Smoldering fires starting inside walls with no conductors within approx 10 feet of the fire,

[Waldemar]

Fires occurring on typically humid days. Suspecting improper grounding or leakage current. HELP... I have been investigating fires for 21 years in a large city and these have been occurring about 20/year.

 

[ppsh]

Single family, duplex, multi family? Wire mesh plaster or stucco?

 

[don_resqcapt19]

There is a theory that over time low level electrical current passing though wood can result in pyrophoric carbonization that can result in a fire.

 

[hbiss]

Fires occurring on typically humid days. Suspecting improper grounding or leakage current.

Going to need a lot more forensic information than that to even make a guess. Have you determined an origin for any of these suspect fires? How do you know about the "smoldering within walls". I assume the smoldering was a precursor to the actual fire?

-Hal

 

[synchro]

Were there any metallic structural elements like beams, trusses, etc. in the vicinity of where the fire started?
Or as was mentioned any metallic reinforcement like steel mesh, corners, etc.?

Mold growth on organic matter like hay has been known to produce sufficient heating to cause fires when the moisture content was relatively high.

 

[WasGSOHM]

10' sounds like a non-electrical cause but leakage current can be checked.

Having seen 400 of these, what else stands out?

Sticking pins in a city map may show clusters.

Making a histogram of
month vs. # of fires
may show a spike.

Heating Degree Days is on the Web for many cities but maybe the National Weather Service can provide you a map of
month vs. Relative Humidity. They should talk to you, it's your tax dollars at work.

 

[tom baker]

I have a video (it was from Mike Holt but don't know if still available) called Open Neutrals, done by the City of Miami Fire Dept, showing fires started in dwelling units due to an open neutral...the neutral current found its way into stucco lath and metal pipes, over a long period of time causing pyrophoric carbonization and starting fires. It was amazing to see the metal lath glowing red hot...Miami FD had heard about pyrophoric carbonization but had never seen it
Is this what is happening in your case? I don't know.

 

[WasGSOHM]

So what is most closely correlated with open neutrals?
-Workmanship?
-Day/night temperature variation?
-Using a certain type of Wirenut?

And open hots cause other problems?

How this may go
first, more questions giving more clues
second, eliminating the unlikely
third, a very few likely causes, ideally only one.

 

[don_resqcapt19]

I am not sure that you would leakage current that could flow on the wood in Chicago, given that most all circuits are run in metal raceways.

 

[WasGSOHM]

So far it's
fire
flammable material
humidity (related to mold)
leakage current through wood or metal
contact between a live conductor and wood or metal

Which causes which is not always clear, which came first is not always clear, but likelihoods can judged.


An open neutral in a grounded raceway would not always have appliance symptoms?

Q for the OP. Did the HOs talk of appliance symptoms? Flickering, whatnot?

 

[Waldemar]

I have a video (it was from Mike Holt but don't know if still available) called Open Neutrals, done by the City of Miami Fire Dept, showing fires started in dwelling units due to an open neutral...the neutral current found its way into stucco lath and metal pipes, over a long period of time causing pyrophoric carbonization and starting fires. It was amazing to see the metal lath glowing red hot...Miami FD had heard about pyrophoric carbonization but had never seen it
Is this what is happening in your case? I don't know.

No, in my case i have a very localized fire within the joist bay, slow burning fire that smolders away 2" x 12" and 2" x 4". when we get there sometimes i get low voltage reading most of the time none. It seems like the fire has been smoldering burning slow for prolong time before it gets discovered by the occupants.

 

[Waldemar]

There is a theory that over time low level electrical current passing though wood can result in pyrophoric carbonization that can result in a fire.

Yes i have reviewed that.

 

[Waldemar]

Going to need a lot more forensic information than that to even make a guess. Have you determined an origin for any of these suspect fires? How do you know about the "smoldering within walls". I assume the smoldering was a precursor to the actual fire?

-Hal

It is not hard to determine that the fire has been burning slow and not rapid with in the wall bay, usually we are talking about 4' by 4' section of wood members just turned to ash with in the wall.

 

[Waldemar]

10' sounds like a non-electrical cause but leakage current can be checked.

Having seen 400 of these, what else stands out?

Sticking pins in a city map may show clusters.

Making a histogram of
month vs. # of fires
may show a spike.

Heating Degree Days is on the Web for many cities but maybe the National Weather Service can provide you a map of
month vs. Relative Humidity. They should talk to you, it's your tax dollars at work.

this fire usually occur in the rain season for example when we have drizzling rain for four days, then we see spike in fires with in the walls.

 

[SSDriver]

Where AFCI's installed on each piece of lumber? If not that must be the cause.

 

[synchro]

No, in my case i have a very localized fire within the joist bay, slow burning fire that smolders away 2" x 12" and 2" x 4". when we get there sometimes i get low voltage reading most of the time none. It seems like the fire has been smoldering burning slow for prolong time before it gets discovered by the occupants.

Is there any consistency in the type of room having the wall with a fire inside it, such as a kitchen, bathroom, living room, bedroom, closet, etc.?

 

[hbiss]

No, in my case i have a very localized fire within the joist bay, slow burning fire that smolders away 2" x 12" and 2" x 4". when we get there sometimes i get low voltage reading most of the time none. It seems like the fire has been smoldering burning slow for prolong time before it gets discovered by the occupants.

2x12 would indicate a floor bay, yes? Voltage reading: how and from where to where? Was there any metal lath or other conducive materials used in the wall or floor construction? Any correlation to occupancy (single family, multi) age of buildings, locations, age and type of electrical service... Are there any common denominators here?

-Hal

 

[mopowr steve]

Take it with a grain of salt, but it seems to me I get more trouble calls about power issues after just as the OP states “after prolonged drizzling rain for days”. From personal experience it often ends up being the crimp connection on POCO lines found to be bad and at many times is the neutral, which would be very plausible to the polyphoric theory causing fires.
Also even if the wire method is conduit, it too will source current to high moisture wood members if the neutral is open.

 

[WasGSOHM]

Open neutral with leaky roof
waits for steady rainfall
to cause a fire.

Steady rainfall happens 20x per year at your location.

I guess there are more houses with open neutrals than with leaky roofs.

Sounds like a $30 moisture meter may be useful.

I don't know that anyone makes a gadget to babysit house wiring for leakage current.

 

[synchro]

... in my case i have a very localized fire within the joist bay, slow burning fire that smolders away 2" x 12" and 2" x 4".

It is not hard to determine that the fire has been burning slow and not rapid with in the wall bay, usually we are talking about 4' by 4' section of wood members just turned to ash with in the wall.

As I understand this the fires are localized to 2x12 joist bays and 2x4 stud walls. In platform framing there'd be 2x4 top plates or bottom plates that separate the joist bays from the stud walls which would act as fire stops. So did the fires burn near the ends of these joists, through these plates, and into the walls?
In older buildings with balloon framing there'd be no horizontal 2x4 plates to act as fire stops.

Where are the 4' x 4' sections of damaged walls typically located: near the bottom, middle, or top of the walls? If it's near the bottom then it seems peculiar that the damaged area would be as wide as it is tall, since the heat of slow burning fires would tend to make the fire progress vertically along the studs instead of horizontally.

This is just speculation, but I wonder if the sulfur and other compounds in Chinese drywall could cause sufficient oxidation reactions under high humidity to start a fire. Were any of these buildings built or remodeled in the 2001 to 2008 time frame when such drywall was used?