Basements fire separation

[Meady]

Please could someone give me a steer on the required levels of fire separation between basements and ground floors?

Situation is a commercial premises; the basement is served with independent stair which is fitted with FD30s at top.  The stair is separated from the main stair to upper floors.

Basement is not ventilated.  Basement is also unoccupied but does contain mains electrical distribution board and gas valve / shut off.

Building Control accepted FD30s at top of stair on basis basement has smoke detection fitted which is linked to building fire alarm system.

Fire Risk Assessor advises that because basement has no smoke / heat ventilation, it must have 60-minute separation and has advised either upgrading door at top of stairs to FD60s or add another FD30s at base of stairway.

In ADB Volume 2, it appears to state that only 30-mins fire separation needed between basement and ground?  Or am I reading this wrongly?  So why would a) Building Control say FD30s is fine as long as smoke detection fitted and b) why is Fire Risk Assessor stating it must have 60 mins separation?

I've also looked at the HM guidance documents for fire safety risk assessments and cannot see anything in them either.

If anyone can help point me in the direction of correct documents / articles to read it would be a great help.

Thank you! ?

[AnthonyB]

It's been a staple of guidance from back in FP Act days and ADB Table B4 still has a 60 minute requirement for basements (going up to 90 minutes where you go deeper than 10m) and the top & bottom door thing has been around for similar years.

As the guidance dates back to the late 20th century it dates from when fire alarm systems were generally manual with limited detection (& even then mostly heat until the 70's) so it's not unsurprising that detection can be used to justify deviation (but I'd expect the whole basement as you aren't just deviating on the door, plus the lobby approach is a form of smoke control that a detector can't compensate for and also you are having a lower FR for the whole ceiling).

A few years ago I dealt with a mill that had unprotected gappy wooden floors that in theory should have been 30 minute and imperforate to smoke on the upper floors and 60 to the basement - this would have been financially impossible as it would have required tenants relocating, false ceilings removed, services re routed and effectively site redevelopment. The sprinklers were too neglected to use, so I proposed a new L1 system (benchmark would be M) as the alarm was non compliant & ancient anyway and upgrading the protection to the internal & external escapes as TDs weren't too bad and it was an awake occupancy familiar with the building. An Enforcement Notice was served during the protracted period of trying to cost and get approval, citing the same issues I'd picked up so any solution has to satisfy them too. After lengthy meetings (& am interrogation!) they agreed with the alternate solution with one exception - the basement ceiling had to be 60 minutes. Considering the savings on the other floors and the fact a notice compliance clock was ticking the client and myself agreed.

The FR Assessor is correct following the traditional benchmarks.

BC shouldn't be suggesting non standard solutions but determining if they will accept the ones suggested by the architect (or in reality their fire engineers) as any alternate solution needs to detail why it's acceptable in a fire strategy (or at least FR assessment) so during the life of the building the methodology is understood and maintained. Also once BC have passed it then it's no longer their problem and becomes a fire service enforcement issue - if a few years down the line an audit picks up the differences, finds them too high a risk they will want the mitigation as to why it's OK - and saying BC passed it holds far less water than it used to due to the amount of things passed that actually don't comply for various reasons.

You don't want to underdrawn the basement ceiling again if you can avoid it, therefore you need to have something that will explain why & how the non benchmark solution is acceptable not just for Building Regulations purposes but for Fire Safety Order ones as well - if you can get that you should be fine for both the immediacy of BC purposes but long term as well.

If it's a smaller old building then it may well have had lesser standards in place for a long time as it won't have needed a fire certificate and whilst there were still requirements to be met and the guidance book was broadly the same in benchmarks to the one for certification these premises were rarely if ever inspected.

[Meady]

Hi AnthonyB - thank you so much for such a detailed reply!  That is really useful information - many thanks!

[AnthonyB]

One of these days I'll have to start invoicing you! ???

Glad to help.

[CaylinBr]

Very detailed answer, thank you, useful for a nooby like me

[Meady]

On 14/01/2022 at 19:59, AnthonyB said:

One of these days I'll have to start invoicing you! ???

Glad to help.

? Would be worth every penny!  Your advice is truly appreciated.  Thank you.