House fire - how to control mvhr

[warby]

3 minutes ago, jack said:

 

 

there must be a reason that MVHR manufacturers recommend simply turning off the MVHR in the event of fire.

I didn't know this, how do they propose it should be closed down?

[Nickfromwales]

I'd assume it would be by interrupting the mains power supply, via a contactor. Maybe some units have a set of zero volt contacts for external shutdown / control. Would be quite simple to do tbh. 

[jack]

One of our smoke alarm mounts has a relay that closes when any of the alarms is triggered.  Our home automation system takes this as an input and... presently does precisely nothing with it!  But we could use it to kill power to the MVHR if desired (and wired).  Personally I don't think it's an issue - building regs don't require it and I can see arguments both ways for leaving it on and turning it off.

For me the main thing is waking up and getting the flock out of the house as soon as there's smouldering.  By the time any fire has got the bit between its teeth, my family and I will be long gone.

[Nickfromwales]

 

[SteamyTea]

Most serious injuries and deaths in house fires are caused by two things, arson and drunkenness.

So choose your drinking buddies carefully.

 

The other option is to make sure that you minimise combustible material within the building.  So LSAF cabling, no combustible furniture fabrics/cushion (they should not be on sale now, we can thank Woolworths for that), keep curtains away from candles etc...

 

[warby]

Thank you everybody for your wise words.

Please do not forget fire and safety, in particular the automatic control of your MVHR should there be a fire.

I will leave it to the moderators to decide whether a new thread should be raised, perhaps a checklist for fire and safety requirements both in design and secondly during a build.

[Stones]

I have seen my fair share of fire related death, and it isn't pretty.  

 

The one that probably sticks out in relation to this thread was a family of five that died in a house fire (20 odd years ago now).  The simple fact was they couldn't get out of the house before the smoke overwhelmed them. That house didn't have MVHR, but did have smoke detectors.  

 

Having a clearly planned escape route and strategy is essential.  In that particular case, doors and windows were all locked from within. The grandmother and two grandchildren were found huddled together at the bottom of the stairs right beside the front door.  We will never know of course, but it makes you wonder if something as simple as the key not being in the lock was ultimately the reason they didn't survive.

 

Speaking to fire crew in the aftermath, to a man they all suggested fire suppresion - a sprinkler system, was the most effective way of giving an escape window to occupants.  The problem sadly, as many of us who have looked at such systems has found, is the cost.  

 

 

[TerryE]

On 26/07/2016 at 18:31, Calvinmiddle said:

 

If there is a fire, the only need is to get the hell out, who cares what the MVHR is doing.

 

Maybe this is a different topic since I agree with the who cares what the MVHR is doing bit, but definitely +1 to evacuating occupants, however my personal view is that immediate evacuation is not always the only option for some classes of fire.  For example, I would recommend keeping a fire blanket in the kitchen and a couple of decent fire extinguishers in the house.  If the fire is localised (e.g. a pan fire on the stove) then killing the seat of the fire immediately is one option.  Clearly if there is any chance that the fire has reached a timber frame fabric then the house should then be evacuated by all occupants until the professionals have given the all clear before being reoccupied.  And the smoke risks shouldn't be underestimated.

 

PS. I haven't been a professional fireman but I did spend 9 weeks standing in for them during a strike in 1978-9 and put out a few fires during that time, so I have probably seen  a lot more house fires than most.

Edited August 3, 2016 by TerryE

[warby]

I hope this is acceptable to quote this reference from http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4575

"Sinnerboys comments throughout this forum are interesting and worthwhile I'd say. He advocates fusible link dampers on any ceiling mounted grilles/vents on lower floors and connecting the motor on the unit to the smoke alarms in that if there is a fire then the fans trip off. Seems like good common sense to me, I'm glad to have read his comments"

also: "

"They're controls on the ducting so that it gets closed off in the case of a fire to stop the fire spreading from room to room through the ducting. See http://www.scottaire.co.uk/circularvalves2.html for examples (no affiliate etc.)"

Perhaps in future my ideas might not be ridiculed by Neanderthals in the future!!!!!!!!!!!!!!!!!!!!!!!!

Just in case I have offended anyone specifically, which of course is not my intention: from Google: neanderthal meaning, definition, what is neanderthal: (of people or beliefs) very old-fashioned and not willing to change

[TerryE]

Peace brothers.  The Neanderthals died out about 3-40,000 years ago largely due to a bit ethnic cleansing by our lot or our ancestors.   Maybe we should continue this on my post since this covers a wider scope than just the MVHR aspects? 

Edited August 3, 2016 by TerryE

[dogman]

Hi all

one idea is to ask the local fire safety officer at the fire station. They will normally come and advise you of what is needed in event of a fire. As we let out the last cottage we built we have annual fire inspections and they are happy to give advise. about all aspects. I know from working in a building with massive smoke extract fans they can only be switched on by the fire service once the fire was out to clear the smoke.

Ask them what they would like as they will be the ones coming to help.

[jack]

The original question was about shutting down certain MVHR vents and turning on full boost in the event of a fire.  We've drifted a bit from that so I think it would be useful to briefly summarise the thread for those who might find it in the future.  

 

It seems that best practice for what to do with an MVHR system in the event of a fire is still developing in the UK, presumably because building regs haven't yet caught up with the increasing use of such systems.

 

One thing several posters seem to agree on is that MVHR inlets and outlets should ideally be closed when a fire is detected.  There also appears to be some consensus that shutting off the MVHR in the event of a fire is useful.  

 

As far as anyone who posted on the thread knows, building regulations do not seem to require either of these actions to be taken, nor do they require full boost in the event of a fire as was mentioned as desirable in the original post. 

 

There also seems to be a consensus that getting people out should be the first priority where there is a fire.

 

To help keep this information together, I note there's also a broader discussion of fire regulations (including some input in relation to MVHR) here:  

Many thanks

[warby]

A.Please consider this scenario:

There are two people in a building and there is a fire.

The first person has limited or no capacity to evacuate the building without assistance due to physical or mental capacity.

The second person is unconscious due to say a fall, or or medical problem, e.g. heart attack, stroke, diabetic coma, etc. 

The smoke detectors can make as much sound as they like these two people are not going to be able to evacuate the building.

How will they die, a.due to smoke and b. due to fire.

There ONLY chance of survival is to be rescued.

Time to rescue them is now critical.

MVHR - if smoke is removed from the burning building you buy time for their rescue. If fresh air is being supplied to fire this increases the fire and reduces the opportunity time for rescue. 

Would some members who said Smoke Detectors and evacuation is the answer like to explain how these two people would survive with your suggestions.

B. A different point - when an insurance assessor investigates the fire do you really think they will pay out fully on when knowingly a householder has installed an MVHR system that increases the fire damage? 

[PeterW]

Given the deformation point of polyethylene is about 140c, the chance of a duct continuing to function in the event of a fire is minimal - it's more likely that the duct will collapse and seal off any flow or extract long before it does anything of use. Normally the fan units and casings on MVHR units are normally polypropylene and urethane foam - both of which have low melting points. 

 

Secondly, flow rates and pressures of MVHR units are less than 100 litres per second at 75Pa. There isn't enough flow in an MVHR unit to pull smoke from a room anyway. 

 

As an example, consider this :

 

- a smoke pellet produces around 24 cubic metres of smoke, enough to fill an average bedroom of 3.5x3.5x2.4m 

- using my commercial MVHR unit on boost, the adjoining Ensuite will extract around 40CuM/hr (the biggest domestic unit can manage roughly 2/3rds of that)

- the supply into that bedroom on boost is around 28CuM/hr 

 

based on those figures it would take 51 minutes on boost to clear the smoke from that room.  What is also clear is that the supply to the room is not sufficient to match the extract from the Ensuite, so it will be constantly drawing in air/smoke under the door to make up the difference meaning it would take over an hour to clear the room notwithstanding the system can at best provide a pressure difference of 160Pa over the outside air. 

 

To to be effective as a smoke clearance method you would need axial metal fans, galvanized ducting and fireproof cabling to a secondary power source - none of which you will see in a standard build domestic property. This all needs to go in at design time, so the spec needs to meet the user requirements and the building regs don't cater for that as they are not designed in that way. 

 

In the situation you describe I would use secondary alerting - most modern managed alarm systems have the ability to both dial out and alerting via SMS or active dialing, with the fire detection system being part of that managed alarm therefore alerting assistance at the earliest opportunity. 

[warby]

The bottom half metre in a room is where an unconscious person is likely to be and that small area might just be kept free of smoke for long enough, with luck and if the source of fire isn't directly in the room; smoke should also be moving away from habitable areas towards extracts, so I don't think we can simulate what might occur in reality.

 

As far as fire is concerned I still feel the answer is a damper on the inlet to shutoff new air entering the building, triggered by a smoke detector; this was the conclusion reached on GBF. As Peter and Jack have said, MVHR manufacturers are recommending turning off the MVHR and in so doing they are acknowledging there is a problem. 

Pipework/ducting should be fire protected by Plasterboard and fire stopping precautions within floor and wall voids for 30 minutes. 

I have 4 fireman friends, two very senior, who told me of horrific scenes where fire traveled within unprotected voids; perhaps best if I don't go into further detail,

Your points are well made, thank you.  

[ProDave]

On 26 July 2016 at 18:49, Stones said:

I have seen my fair share of fire related death, and it isn't pretty.

 

The one that probably sticks out in relation to this thread was a family of five that died in a house fire (20 odd years ago now).  The simple fact was they couldn't get out of the house before the smoke overwhelmed them. That house didn't have MVHR, but did have smoke detectors.

 

Having a clearly planned escape route and strategy is essential.  In that particular case, doors and windows were all locked from within. The grandmother and two grandchildren were found huddled together at the bottom of the stairs right beside the front door.  We will never know of course, but it makes you wonder if something as simple as the key not being in the lock was ultimately the reason they didn't survive.

 

Speaking to fire crew in the aftermath, to a man they all suggested fire suppresion - a sprinkler system, was the most effective way of giving an escape window to occupants.  The problem sadly, as many of us who have looked at such systems has found, is the cost.

 

 

Building regulations now prevent you from having locking windows to escape routes (bedroom windows for example) So that would not now happen.  Although not a building regulation, I would not have entrance doors that need a key to open them from inside.

 

I also point out that wiring regulations now require that cables above exit passages must be supported by non metalic means to prevent firefighters getting entangled by drooping cables.

 

Also, related to the melting point of ducting. Do you think with a full fire raging, and the melting point of PVC cable, that the power feed to the mvhr will still be on and working for very long after a fire starts?

 

Perhaps we should all wire smoke alarms and mvhr feeds in MICC cable which is about the only thing that would last any length of time in a fire.
 

[TerryE]

14 hours ago, warby said:

A.Please consider this scenario ...

 

Martin, the purpose of an MVHR is mechanically ventilate a reasonably airtight house whilst retaining the heat that would otherwise be dumped during ventilation.  Most MVHRs can recycle the whole house volume in 2 hours but will normally be on tick-over doing so perhaps every 4 hours.  This is perfectly adequate to keep the house fresh and moisture-free.  It is not designed to perform emergency smoke dumping.    As Dave says, the BRs now give other guidance and escape routes and means of clearing smoke.  I feel that you are using the wrong tool to address a very real issue.  After having thought about this, so long as the MVHR shuts down and any ducting channels are properly protected it should not worsen the fire risks. 

 

My parents lived well into to their 90s and my mother had increasing dementia for the last 10 years of her life; towards the end neither was capable of standing after a fall.  Both had emergency call buttons around their necks and we encouraged (with minimal success) my father to carry his mobile on him at all times.  We and social services made a number of modifications to their house to enable them to continue to live in it and in my father's case until his terminal admission to hospital.  Yes fire is a risk and the outcome might be frightful, but so is simply lying on a floor unable to move or regain standing, and slowly freezing to death or starving.  You must live in a dwelling matched to your capabilities, and whether you have MVHR or not really isn't a material factor in this judgement.   So for example in such cases any smoke detectors should be automatically link to an alarm systems and included in response scenarios.

 

14 hours ago, warby said:

B. A different point - when an insurance assessor investigates the fire do you really think they will pay out fully on when knowingly a householder has installed an MVHR system that increases the fire damage?

 

My answer is simple: I believe that it will make no difference, if the house is built to current BRs and correctly maintained.  There are other risk factors for fire that are far more material, for example does the house have open fires or do the occupants smoke?  And for example a house fitted with MVHR almost certainly won't have open fires. 

Edited August 5, 2016 by TerryE

[jack]

12 minutes ago, TerryE said:

My answer is simple: I believe that it will make no difference, if the house is built to current BRs and correctly maintained.  There are other risk factors for fire that are far more material, for example does the house have open fires or do the occupants smoke?  And for example a house fitted with MVHR almost certainly won't have open fires. 

 

I agree Terry.  In addition, what little guidance can be found from the MVHR manufacturers seems to suggest fire-closing extracts in the kitchen, and switching off the MVHR in the case of a fire.  If you follow that advice and meet building regulations, I can't see why an insurer wouldn't pay up.

 

Indeed, departing from that approach (which, Warby, I respectfully think you are risking when you propose boosting during a fire) seems more likely to raise question marks with an insurer.

 

If insurance is of concern, the safest thing is to ask two or three insurers for their written recommendations, or better yet get their written approval of what you propose to do.  If you follow that, they can hardly complain!

[TerryE]

1 hour ago, jack said:

In addition, what little guidance can be found from the MVHR manufacturers seems to suggest fire-closing extracts in the kitchen, and switching off the MVHR in the case of a fire.

 

 

Hummnnn, need to think about this one, given that we are still in first fit.   Most of our extracts are in our wet rooms where their is minimal fire risk.  The double extract in our kitchen area is the obvious exception, and a source of risk.  I would appreciate comments / advice from other house builders who have addressed this.

[Nickfromwales]

Intumescent collars on the duct at the plenum / ceiling junction? Simple and effective as a terminal means of control. 

If the mvhr fan gets shut down then doesn't there still exist a path between plenum and atmosphere? If so, would heat / convection circulation then naturally draw through the ductwork, regardless of whether it's extract or inlet?

[TerryE]

Part of me says that this would be a real pain for a "false alarm", but thinking about this: if its getting hot enough for the collar to activate then this is by far the best thing to do in the circumstances. 

 

Time for you and me to go to bed.  Or we'll both be getting grief in the morning!  And I've got the waterboard turning up at 08:00 to dig up the road and put in my water supply.  Sweet dreams!!

[Barney12]

On 5 August 2016 at 08:18, warby said:

 

B. A different point - when an insurance assessor investigates the fire do you really think they will pay out fully on when knowingly a householder has installed an MVHR system that increases the fire damage? 

 

As someone with a reasonable level of experience in the domestic buildings insurance market I can assure you this is a non point.

If you wanted to be 'belt and braces' about it (and I can see absolutely no need to) you could simply disclose it at the point of taking out the insurance. It's a separate subject but 'disclosure' of issues that you believe may affect your cover is rather useful, just ensure you retain proof that you did indeed disclose them.