Use of space within protected stairways

[wainy1]

I have recently undertaken a FRA of a building which contains a number of bedrooms accessed directly from a protected staircase.
My review of the guidance (principally HM guide and Approved Document B) in determining if this situation is acceptable, reminded me I have query relating to the use of the space within a protected stairway.

4.38 (d) of Approved Document B states cupboards in protected stairways should be limited to "cupboards enclosed with fire resisting construction, if it is not in the only stair serving the building or part of the building".

Protected stairways should be kept clear of combustible materials and therefore the fire should not occur within the stairway enclosure. This leads me to deduce the purpose of the fire resisting enclosure of the cupboard is to restrict the spread of fire from the cupboard to the stairway. In situations where no automatic detection is provided within the cupboard, the alarm will not be raised until the fire breaches the fire resisting enclosure which will be at a later time from the point of ignition.
Sorry for the long winded description; can anyone provide the rationale for the fire resisting construction, without AFD within the cupboard it would appear to worsen the situation.

Many thanks in anticipation

[kurnal]

Is the cupboard any different to a room opening onto the staircase? Enter the old chestnut about domestic premises with smoke detection only in the staircase- is it better to leave the door open to ensure earliest warning of fire or closed to ensure maximum protection to the staircase. The fact is that although earlier warning will be given conditions in t e staircase will deteriorate to become untenable far more quickly giving occupants a much smaller window of opportunity to escape safely.

The same goes for your cupboard - one built of matchwood will fail very early in a fire giving almost no opportunity to escape. One of FR construction will probably give a window of say up to 30 minutes after the fire starts for people to smell burning,  investigate and escape safely. Provided they don't open the door!

[lancsfirepro]

A FR door to a cupboard as described provides separation from whatever the contents are to the staircase and vice versa.  Who knows what someone has put in there; perhaps cleaning products or materials that do not like to be mixed.  Conversely, a fire started in the staircase by say, a pram against a wall heater, would be prevented from involving the contents of said cupboard.
That dealt with; if there is detection in the staircase but not in the cupboard, would it not be the correct course of action to fit intumescent strips only (i.e. without cold smoke seals) to the cupboard door in order to allow a little smoke to pass the door to activate the detector in the staircase?  In any case, once the intumescent strips have done their job, a fire within a cupboard would surely very quickly run out of oxygen.
Doesn't BS5839-1 only recommend detection in cupboards over 1m2 in an L1/P1 system (unless there's an arson risk)?

[nearlythere]

There is that thing about multi level or occupancy buildings with single or double door protection which seemed to be the answer to everything. But what it meant was that, in theory, people in building with variable working hours could find themselves above the ground floor in an otherwise empty building with a nice little fire getting out of control in the ground floor and only showing up when it has entered the stairway, climbed and few flights and knocks on the doors on the top floor. That's unless it hasn't gone through the ceiling first.

IMHO multi story buildings should have at least a Cat L3 system. Not hard to put it in a stairway.

[nearlythere]

There is that thing about multi level or occupancy buildings with single or double door protection which seemed to be the answer to everything. But what it meant was that, in theory, people in building with variable working hours could find themselves above the ground floor in an otherwise empty building with a nice little fire getting out of control in the ground floor and only showing up when it has entered the stairway, climbed and few flights and knocks on the doors on the top floor. That's unless it hasn't gone through the ceiling first.

IMHO multi story buildings should have at least a Cat L3 system. Not hard to put it in a stairway.

Of course that should have read Cat L4 system.

[AnthonyB]

There is that thing about multi level or occupancy buildings with single or double door protection which seemed to be the answer to everything. But what it meant was that, in theory, people in building with variable working hours could find themselves above the ground floor in an otherwise empty building with a nice little fire getting out of control in the ground floor and only showing up when it has entered the stairway, climbed and few flights and knocks on the doors on the top floor. That's unless it hasn't gone through the ceiling first.

IMHO multi story buildings should have at least a Cat L3 system. Not hard to put it in a stairway.

Exactly what happened in the 1977 Murray House Fire, China Lane, Manchester- all 7 staff on the evening shift in the 5th floor tenancy were killed by a fire that started in the basement cafe (that had shut for the day at the time of ignition).

The place had an OSRP certificate, fire doors (that did check the smoke and fire for a while as designed) and a manual electrical fire alarm, but the lack of AFD meant that the staff were unaware of the fire until the main internal stair was untenable and the smoke logging into the corridor that the deceased office was off was such that it deterred them from going the other way down the corridor to the external escape route (although there is conjecture that despite the smoke it would briefly have remained tenable long enough to escape, just their fear put them off.)

[Golden]

I always recommend that the occupier discusses this with the landlord under article 22 and give an explanation of the risks involved; unfortunately most guides don't give sufficient detail and I wonder if this is because it would be too difficult to enforce.