Having specialised in fire doors (amongst other things) in a previous life, and having seen loads of fire resistance tests on timber doorsets, both to BS 476: Part 8: 1972 and Part 22: 1987, my observations are as follows:
• Door stop size does not make a significant difference to the fire resistance rating of a timber doorset;
• Door stop size does not make any difference to the smoke sealing ability of a timber doorset (TRADA did some research that demonstrated this, I seem to recall);
• People who say that because a door passed a test that was superseded nearly 30 years ago it is automatically still OK are (in my view) missing the fact that the benchmark of acceptability as regards safety performance changes over the years, and when assessing safety one has to refer to current good practice – not 30-year-old good practice. If (as is stated) some of these were installed in 1997 they fell well short of the good practice benchmark that was a requirement of that time;
• When a doorset is described as being ’30 minutes’ fire-resisting that does not mean it will last 30 mins in a fire – it might last longer or it might fail more quickly. The Fire resistance tests are a ranking methodology, used as such in the guidance to the Building Regulations, not a means of determining ultimate fire performance;
The above does not mean that I consider that every existing fire door should be upgraded to the current standard. It means, though, that those undertaking the risk assessment need to understand that doors that aren’t up to current standards would not provide the current ‘benchmark’ level of fire separation and/or smoke sealing performance. They then need to assess whether that is acceptable;
My experience tends to be that you can tolerate a certain degree of flexibility in fire resistance performance (say, accepting 20 mins where the AD-B would require 30, if there are no hazards that are ‘unusual’), and there’s plenty of advice available regarding how to judge the fire resistance of existing timber doorsets (and upgrade if necessary), but that it’s more often than not smoke sealing that is critical. If you need smoke sealing then the only way you will get that achieved effectively is by having correctly installed, well-fitting doors that incorporate cold smoke seals. Having a big stop on a door frame will make little difference to smoke sealing performance. If you therefore conclude that you need to fit smoke seals, in most cases you may as well fit combined intumescent/smoke seals, which give you the benefit of improved fire performance at next to no additional cost.
Finally, there was, of course, the determination (
http://www.communities.gov.uk/documents/fire/pdf/heritagehotel.pdf) that dealt with this issue and had as one of its conclusions “
It is considered that the existing doors (even with self closing devices fitted) cannot be relied upon to prevent the egress of smoke at the early stages of a fire”. As the Determination states, this only applies to the case in question and in consideration of the particular risks found in that premises, but whether or not one likes or agrees with the conclusion of the determination, it’s now in the public arena and we have a responsibility to consider the ‘good practice’ benchmark that it provides when we’re making our safety decisions.
In summary, I think that the benefits of upgrading the fire and particularly the smoke resistance performance of doorsets is often dismissed too lightly. It’s not that difficult to achieve and in certain cases, to protect certain risks, it can be hard to conceive how a case can be made for not achieving a certain minimum level of fire and smoke sealing performance.
