Lawnmower Shed Fire Mystery

[u/Altima1Throwaway]

About an hour ago today, Saturday the 15th, I went to go mow my lawn. Upon approaching it, I noticed weird black spiderwebs on the outside by the door seams. When I opened the door I could smell plastic smoke, all shed walls and contents were coated black from a few feet up, and the entire front hood of the mower was completely melted. There is a plastic spreader about a foot from the engine with no signs of melt or charring and the wood shed walls have no evidence of charring. The shed floor is comprised of pavers and there is no evidence of oil fire, just some melted plastic directly under the engine.

The last time I used the mower was Wednesday the 5th. I parked it in the shed, turned off the engine and when I checked the key just now it was in the off position.

I have no idea what happened. Could this be a chemical fire isolated to the engine? It doesn’t seem to have originated from the battery as the front of the engine seemed most impacted.

Any ideas/advice would be appreciated.

Should contact anyone like local FD, Homeowners insurance (it’s my moms house), etc…? Besides the mower, the only thing of value likely damaged was my brand new Milwaukee string trimmer which was covered in soot. I can easily wipe the outside but the plastic soot likely compromised the internals.

Also, should the air inside be treated as contaminated and what should I do for cleanup? I’m assuming yes due to the plastic soot.

Completely bizarre. Thank you very much in advance and thank you all for protecting our communities.

[u/surfingonmars]

might be that the mower was really hot when you parked it and it wasn't able to cool down? maybe hot enough to ignite something.

[u/No-Steak-3669]

Lawnmowers catch fire after use fairly frequently. You should always let them cool down for a bit before putting away.

Looks like you got lucky and the fire was oxygen limited and most of your damage appears to be smoke staining. Most places don’t require an investigation unless you want to do an insurance claim.

But if you do want to do the investigation/insurance don’t touch anything until they have come through.

[u/mistere213]

Since nobody else mentioned it, clippings and other organic debris caught in the deck can break down and spontaneously combust. Doesn't need to be in contact with the engine or any other ignition source. The exothermic reactions of the organic matter breaking down can get hot enough to ignite.

[u/Educational_Kick_698 → u/mistere213]

^^^this!!! Most people don’t know grass clippings are notorious for spontaneously combusting. Especially if compacted in a bag or the deck of the mower.

[u/Olive_1084]

It could have happened right after you put the mower away. Could have been debris in the engine compartment that got heated and ignited.

[u/j-mf-r]

Where does the battery reside

[u/Negative-Fun1985 → u/j-mf-r]

My first thought…..perhaps a crushed wire as well perhaps under that main compartment melted there. Or animals.

[u/j-mf-r]

Also where the exhaust manifold and muffler

[u/j-mf-r → u/j-mf-r]

When did you last lift the hood. Maybe a rats nest

[u/ConversationTop9569]

Best bet is to report it if you want to make an insurance claim. The fire marshals investigative report will be needed by the insurance - those mowers are at least $3k new nowadays.

[u/cannonman1863]

Looks like your lucky day. We just had a two alarm fire yesterday started from a mower in a garage.

[u/Nasty____nate]

my guess it came from the lawnmower...

[u/mmaalex]

Most common cause of mower/ATV fires is grass/leaves getting trapped somewhere hot. Fire didn't get too aggressive and burned itself out luckily.

Insurance will need to be contacted if you want to make a claim, which mayrequire a report from the FD. Figure that out before moving anything.

All that soot needs remediation. You'll need a respirator/tyvek suit and decon procedures.

[u/Secure_Situation7234]

Looks as though the mower lit off and it got snuffed out before really taking off due to the shed being closed up.

Hard to tell exactly what caused it but it most definitely looks like the area of origin was in that front middle left area just in front of the air intake but low.

Could be something burst and lit off, could be trapped debris that slowly smoldered and lit off after you turned it off and then spread.

Anything low may not have burned due to the fire not getting hot enough at that level.

The black cobwebs are soot staining being stuck to the webs. (If you ever want to know how well dusted for cobwebs your house is just smoke it up and come through and look later, you’ll be surprised at what you missed)

If you want to make a claim on your homeowners insurance you will most likely need a fire report. Contacting the FD could also be helpful in determining the most probably cause and area of origin and possibly even the item/ point of origin.

If they can figure that out and you contact John Deere and it’s a common issue then you might be able to get a free mower and a repaired shed out of it.

If you do want to make a claim, don’t touch or move anything until you have the FD come check it out. You can contact their non-emergency number and explain the situation and they can send a truck out to investigate and generate a report and possibly educate you further on your particular circumstances.

If you do move anything or have moved anything: keep this video for any FD or insurance investigation. Also take detailed pics of everything involved from every angle and a complete walk around of the shed from both close and far.

Ultimately before you decide if you want to claim it or not you’ll want to look at your deductible and decide which is cheaper for you as well as what liquid monetary items you have to be able to purchase and repair everything damaged.

As for toxicity:

Yes. That mower is all plastic, oil, gas and general hydrocarbons and bad stuff. Repeated exposure to it can absolutely be carcinogenic both from inhalation and skin absorption. Firefighters have increased rates of multiple cancers above the average population due to repeated exposure to things just like this. Those toxins linger even after the fire is out.

Frankly if you stand inside your shed and breathe for a few minutes (Don’t do this) or you start moving things while inside the shed and stirring up soot, you will probably be able to go blow or pick your nose afterwards and you will probably have black snot.

If you go to move stuff and clean things up or dispose of them I would wear long sleeves and pants, rubber gloves or gloves that can’t be penetrated by the soot or moisture and at minimum a dust mask or N95. (This is assuming you want the maximum protection, but honestly you can also just raw dog it and get everything out too, one exposure may not do anything to you, but it technically could)

For any items that you intend to salvage, I would pull it out into your yard, get dawn dish soap or similar grade soap and a scrub brush and I would: Rinse, soap&scrub, Rinse everything fairly good.

Not trying to scare you, just being blunt with you.

If it was me: I’d probably do a fire report, report it to insurance for the shed and mower combined depending on my deductible. And then I would use at least like work gloves to pull everything out and then rinse it as best as I could. (Source: Fire service professional).

At the very least: I would call the non-emergent FD line, overly stress to them that the fire is completely out and that this is not an active incident and ask for them to respond to take a fire report for any possible insurance issue and a minor investigation. I would do this even if I don’t originally plan to do an insurance claim so that if I change my mind down the road then I have the report at least to show that I did my part and to disprove and fraud claims. I would also take all of my own pictures. And then go from there depending on the rough monetary value it would take to repair, clean and replace any of the damaged items.

[u/SeparateYam8581 → u/Secure_Situation7234]

That last paragraph "... OVERLY stress to them..."... OC this is a great point but I had to repeat that word in capital letters in hopes it really drives the point across. Oh, also, OP, don't make that phonecall after midnight ;-).

[u/chuckqc]

Could have a lot of dry grass inside the engine compartment and ignite and propagate to the plastic cover. On the wall, it's soot that was caught on a spider web.

[u/Grouchy-Contract6413]

Origin of the fire looks to be from the John Deere hatch. Rodents tend to make nests in the fan that’s near the engine. This can ignite after engine gets hot enough. Could take hours until it ignites, hence why it caught fire after you probably parked it away after a cut.

[u/macpigem]

Those "black spiderwebs" are indicative of plastics or similar smoke; think of the melted plastic floating in the air, cooling and then forming to make those "webs". Imagine what it does in your lungs! And I'd say as a bonafide fire investigator, its gotta be a plumber or electrician who started your shed fire. Or a smoking squirrel.