Be Careful Out There, Hear

[ken hatch]

Damn Bubba you almost burned the house down. The shop was still hot from the day and I had it closed up so it wasn't cooling off. I'd wiped the tool chest lid once more with the BLO soaked rag before taking a short break for some tea and a cool down. I left the rag bunched and on the top of the tool chest while I cooled off. As I was going back to the shop I noticed a smell and my eyes were burning, it was stronger in the shop but there was no smoke. I looked around and noticed the BLO rag. When I picked it up it was very warm, unfolding it reviled black burned areas. Here is a photo of the rag:



I couldn't have been out of the shop more than 45 minutes to an hour and it was a single rag setting in the open. Normally once I finish with a rag I'll put it in a metal bucket filled with water until I can dump them in the trash but even that will be no more. If I am going to leave the shop for any reason finished or not with the rag it is going in the bucket and I'll make sure the bucket has enough water to cover the rags.

ken

[David Wong]

Wow. Glad you caught it in time. A really graphic reminder to be careful.

[Patrick Chase]

I left the rag bunched and on the top of the tool chest while I cooled off

The key word here is "bunched".

When you did that you took a large volume of polymerizing oil and shaped it so that it didn't have much exposed surface area. Polymerization is exothermic, and that heat must either dissipate via the exposed surface or warm up the interior. When you bunched the rag you created a configuration that couldn't dissipate the heat, so it warmed up instead. Whether the rag is wadded/bunched is more important than the other factors you cite (single vs multiple, inside vs out, etc).

You are very lucky, as the time window from "smell smoke" to "ignition" isn't long.

[Stanley Covington]

The key word here is "bunched".

When you did that you took a large volume of polymerizing oil and shaped it so that it didn't have much exposed surface area. Polymerization is exothermic, and that heat must either dissipate via the exposed surface or warm up the interior. When you bunched the rag you created a configuration that couldn't dissipate the heat, so it heated instead. Whether the rag is wadded/bunched is more important than the other factors you cite (single vs multiple, inside vs out, etc).

You are very lucky, as the time window from "smell smoke" to "ignition" isn't long.

Thanks for the explanation, Patrick. Clears up some questions I had.

Stan

[Frederick Skelly]

Man, that's scary Ken. Very glad you caught it in time!
Fred

[Mike Cherry]

Truly scary. Good thing you were home and around the shop.

[Mike Holbrook]

Good post Ken, we certainly need to remind ourselves of that danger on a regular basis as your picture so graphically does.

[ken hatch]

Thanks Guys,

I'm glad I went back to the shop but if I hadn't planned to go back the rag would have been in the bucket and would not have been a problem. The major takeaway for me was just how quickly it reached combustion.

ken

[James Pallas]

Ken, glad to hear you didn't suffer any greater loss. This oil stuff is indeed dangerous. My experience was also in the desert SW (New Mexico). Rags that had been used to wipe Watco Danish oil. Hung over a pallet stretched out, outdoors. Warm and dry, not terrible hot, maybe eighty or so. Went up in a blaze. I don't know the chemistry and don't care, all oil rags go in the water immediately after used up, no drying out, no reuse. Too risky for me. I don't think anyone can give a fool proof theory other than in the water or purposely and carefully burn up.
Jim

[Jim Koepke]

I will leave tools and scraps where they lay when taking a break, but never a rag with BLO or other finishes.

Glad to hear it was only a close call reminder.

jtk

[ken hatch]

The key word here is "bunched".

When you did that you took a large volume of polymerizing oil and shaped it so that it didn't have much exposed surface area. Polymerization is exothermic, and that heat must either dissipate via the exposed surface or warm up the interior. When you bunched the rag you created a configuration that couldn't dissipate the heat, so it warmed up instead. Whether the rag is wadded/bunched is more important than the other factors you cite (single vs multiple, inside vs out, etc).

You are very lucky, as the time window from "smell smoke" to "ignition" isn't long.

Patrick,

Yep, I know and thought I understood all that, in fact I thought I was following "best practices". Shame on me....I never thought it could heat to combustion that quickly. The time from taking the last wipe, walking inside the house, drinking a glass of iced tea and then returning to the shop couldn't have been more than 45 minutes, if that.

Dodged the bullet once, it will not get a second chance.

ken

[ken hatch]

Ken, glad to hear you didn't suffer any greater loss. This oil stuff is indeed dangerous. My experience was also in the desert SW (New Mexico). Rags that had been used to wipe Watco Danish oil. Hung over a pallet stretched out, outdoors. Warm and dry, not terrible hot, maybe eighty or so. Went up in a blaze. I don't know the chemistry and don't care, all oil rags go in the water immediately after used up, no drying out, no reuse. Too risky for me. I don't think anyone can give a fool proof theory other than in the water or purposely and carefully burn up.
Jim

James,

That is my normal routine, I have an old metal milk pail that I keep half full of water just to hold oil rags until I can take 'em to the outside trash bucket. But I would not put 'em in the bucket until I had finished what ever use I had for the rag or shut the shop down for the day. New routine: If I walk out of the shop, even just to get a drink of water or whatever, the used rag is going into the water bucket and I will start over when I come back.

ken

[Dave Beauchesne]

Not to hi-jack the thread, but a buddy was in his stand alone shop one evening - he was vacuuming with a shop vac and the power went out. Went into the house - got about some other things with the power out - eventually went to bed.

Got up the next day, went to the shop ( power had been restored ) and it was about 100F in the shop - vacuum was running and smelling very hot. The sides of the plastic motor cover were starting to sluff - could have easily caught on fire. Of course, he didn't unplug it when the power went off.

Just another reminder of shop safety. Glad this rag didn't burn down the house !!!

Dave B

[Brad Barnhart]

Wow! Glad it didn't damage your work piece, hoss. My shop is pretty small, tools on every wall, 2 lathes, what have ya. I use Watco finishes regularly. When I'm done with a project, I always drape the rag over one of the lathes, or over the end of the RAS until it dries, then throw the rag in the trash. I haven't had any issues that way. You had a good eye opener, Mr. Ken. God bless & take care.

[Patrick Chase]

Ken, glad to hear you didn't suffer any greater loss. This oil stuff is indeed dangerous. My experience was also in the desert SW (New Mexico). Rags that had been used to wipe Watco Danish oil. Hung over a pallet stretched out, outdoors. Warm and dry, not terrible hot, maybe eighty or so. Went up in a blaze. I don't know the chemistry and don't care, all oil rags go in the water immediately after used up, no drying out, no reuse. Too risky for me. I don't think anyone can give a fool proof theory other than in the water or purposely and carefully burn up.
Jim

The nominal autoignition temperature for an "oil-soaked rag" with light mineral/distillate oil (one that doesn't polymerize and doesn't contribute any heat of its own) is only about 150F IIRC. You could easily get there in direct sunlight on the wrong surface, even at fairly modest air temperatures as you describe.

Also "stretched out on a pallet" or any other insulating surface will cause about 2X as much temperature rise from polymerization as hanging with both sides exposed to air. Half the radiative surface area means double the temperature rise.

Probably the best solution I've heard is one George described: Stretch the rag out on a metal trash-can lid. The metal lid acts as a radiator with greater surface area than the rag, so it's even better than hanging with both sides exposed, and it also acts as a fire barrier if the rag goes anyway.

Water will certainly prevent flare-ups while the rag is immersed, but doesn't that just suspend polymerization (by blocking oxygen) and leave the problem for later, after the water dries out? I don't know the answer, it just seems to me to not be a permanent fix. The oil isn't truly safe until it's full polymerized, right?