CRF & Timber Substrate

It seems the ISO 9239-1 default substrate when testing carpet and underlay is 6mm fibro cement sheet.
The Lab certificates do not permit substitution of materials. Does this effectively prevent the use of carpet on timber floors?
Pretty much every carpet and test certificate i can find uses the default Fibro substrate.
Can anyone give guidance or have appropriate experience knowledge of this?

Hi Frank
You are right on the money as most CRF tests use fibro cement to simulate non-combustible flooring. EN13238:2010 provides test procedures for CRF testing including rules for substrate selection. I haven’t read it but as you suggest could be a lot of unsprinklered buildings with correct flooring CRF but wrong substrate!

Thanks John.
I was hoping for a magic fix, I should be old enough to know better.

I wonder how much difference it makes, since flame spread over the sample is a driven by heating from the flame front. BRANZ SR181 looks at flooring tests.
I wouldn’t imagine that carpet is thermally thin, and by the time it burns through and the wood catches fire, the flame front has moved on or the test is finished. With wood being 2* the limit, does it also make a difference to the outcome, especially for most floorings that pass with a large margin.

Thanks Geoff,
Your comments reflect my own thinking.
I only raised it because product compliance seems to be open to challenge for even small variations to protoype testing.

What variations to the test specimen does ISO 9239-1:2010 allow?

Hi Grant,
A bit late but thankyou for your comments. I think they confirmed what I was thinking.