Pressurised Staircase

[David Rooney 2]

We are looking at a small single staircase office - 5 storeys. I suspect this was a large town house that's been converted. The staircase is pressurised and again I'm guessing this is at least 15 years + in age.

There is a single office on each floor - no lobbies just a single door off the stair and straight into the office. Each Office has an automatic smoke vent window that opens to air on fire alarm activation.

However, the office doors leading to the staircase are not automatically opened on fire condition so when the fans switch on there isn't anywhere for the air to go except for "natural leakage" around the doors and through the floors to the windows.

We are going to put this back to the risk assessors but can anyone explain why this arrangement is required in the first place ??

Could we do away with the pressurisation kit completely ??
 

[Revol]

It sounds like this was a fire engineered building as the description you provide wouldn't meet prescriptive guidance. Not too sure I'd be over the moon with this solution today - is it sprinklered as well?

The strategy is to create a positive pressure in the stair - if the door on the fire floor opened automatically as well as the smoke vent (window) on the floor plate the fans in the stair would have to work very hard to maintain a positive pressure. Its about trying to prevent smoke entering the single escape route rather than clearing smoke form the offices.
 

[AnthonyB]

It's one of the few cases where the usual gap & touching brush seal requirements on fire doors don't apply so the pressure can leak in a controlled manner and that you are able to open the doors (no leakage and the pressure would make the door difficult to open if hung in the direction of escape).

As said the office vents are more more pressure relief than smoke venting.

You need to ensure the system is kept in working order as it is mitigation for an otherwise non compliant situation unless an alternative mitigation can be proposed that is considered acceptable.

[David Rooney 2]

Thanks both ... I understand the principle as we have looked after a few and am familiar with 12101-6.

No it's not sprinklered and yes I would imagine it would be be quite difficult to open a door onto the staircase once it is pressurised.

I have a newton meter on hand .... 

We will refer back to the RA but am interested to know why we could not just simply vent the staircase with a 1m Sq vent to the roof ?

[lyledunn]

If it?s only 15 years then likely BC will have been provided with a FP application of which the system you refer to will have been part. If you intend to alter the system, I would contend that you need BC approval.

[David Rooney 2]

If it?s only 15 years then likely BC will have been provided with a FP application of which the system you refer to will have been part. If you intend to alter the system, I would contend that you need BC approval.

Absolutely ... hence referal to the RA who can question it up the chain .......