Phased Evacuation & Sub Surface Areas

[Messy]

I am looking for the standard (BS?) which details the elements of phased evacuation. I am interested to research the order of evacuation - and in particular, the need to prioritise pre-movement from areas below ground.  

I am considering an office block of 18 floors (from ground level, plus several sub surface levels) who have a city trading floor (hedge fund) on a sub surface level. The current set up is that when a single detector goes into full alarm anywhere in the building (by virtue of the amount of smoke or after a time delay), the sub surface levels are all evacuated, but many of the upper floors stay where they are. This is the case even for a single head activation in a plant room, perhaps 21 floors above the hedge fund staff.

The hedge fund company aren't too happy having to turn out for a fire so many floors away, especially when upper floors closer to the 'fire' stay put. I do understand the issues relating to fire development in sub surface floors and the resultant evacuation difficulties, but this system does not seem to be based on any reasonable risk based approach.

I am considering developing a system where a nominal horizontal threshold is established - say at the 4th or 5th floor. When a single detector goes to full alarm below this threshold, the sub surface areas would evacuate to allow suficent time to reach the ground floor. Above the threshold, the sub surface areas would be notified (by a VAS) but would remain in place as the fire is not likely to immediately threaten the MOE from the sub surface areas.

The usual rules would apply regarding those with mobility impairments moving immediately. The building is low risk office occupancy, but with a L2 (almost L1) & a voice alarm system. Management of fire safety is generally good.

I would like to study the appropriate British Standard in detail before considering a variation. I have looked a BS9999-2008, this only has a few paragraphs on the subject.

I would also be interested in opinions and views regarding my proposal

Thanks

[kurnal]

I will have a dig through some old stuff over the weekend, first thoughts would be london building act guidance, bs5588 and the preceding cp3 guidance, and possibly take a look if there is any reference in cibse guidance. Post war building studies has something on the design and sizing of staircases. The beauty of such old guidance is that it usually explains the rationale behind the recommendations.

[kurnal]

Have checked BS5588-3 1988 - theres no more useful background info in there other than for the tables of staircase width. There is a bit of info and background in Post War Building Studies 29 but its all mixed up with other less useful and less relevant stuff.

I don't have a copy of CP3 Chapter 4 Part 3 - that might be worth a look if anyone has a copy.

[kurnal]

I have found a useful BRE document IP1/79 entitled Fire Risks in High Rise Buildings that lists the historic fire safety legislation and guidance documents - it was authored by REH Read and itself summarised a more in depth review entitled CP1.

Can send you a copy if you wish- its only 3 pages. There are several references to LCC guidance and rules.

The bottom line is that to me it seems that the guidance on phased evacuation is linked to fire compartmentation and staircase protection and width. The number of floors to be evacuated, sequence of evacuation and the cause and effect are not prescriptive, and therefore the fire risk assessment may legitimately be used to vary existing practices. No doubt someone will remind us of Reverse ALARP and suggest that we should be focussing on minimising the risk from fire without regard for the clients wishes but that argument is for another day.

[nearlythere]

Can you send me also K please?

[Golden]

I'm a bit intrigued at this as you mention a time delay for investigation - surely if the event is investigated there is either a fire or not so they would have to evacuate this building anyway. However it is a bit strange to go for the basement first every time as it is normal to go for the areas in the immediate area of the actuation. The 5839 explanation is

"In certain large or high-rise buildings, it might be desirable to evacuate first those areas closest to the fire and immediately above it; other areas are evacuated thereafter. A particular example of this arrangement, commonly used in high‑rise buildings, is known as phased evacuation."

[Golden]

A paper from the losers across the pond ..... http://www.accem.org/pdf/evacsys.pdf

Just a little more information.

[Messy]

I'm a bit intrigued at this as you mention a time delay for investigation - surely if the event is investigated there is either a fire or not so they would have to evacuate this building anyway.

I am not sure I fully understand your comment. This premises operates a staff time delay system where the operation of a single head to a 'pre-alarm' status operates an alert to the FM staff who carry out a search. The alarm stays silent during the pre determined search time and no other staff or visitors are aware of the activation and nobody evacuates. The alarm only goes to a 'full' alarm if the time limit is exceeded, if a second head is actuated or if the control panel is switch to full alarm manual. This is a near L1 AFD system so coverage is extensive

Any evacuation is completed with those at risk going first. For some reason, the sub surface areas have been deemed as at immediate risk - so turn out first on all full alarms - something I disagree when small fire is 13 floors away!!!

Thanks for the comments. All very useful stuff

[Golden]

Thanks Messy I was just trying to confirm the opening post. I fully agree with you and think Kurnal's advice (reverse ALARP point taken but excepted) to vary the procedures is wise and providing there is no real justification for evacuating sub-surface first this would be the way forward? In my experience of buildings housing trading floors and the like the fire safety measures were always installed to ensure that the floors would only be evacuated as a last resort. I would have thought that for a building this size and complexity there are some records detailing why this procedure was initially adopted?