations to ensure that only non-combustible
materials are used on the facades of buildings above certain heights, ranging from 12m to 25m.

[end quote]

Fifth, further down in the same article, the UK government apparently told the Guardian that such
cladding is no longer compliant with UK regulations:

[begin quote
https://www.theguardian.com/uk-news/2017/jun/16/experts-urge-ban-on-use-of-combustible-materials-in-tower-blocks
]

The Department for Communities and Local Government said: “Cladding using a composite aluminium
panel with a polyethylene core would be non-compliant with current Building Regulations guidance.
This material should not be used as cladding on buildings over 18m in height.”

[end quote]

But higher up in that article is also written

[begin quote]

British building regulations allow aluminium cladding with a plastic core to be used on tower blocks
if they pass a test that shows that fire cannot spread over its surface.

[end quote]

Putting those two together says the cladding is compliant with building regulations but violates
current building regulations guidance. So, "you can do it, but don't." That doesn't seem quite
right. Can anyone here clarify?

PBL

Prof. Peter Bernard Ladkin, Bielefeld, Germany
MoreInCommon
Je suis Charlie
Tel+msg +49 (0)521 880 7319  www.rvs-bi.de





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