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Intumescent/non-combustible sleeving/ducting in timber-framed buildings.

Farmboy
PE magazine have run the article 'Wiring Timber-Frame Buildings' (a typical construction example shown in the attachment), which seems similar to those alluded to by ES1st (in their BP Guide 5, Fire Safety).


When installing wall fans in timber-framed buildings, one option is to use intumescent sleeving (such as shown in the attachment) for flexible ducting (but seems quite expensive at approx £60 for a standard 100mm ducting up to 500mm). Another option is use non-combustible/metal ducting (as suggested in BPG5). However, does anyone know of a supplier for such metal ducting (fire rated or proven for such use)? When I ask wholesalers and fan manufacturers, they all seem bemused (with some saying they don't think anyone bothers to use them), and as yet a google search reveals little help.


F
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    I would have thought that by the time a room fire had become so intense that sparks or flames were being sucked into the extractor fan, the smoke alarms or fire alarms would have sounded and the fire would either have been put our with a fire extinguisher or the room door closed, area evacuated, and the fire and rescue people summoned.



    Building regs seem to have other ideas - hence the requirement for certain building elements to have a 60-, 90- or 120-minute fire resistance. Sticking a plastic "chimney" right through such an element I would have thought would compromise it quite significantly. Even without the fan running the duct will likely induce a chimney effect and draw hot products of combustion through quite effectively.


      - Andy.
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    AJJewsbury:




    I would have thought that by the time a room fire had become so intense that sparks or flames were being sucked into the extractor fan, the smoke alarms or fire alarms would have sounded and the fire would either have been put our with a fire extinguisher or the room door closed, area evacuated, and the fire and rescue people summoned.



    Building regs seem to have other ideas - hence the requirement for certain building elements to have a 60-, 90- or 120-minute fire resistance. Sticking a plastic "chimney" right through such an element I would have thought would compromise it quite significantly. Even without the fan running the duct will likely induce a chimney effect and draw hot products of combustion through quite effectively.


      - Andy.

     




    Perhaps with vertical air ducting, but a horizontal hole through a wall would act in a different way. That is what the illustration in Professional Electrician shows relating to an extractor fan, that the O.P. refers to.


    Z.

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    AJJewsbury:




    I would have thought that by the time a room fire had become so intense that sparks or flames were being sucked into the extractor fan, the smoke alarms or fire alarms would have sounded and the fire would either have been put our with a fire extinguisher or the room door closed, area evacuated, and the fire and rescue people summoned.



    Building regs seem to have other ideas - hence the requirement for certain building elements to have a 60-, 90- or 120-minute fire resistance. Sticking a plastic "chimney" right through such an element I would have thought would compromise it quite significantly. Even without the fan running the duct will likely induce a chimney effect and draw hot products of combustion through quite effectively.


      - Andy.

     




    Apparently, it's to do with whether the pipe/duct breaches a fire separating compartment, not that a hole in the wall allows a building to burn per se. If the pipe breaches, for example, a fire separating wall between two joined dwellings, or breaches a wall/service ducting within a dwelling that acts as a safe route for people to evacuate the building (e.g. from a third floor down a set of stairs and out the door), then fire rated ducting has to be used, typically by the use of intumescent material. If, however, the ventilation pipe does not breach such a wall/barrier, there is no requirement to use fire rated ducting, so basically the building can be left vulnerable to burning via the use of e.g. plastic pipe, because the main issue is about evacuating people quickly and safely, not nescessarily protecting the domestic building. Personally, I'd prefer to maintain the integrity of the fire barrier regardless of location, and it seems intumescent material rather than metal is the way to go in timber-framed buildings.


    F 

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    The initial post started talking about wall fans in timber framed houses. Normally these are situated on an outside wall so the ducting is very short and does not run through other people's property, especially in timber framed homes I imagine. In larger homes thing may be more complicated if air ducting runs through other people's homes or communal areas. The weak point is of course any plastic fan. In large buildings automatic fire stopper louvres can be installed in metal ducting, operated by electric motors, weights or springs.


    Fire dampers. https://en.wikipedia.org/wiki/Fire_damper


    Testing the devices is extreme. https://www.youtube.com/watch?v=a5Vv0JwezB0


    Z.
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    Perhaps with vertical air ducting, but a horizontal hole through a wall would act in a different way.



    Not my area of expertise, but as I understand things a short length of horizontal ducting wouldn't necessarily prevent the chimney effect - just as long as the fire is below the ultimate outlet point the heat & products of combustion can convect up/through just the same. It's common enough to see horizontal flue outlets on some wood burning stoves (later turning upwards) - and they seem to draw OK.


      - Andy.
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    AJJewsbury:




    Perhaps with vertical air ducting, but a horizontal hole through a wall would act in a different way.



    Not my area of expertise, but as I understand things a short length of horizontal ducting wouldn't necessarily prevent the chimney effect - just as long as the fire is below the ultimate outlet point the heat & products of combustion can convect up/through just the same. It's common enough to see horizontal flue outlets on some wood burning stoves (later turning upwards) - and they seem to draw OK.


      - Andy.

     




    They probably draw o.k. because of the vast vertical chimney above the 45 degree angle.


    Z.





     

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    They probably draw o.k. because of the vast vertical chimney



    Indeed - giving the overall difference in height between fire and outlet I mentioned earlier. If the fire was lower than the fan you'd have a similar overall arrangement (I don't think that it goes vertical (room) then horizontal (duct) rather than the other way around (horiz flue then vert flue) will make any difference). You might not get quite the amount of draw as you would from a properly designed chimney & stove, but the general drift will be the same.


        - Andy.

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