Shed spontaneously combusting

[Retxy]

Ive read this can happen but i need proof to show my hard headed construction foreman (my very ornery, but very free $$ father). Does anyone have any reference materials, pamphlets, or anything they rexommend?  I thought i saw a handout online but im coming up empty 

 

Thanks!!

[Rae Reich]

Do you mean a kiln shed? Gas or electric kiln?

A work shed or glazing shed?  We don’t usually use combustible materials there.

 

[PeterH]

Loosely related threads?

 

... I had my new electric kiln "professionally" wired in the garage and was assured all was fine ... went outside during my first high firing to find fire ripping up the wall, following the wires.

[Pres]

I really believe your post needs clarification.  There are several questionable pieces of information that you do not supply

• What type of shed? A kiln shed for a kiln, a shed to use as a working studio, or just any shed?
• You talk about spontaneous combustion, but in what reference other than the shed
• You don't mention anything about power to the shed or type of construction, even though I would assume it would be wood of some sort.

Without the answers to at least some of these points this strand will make no sense and not give you any viable conclusions.

 

best,

Pres

[Retxy]

Sorry team, had the flu and my brain wasnt isnt working. 

Wood shed used to house electric kilns. No wiring internal as extension cords are being utilized. The wood retaining heat then catching fire later is what im concerned about.

 

Thanks so much for the links!!

 

 

[Kelly in AK]

No extension cords!!! That’s a very real and tangible fire risk.

The idea of the wooden structure combusting, I’m not sure that can be proven or disproven without more information. I believe it’s mostly related to clearance (how many inches above, below, and around) and ventilation. 

[Bill Kielb]

2 hours ago, Retxy said:

Wood shed used to house electric kilns. No wiring internal as extension cords are being utilized. The wood retaining heat then catching fire later is what im concerned about.

Yes as wood heats it becomes dry and if heated long enough even at low temperatures (used to be >212 degrees f) it can begin to burn. So not spontaneously but considerably less than prox. 450 degrees. It becomes rather complex with fires starting inside framed wall cavities, likely due to penetrating hardware, air space, non approved construction methods etc…. Best advice IMO is to be cautious, which most codes are which is why I always suggest use code approved construction practices. Substituting cement board for instance instead of type X fire rated gypsum board can be a problem, even though it intuitively seems like a good idea. Here is some early reading of a series of fires that began in restaurants https://www.warrenforensics.com/wp-content/uploads/2016/06/PUBLICATION-Low_Temperature_Ignition_Wood-.pdf.

If you read through, the analysis points to things unforeseen, by the manufacture and the fire safe construction practices at the time. So not spontaneous, but worth real consideration especially when long term heating is the norm. So probably wise to follow the most current codes and be conservative with appropriate spacing understanding that manufactures cannot test all possible scenarios. (What actually happened to one of the manufactures in the paper above).

BTW - Absolutely no extension cords!, if you applied for a permit for this structure most likely cords would not be allowed. My suggestion stay safe, most folks can’t recover easily from a fire in their home or shed in this case. If folks don’t want to meet or exceed code, generally it is to save on cost but likely almost always more risky. Cement board on spacers may intuitively seem great but as noted lag bolts likely were a significant contributor to the fires above. The lesson: I suggest use stuff with real ratings, not just what intuitively seems ok.

Edited August 17 by Bill Kielb

[davidh4976]

I've done temperature measurements on our kilns using a digital infrared thermometer while the kiln was at peak firing temperature. An example is our Skutt 1027 which reached 200 degrees on the side. (This is typical of several different kiln models I have measured.) If the kiln is installed the manufacturer recommended distance from the shed wall, the shed wall should be considerably lower temperature, and I  suspect below the 170F cited in the article.

But, the top of the kiln reached 300F. I don't know how much the top of the kiln might influence wall temperature.

I will try to measure wall temperatures next to and above the the two kilns that have nearby walls. If anyone else can also do that, it would be interesting to see the results. 

[Min]

In all likelihood you could kiss your home insurance coverage goodbye if there was ever a house fire and the kilns wiring not being up to code. 

[Hulk]

"Ignition point, wood" search string (I'm using Google) returned several sources.
In short, well over 400°F, but special conditions can lower that (as Bill points out; try adding/and-ing "low temperature ignition" to your search) - wood types, coatings, volatile liquids, sawdust/chips, humidity...

The term "spontaneous" has special meanings that generally would not apply to a clean and dry structure.

 

Added: spontaneous combustion as defined and described by Wikipedia (Spontaneous combustion - Wikipedia), where oxidation and/or fermentation, lead to thermal runaway, autoignition, etc. I'm not seeing where that applies here.

I'm referring to the OP's use of the term.

To me, the big concern is wiring and a safe setup.

Bill, your entry includes "So not spontaneous..." - hence, I believed you were not addressing spontaneous combustion.

 

Edited August 18 by Hulk
See Added:

[Bill Kielb]

On 8/17/2024 at 10:18 AM, Hulk said:

The term "spontaneous" has special meanings that generally would not apply to a clean and dry structure.

I was using spontaneous as in fire science where the spontaneous event is usually ignition and flame. Most often preceded by gradual heating / smoldering. Not so much as in an explosion where PEL is exceeded followed by a rapid cascade event. The OP may be viewing this as a stored energy event which at some point later without the addition of energy the shed will just burst into flames. 

To that I would say the use of the term spontaneous combustion usually describes a gradual heating process. The spontaneous part would be when the material begins to ignite for whatever reason but almost always takes the addition of energy or continued buildup of heat. Kilns can provide long term heating potentially lowering the ignition point of the construction products used. I would argue, drying is a component to lowering the ignition point of many materials so a contributor to spontaneous combustion.

Semantics I guess, but definitely not as in memory of having been fired in and later just suddenly bursting into flames. I believe generally gradual growth, thermal runaway, auto ignition apply …… as in an accretive type process.

Edited August 19 by Bill Kielb

[Mark C.]

My studio building is NOT covered by my homeowners. My agent years ago said no. The studio is not conected to home. Its covered for fire and contents by my business liability coverage and for less that replacement. That policy covers me at shows and theft of wares in van etc-its a seperate policy than homeowners.

 

shed busting into flames means you did not plan on enough space from walls and built it wrong or your wood stove was not vented right. Or your electrical was a poor job-what the heck poof

Edited August 19 by Mark C.

[Bill Kielb]

16 hours ago, Mark C. said:

My studio building is NOT covered by my homeowners. My agent years ago said no. The studio is not conected to home. Its covered for fire and contents by my business liability coverage and for less that replacement. That policy covers me at shows and theft of wares in van etc-its a seperate policy than homeowners.

Does your homeowners policy exclude damage to the home as a result of fire, explosion, etc.. that may affect your home or is the home policy limited in some way?  Just curious if and how they might restrict this.

[Mark C.]

Not to my knowledge -the home policy does cover fire etc. When My agent back in the 80s came by for a visit (they never do visit nowadays) he did not like the old wood single studio with gas kilns and took it off the homeowners policy -all other outbuilding are still on it .

[neilestrick]

Safely installing a kiln:

1. Electrical circuit done to local codes and manufacturer's recommendations. NO EXTENSION CORDS.

2. Kiln is set on the stand it came with or equivalent, or up on cinder blocks that have the open sections visible (horizontal) so air can flow through. 

3. Kiln room floor must be non-flammable. If you have a wood floor, put down two layers of cement board or a layer of cement blocks that extend at least a foot beyond the edge of the kiln. 

4. Kiln walls should be at least 16" from anything flammable.

5. Good ventilation is needed to remove both fumes and heat from the kiln.

[davidh4976]

I was able to take some temperature measurements with a firing I did today. This was with a Skutt 818 which is on the smaller side, but the temperature on the top and sides of the kiln were actually higher than measured on the bigger kilns we have.  I had a sheet of plywood 11 inches away from the kiln sides. I fired to a peak temperature of 2200F (roughly cone 6).  At no time did any part of the plywood exceed 153F which is below the 170F mentioned in the article for combustibility due to long term exposure. The Skutt manual says the kiln should be 18 inches from a wall. I located  the plywood 11 inches from the kiln to get a worse case scenario. My personal conclusion is that a kiln, properly located 18 inches from a wall, does not cause a significant risk of catching typical walls on fire. You should draw your own conclusion.

One might argue that a larger kiln would heat the wall up more, but my measurements on a Skutt 1227 and a larger Paragon VIK28 all showed lower temperatures on the exterior kiln wall and top. I have not been able to measure a room wall temperature on those bigger kilns yet.

I measured using a digital infrared thermometer. The top of the kiln measured 420F max, the sides measured 270F max (the metal part and not the seams between bricks which were hotter). The ambient temperature was 95F.  The hottest point on the plywood was directly next to the side of the kiln. Plywood temperatures above the height of the kiln top were markedly lower.  [Our bigger Skutt 1227 typically has temperature readings of 300F on the top and 200F on the sides.]

[Bill Kielb]

1 hour ago, davidh4976 said:

One might argue that a larger kiln would heat the wall up more, but my measurements on a Skutt 1227 and a larger Paragon VIK28 all showed lower temperatures on the exterior kiln wall and top. I have not been able to measure a room wall temperature on those bigger kilns yet.

I measured using a digital infrared thermometer. The top of the kiln measured 420F max, the sides measured 270F max (the metal part and not the seams between bricks which were hotter). The ambient temperature was 95F.  The hottest point on the plywood was directly next to the side of the kiln. Plywood temperatures above the height of the kiln top were markedly lower.  [Our bigger Skutt 1227 typically has temperature readings of 300F on the top and 200F on the sides.]

Nice! My only caution would be a shed that has no mechanical cooling very likely will exceed 200 - 300 degrees or much more at the ceiling depending on what is cooling the structure. Today, here it was in the upper 90’s so available cooling was limited from outdoor air. Anything contained in a shed will warm from radiation, convection and conduction so infrared is great and recommended spacing definitely a plus. Well thought out practical installations and monitored firings very doable. I guess the point would be don’t skimp on common sense safe operation.

[davidh4976]

I just quickly went to my garage and measured the ceiling temp right above the kiln. It is 120F, but the kiln lid has cooled to 300F. The 2-car garage has been closed throughout the firing. The garage has a small 6 inch exhaust fan near the kiln that is is just enough to extract fumes from the garage (it's not attached to the kiln). For the next firing, I will measure the ceiling temp at peak temp. Outside temp today has been 80F-to-86F during the peak firing time.  A smaller shed may indeed contain the heat more and some sort of ventilation is a very good thing.  I suspect that an open door on a shed would be adequate.  An electric exhaust fan would be even better.  A metal shed would completely eliminate any concern!  BTW, I have a internet-connected fire/smoke/CO detector in the garage that will alarm to my phone and trigger all of the other detector/alarms in the house if it detects anything (Nest brand; recommended).

[Bill Kielb]

2 hours ago, davidh4976 said:

A smaller shed may indeed contain the heat more and some sort of ventilation is a very good thing.  I suspect that an open door on a shed would be adequate.  An electric exhaust fan would be even better.

Depending totally on cooling, if the kiln lid was 300 degrees, the ceiling will be  300 degrees without cooling the kiln lid will continue to heat. Predicting that for everyone and every circumstance is really difficult. Use common sense, ensure there’s enough ventilation for all unknown circumstances would be my suggestion. Ovens get to be 500+ degrees with far less energy because there is more heating than cooling. Stay safe, follow codes and best practices.

Edited August 28 by Bill Kielb

[davidh4976]

OK, another firing and another set of readings. This time, I included the ceiling temperature above the kiln and the floor temperature for good measure, and the plywood sheet was 18" away from the kiln to emulate the Skutt recommended clearance from walls. Again, this is a Skutt 818 which is smaller than the other kilns I use but the 818 seems to be a bit hotter on the outside than the other, bigger kilns.  The firing was in a two car garage with the doors closed. There is a  6” 340CFM room exhaust fan to the outside.

There is no kiln vent removing air directly from the kiln. I had the following readings at the kiln's internal peak of 2200F

(approximately cone 6). All readings were of the hottest spot I could find in the described areas.

• Wall (18” away; hottest point was adjacent to the kiln and not above kiln-top level ): 137F
• 8’ ceiling (5’ directly above kiln): 128F

• Top of kiln lid: 415F

• Metal sides of kiln: 268F

• Concrete floor 12” below kiln (kiln on rolling stand): 105F

• Ambient inside garage: 99F

• Ambient outside garage: 85F

 

Except for the kiln itself, all readings were below the 170F mentioned in the article for combustibility due to long term exposure.

Might it be hotter in a small shed? Possibly, and I look forward to seeing measurements from anyone who uses a small shed.

In the meantime, I'm comfortable that my setup does not run the risk of combustion due to long term exposure.  Your mileage may vary!

[Bill Kielb]

@davidh4976 I think your setup is fine and you have enough built in cooling along with the 340 CFM exhaust which brings in 340 CFM of (85 degree in this case) outdoor air to keep your room at about 99 degrees. Interesting that the surface temperature above and adjacent is considerably warmer (20% - 30%) so likely by radiation. It’s important to have enough cooling natural and or mechanical to keep the room reasonably cool else surfaces may heat up to 170 degrees or more, meaning 18” away no longer ensures the surfaces will be as cool as the ambient temperature due primarily to radiation and distance.

More interesting 99 degree ambient and surface temperatures in the 128 - 137 range, I mention this because the typical control board safety is 100 degrees and you measured 99 degrees ambient which is very close to the board safety temperature. So for various reasons on this day your small kiln heated the space to 99 degrees or very close to shutdown. For those days 85 and over you may want to open your overhead door a bit to see if you can reduce that high interior ambient temperature.

Operating electronics at elevated temperatures generally can reduce the lifespan of the equipment. Some cooling is an important assumption that makes the 18” rule actually work and you have confirmed surfaces adjacent and above can become significantly hotter than ambient. Skutt provides the thermal output of there kilns and is mentioned in the designing a kiln room manual so that reasonable HVAC can be included in the design.

Edited September 5 by Bill Kielb

[davidh4976]

The Skutt controllers manufactured after 2013 have the 100F rating. The Skutt controllers manufactured prior to 2013, like mine, have a 105F rating so I have a little bit of room. I hesitate to keep the doors open because we have critters that like to come in! I've thought about adding an intake vent, but just settle on firing on days/times that are not too hot outside and that works for me.  

[Bill Kielb]

2 hours ago, davidh4976 said:

I've thought about adding an intake vent, but just settle on firing on days/times that are not too hot outside and that works for me

The make up air is coming from outdoors, all those doors are plenty leaky. This is actually easy to figure out if you ever have the need. I have a firing spreadsheet that I share with anyone who requests it, (still receive periodic requests)  I am currently in the process of  adding to it and making a well illustrated (free to use ) spreadsheet with multiple tabs where folks can simply add conditions to it to get an answer for many of these common questions that arise. I can think of at least 10 common issues that are light engineering that can be put in a very layman format for folks to use. For now if you like PM me, we can figure cfm required for max condition of let’s say 95 degree outdoor temp. Also have a decent economical way to do this on a thermostat so the fan can just ramp up to the required CFM for when it’s much cooler outside and not waste electric or over cool the space.

[Mark C.]

shed spontaneously combusting=an urban legend in the beginning stages?

[Bill Kielb]

4 hours ago, Mark C. said:

=an urban legend in the beginning stages?

Maybe, but is a thing, often makes the news. Maybe not spontaneous but probably happens far more than it ought to.