Fire Safety in Tight Houses
rockies63
| Posted in General Questions on
I was watching this show on fire safety and they were talking about how changes in the building codes and the tightening of the building envelope (in regards to air infiltration) was causing the nature of house fires to intensify.
https://www.cbc.ca/natureofthings/episodes/into-the-fire
They also said that the window of opportunity too escape a house fire has been cut from approximately 17 minutes to about 3 minutes due to the kinds of building materials and home furnishings selected.
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Here in DC almost all new construction requires sprinklers. I've read -- but don't have a cite, nor do I know if it's actually true, but I'm going to repeat it anyway -- that there has never been a fire death in a residence with functioning sprinklers.
The issue these days is with the smoke from plastics and foams being especially toxic. Smoke inhalation can knock you out before you have a chance to escape the flames.
Did they elaborate on why a tighter house would be worse?
After watching the whole video, I have a different view than the poster. The video is about a fire started in furniture, which is made with plastic products, not about forest fires.
The reference to a tight house is about when the fire is growing, it does at a slower pace than when a door or window is open, and then oxygen exaggerates the fire, which is normal in any combustion. Fires need oxygen.
Per the UL's Firefighter Safety Research Institute (FRSI), all fire training recommendations tell you that you want to avoid opening a door or window and leaving it open, when you're in a house fire, shut it behind you to slow it down. Doors are firestops, even though it’ll eventually get burned, and lessens smoke damage.
Firefighter break windows and cut holes on roofs to ventilate gases and improve visibility, especially if they are looking for victims.
This is probably a good opportunity to make folks aware of home sprinklers!
I was watching a video from a research center where they had 2 identical apartments, one had "legacy" type furniture made of wood, leather, cotton, wool etc. The other had modern items made of primarily plastics, polymers etc.
Identical fire were ignited in both, and the legacy apartment took about 25 mins to flash-over. The modern one was 3.5 minutes to flash-over.
In the commercial world, fire safety is paramount. It is common to hear about "noncom" (noncombustible) construction. That means mostly steel and concrete for framing, and if we want to put in any plywood (such as a backboard for utilities), we have to use treated "noncom" plywood which is treated for fire resistance and has a red/pink color. A lot of emphasis is put on "firestopping" any penetrations of firewalls, and that firestopping has to be done with things like mineral wool and intumescent fire rated sealants. All that effort into firestopping and noncom construction is to slow the spread of fire.
BTW -- sprinklers are intended to slow the spread of fire and help contain it, they are NOT intended to actually extinguish a fire. The purpose of sprinklers is to buy people time to get out, and to keep things from getting out of control until the fire department can get there to put out the fire. Fire sprinklers also CANNOT all go off together the way you see in the movies. Every sprinkler head has it's own small heat-activated valve. The old style used a fusible lead link (which you could see, it looked like a vertical gray bar connecting two metal levers near the head), the new ones use a small glass vial filled with alcohol (typically red in color, and near the middle of the newer sprinkler heads). The lead fuse would melt, releasing the levers, which would let the valve plug pop out to activate the sprinkler. In the new heads, the alcohol filled glass vial ruptures and lets out the valve plug. All such systems are supposed to have flow sensors at the main water supply that will set off the fire alarm if water flow is detected, so the spinkler heads double as heat sensors for the fire alarm.
It doesn't hurt to seal off things commercial style in your home. Air sealing helps slow fire and smoke spread too. You can gain time by building with 5/8" drywall everywhere (the commerical standard), which is more fire resistance (read that as "it takes longer to burn through a wall"). I only use 5/8" drywall in my own projects, including my house, since it's a cheap upgrade, it gives a flatter and more solid wall, it is better for sound transmission (the house is quieter between rooms), and it's more fire resistant. Note that adding mineral wool in interior walls also helps to slow fire spread.
Modern construction is likely to slow the spread of fire. Modern building materials aren't really any worse in terms of fire -- today's lumber, drywall, and fiberglass aren't any different than yesterday's. Mineral wool is even better than fiberglass. Cheap home furnishings can be a problem -- a sofa with foam cushions is going to be worse than a sofa with down, for example, in terms of smoke production.
Bill
Good info, Bill. There are municipalities in the Southwest and West where sprinklers are required on all new construction, others with homes above 3k sf, and of course, most homes over 6k-7k sf. Water shortages to fight fires is the primary reason.
I also design all my homes with 100% 5/8 drywall at walls and ceilings, plus any house with a "bonus" or habitable room above garages, and adding all these new solar batteries, chargers and EVs, are making me specify 2 layers of Type-C drywall in the garage. It's really a safe and inexpensive upgrade.
I'm a big advocate of fire rated rooms for batteries. In my work, I deal with large battery rooms and those have always been built with at least a 1 hour fire rating (which includes using fire rated doors!). There are hydrogen sensors, and exhaust systems. Nothing in the rooms is combustible, either. The telecom industry has over a century of experience with battery rooms.
In the residential world, permanently installed standby battery systems are very new. You don't have the same issues with hydrogen release with the new lithium batteries, but you have a HUGE fire risk if they ever have a catastrophic fault. I recommend building a fire rated room dedicated to the batteries for this reason, and putting a heat sensor in there that triggers a fire alarm in the occupied portion of the structure. Lithium fires are very dangerous, and difficult to put out, so it's best to build structures that can contain those fires until the occupants can safely get out.
Note that water-based sprinkler systems can be an issue in electrical rooms. We usually use dry pipe preaction and VESDA (a fancy electric nose that sniffs for smoke, basically), but those aren't practical for residential use. What MIGHT be something to look into would be a small CO2 based clean agent system. There are also those built-in fire extinguishers that might be useful here (although I've never worked with those myself).
Bill
I think there are a few things all jumbled up together in this discussion that are perhaps better separated out.
- The house itself. Newly constructed, code compliant houses are remarkably safe. Unlike older buildings, the fires that occur in them are almost never caused by the house itself.
- Occupant behavior. if you eliminate potentially dangerous occupant behavior and do routine maintenance, the risk of fire is reduced to almost zero. That is unattended cook-tops, open flames (candles and matches), smoking, storing volatile chemicals, and portable heaters. Dryer vents and chimneys need periodic cleaning.
- Furnishings. As the program said, once a fire starts, the materials in some furnishings reduce the time you have to escape and are probably best avoided.
If you deal with the issues above, the statistical probability of having a fire in your house becomes so low I'm not sure sprinklers make sense. That's a separate issue than whether from a policy perspective they should be mandated.
There has been a rash of deadly fires of late, including apartment fires in New York, Chicago, Arlington, etc. with significant loss of life, including children.
Much of my work consists of analyzing and enforcing fire safety in construction, from the plan review stage through to site inspections. I find the work fascinating and fulfilling. I often get pushback from owners and contractors because of increased costs and time to achieve the required fire safety, but what keeps me focused is these stories of where things went wrong and people were killed.
A basic theory of fire safety is compartmentalization, where a building is separated in various fire rated compartments both vertically and horizontally. The goal is in the event of a fire in one compartment, a person(s) can safely make it from where they are in the building to an exterior exit, traveling through safe floor areas and exit compartments along the way.
These compartments are built of fire separations with a fire resistance rating, measured in time (ex. 1hr, or 2hr) depending on a host of factors. As a rule, if the less aware or capable the occupants are (think sleeping, or hospitals) the higher the level of safety. Also, if there is a high combustible loading expected (think industrial, or mercantile).
As mentioned above, the devil is in the details. Materials used in your wall and floor assemblies, fire stopping, sprinklers, alarms, exits and access to exits. Things like depressurization can be critical in highrise type buildings to limit the stack effect of smoke.
There are case studies that show where things went very wrong, like the Station nightclub fire, or the Grenfell Tower fire. From these tragedies come the building codes of today.
I'm late to the party here, but looks like there's been a lot of jazz hands on keyboard on this.
I watched that video, it was 7 minutes of crude interior fire testing with scary sound effects and 37 minutes about wildfires. This video has merely a blip of info regarding interior fire dynamics and you shouldn't base anything regarding residential fire safety from it other than fire is hot and not good.
If you want to learn about fire dynamics and how ventilation plays a role, here's a 3 part, 3 hour course on fire dynamics, ventilation, flow paths and firefighting tactics.
https://www.youtube.com/watch?v=82OJqcftNVg
But none-the-less I'm going to address to OP's concern:
That part where the chief says stuff about modern homes and air tightness then "when you open a door, bang it lights up" (cut scene) then says he says something like "in the past it took 17 minutes from smoke detector to fully involved, now it takes 4 minutes"
I'm sorry to say, this was a bit of editors magic, those are two different topics in the two separate scenes.
The first part regarding tight homes, is a consideration for firefighting becasue airtightness makes it more prone for an oxygen limited fire and can promote conditions for a backdraft or flashover.
In the second part, he's talking about the heat release rate of modern furniture compared to older furniture. This has nothing to do with air tightness. A good house fire in a not-so-tight house with foam couches and full of plastics and garbage will still party like its 1999. The minor cracks in your framing aren't saving anyone by ventilating all the smoke and heat out. A room in a house is still a compartment trapping heat and smoke within it.
In fact, if we want to get deeper in the weeds of this, lets look at a typic fire growth curve from NIST:
https://www.nist.gov/sites/default/files/styles/2800_x_2800_limit/public/images/fire/typical-fire-behavior_1.jpg?itok=Paw0sD2r
That part where the chief says "bang", he's referring to the point on the chart that says "Fire Dept. Vents"
So in fact, the opposite of what the video alluded to is closer to reality. The tighter the house and the more compartmentalized the fire is, the lower the point of "fire underventilated" on the chart and where it begins the initial decay phase. This could potentially give you a greater chance of survivability becasue the lack of oxygen might choke the fire out sooner. And when a door or window is opened and left open, oxygen is introduced via ventilation, and in the words of Chief of fire innovation of Ottawa "bang, it lights up"
Now, lets talk about smoke. Smoke kills people first, well before any heat. The burning of the body is an afterthought. Modern foam and plastic-y materials produce significantly more toxic smoke at a faster rate than our home contents did years ago. Products of combustion like Hydrogen Cyanide, Benzene, Toluene, etc. (bad stuff). Here's some nice light reading on the thermal decomposition of just poly-foams:
https://firesciencereviews.springeropen.com/articles/10.1186/s40038-016-0012-3#Sec9
Also, Here's a nice video from UL to compare heat release rate (and time) of old vs new furniture. (Note: this is not an oxygen limited fire in a tight home as discussed above):
https://vimeo.com/463653907?embedded=true&source=video_title&owner=43463622
So... with all this: Are tight homes making your chances of getting out of a fire worse? No, your furniture is making it worse.
What's funny is that building codes are increasingly getting more fire safe as revisions go on. Yet some people are still trying to blame 'codes' & 'air tightness'. For instance, none of us in this thread mentioned anything like structural collapse or other critical failures due to fire, because they generally don't happen in the first 4-17 minutes or even 30 minutes of a house fire. Structural collapse doesn't happen for a while in a code built house becasue the building codes are designed for that. Now, residential domicile codes regarding fire safety are piddly compared to Part 3 commercial buildings, but there's still good emphasis in place on passive systems like gypsum drywall, mineral wool, and fire blocking etc.
And to the sprinkler talk: I know NFPA 13 differentiates sprinkler systems for fire control vs suppression, but let me tell you from my practical experience that sprinkler systems put out fires of most general Class A contents. It puts water on the fire. There are times I've seen them not put it out, and that's when there's an overhead obstruction of the water being able to get to the base of the flame, to which it still is controlling it from spreading. Residential sprinkler systems save lives, becasue your most vulnerable when your sleeping, a lot can happen in 8 hours (or 4 minutes apparently). Malcolm touched on the topic that houses themselves don't spontaneously combust (usually), and its the inhabitants that do things that cause the fire. I agree. To be human is to err. So as designers, how do we design against that? I'd say a residential fire suppression system (fire sprinklers) is pretty easy to implement and cheap enough these days. I plumb solely with Uponor pex, and they have a residential fire sprinkler system that ties in with the Potable plumbing system. They actually do the design and parts list if you ask them to. Use concealed heads so your kids can't kick a soccer ball into it them and set it off and they're barely noticeable among all your downlights and (hopefully) smoke detectors. Burst washing machine hoses have a higher likelihood of causing water damage in your home than a sprinkler system does. Its not rocket surgery.
Sorry for the rant, take it as you may,
Jamie
Jamie,
I'm sorry but I can't agree that is a rant. Too much useful information to be characterized that way.
Deleted
Malcolm,
Thank you for the kind words.
Although I do love a good rant. I tried to structure this better than I normally would.