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Smoke Explosion

Started by Autocar, January 07, 2014, 04:31:52 PM

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Autocar

With the crazy teperatures and wind my furnace is eating wood like a rabid beaver,last night I got up and throwed in four peaces of big hickory. I have a six foot patio door on the up stairs bedroom and I hop back in bed and it wasn't long I heard a strange noise and the patio out side lite up red with embers flying everywhere. The two dogs beat me out of bed but I bailed out and put my pants on ripped down stairs and ran to the garage. Opened the door and the six cats were setting on top of the furnace looking at me like life is great what are you doing out here. I have the pipes screwed togather plus fixed so it dosen't blow out of the flue. Its probably 26 feet up to the top of the flue from the entrance of the furnace pipe. Scared the tar out of me I sleep with one eye open the rest of the night. 
Bill

beenthere

south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Autocar

No I don't think so Ive had this over the years and when you have heavy smoke and the draft door closes then it gets a little air I guess and it burst back into flame trying to burn the smoke making a explosion.
Bill

Alcranb

Autocar what you experienced was a classic flashover. The gases ie. smoke was rich enough that when they finally ignited they in a sense exploded.
"Twenty years from now, you will be more disappointed by the things you didn't do than by the ones you did do.  So throw off the bowlines.  Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.  (Mark Twain)

Sonofman

Autocar, I had a similar problem last night. I am usually able to keep my house warm with a lesser burn through the night in this warmer climate. Not, however, last night. I had to completely fill it with my long wood to get enough in for an all night burn. The longer wood , 24" or so, puts the back of the wood at the back end of the firebox. This means the fire burns off the wood then almost straight up the chimney. It was burning hard and long in single digits with a 15-25 mph wind. The first burn had sparks flying everywhere. The fire had burned up the chimney to my chimney cap which had a fair amount of creasote build up. The creasote was smoldering and popping off sparks. These were flung by the wind all over the yard. I spent an exciting 15 min or so chasing them and stomping them out. No snow on the ground. After this first burn, things were less exciting. The fire was still going up the chimney but all the creasote was gone so no more sparks.

I also found on the CB Classic, you can adjust how wide the draft damper opens. Mine was set at widest from the factory, I moved it to the smallest last night also. That helped too.
Located due west of Due West.

r.man

I used to be able to make my OWB, woof right out the door. This is why there is some sort of explosion prevention device on most modern stoves. Most use a double latch but one I saw used an apron that covered the door area when the main door had been opened. If you want to see what a fireball from one of these looks like you need to have a roaring fire, cut off the combustion air and then quickly fling open the door after a few seconds. Keep your head back or you will singe stuff. The waiting time will vary with the local conditions and the type of stove. Many new owners of OWBs in my area experienced this phenomena without warning until we got talking among ourselves and started giving advice new owners.
Life is too short or my list is too long, not sure which. Dec 2014

thecfarm

I have a spring loaded flapper on my Heatmor. I open the outer door,give it a few seconds,this allows air into the fire box,than open the main door. But can also tell by the temp of the water if a flash back will happen too. Water at about 185,be careful. 180 should be all set.
Model 6020-20hp Manual Thomas bandsaw,TC40A 4wd 40 hp New Holland tractor, 450 Norse Winch, Heatmor 400 OWB,YCC 1978-79

Sonofman

Yeah, If the water temperature indicates it has recently shut down, I either wait or open the door verrrrry carefully.
Located due west of Due West.

r.man

Cfarm, my friend has a Heatmor so I know about the outer door flap. For those of you who are not familiar with them the Heatmor is one of the sleekest of the OWBs because it has an outer shed looking door that hides the fire door, controls etc. When the outer door is opened a small combustion air flap opens to help prevent blow back. This is in addition to a double latch fire door. I have used the outer door flap to keep his at a fairly low fire rate when he is not using the system. By leaving the outer door ajar but propped closed and turning the combustion fan a small amount of  wood has enough combustion air to burn but when it depletes the wood it doesn't have cold outer air being blown into the firebox by the combustion blower. Not something the manufacturer intended but handy nonetheless.
Life is too short or my list is too long, not sure which. Dec 2014

doctorb

While this topic is not discussed by the manufacturers, it's of significant relevance to OWB owners.

Thecfarm and sonofman are 100% correct.  Learn to load your stove when it's safe.  The best time to load your stove is just before the water temp is decreased enough to kick the fans and firebox ignition on.  I run my 2300 between 185-195 degrees.

If the water tenp is high, and the fans are off -Watch Out.  If you slowly open thevfirebox door and the smoke is orange or rust colored - Watch Out.  In these situations the fan driven combustion has just ended.  There is a build up after fan shutdown of non-combusted particles, visible as this off colored smoke.  If the smoke's not gray and it's not white, look out.  The addition of new oxygen by opening the door causes an "explosion". This is, IMO, the most dangerous part of using an OWB.

So my recommendation is to look at the water temp and look at whether the stove is cycled off or whether the fans are still running.  If the fans are still running, then no buildup of non-combusted smoke has occurred in the firebox because the fans are moving that air.  If the fans are off, and your water temp is at he high limit you have set for your stove, my advice is to wait a bit and open that door to load at a safer tine in the cycle.
My father once said, "This is my son who wanted to grow up and become a doctor.  So far, he's only become a doctor."

stratford 50

I find the best time to fill my furnace is when the fan is on and has raised the water temp 1-2 degrees, It allows me to scrape down the sides and clear out the side air ports. then I place hot coals in front of the air holes to see if I have good airflow by igniting the coals.

stumper

Because I do not normally have time to adjust my loading time.  I have learned to wear a hat, and stand behind the door, then open it a good crack, and wait.

Failure to do so does save on hair cuts, though.

DeerMeadowFarm

Quote from: stumper on January 08, 2014, 08:26:03 AM
Failure to do so does save on hair cuts, though.

Shaving too....  ;)

r.man

I don't know where everyone's sense of adventure went. The point is not to stop the fireball from happening, the idea is to avoid being caught in it. An OWB is like a fireball gun, always assume it is loaded and act accordingly. Fling the door open while ducking back and hope to see the same action as you do at the circus when the firebreather does their thing. Quite impressive sometimes and to me always disappointing when only a puff of smoke comes out.
Life is too short or my list is too long, not sure which. Dec 2014

Al_Smith

So then with what's been said this fireball thing could be a build up of methane or some other combustable gas within the flue.

sam-tip

Sounds like a big Back Draft.   I have seen my E3200 do it many time after hard burns just after the next air pulse.   I have found my rain cap in the drive way during a calm day.  Blew it off the stack.  Tried to video it but now my door seal is not as air tight.   I thought the door was going to blow off during some of the back drafts. 
Central Boiler E3200 WiFi
Many many ported chainsaws. 201 to 3120
TM log splitter pro30 6 way head
D&L 1020 swing blade sawmill for slabbing
Timberking 1220

Al_Smith

Well it would make sense if the unit had a fan induced draft that was shut off there would be a build up of combustable gas .Especial with 26 feet of flue pipe .Blam blow the flue cap into the next county .

doctorb

r.man-  Well, I'd like to think that I have a sense of adventure, but since my OWB is located under cover in my shed, I don't like the idea of charring the rafters. :D
My father once said, "This is my son who wanted to grow up and become a doctor.  So far, he's only become a doctor."

firechief

Yep thats a classic backdraft.  With the introduction of air into the firebox the combination of heat and gasses can have quite the fireball. Dr. B is correct that the timing makes a great deal of difference.  Also, opening the bypass and letting a good portion of those gasses escape will help also.
I usually don't have the patience to do that but truth be told.... I love fire !!

David-L

Sonofman, simply put and this is a rule to follow if you have an OWB. I have seen many a singed hair around. This can be very serious if you ain't paying attention.

                                               David L
In two days from now, tomorrow will be yesterday.

Sonofman

I have not singed anything, but the first time I did it, I thought I was going to have to change my underware.  :D :D
Located due west of Due West.

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