It burns.So does PIR. Rockwool does not.
If I abandon the idea of using rockwool in my new "workshop" and storage, and use EPS, I will have a wall structure like this:
Outside | prefab concrete|25mm EPS|50mm EPS|Visqueen|12.5mm plasterboard|Inside
As the EPS will be covered, is that reasonable from the fire point of view?
It does burn, but AIUI any building grade material[1] is treated with fire retardants so it only ignites once it's reached a sufficient temperature. In other words you can't ignite it with a spark, you need a blowtorch (or a fire of equivalent proportions).
So I'd question what's going in this building that might be sufficiently flammable that would be hot enough to ignite the insulation? And once the fire has reached that temperature, does it matter if the insulation catches fire? It'll make a bigger fire for sure, but if your building is already ablaze and everything inside is toast, does it matter that the toast is extra crispy?
If you /are/ doing angle grinding or arc welding or whatever, I wouldn't be having bare insulation on the inside (due to melting damage, mainly), but some non-flammable wall coverings (eg plasterboard) should handle it. A metal spark is very hot, but I'd have thought it hasn't a lot of energy to transfer to the plasterboard to start an actual fire if the PB isn't going to catch light if exposed to a source of ignition. And you'd need to get the PB red hot before you can think about igniting the insulation behind it.
(although it might smoke well before that, which might be a consideration if egress is difficult for occupants when a fire has started)
Theo (IANA fire expert, DYOR)
[1] Possibly not the EPS that your TV came packaged in, which is why it's perhaps not a good idea to 'repurpose' that.
Yes. A fire needs fuel, air and a source of ignition. Exclude the air and it should be fairly safe.
Since the inner and outer layers are rigid fairly inert and exclude the air. I would say that you are OK with that choice of insulation.
If you are concerned then you could use magnesium oxychloride board instead which is very effective as a fire barrier and how they faked the fire certification of the dodgy products that led to the Grenfell fire.
The PB should give you 20 to 30 mins of fire protection. Also EPS intended for building insulation use is often formulated with a self extinguishing additive. So while it will burn if exposed to an established fire, it should not assist a small fire in starting or propagating.
PIR does not burn in a 'normal' domestic fire. It just chars and smells but does not contribute to the fire until the temperature gets up to about 1000C. This is what happened with Grenfell because the aluminium cladding burnt at very high temperature. So unless you are welding on an alumnium shelled vehicle, or one with a lot of aluminium or magnesium castings then you don't need to worry about PIR. If you have lined the garage with PB you have 30 minutes to get out or do some DIY fire-fighting anyway.
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