Ceiling diffusers and fire safety

[Archer]

Hi all, 

 

Does anyone know the regs around ceiling diffusers? I'm actually installing ducted air heating and cooling with the kit in the loft and ceiling vents coming through the plasterboard separating ceiling. What's the normal practice, do you install fire rated diffusers (like with spot lights) or intumescent compression sleaves on the ducts themselves... or nothing - is it just less of an issue with ducts and air outlets?

 

Any advice appreciated. I'm finding it a bit of a minefield to find good looking diffusers that can be adjusted for airflow (ie. dampers) and also direction of flow which is needed for heating and cooling. Would be nice not to have to add fire into the mix! 

[mike2016]

Just saw these on bpc's website. Intumescent and adjustable flow. They have different sizes and other fire products too:

https://www.bpcventilation.com/metal-fire-protection-valve-supply

 

[Mike]

4 hours ago, Archer said:

do you install fire rated diffusers

Not in a domestic build, no.

[Archer]

Apparently with heated air you want the flow directed downwards to avoid keeping the heat at ceiling level, with chilled air you want an adjustable vane which directs air out horizontally so that it then slowly falls and mixes. There are a few diffuser products that have a wax actuator which automatically changes the vane direction based on whether the air flow is hot or cold. 

 

I'm struggling to find a product that has adjustable vanes (ie vertical/horizontal flow), also adjustable dampers (for overall air volume) plus the intumescent properties. 

 

Makes me think that mostly people don't worry about one or two of those properties. I think the dampers can be addressed on the main air handling indoor unit rather than the supply diffuser. Fire stopping seems pretty crucial but maybe leaving the duct is easier. 

 

 

[Archer]

7 minutes ago, Mike said:

Not in a domestic build, no.

Is that because the risk is seen as low - ie. because the duct penetration is pretty small anyway for fire presumably? Should I worry about pumping smoke around the house or is that overthinking it...

[Mike]

1 minute ago, Archer said:

Should I worry about pumping smoke around the house

It would more likely do the opposite - continue to bring in fresh air and help evacuate the smoke. Not that I want to wait around and find out.

[Nickfromwales]

1 hour ago, Mike said:

continue to bring in fresh air and

.....fan the flames by supplying fresh oxygenated air in abundance! For preservation of the fabric of a dwelling, you'd discover the fire and close that compartment off as best as possible (close the doors) and get the hell out of there, and then raise the alarm. If the meter is outside then yank the fuse to the house to shut off the MVHR.

MVHR would not evacuate smoke, no chance. Dedicated smoke evacuation fans for stairwells etc move huge amounts of air, whereas MVHR at trickle is like a squirrel coughing.

 

You may be asked to install intumescent air valves (ceiling diffusers) but most are just happy with fire-rated spots. This will soon change I believe, as a ceiling should be 30 mins FR throughout. You can buy a self-adhesive intumescent strip to apply  to the internal bore but you'd need prior approval from your BCO before assuming it's fine to go with that.

[JohnMo]

If you had a bad fire wouldn't RCD just trip?

[Nickfromwales]

1 hour ago, JohnMo said:

If you had a bad fire wouldn't RCD just trip?

RCD to lights and sockets, yes, MVHR normally in the plant so would prob be one of the last trips to go. Nobody has front-of-house RCD CU's anymore, do they? Possible if it's a retro-fit I suppose, but during most conversion / refurbishments the CU needs replacing to get a new cert done on the electrical adaptations.

 

All relatively academic as the rule is, see a fire, GTF out. I am just saying to preserve the dwelling, whilst waiting on the fire brigade, stopping air getting in will slow the fire down a lot.

[JohnMo]

20 minutes ago, Nickfromwales said:

see a fire, smell, GTF out.

Exactly

 

Been in the air force and oil and gas industry, but went to a big electrical suppliers factory, fire alarm went off (not a practice) everyone just sat there, until they smelt the smoke - real fire. One one injured but was taken aback by the piss poor attitude.

[Nickfromwales]

1 hour ago, JohnMo said:

Exactly

 

Been in the air force and oil and gas industry, but went to a big electrical suppliers factory, fire alarm went off (not a practice) everyone just sat there, until they smelt the smoke - real fire. One one injured but was taken aback by the piss poor attitude.

If I’m in a hotel and the fire alarm goes off, I get out of bed and lay on the floor. 
Unless it gets to north of 45°C I’m not too concerned. 

[Mike]

3 hours ago, Nickfromwales said:

4 hours ago, Mike said:

continue to bring in fresh air and

.....fan the flames by supplying fresh oxygenated air in abundance! For preservation of the fabric of a dwelling, you'd discover the fire and close that compartment off as best as possible (close the doors) and get the hell out of there, and then raise the alarm. If the meter is outside then yank the fuse to the house to shut off the MVHR.

MVHR would not evacuate smoke, no chance.

You're reading too much into my reply. MVHR is more likely to help evacuate the smoke, rather than pump it around the house. Of course it's not to be relied on as an aid or a protection for the building.

 

The amount of air in and smoke out is going to be minimal, so it will only have a small impact on 'fanning the flames' and smoke reduction, but of the two smoke is the biggest threat to life - 'overcome by gas or smoke” is the biggest cause of death in fires - 33% of deaths in financial year 2020 to 2021.

 

 

[dpmiller]

our aico smokes are on a relay box that I've configured to kill the MVHR (and bring on escape lights) on sensing smoke, whilst putting the system into boost in case of CO alarm. Yes, getting out is no1, but aving fabric and recovering is important too...

[TonyT]

Wouldn’t you need fire dampers ?