Author Topic: Heat calculation  (Read 431 times)

Offline lyledunn

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Heat calculation
« on: January 10, 2019, 06:56:51 PM »
If one knew the geometry and constructional make up of a room as well as the fire loading within, is it possible to predict the effect on the enclosing elements with any degree of accuracy?
I am thinking of a room, totally enclosed in 60 min fire resistant plasterboard and fitted out with loose furniture and soft furnishings. I am interested in the response of the plasterboard, especially on the ceiling.

Offline Fishy

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Re: Heat calculation
« Reply #1 on: January 15, 2019, 08:38:40 AM »
I a word, no.

Longer answer... there are techniques available to determine (based upon fire load) whether structural fire protection (which might include plasterboard) is adequate or not (in terms of load-bearing capacity) - normally defined within the relevant structural Eurocode (e.g. EN1993-1-2 - see here: https://eurocodes.jrc.ec.europa.eu/doc/2012_11_WS_fire/presentations/04-ZHAO-EC-FireDesign-WS.pdf ).  This is only, however, relevant to load-bearing capacity (R), not 'E' and 'I'.

The issue with fire separating elements is that their fire resistance is often not entirely controlled by the heat energy input alone - e.g. they can be sensitive to the rate of heat rise.  Their response is often not linear - failure can be sudden and not necessarily predictable (e.g. due to distortion - most fire separating elements fail the fire test due to gaps forming because of distortion, not burn-through).  They can be extremely sensitive to the smallest variation in constructional detail (e.g. fixing type and spacing, joint detailing etc)

The difficulty is compounded when the element is also load-bearing (e.g. it's a floor).  A good example - we had a case where someone had built a timber load-bearing partition that needed 60 mins fire resistance using the board details from a tested 2-hour non-loadbearing partition.  They argued that the boards would stay in place and protect the studs for at least 60 mins, hence all was fine.  We refused to endorse this approach, & eventually the construction was fire tested.  The 'two-hour' non-loadbearing board make-up did 40 mins in the load-bearing construction!

Like I say, I know of no published and verified methodology of doing what you describe (i.e. demonstrating that a fire separating element will stay in place and effective for the length of time required for full 'burn-out' of a compartment).  I've seen people try, but their approaches have never stood up to technical scrutiny, in my experience.

There's probably a PhD in this, if someone were so inclined...!

« Last Edit: January 15, 2019, 08:43:37 AM by Fishy »

Offline lyledunn

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Re: Heat calculation
« Reply #2 on: January 16, 2019, 07:54:59 AM »
Thank you Fishy for your detailed answer. I have noticed recently that determinations reached by fire engineers that are not supported by test procedures relevant to the situation are failing to make passage through BC. Your example perhaps illustrates the reason.

Offline wee brian

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Re: Heat calculation
« Reply #3 on: May 29, 2019, 02:34:57 PM »
Its called time equivalency - you can calculate a period of fire resistance based on the room geometry/fire load/ventilation/insulation conditions.

Whether a construction will deliver that level of fire resistance is based on the usual tests etc etc..

Offline Fishy

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Re: Heat calculation
« Reply #4 on: May 29, 2019, 04:04:13 PM »
Its called time equivalency - you can calculate a period of fire resistance based on the room geometry/fire load/ventilation/insulation conditions.

Whether a construction will deliver that level of fire resistance is based on the usual tests etc etc..

Quite right, WB - but so far as I'm aware time equivalence has only ever been validated for structural members with respect to load-bearing capacity only. 

No-one has ever convinced me that they could predict the performance of fire separating elements in the same way, as it's hard to see how you could take into account the effects of distortion (especially differential distortion between different materials), cracking, joints, interfaces and failure due to sustained flaming.  As the OP stated a particular interest in 'enclosing elements' I fed back along these lines.

if anyone does have any references to convincing research validating time equivalence against the BS EN 13501-2 'E' and 'I' criteria, then I'd be very interested in a pointer to where it could be found?

Offline wee brian

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Re: Heat calculation
« Reply #5 on: May 29, 2019, 04:39:36 PM »
Interesting point - I see what you are saying.