iDRY Vacuum Kilns

Sponsors:

fireball out the door

Started by r.man, February 21, 2015, 11:03:59 AM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

r.man

I have had a number of OWBs in the last 15 or so years so I have lots of experience with fireballs big and small coming out the door. I like to occasionally cause one just for the fun of it but yesterday I saw something new. I had the door open, the combustion fan on because the switch is broken, and was loading the stove after splitting a too large block into a number of manageable pieces. The door had been open for about 2 minutes and was smoking very heavily when it converted to a fireball and started burning clean. I have never seen a fireball occur in these circumstances before but it didn't cost me any eyebrows since I was already avoiding the thick smoke. Live and learn, just wanted to give others a heads up.
Life is too short or my list is too long, not sure which. Dec 2014

Dave Shepard

I've gotten some weird results when feeding my OWB. When I started feeding it yesterday, it was almost at the high end of a heat cycle, which is usually the worst time to feed it. It was drafting really well, and as the door was open, getting a ton of air. It starting sending fireballs up the stack. I guess the unburned gasses would build up in the stack then ignite. It was kind of like a pulse jet, only much slower. :D
Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

DDDfarmer

Lost out on winning first prize in a "whiskerino" contest at the carnival last week. That is who can grow the best beard over the winter.  Filling the owb and lost a good portion of my chin, eyebrows, eyelashes and even more from my fur hat :-\. 
Treefarmer C5C with cancar 20 (gearmatic 119) winch, Husky 562xp 576xp chainsaws

Dave Shepard

I found that you can cover up where your hair has been singed with a hat, but going out in public with one and a quarter eyebrows takes some courage.  :D
Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

Autocar

Thick smoke plus oxygen = Fireball  ;).
Bill

firemedic589

What you're seeing is a "backdraft", only in a smaller setting. This is one of a firefighter's worse scenarios to be in. A tight compartment (doesn't leak air/smoke from all over), high heat conditions with not a lot of visable fire, and a lot of thick dark smoke. When you open the door the compartment is completely full of smoke with very little oxygen. As the smoke exits the plane between the fire base and the smoke rises, this is called the neutral plane, oxygen is being sucked in. Remember, smoke is nothing more than unburned fuel.

When the right amount of oxygen has mixed with the smoke and the high heat conditions, combustion occurs causing the fireball. Typically, after the fireball the whole compartment can either be full of fire or no fire with very little smoke.

But eitherway, you will certainly loose facial hair if your standing too close when you open the door. But be careful, if you inhale this superheated air if can cause major damage to your lungs.

r.man

Hey Fire, the odd thing was that the door had been open at least 2 minutes. When I started there wasn't much smoke, that came from me stirring up what was in the stove and then adding more wood. The amount and thickness of smoke was unusual and in 15 years my stoves have never flared after the door has been opened for a while. I have seen flames come out the door but it builds up to it gradually. This was a burst and conversion of thick smoke to ball and clean flame and it didn't happen as the door was opened, which until then had been the only dangerous time I had experienced.
Life is too short or my list is too long, not sure which. Dec 2014

beenthere

I've heard this referred to as "flashover" from firefighters working in houses. But see there is also a "backdraft" referring to the declining stages of a burn.

Regardless, whatever it is called, it seems to boil down to an accumulation of unburned gases that suddenly ignite.

To me, you need to look for the reason these gases didn't exit the flue when you had the door open and the fan going. Appears there is some blockage where you least expect it.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

DDDfarmer

For me it wasn't a backdraft or fireball.  The door is roughly 24"x17"  I rolled a block that was 15" or so into the firebox and the heat it forced out the opening did the damage.
Treefarmer C5C with cancar 20 (gearmatic 119) winch, Husky 562xp 576xp chainsaws

r.man

Beenthere I know why the smoke comes out the door, poor design. With the blower system it relies on positive pressure inside the firebox to move the smoke under a lip at the back to get it into the flue area. The door opening is higher in the firebox so it is easier for the smoke to exit there with the door open. Not a design I would recommend.
Life is too short or my list is too long, not sure which. Dec 2014

Dave Shepard

The Central is the same way, as is the Woodmaster. The Woodmaster has a baffle you can move when filling. The reason they follow like that is to give the heat maximum opportunity to get absorbed by the water jacket. The only time I have trouble with mine is when it is at the high end of a cycle and really cooking.
Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

Corley5

I've been burning bagged black cherry planer shavings in my OWB.  I don't open the door for several burn cycles after stuffing it with three 36 gallon bags  ;) ;D :) :) 
Burnt Gunpowder is the Smell Of Freedom

doctorb

My experience is to look critically at the smoke when you open the door just a crack.  White or white/gray smoke seems to rarely, if ever, ignite once the door is opened.  If you see rust colored or almost orange colored smoke, shut the door.  I have always assumed that this very dense smoke has significantly more particulate matter than the normal white smoke.  It's best to come back at another part of the burn cycle.  This is especially bad at the high end of the burn cycle when the stove is cycling down or just after the burn cycle is completed.  Another suggestion is to open the damper for a long time prior to opening the door when the burn cycle is in the "fireball may occur" range.  When I see those temps and the unit is about to or has just shut down, I open the damper and then go and load the wheelbarrow.  This delay technique help prevent fireballs.
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."

r.man

The heatmors have two safety features on them, the normal two stage door latch and a small draft door that opens when the outer insulated door is opened. The first discourages fireballs popping out of a door being flung open and the second burns up the explosive gases before the inner door is opened.
Life is too short or my list is too long, not sure which. Dec 2014

Glenn

RMAN - is your owb a pinetree one made in Combermere??  A local guy here got very badly burnt when his clothing ccaught on fire when he opened the door and it back drafted.  He spent months in a burn unit.

garret

For as much as these Phase 2 units cost, I think it is appalling there isn't a better draft solution when loading.  To me it isn't the hazard as I am familiar how to mitigate that, it is the risk of COPD later in life.  I have already developed what I refer to as my "woodburner cough".  I think I am going to experiment with a draft fan this spring.
E-Classic 2400 comfortably heating 4,200 sq.ft. and unlimited DHW, Off-grid, Photovoltaic-powered pumps in gloomy SW PA , 34 t splitter, numerous Husky chainsaws

r.man

Glenn, mine is a Pinetree which has no safety devices to protect the operator. To me the devices are only needed to protect a new operator anyone who has opened one of these a few times knows enough to get out of range. Probably shouldn't operate one without safeties if your gaurd is down.
Life is too short or my list is too long, not sure which. Dec 2014

Glenn

RMAN - i know the pinetrees well !!  Lots of them all over this area.  Small company that didn't last long.

Engineer

That phenomenon happens quite frequently with my Central Boiler CL5648.  Especially at the high end of a burn cycle, and even worse when the damper clangs shut and has been shut for a couple of minutes.  I will open the door and get a huge plume of brown-black smoke, and I can watch the interface between the smoke and unburned gases rise up in the firebox.  A few licks of flame is all it takes to get a flashover.  I had one so bad this past fall that it melted the light bulb cover on the front of the boiler, and peeled a good portion of paint off the siding above the door.  I've found that if I can push all the coals to the back of the firebox quickly enough, I still get a flashover but it mostly goes up the stack and is a bit safer.

woodmills1

the left front of my hair on my head is yellow and some people look at me wierd
James Mills,Lovely wife,collect old tools,vacuuming fool,36 bdft/hr,oak paper cutter,ebonic yooper rapper nauga seller, Blue Ox? its not fast, 2 cat family, LT70,edger, 375 bd ft/hr, we like Bob,free heat,no oil 12 years,big splitter, baked stuffed lobster, still cuttin the logs dere IAM

Dave Shepard

I've got a good video to put in here once I figure out how to upload it. Less fireball, more continuous blow torch. :D
Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

Dave Shepard

Always remember to duck when opening the door! :D

http://youtu.be/Zt2CMbBwN5Y
Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

beenthere

 :o
That'll draw some attention from the safety guru's out to squelch OWB's.   :o
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

doctorb

I don't ever, and I mean never, have anything quite as continuous like that.  Are your fans stuck in the on position?  Is the damper to the chimney locked closed?  Wow.
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."

thecfarm

That will bring the temp up quite.
Model 6020-20hp Manual Thomas bandsaw,TC40A 4wd 40 hp New Holland tractor, 450 Norse Winch, Heatmor 400 OWB,YCC 1978-79

Thank You Sponsors!