?AFD in lieu of fire resisting lobbies - single staircase?

[saddlers]

Phil,
DCLG have recently admitted that there is a typo in that section of the new ADB, in that para 4.34a should read "except for small premises covered in paragraph 4.6a"

This information was given by Brian Martin (DCLG) at the RICS seminars on the new ADB.

[jokar]

Whilst B1 in its old and new guise will recommend lobbies, ADB allows other alternatives on an engineered basis and therefore all guidance is up for grabs if justification is correct.

[PhilB]

Hi Saddlers

The version I am reading already says "except for small premises covered in paragraph 4.6a"

[kurnal]

How many storeys is your building? I am not quite clear on the height of the top floor.
Is there a direct route to an exit door from the foot of the stair, without going through another room?
There is little point thinking about changing doors from 30 to 60 minutes - nothing is to be gained by this.

And a lobby  built into a  room just for the sake of creating a lobby achieve very little in terms of contributing to fire safety. and ruin the use and appearance of the building whilst a lobby separating a small section of  existing corridor can be a worthwhile improvement and look ok.  

If I have understood you correctly, I cannot see much point in subdividing a single staircase along the line of the escape route.

I believe the answer, subject to the questions above, may be through the risk assessment- to look at risk, and to incorporate a heritage cost/ financial cost/ building usability cost versus  benefits analysis of any proposed additional risk control measures.

If you can email some plan drawings of the building I  would be happy to offer some free advice.

[saddlers]

Phil,
We must have bought the cheap copies again!!!

Jokar,
I agree that ADB is not gospel and that engineered solutions are suitable alternatives, and I am a strong supporter of such, I have just never come across using AFD instead of lobbies. I have always looked for lobbies in a single stair scenario with more than one storey above or below ground.

I know in a well managed building, I have always questioned the advantages of lobby provision, combined with the fact that in an office AFD would not necessarily be required. I know I would rather an alarm tell me at an early stage that there is a problem so I can get out rather than rely on fire separation to protect me from a raging inferno!!!

But at what point do you draw the line, how many storeys before you insist on the lobby, I know there are a host of factors that would influence such a decision, but you cannot get away from the fact that at some point it is no good knowing there is a fire on the ground floor, if by the time you have left your storey and got to that point that the stair is compromised.

I would be interested on your views/experience in these situations.

Another good topic on a great forum!!!

[PhilB]

Generally speaking lobbys were recommended in old guides because you could not rely on old structure to give adequate protection. Hence the difference in recommendations between blue, lilac guide and ADB.

For example three storey small building office with a single stair ADB would allow single door, home office guides required lobbies if you could not get out of building within travel distance. The premise was that the single door in ADB is a nice new door in a new partition.

ADB requires lobbys for tall buildings when you are likely to be in the stairway for a considerable time as you make your escape.

In my opinion for smaller buildings with a single stair a decent fire door and AFD is a suitable alternative to a lobby.

[kurnal]

In the early days of the FP Act 1971, before smoke detection was widely used, the lobby approach to single staircase buildings was commonplace, including sleeping accommodation and hotels. I am talking the red hotels guide- which incidentally allowed 13metre dead end bedroom corridors, Boy we were pedantic in those days and ruined many a fine building!
As smoke detection became affordable, reliable and commonplace,  where a building did not lend itself to lobby protection, it became common practice to to trade off the lobbies for smoke detection- in the early days L3 detection was regarded as covering stairs and corridors only. Nothing in rooms and self closers were not required on hotel bedroom doors, unless in a dead end. Enforcement Officers were happy to agree that the early detection was a fair trade off for the staircase protection
Then the interpretation of L3 was clarified and detection had to be provided in rooms off escape routes, and L2 became the prescribed standard for life risks. Hotels were required to have self closers fitted, the lilac guide replaced the red guide, and fire door seals appeared on the scene.

As L2 detection was now the norm, enforcement officers started to ask for the lobbies back on single staircase buildings-after all early detection was now a standard requirement for all buildings. Hey ho we go a full circle. The same officers who were happy to accept a single door protection with detection for many years now wanting lobby protection back. Why? Because the benefits of smoke detection were universally accepted, all sleeping accommodation required it so they were no longer able to trade off against it.

Thank goodness for the risk assessment approach.

And that there is still room for trade offs in some types of use- for example office and commercial buildings where smoke detection is not yet the automatic benchmark standard.

As for the new ADB and whether it should read 4.6.or 4.6a- mine says 4.6- I dont know. My version brings it into line with how I read and understand BS5588,i think your amendment takes it out of step. I would be interested  to hear your interpretation of this saddlers.

And interesting as this technical discussion is we mustn't lose track of the real world and I wager theres more single stair office buildings without lobby proection than have it.  And at the other extreme new buildings are going up that appear to throw all convention out of the window even to the extent of smoke curtains to protect  firefighting lobbies, staircase widths, compartmentation, travel distances. They do this by the use of a whole range of proprietory software programs which they seem to select, mix and match to suit the desired outcome.

My boss used to slap me when I used a mixture of guidance on a job! Are they not doing the same, and as all these programs make assumptions and approximations there is a huge risk of compounding an error in my view.

[Tom Sutton]

The blue guide although irrelevant, stated

Shops and offices which are of normal fire risk and have floor areas in excess of 280m2 with not more than 4 floors above the ground floor.

(d) In these circumstances, the stairway will need to be separated from the remainder of the building in the manner recommended paragraphs 14.39 and 14.44 (see also diagram 12 and paragraph 14.46). Where it is impracticable to achieve two fire door separation in accordance with paragraph 14.39 in a building with not more than 2 floors above the ground floor, the stairway should be made a protected route and suitable automatic fire detection arrangements provide in the building (see paragraphs 15.12 to 15.14).

Also in days of yore, in my experience, a fire door without a self closer was considered not to be a fire door, except for cupboards.

[saddlers]

Kurnal,
I must admit I have always looked to the lobby approach if more than a GF & FF on single stairs, but as I previously said, I have never really been 100% confident of the benefits in offices without AFD. I suppose if you reverse that principle, it would make sense that AFD could be considered as a possible trade off, but I have never interpreted the guidance that way (although I have not have the luxury of seeing how much of this guidance has evolved over time).

The clause 10 guidance has always caused me a bit of confusion because it seems to contradict itself, and therefore it may be I am not interpreting it correctly, but I had looked at it as:

10.2.1 - "it replaces the recommendations on number and siting of exits and protected stairways and travel distances" but does indicate whether the lobby consideration in clause 9 is part of this.

10.2.1.a - "the premises should be in single occupancy and not comprise more than a basement, ground floor and first storey"

10.2.4 - "There should not be less than two protected stairs......except......an office building comprising not more than 5 storeys above the ground storey......"

No wonder we get confused!!

In that you could have a single stair in offices up to 5 storeys, but you still had to have lobby protection, and I guess my interpretation would have been mainly based on the fact that ADB says 11m for single stair and lobbies where more than one storey above or below ground, and I guess I automatically saw that as being both sets of guidance stating the same principles (for once!!!)

I have to agree that whilst calculation for smoke flows etc is succesful because it is a scientific calculation on known fluid dynamics, the calculations on occupancy movement are trying to predict human nature, and I think one thing you can say for certain about human nature is that it is is uncertain!! I know studies can assist in making assumptions more accurate, but you will always get us humans doing something that no-one expects them to do, and at times it is very easy to become blinkered when you think you have found the perfect solution!!

But as you say the fundamentals of fire safety have definitely improved in the real world, and hopefully will continue to do so!!

[jokar]

A number of small premises with a single staircase have never had enough space to provide a lobby scenario and AFD as a compensatory feature has always been a good recommendation.  The lobby theory is that 2 door protection is better than 1 but that may not be the case.  A door that meets the test standard for 30 minutes at 800 degrees and then the fire breaks through menas that the second door is already subjected to intense heat and fire and may not although tested to 30 minutes meet that standard.  The other issues if of course the looby walls have only to be 30 minutes and a fire could break through there and you would not have 30 minute protection.  ADB as it currently stands allows small sleeping risks premises with a single staircase to have single door protection for a limited number of floors.  The new guides accept this as well.  rom anotjer thread on this subject, a 60 minute door set will afford much more protection than a lobby approach.

[Tom Sutton]

I do not think double door protection was designed to increase the fire resistance it was more about smoke control. In the rare occassion of tall buildings with a single staircase we required a one hour, ventilated lobby and only accepted them as a last resort.

[kurnal]

A ventilated loby certainly can do a great deal to protect a staircase. A small unventilated lobby artificially created inthe corner of a room to create "doube door protection" would do very little.If I recall it was partly about smoke control and partly about keeping the fire loading from within the room away from the door protecting the staircase, so there would be no fuel close to the door..

Personally I cant see that a one hour door would create much advantage over a half hour door. The main weakness will be around the edges between leaf and frame (where the two are almost identical- the hour door may be thicker) the fact that it may be wedged and persons are equally likely to pass through it in making their escape, causing the same amount of smoke to enter the stair.  If they havent escaped within 20 - 30 minutes then they may find a difference. The essence is that I believe there will be little difference during the evacuation phase between the half and the one hour door.

[Tom Sutton]

But we never required one hour separation we assumed a building could be evacuated in half an hour and this was born out by witnessing fire drills which usually took ten to twenty minutes to clear the building. The exception to the rule was tall single staircase were we required one hour protection half an hour to evacuate, half an hour to fight the fire. Tall was considered to be over four storeys the height a wheeled escape could reach.

[kurnal]

Yeah TW I was referring to the post and thread thats now evaporated about creating lobbies where currently there are none and in that situation the provision of a single one hour door rather than two 30s.

Tall buildings are something else.

Down chocks! Out carriage!

[Tom Sutton]

I apologise for banging on, but I consider it is important to understand the reasons behind any decisions.

I once read a transcript regarding a BCO requiring double door protection in a HMO and the landlord appealed. The magistrate asked the BCO why did he needed double door protection and his reply was, “it is in accordance with the appropriate guidance”. The magistrate did not accept this and asked again, when the BCO could not give a satisfactory answer he proceeded to rip the BCO up for toilet paper. Since that I have always tried to understand the “WHY”.

His response could have been something like the following:-

In a building with only one staircase it needs to be protected to a higher degree, consider a building with two staircases if you lose one, you have the other as a backup. In a building with one staircase with two door protection, again if you lose one you still have the other for a back up.
The staircase could be render impassable, first by mechanical fault (defective fire door or self closer?), satisfactory management should eradicate this possibility.  Second cold smoke percolating into the staircase, but if the doors are fitted correctly and adequate permanent ventilation of the staircase this should also not cause a problem. Thirdly heat, which with time would bypass both doors, but all the occupants should have evacuated the building by this time.

My response the problem in this thread would be:-

If the lobby was removed or omitted would suitable smoke AFD system on the risk side achieve the same results? As the detector heads should warn the occupants early in the cold smoke phase then the occupants should be well clear of the building before the heat phase and the staircase remain passable, therefore AFD would be a satisfactory solution.

Must now go and lie down in the quite room with pretty lights where I cannot hurt myself.