A risk based argument for the removal of an AOV

[Hi Tower]

I am wondering if those of you out there would mull over the following and provide feedback on my argument for the removal of this block of flats AOV?

I recently assessed a block of flats that's structure consisted of:
3 storey;
2 flats per floor, each with internal lobby and 30 minute fire resisting final exit door (protected staircase) including intumescent strips, cold smoke seals and self closer;
Purpose built - late 80's by reputable local developer;
mainly non-combustible;
single enclosed staircase with no externally openable windows;
AOV in ceiling of stair; likley to have been requirement of CP3/BS5588 at time of build.  Cannot confirm this from BC as archives disgarded after 15 years.  AOV currently non-serviceable.
Common area compartmentation between flats and stairway is uncompromised - concrete block with render;
Soundness of compartmentation inside flats for above and below unknown - however; beam and block construction and well looked after block without obvious signs of neglect in a fairly affluent location.
Fire strategy - Stay put.
The residents are keen not to incur any unnecesary maintenance costs - in particular to fire safety, the servicability of the AOV.

Taking into account the following points I believe it is reasonable to consider that the AOV be removed:

• Based on the design and materials used in this building's construction I believe it is reasonable to consider that the fire strategy (stay put) is correct;
• As adequate protection has been provided to the staircase it is unlikely that copious amounts of heat and smoke will disperse into it/li]
  

• With consideration of the adopted stay put policy the staircase is not needed for escape;
• Although access cannot be made to each flat it is of my view that it is reasonable to consider from the materials used in construction that compartmentation is and will remain sound

what do your alls reckon and based on the previous thread's comments by jokar that the FRS are being prescriptive opposed to risk based is there any point in taking the argument to them anyway?


Not sure if anyone out there has the statistics but another thought was on how many occasions over the past so many years has it been necessary that AOV be activated so as to prevent injury or loss of life.  This stat alone could if weighted on the wrong side of safety disslove my argument immediately; however; if its one in a million maybe I could use it as further argumentable weight.

[Phoenix]

From your description, your building would fall under the category illustrated by Diagram 9b in ADB (check t.d.s).  If this was built today it wouldn't require an AOV in the staircase enclosure.  But it would probably be unreasonable not to have any ventilation in the staircase (ADB therefore recommends an OV at the head) and as you say you don't have any openable windows I would suggest that the AOV be converted to an OV (I'm assuming it's at the head of the stairs) with a yellow box operating mechanism at ground floor level.  It would be a smallish expense for the residents but it would bring them up to date and it would be cheap and simple to maintain.

Stu

[kurnal]

Just to add to phoenix' comments, from what you say HT this block would have been built to the 1971 edition of CP3 chapter4 part 1. Thats all there was then in terms of design documents. (I believe.)

Para 3.4.5 states that stairways without permanent ventilation should have openable windows at each storey height or 3.4.6 where the stairway is not sited against an external wall or has no opening windows it should have a permanent vent at the top of 1sqm.

I dont agree with you that the staircase will not be needed for escape. It will be for occupants of the flat involved and it might be for others  if a fire escalates and the fire service deem evacuation to be necessary. It will almost cetainly be used for access by the fire service. In these circumstances the guidance was always explicit that the opening vents were intended for use by the fire service to clear smoke from the staircase should this be necessary for evacuation or to maintain tenable conditions for firefighting.

Since it has a vent it is very difficult and inappropriate to try and  "risk assess" it away, it seems to me that Phoenix' suggestion is likely to be the best.
These situations are always difficult. We see many similar existing blocks with little or no ventilation at all. And we always try and make a judgement as to what is reasonabbly practicable in the circumstances, are there windows that could be converted to opening or even smashed by the fire service in an emergency? Came across one 1980s conversion with a domestic smoke detector which switched on a vent axia bathroom style fan, in that case I gave them the option of a louvred vent to roof level or full AFD and an all out policy.

Its a real problem for housing associations with a huge range of existing properties all requiring some work and a limited budget. Thats why I sometimes resort to the fire service smashing existing windows in an emergency as a short term measure and providing opening casements on the longer term on replacement of windows. I tend to reserve that one for those flats where the staircase is approached from a common lobby like yours, and where there is no such lobby then the windows to be replaced or an opening vent installed. Thats my idea of a risk based approach bto these problems.

[Hi Tower]

Stu/Kurnal
Thanks for your replies - some comments.
Kurnal, you are right I missed the obvious point in that there is a need for the occupants of the fire compartment to use the stairs and understand the requirements for firefighting and option for all out - still suggest though that fire doors should with cold smoke seals and strips adequately protect the stair from copious amounts of smoke - along with the lobby construction.  If only I could get my hands on stats that said how many times these things actually activated in anger and when they did, was it really necessary!!

What about going from where the block is now (AOV - smoke detector activated, required at time of build) to your suggestions of OV? - am I right in that I need to seek approval from BC as regulation 2, a&b of Building Regulations 2010 says such a thing would be a material alteration? also going on your suggestion Stu converting from AOV to OV which still used an electronic system wouldn't really reduce much of the residents costs - THEIR main objective.  Would a vent that is physically opened be acceptable - bearing in mind, as you say the requirement for the AOV in today's App.doc B is not necessary?

(For reference - Absolutely no windows to smash or otherwise)

[Phoenix]

Irrespective of the presence of smoke seals, etc on the doors, when the fire service are tackling the fire there may be a fair bit of smoke entering the stairs and there really should be some means for dispersing that smoke.  There will probably, at this stage, bear in mind, be people in the other flats that share the stairs.  They should be able to leave the building if they so choose and, as kurnal points out, if the compartmentation isn't up to scratch between flats they may have to leave the building to escape the fire.

On that basis you will struggle to argue that no ventilation at all is required. 

If you went for an OV that is openable from the ground floor (and that might be achievable by some physical - non-electrical - cable mechanism - they do exist) then your alteration will probably not be deemed a material alteration under the Building Regs - frankly, you'll be improving the current situation.  So you can just do it.  If you want the operating mechanism to be at the head of the staircase then you're dropping below the normally acceptable standard and the proposed alteration would be material for the Building Regs and you should apply for approval and you may not get it.

But you could argue this:  The idea of the operating mechanism at ground floor is so that fire fighters can operate it on entry to ease their movement up the stairs.  But when they arrive there shouldn't be any significant smoke in the stairs because we're only anticipating large quantities of smoke entering the stairs once the fire fighting commences with doors open.  If the fire fighters open the vent before they open the flat door then that could be seen as equivalent to them opening it by means of the normal ground floor operating switch.  There might be an argument there for the operating mechanism to be at the site of the vent instead of remote from it at ground floor.  It would be interesting to hear other people's objections to this.

Stu