Yet more on Grenfell and panel testing

Pure zinc

Reply to
The Natural Philosopher
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load it with mica as a filler, or similar

Reply to
The Natural Philosopher

Presumably the mineral additive is the retardant, the A2 versions (of other cladding products) seem to be pure mineral.

Reply to
Andy Burns

Many polymers (plastics) contain mineral fillers to modify their mechanical and other properties. Fillers such as talc, kaolin, chalk (whiting), titania, gibbsite, mica etc. are widely used. They can also increase the fire resistance of the polymer. Minerals that decompose on modest heating, liberating water vapour or CO2, are best for fire retarding, but even inert fillers reduce the tendency to burn simply by a dilution effect.

See e.g.

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Reply to
Chris Hogg

Ah we obviously had the wrong type of fire breaking out. I'll have a word with God if he exists if I were him. In denial springs to mind Seems the same sort of denial mechanism we often here when aircraft crashes are down to what are termed freak coincidences. Or like both Shuttle losses where as Dear old Peter Sellars put it so succinctly in his party political speech. I do not consider existing conditions, likely. Brian

Reply to
Brian Gaff

ITYF that the answer to this question is "Yes" - that's why the are all failing

tim

Reply to
tim...

In message , at 11:54:11 on Fri, 30 Jun

2017, tim... remarked:

Where will I "find" evidence of this?

Reply to
Roland Perry

Or the original method of testing was flawed.

Reply to
alan_m

AIUI the original fire testing did not penetrate the metal coating, whereas at Grenfell the fire melted the coating, enabling the core to behave like a firelighter. Thus we know relying on the metal face to stop fire does not work, the material behind it has to be non-flammable in future. Anything l ess will only add a big stack of fuel to a fire.

NT

Reply to
tabbypurr

Wasn't that when the armchair experts here were claiming a saving of £5k or so was involved? £300k is rather more significant.

Reply to
mechanic

Where's he complaining about them? Explaining their limitations is hardly complaining.

Reply to
mechanic

I don't think anyone here actually came up with the figure of £5k, just reported that "someone else" had said that it was £2/sheet cheaper and had arrived at the figure.

Reply to
Andy Burns

Pure zinc. Not uncommon as a cheaper alternative to lead these days.

PE as a binder mixed with an inert foamed mineral like alumina or silica. Much less amenable to burning and less fuel when it does.

Zinc melts at a lower temperature than aluminium so if it had been zinc and pure PE core then the resulting fire might well have been worse.

On buildings higher than 18m A2 rated cladding is the sort of stuff they probably should have been using if they wanted it not to be vulnerable to fire (I notice that >18m seems to be appearing everywhere now).

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(likely even more expensive still)

Reply to
Martin Brown

I'm not sure that burning is the relevant parameter here. Zinc has a lower melting point that aluminium (419.5C cf. 660.3C), so as MB mentioned earlier in this thread, the zinc might have melted and exposed the cladding core at a lower temperature than ally.

Reading what's available on the net about aluminium in fires, it generally says that aluminium melts long before it starts to burn. See for example

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OTOH when it does start to burn, it liberates an awful lot of heat, viz. the thermite process

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But this takes a very high temperature to set it going, magnesium ribbon or a propane torch being common.

Zinc 'burns' when it starts to boil at 907C.

How all that impinges on the Grenfell fire, and whether the burning of HMS Sheffield is relevant, as has been mentioned elsewhere, I'm not sure.

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Reply to
Chris Hogg

Its a panel, its flat, its painted what's going to look different?

Reply to
dennis

Thats the difference between the original zinc panels and the alu panels. It was suggested that the FR variant of the alu panels was only £5k. So they could have saved ~£290k and had some fire resistance.

Reply to
dennis

just listening to the people discussing it on TV has led me to that conclusion

of course, this could have been misreporting (or my misunderstanding)

I doubt that the answer is secret, just finding someone that you know (who knows someone) who's involved in the process will probably get you the answer

you probably have better contacts than most of us

tim

Reply to
tim...

ITYM "safer" alternative

tim

Reply to
tim...

The planning dept was probably more interested in the change from champagne finish to silver/grey finish, plus the lack of contrast from the new grey to another section that was already a different grey, so had to also be changed to maintain a higher contrast ... the zinc->alu change was approved as part of that.

Reply to
Andy Burns

Well that's the thing. I'm trying to understand whether, once the fire got going on the outside, the zinc would burn more easily than the ally, and to worse effect.

Reply to
Tim Streater

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