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Guidance On The Appropriate Use Of PU Foam

Sharpfibre

Saturday, January 04, 2014

There are a variety of PU foams available in pressurised cans that can be either applied via hand or gun application.  The foam is typically expelled from the can into long nozzles in the form of a sticky liquid, which then rapidly expands to in the region of 40 times its original size.  As the liquid expands it creates rigid foam, which is a useful tool when it comes to passive fire protection and specifically fire sealing.  

However, it is not uncommon for PU foams to be used in applications in which there are not suitable for.  In such instances the performance of PU foams can be jeopardised; thus undermining the passive fire system of the property and putting lives at risk.    

Reaction to Fire versus Fire Resistance

When you look at available PU foams, many will state that they are ‘Fire Rated’ in accordance with British or European standards, citing Class 0, Class B1 or similar.  It is important to recognise that these are ‘Reaction to Fire’ classifications and not ‘Fire Resistance’ classifications.  As such, they relate to the materials performance in terms of ignitability, surface spread of flame and heat release characteristics.  

In comparison, ‘Fire Resistance’ in the context of PU foams relates to the ability of a floor or wall to maintain fire separation, thus preventing flames spreading from one building compartment to another.  In order for the PU foam used in service penetration and linear gap applications to be compliant, it must meet the relevant national or European fire resistance test Standards.  In the UK the appropriate Standards are; BS 476: Parts 20/22, BS EN 1366-4 for linear gaps and BS EN 1366-3 for service penetration seals.  

Once the PU foam has been tested to the required Standard, in order to meet agreed industry guidance, it must then be assessed by a qualified person or organisation.  Where the product is to be used outside of the scope of application that it was tested for, expert guidance must be sought.  Following the introduction of CE marking of penetration and linear gap seals in 2013, when the Construction Products Regulation replaced the Construction Products Directive, extending the scope of application foams for these purposes must be undertaken in accordance with Extended Application Standards.  

Guidance On Usage

PU foams are combustible and the rate at which combustion occurs depends on the level of oxygen that is available and the presence of conductors that are able to transfer heat into the seal.  In respects to the levels of oxygen, the gap, opening width and seal depth is a key factor in determining fire performance.  With the transfer of heat into the seal via conductors, the presence of metallic pipes or cables will have a detrimental effect on fire performance.  

Under UK guidance, any openings for plastic pipes up to 40mm o/d only need to be fire stopped around the pipe, without a metallic sleeve or pipe closure device being used.  In such circumstances the seal around the pipe must be non-combustible in order to limit the size of any resultant opening in the fire separating construction.  As such, the use of PU foam is not suitable.  

Plastic pipes can also be sealed with intumescent wrap systems, which are designed to expand during a fire, thus crushing the softened pipe and closing the penetration.  These systems require an external restraint so that the expansion is focussed inwards, therefore crushing the pipe.  If PU foam is to be used around such a device in order to seal the opening, there must be available evidence that demonstrates the required fire performance under test.  

Finally, it is important to consider the bonding properties of the PU foam under fire conditions in relation to other elements.  Such an example being where foam is used to bond the frame of a fire resistant door to a structural opening, without the use of additional mechanical fixings.  In such applications the erosion of the foam as it burns can weaken the stability of the frame.  If the weakening is significant, it can have a detrimental effect on the door assembly in terms of fire performance.  Therefore, as with our earlier example of intumescent pipe wrap, evidence of performance for the intended application must be available before installation takes place. 

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