Natural Smoke Ventilation

[David Rooney]

I've scanned the titles of BS EN 12101 and read the bits I can find in Doc B but I still can't find the definitive requirements for an AOV smoke vent system as in ... how long should the battery standby by for the AOVs and if you should be able to open each fire floor AOV as you see fit (eg if there is smoke in any lobby then the AOV on that floor should open) of if the original fire floor ONLY (plus stair AOV) should open and everything stays closed regardless.

Doc B states that only the fire floor AOV should open (along with the Stair Well Vent) and that all others "remain closed".

Also ...

I have a typical 5 storey block, lift lobby with ASD and 4 front doors to flats is separate to the stairwell (stairwell has no ASD).

There is an AOV to air from each lift lobby and an AOV in the stairwell to air (so far (seems to me) so good according to the guides).


The problem I have is that there are also room stats in each lobby that cause all AOV to open in the event of high ambient temperature so in theory, a fire could open all AOVs via the stats as well as open the fire floor AOV via the lobby Smoke Detector.

So ..... does anyone know ......

Which document tells me about battery standby, cable specifications etc
Which document tells me about the system operation ie. should only the fire floor AOV open or can others open as a fire progresses ?

Thank you

[kurnal]

For starters David the room stats which are linked to the aovs should be over ridden should any of the smoke detectors controlling the aovs trigger. Only the vents on the floor (s)  where smoke is detected, together with those at the head of the shaft and in the staircase should be open in a fire situation.  I will give more thouht to your other queries this evening

[kurnal]

Dave I have had a quick look round and this is not the final answer but the specific questions over the standard of the standby supply, cable resilience and number of supported cycles do not appear to be mentioned in the old BS 7346, BS 5588-1, or the current  BS 9991, or BS9999. All of these documents refer to manual controls for fire service use and specify the functional requirement for all vents to remain closed other than for those on the floor levels where smoke is detected, the staircase and the head of the shaft. There are more specific requirements for the ventilation of fire fighting shafts. None of these documents give guidance on dual purpose systems used also for ambient ventilation, this is becoming very common as the thermal efficiency of the buildings has improved. Many are stiflingly hot in summer. I have found that in the high rise blocks the open vents for ambient temperature controls can play havoc with fire doors due to wind pressures  which can then overcome the intended stack effect.
 
As for the other queries I believe the definitive current guidance should be EN12101-4 but I cant find this listed as an available document on the BSI website. EN 12101-2 refers to the method of test for individual vents and refers to the number of cycles - 10000 cycles on dual purpose systems before testing the smoke control functions on the least resilient power supply but again does not refer to the number of cycles in this mode.

I will try and follow this up a little more tomorrow but in the meantime would welcome help and advice from others if they are able.

[Golden]

Hi David and Kurnal,

I've just had a look at 12101 part 10 - 2005 'Power Supplies' and have copied some relevant sections below - sorry I haven't got time to go through it in detail but a bit busy at the moment!!

If a smoke and heat control system fails to the fire operational position on loss of power, only one power source shall be required. For non-fail safe smoke and heat control systems there shall be at least two power
sources: the primary power source and the secondary power source. The primary power source shall be designed to operate from the public electricity supply or an equivalent system. The secondary power source,
for example batteries or a generator, shall be permanently available, tested and maintained.
Each power source, on its own, shall be capable of operating those parts of the smoke and heat control system for which it is intended.
If the primary power source fails, then the p.s.e. shall be automatically switched over to a secondary power source. When the primary power source is restored, the p.s.e. shall be automatically switched back.
If the switching from one power source to the other causes an interruption in supply of power, the duration of the interruption shall be specified in the manufacturer?s data (see Clause 9).
Where there are two or more power sources, failure of one of the power sources shall not cause the failure of any other power source or the failure of the supply of power to the system.

The secondary power source may also be used for other functions, e.g. day to day comfort ventilation. When used in this way the p.s.e. shall ensure that sufficient power is retained for emergency use as specified in
Clause 6, e.g. by preventing further use for the other functions.

6.2.2 At the end of the maximum standby period supplying the maximum standby current Imax a the battery shall be capable of supplying the maximum short duration current Imax b for a period of 180 s with the output voltage within the range specified by the manufacturer.
NOTE 1 To allow for possible failures of equipment or of the incoming mains supply, the secondary supply should be capable of maintaining the system in operation for at least 72 h, unless provision is made for immediate notification of failure, either by local or remote supervision of the system, and a repair contract is in force giving a maximum repair period of less than 24 h. In this case the minimum standby capacity may be reduced from 72 h to 30 h or may be further reduced to 4 h if spares, repair personnel and a standby generator are available on site at all times.

The actuation of the vents is covered in AD B para 2.26 which states "In single stair buildings the smoke vents on the fire floor and at the head of the stair should be actuated by means of smoke detectors in the
common access space providing access to the flats. In buildings with more than one stair the smoke vents may be actuated manually (and accordingly smoke detection is not required for ventilation purposes). However, where manual actuation is used, the control system should be designed to ensure that the vent at the head of the stair will be opened either before, or at the same time, as the vent on the fire floor."

Hope this helps.

[Tom Sutton]

Check out http://www.feta.co.uk/uploaded_images/files/SCA%20Residential%20guide%20June%202012%20Revision%201(1).pdf may help.

[kurnal]

Thanks Golden and Tom. Most useful. The only thing not covered as far as I can see is the provision of safeguards for combined use of the system for ambient temperature as well as for smoke control. (Other than the power supply) I will try and check out what is happening with EN 12101-4 . From the information provided by Golden It is clear that combined systems will need a back up power supply as there will be a need to open some vents and close others in a fire situation.

So therefore in multi stair buildings combined systems with manual control only would not be permissible as implied by ADB?  A case of EN 12101 over riding the base recommendations of ADB.

Hope this has been of use Dave, has anything come up on your fire engineers forum?

[wee brian]

Just because it has a batteries and wires in the system doesn't mean its not manually operated (eg a person has to throw a switch or turn a handle)

[kurnal]

Agreed Wee B but if these sysems have thermistor operated contols to open the smoke vents for control of ambient temperature then they may be open on the wrong floors at the time of a fire. If this were the case it would be essential to have automatic smoke  detection to over ride the heat contols.

[David Rooney]

Thanks one and all for the input ......

I've got 12101-2 stupidly thinking that everything I might want to know about natural ventilation might just be contained in a single document but ho hum ......

I've got the FETA document thanks but again it doesn't really tell me what I need to know.

I can override any open vents and make them close except the fire floor and stair vent via cause and effects but the panel isn't clever enough as it stands to "lockout" the other windows. So as it stands if smoke progresses up the floors or someone simply chooses to operate a manual release then each window will open in turn.

And that's the bit I'm not sure about - should they all remain closed regardless or is it permissible for more then one lobby vent to be open ??

It is worrying as we are following a "smoke vent specialist" firm around and checking their work on behalf of the client .... they have already commissioned and signed off 3 buildings where stats open all the AOVs and they will never shut - not even if the rain sensor activates because a. it isn't connected and b. it isn't programmed right!!

The standby batteries in the control panel and the AOV panel would also be lucky to last 24 hours.

I also have an issue because the vents open to air from the lobby, a small "railing" typical 4ft high and 2 ft wide stops anyone falling out the open vent but this rail is installed 6" from the vent. So anyone could stick anything they like in the vent to stop it from closing - including a child's arm !!

[kurnal]

Hi David

Colt are doing a webinar on this topic on the 18th- might be worth a look?
https://attendee.gotowebinar.com/register/5253173354839394561?utm_source=hs_email&utm_medium=email&utm_content=21931164&_hsenc=p2ANqtz-9_S95L92ee5ndNA9aVXlOUtnlUFJc0RfJJxu1lFfexzcLYUMB491PwUA_nobxaSmy-dIAWKX5E01JGqUDCSiO0rLC8XcY8CZhofBakxw00tEKM5nQ&_hsmi=21931164

Hope the link works.

The situation is normally that we plan for a single fire at any time and so normally would only expect the vents on the floor of origin to open but the wisdom of this has been thrown into some doubt with recent fires especially where duplex apartments are involved. We then hope that the system will then have manual controls for fire service use to operate other vents if required to maintain conditions for firefighting. This is well explained in the FETA document, it is important to remember that the purpose of the vents in the lobby adjacent to the staircase are NOT to keep the lobby smoke free but to release any positive pressure that might build up in the lobby and thus cause smoke to penetrate into the staircase. Staircase protection is what its all about.

The 24 hour backup does not sound very robust especially in a building with no management daily checks- if the mains power subcircuit should fail will anyone notice and report the fault buzzer and in the meantime will the ambient temperature control system be draining the battery? Hopefully the ambient system fails safe on failure of the power supply? Even so is the 24 hours based on a number of operations or quiescent current?

[kurnal]

Another thought, although I have not got a copy of Part 10 I have a view only licence with BSI online so if you have any specific queries pm me and I can take a look. The licence does not allow me to copy or print however unless I buy and I only buy those standards that I feel are core to my business. I think your query has raised many issues for the industry and indicated a need for the national fire safety guidance in ADB and BS9999 and 9991 to be further updated.

I have not been asked questions to this detail previously and  I wager that there are many nasty things hiding under a mountain of stones. Like you I have come across many inadequate, incorrectly configured, non maintained and vandalised systems in my work but must admit have never considered some of the technical issues you have raised such as power supply resilience and duration in the past. The rain sensor issue is a regular one!

Residents should be discouraged from operating manual controls, these are for fire service use and where a smoke shaft is provided if opened on other floors may cause smoke contamination of floors above the fire. I guess it shouldn't affect the staircase protection but is undesirable non the less.

[Tom Sutton]

David you need BS EN 12101-10 and most probably others,

The batteries should be capable of maintaining the system in operation for at least 72 h, unless a failure in the primary supply is immediately indicated, and a repair contract is in force giving a maximum repair period of less than 24 h then the 72 h can be reduced to 30 h. It can be reduced to 4 h if spares, repair personnel and a standby generator are available on site at all times.

[David Rooney]

Thanks Kurnal

You say "Staircase protection is what its all about" so why out of interest are there no detectors in the staircase?

The 24 hour backup is based on the actual quiescent current and the 5839 formula, roughly modified (by me) to allow for 5 full load operations (made up figure!!) of all the vents.

It's just difficult to put these observations to the client without definitive guidance as I'm sure he's going to go back to the original installers.

I'm still trying to get sight of an original specification!! 

Thanks for the link .... it just seems to "hang" but I googled colt and found the details ... and it still hangs!!

[Golden]

David the webinars are very good if you have the patience to get through to the end as they can be a bit slow going!!

[kurnal]

Thanks Kurnal

You say "Staircase protection is what its all about" so why out of interest are there no detectors in the staircase?

The 24 hour backup is based on the actual quiescent current and the 5839 formula, roughly modified (by me) to allow for 5 full load operations (made up figure!!) of all the vents.

It's just difficult to put these observations to the client without definitive guidance as I'm sure he's going to go back to the original installers.

I'm still trying to get sight of an original specification!! 

Thanks for the link .... it just seems to "hang" but I googled colt and found the details ... and it still hangs!!

The staircase vents should open at the same time as those in the lobby and the staircase should be a completely sterile area with class O surfaces etc so there should be no chance of a fire in the staircase - and if there was this would comeletely undermine the whole strategy. Thats not to say many designers do put smoke detectors in there sometimes only at the top and sometimes at all levels. Personally I prefer to see them as a belt and braces measure especially where windows are used as vents in the staircase rather than a roof mounted vent.
Another problem is often electromagnets  magnets are used to open roof vents and then theres no way of closing them w2ithout a ladder.
The colt link was sent by email, i will forward it to you direct- the link worked for me from the email yesterday.