Help problem-solving..."it all went BOOM"--KQ 380

[Rusnakes]

Greetings all,

Well...just had the experience of a lifetime and I'm trying to sort out what exactly were the precipitating factors and how to prevent them in the future. Here goes:

Weather today, which may be a factor: it was unseasonably warm today (high of 57). It was 44*F when this happened below. We didn't have gale force winds, but it is windier than usual (right now 15 mph with some gusts; a cold front is moving in currently).

What happened:

I came in to our kitchen where our KQ 380 had a small bit of coals left. I put on some maple and a little willow kindling to get the fire going to make dinner. Once it took off, I put on a two smaller logs (2-4" thick) to start up. About 10 minutes later (after the smaller logs were going), I put on a couple more smaller logs (same size) and waited for the stove to get up to temp to hopefully start to bake. Nothing unusual so far.

I then started prepping dinner and went back to the stove. The stovetop seemed to be getting a great deal warmer (faster than usual), so I turned the dampers down halfway or so (which usually works to slow a fire greatly in our KQ).

I put our dinner in the oven (it was 300 degrees in the oven by then), but left the oven damper closed to warm the firebox sid of the oven up a bit more. I went back to food prep and a few minutes later, I heard what sounded like a small BOOM and my glass pan in the stove seemed to have jumped. Odd. My guess at the time was that one of the logs had broken up from burning down and the wood on top of it dropped.

So, I went the to stove and opened up the door (the coals had appeared to die down, but the stovetop was still remaining quite hot). There was a whooshing flash of yellow fire that went from the bed of coals under the oven. I closed the door back quickly, turned down the dampers, and left it alone for a while (8-10 minutes). My worry was that it was creosote that caught fire (I don't believe this to be the case, because we work hard to keep our stove very clean, but it crossed my mind, since there are parts around the oven that we cannot reach to monitor for any buildup of creosote, etc.).

After the 10-minute wait, I went back to the stove again and messed with the dampers, since the coals were not glowing anymore at all. They lit back up with the dampers open a bit, but a poof of smoke came out the top damper. Odd. I shut the dampers down again.

From there I waited again for another 5 or so minutes and the stove appeared to be cooling down. So, again I opened up the damper a bit and the coals lit up. Everything appeared decent. I waited a while then opened the door and moved the coals around with the poker, not wanting a log to fall again (assuming that was the issue before). All seemed fine. I went back to food prep.

At that point, I kneeled on the floor in front of the stove with a flashlight to just check things out (I was still worried something was wrong), to try to see inside the stove to make sure everything was okay. Everything looked decent. The stovetop was still pretty warm, but the oven was starting to cool off. I opened the door to move the coals around a bit and a MASSIVE flash of white light and a bit of flames rushed out the doortoward my face, blowing the cover off the stovetop over the firebox. I slammed the door closed and shut everything down (including turning the thermostat down all the way on the back). So, yeah. Not cool. I'm fine, but it was dangerous for sure.

So, here's my theory--the wind and warm-ish temps were creating a poor draft and the flue gases built up in the stove. The wood/coals warmed the stovetop up quite a bit (oddly more than normal), but the gases were not escaping sufficiently enough for the amount of wood being burned. So, the gases blew up when I introduced air (O2) into the fire box.

Now, how to prevent this, if I'm correct? Totally freaked me out. Not gonna lie. I love my KQ, but this one scared the crap out of me. LOL Help?

 

[jatoxico]

Don't know anything about KQ stoves but it does sound like the wood was outgassing (evid by rapid temp rise) but were being starved for air which when introduced with open door, the gases ignited. Kinda like when a stoves huffs.

I think @coaly has a KQ in his kitchen and he knows his stuff. Maybe he'll be nice enough to chime in.

 

[ratsrepus]

wood gases collect in the top of the stove and ignite. My Jotul was good for that. I would say char the wood real good before turning the air down. I think the tube type stoves are more apt to backfire

 

[Rusnakes]

I found this article. Seems like I might have possibly overloaded it too quickly. I think the puffback at the beginning was an indicator, but with the wood that was in there, it was impossible to keep the stove open enough to not overheat the stovetop. It was unusual how hot the stovetop got (very hot, very fast). I wondered if the wind and warmer temps created negative pressure in the flue as well. You could hear it whoosh once in a while at the chimney cap (from inside the house). Totally scared the crap out of me (I joke that I love my KQ so much that I will die right next to it, but I wasn't thinking in that way LOL).

https://www.hearth.com/talk/wiki/prevent-puffback-aka-flashback/

 

[ratsrepus]

whats a KQ380, who makes that?

 

[Rusnakes]

whats a KQ380, who makes that?

Kitchen Queen 380. It's an Amish-made wood cookstove.

 

[showrguy]

Sooo...
What was for dinner ??
Or did you give up on that task ??

 

[Rusnakes]

Sooo...
What was for dinner ??
Or did you give up on that task ??

Hahah! Spaghetti squash (baked then sauteed), red sauce, rolls, and a large salad. And YES...totally abandoned it. LOL Eating a PB&J as we speak.

 

[Sawset]

Been there, done that, happened here 3 times. Twice from shutting the side door too quickly on a hot stove. Once from damping down too far on a fresh reload. Need to see flames after damping down. Being aware of those things - it hasn't happened since, that was a decade ago.

 

[Rusnakes]

It was a powerful lesson. We've not had that happen before, but we did split our wood a lot smaller this year for the cookstove, which is likely a contributing factor. I swore I was going to be blind in my right eye, that flash was so bright!

 

[wooduser]

. I opened the door to move the coals around a bit and a MASSIVE flash of white light and a bit of flames rushed out the doortoward my face, blowing the cover off the stovetop over the firebox

Fast, too, isn't it?

In the gas fired equipment I worked on as a repairman, this kind of condition was called "delayed ignition." It was typically caused by a dirty pilot light that didn't light the burners promptly, or dirty burners that failed to light up all the burners immediately.

The result was that unburned gas accumulated, until it finally spilled out towards another burner or the pilot and it lit off all at once ---- BAM! and it could reach out 2-3 feet in front of the appliance to find oxygen to burn. This could make repairman red faced after such an experience, and not from embarrassment either ---from burns to the face. You tended to learn real quick how to avoid that, though.

I'm reminded of the professor who helped develop modern epa rated stoves. He related in his published report that he had trouble with explosions from his stoves when he was developing them ---I'm imagining the same kind of thing that happened to you.

And consider the EPA stove that gets loaded with a fresh charge of wood laid down over hot coals or in a hot stove. It's bound to be, designed to be producing wood gas in quantity, but it has to be designed to avoid that kind of explosion and instead to be capturing those hot wood gasses and burning them safely. I'm guessing that is part of the challenge of designing epa standard stoves.

 

[begreen]

And consider the EPA stove that gets loaded with a fresh charge of wood laid down over hot coals or in a hot stove. It's bound to be, designed to be producing wood gas in quantity, but it has to be designed to avoid that kind of explosion and instead to be capturing those hot wood gasses and burning them safely. I'm guessing that is part of the challenge of designing epa standard stoves.

Happens in old smoke dragons too. It's more common with partially seasoned wood that smolders when the air is shut down. At that point if a flame shows up it will ignite the stove full of wood gases. I have heard of the lids being blown off some old stoves this way. Moral of the story is don't let the wood smolder.

 

[jetsam]

Wood gas is similar enough to propane that you can use it to run an engine. It never caught on much because it is so dirty and filtration is a significant challenge, but you can go on youtube and see wood gas vehicles and generators made from WW2 to present day.