Mini explosion?

[MoDoug]

A few times this season, I've had what I can best describe as a mini explosion in the stove. It's a low rumbling noise, and it's usually in the coaling phase. The flue temps are on the low side, around 500 degrees, with the stove top temp around 350. The mini explosion tonight caused a little rattling of the pipes, reminded me of when a sonic boom hits, but on a much smaller scale of course. The fire brick and welds all look good. I'm thinking maybe a pocket of gas in the wood finally letting loose? Has anyone else experienced this?

Edit - I should also mention the wood I'm burning, while I haven't checked the moisture content, is scrounge wood that was long dead, and covered.

 

[Rickb]

Probably a back puff. Its when you get a build of of gasses then some wind or something else pushes extra air into the mix. I have gotten a couple over the years but im using a cat stove turned all the way down.

 

[MoDoug]

I don't know anything about back puffing, but wouldn't the buildup of gases happen during the initial stage of a fire? This is happening in the coaling stage, the flames have long died down, and there weren't any extreme temperatures before hand. When it happens, we only hear it, there's no sparks flying around, or signs of an explosion.

 

[Rearscreen]

Substitute smoke particles for grain dust and there you have it:

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[begreen]

I don't know anything about back puffing, but wouldn't the buildup of gases happen during the initial stage of a fire? This is happening in the coaling stage, the flames have long died down, and there weren't any extreme temperatures before hand. When it happens, we only hear it, there's no sparks flying around, or signs of an explosion.

If the wood is damp in the core then that part may still be outgassing, while other parts are in the coaling stage.

 

[MoDoug]

If the wood is damp in the core then that part may still be outgassing, while other parts are in the coaling stage.

This is mostly what I've been thinking. We sit about 12 feet from it, pretty much facing it and the TV and there's no apparent disturbance from it, other than the sound.

 

[MoDoug]

Substitute smoke particles for grain dust and there you have it:

Perhaps the perfect storm in the wood stove?

I have wondered how grain elevators explode.

 

[Woodsplitter67]

sounds like back puff.. a building up of gasses when no flame is present and then it lights off..

 

[MoDoug]

sounds like back puff.. a building up of gasses when no flame is present and then it lights off..

back puff must be the name for it, I imagine backpuffing as sending flames and smoke, but like anything I'm sure there's different levels of it.

 

[gthomas785]

back puff must be the name for it, I imagine backpuffing as sending flames and smoke, but like anything I'm sure there's different levels of it.

Absolutely. I've had all kinds of backpuffs. One time after turning down the air on a load of small branches too fast, I got an explosion that literally lifted the griddle of my stove and sent embers flying into the room. I've also had the "silent but deadly" backpuffs where you don't see or hear anything but you catch a whiff of wood smoke in the room and you know something's going on.

 

[MoDoug]

Absolutely. I've had all kinds of backpuffs. One time after turning down the air on a load of small branches too fast, I got an explosion that literally lifted the griddle of my stove and sent embers flying into the room.

That had to be some unwanted excitement. I hope mine never get to that.. but things like that are never expected., they just happen..

 

[gthomas785]

That had to be some unwanted excitement. I hope mine never get to that.. but things like that are never expected., they just happen..

They may not be expected but I've mostly learned how to avoid it. The most exciting ones are almost always caused predictably by shutting down a raging fire too fast. However the ones like what you experienced are harder to predict, luckily they are usually not as violent.

 

[peakbagger]

Most of the original VC Defiant owners are well aware of backpuffs. Folks load them full of wood before bed and leave the thermostatic air control in the same position. The stove starts cranking and then the air control closes. This puts the stove in over gasification cycle so unburnt gases are going up the stack. At some point it ignites. Most Defiant owners have cast iron steamers on top of the cooking plate that will lift up with a puff if there is not a weight on it. . And more than few have been replaced with new stove as the owner was unwilling to work around the stoves quirks to avoid the puffs.

 

[Sawset]

Absolutely. I've had all kinds of backpuffs. One time after turning down the air on a load of small branches too fast, I got an explosion that literally lifted the griddle of my stove and sent embers flying into the room. I've also had the "silent but deadly" backpuffs where you don't see or hear anything but you catch a whiff of wood smoke in the room and you know something's going on.

THis.
Except here, the little puffs exit from all orifices, even ones that shouldn't exist. Kind of like in the cartoons when the bad guy gets messed with by buggs, and then steams and blows.
One time early on I closed the door too quick on a hot fire, completely snuffed the fire, and a flame front came down the chimney that sounded like the trade towers crashing one floor at a time. Just stood there and pondered life for a moment.
Another though was similar to yours, some dry wood shop scraps, low to no flame, let out a little fluff, silent but deadly.

 

[MongoMongoson]

Yes, backpuffs sure can be exciting. The last one I had was with my All Nighter. I started a fire, and it was getting a little too aggressive so I turned it down... a little too aggressively. When I opened the air vents again, I was half expecting a back puff because I realized what I had done after I had closed them down too much. Sure enough, I got a good healthy "whomf" out of it and some smoke puffed out of the air vents. I chuckled to myself knowingly because it didn't surprise me (after all, I know sooo much about burning wood and stoves and stuff), and went back to doing my dishes. Then I smelled PAINT burning and saw that the cap on my stove pipe cleanout T that attaches to my class A chimney was starting to glow. No more chuckling, to be sure. I shut the air down again all the way and watched the T glow. On the Selkirk DSP cleanout Ts you can look between the layers, past the cap, from below, so I could see the inner layer glowing and that glow was slowly going up...

Went outside, smoke looked pretty normal coming out of the chimney (not black, no cinders) back inside, still glowing but settling down (unlike my heart).

So that was it. Just the stuff in the cleanout burned, but what I learned that day was that backpuffing is not always harmless. No harm done to my chimney, but I did replace that cleanout T.

That was also the day that it was decided we were getting a new, modern stove that makes less creosote.

The stove pipe between the stove and the cleanout didn't light up, and the Class A didn't either. I watched very carefully for hours, and never saw any indication that the creosote in the chimney was burning. I didn't open the stove for 24 hours.

When I took it all apart the stove pipe was normal looking for 2 months of burning - not burned out clean anyway.
The chimney looked normal, too, with a little accumulation that wasn't all burned out. The creosote in the cleanout T was burned.

With the All Nighter smoke dragon, we would get creosote crispies that formed on the chimney cap, and then they would curl up and fall off, landing in the cleanout T. Every once in a while you'd hear them go "clink" on the cleanout T cap. I think that's what lit up.

Anyway, that's my story about backpuffing and how it isn't always as harmless as I thought it was. My cleanout T is about 9 feet above my stove top. It is hard for me to imagine a fireball rushing up the stack from a backpuff and igniting it up there... but that is what happened. I didn't have any paper or cardboard or anything crazy like that in the stove, or I'd think some fluffy burning paper junk got pushed up by the backpuff and landed in the cleanout T.