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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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    Unsurprisingly, a Ventilation supplies Company are the people to go to for such items.

    We occasionaly use intumescent collars in flats. They seal the hole when they get too hot.
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    Hopefully plastic cased ventilation fans are made of a non-flammable material. Also hopefully the fan motor has a thermal cut-out device embedded into its windings. Hopefully we fuse the fan according to the maker's instructions, often 3 Amps. maximum. Hopefully the thermal wall insulation in the wooden framed homes is flame retardant. Statistics show that fan fires are prevalent. Possibly they are positioned incorrectly like over a hot cooker and a buildup of grease occurs within the fan. Personally I have never found a big black molten plastic blob on the floor under a wall extractor fan, but I suppose that it does happen. I have found brown marks inside the fan timer module where the large Voltage dropper resistor gets hot, and even a charred circuit board, but no evidence of fire.


    I imagine that a conventional cheap flexible metal wall sleeve duct will contain a fire for a period of time. The danger might be from a fan catching fire and igniting interior floor coverings or furniture in a timber or brick built house.


    Some makes of extractor fan have GS approval. To what extent that covers fire safety I would have to research.

    https://www.vent-axia.com/range/basics-slim-line-range


    Z.
  • 0
    Now if this smouldering fan had fallen into an older style metal bath rather than a plastic bath....then things may have been different.

    https://www.kentonline.co.uk/dartford/news/faulty-extractor-fan-leads-to-25511/


    Z.


  • 0
    Caught in time.

    http://www.dsfire.gov.uk/news/newsdesk/IncidentDetail.cfm?IncidentID=45038&siteCategoryId=3&T1ID=26&T2ID=41


    Z.
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    Zoomup:

    Hopefully plastic cased ventilation fans are made of a non-flammable material. Also hopefully the fan motor has a thermal cut-out device embedded into its windings. Hopefully we fuse the fan according to the maker's instructions, often 3 Amps. maximum. Hopefully the thermal wall insulation in the wooden framed homes is flame retardant. Statistics show that fan fires are prevalent. Possibly they are positioned incorrectly like over a hot cooker and a buildup of grease occurs within the fan. Personally I have never found a big black molten plastic blob on the floor under a wall extractor fan, but I suppose that it does happen. I have found brown marks inside the fan timer module where the large Voltage dropper resistor gets hot, and even a charred circuit board, but no evidence of fire.


    I imagine that a conventional cheap flexible metal wall sleeve duct will contain a fire for a period of time. The danger might be from a fan catching fire and igniting interior floor coverings or furniture in a timber or brick built house.


    Some makes of extractor fan have GS approval. To what extent that covers fire safety I would have to research.

    https://www.vent-axia.com/range/basics-slim-line-range


    Z.




    Apparently it's not just fans themselves catching fire that's the problem, it's also that if there's a fire in a room when the fan is running, it can suck the flames into the pipe, so if plastic melt it and get into the wall void etc.


    I'll do as mentioned and contact ventilation supplies co's and see what's available, flexible or otherwise that's fire rated.


    The PE article mentioned that building regulations regarding timber framed buildings are being reviewed and may change later in the year, so liaise with building standards for further advice.


    F

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    alanblaby:

    Unsurprisingly, a Ventilation supplies Company are the people to go to for such items.

    We occasionaly use intumescent collars in flats. They seal the hole when they get too hot.




    Collars seem appropriate for horizontal application, such as for ceiling fans where gravity is pulling the intumescent material down onto the e.g. plasterboard, so can fill the hole when activated. However, i wonder about use in vertical applications such as in walls, where when the fan spigot and plastic vent pipe melts, there's nothing holding the intumescent  collar in place, so it could drop down in the wall void away from the fire before sealing the hole.


    F

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    If you need funny shaped one off making that are not in the normal suppliers catalogues, I can recommend Envirgraf   here as being very helpful, I have no commercial interest, except as a happy occasional customer, as having had things made  specially for me,  one memorable for example for a funny shaped cat flap bridging fire zones.
  • 0

    alanblaby:

    Unsurprisingly, a Ventilation supplies Company are the people to go to for such items.

    We occasionaly use intumescent collars in flats. They seal the hole when they get too hot.




    Unsurprisingly, maybe, but surprisingly, useless. I called three Co's today and they all said they don't do anything specifically fire rated, they can't say that their metal pipes/ducts will be of use in preventing fire entering the wall void, and why bother anyway, they've not been asked this before, so just use plastic flexible pipe as others do (furthermore, a manufacturer of intumescent collars said their collars are tested for ceiling use only, not walls, so best to check whether collars used are for use in walls).


    So, looks like it's a case of giving people the option of plastic pipe or the pricier intumescent sleeve, and forget about metal.


    F

  • 0
    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.


    Z.
  • 0
    Presumably the same thinking should apply for timber fire resisting elements in non-timber framed buildings too - i.e. the suspended floor/ceiling below a 2nd floor or between flats.


    I'm not sure that simple metal ducting would of itself be a help - it would soon reach the temperature of the fire and so risk setting light to anything flammable touching or near to it. You'd almost have to treat it like a metal flue from a combustion appliance have have sizeable spacings all around to anything flammable.


      - Andy.

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