Close call and a lucky escape....

[imageel]

I was in my workshop yesterday processing my 2nd pallet load of Baltic pine woodblock flooring described here and found that with this batch I was getting ~25% wastage since these blocks had shrunk such that when viewed on end the block sides were almost v shaped top to bottom and by the time I had straightened one edge to 90 degree to the top the block overall was undersized by 2-3mm in comparison to my target finished width of 71mm.
So to salvage these I planned to trim the non-straightened edge by running through my table saw to take ~5mm off and then run them through the jointer to clean the face up and using strips from a sacrificial block laminate them back to the desired size.
This was a bit of a diversion from my prior workflow but I thought it worth the effort to save more blocks from the skip and whilst it was a mind numbingly repetitive process I thought tbh the whole job from start to end was similarly repetitive but with a good workflow was doable!
So set the fence on the saw and started processing the undersized blocks ripping the longer side with the other finished side against the fence. My table saw is a cheapo APTC model with almost farcical dust extraction so I had my 100mm chip extractor pipe taped up onto the factory fitted shroud encasing the blade and the excess merely extracting residual dust from the table saw body.
My chip extractor is a home-built one using a 220l oil drum sized plastic drum with a 450mm tall cyclone fabbed out of 2mm perspex in a routed frame the same diameter as the drum top and atop that a re-purposed Jet DC-1100a motor/fan unit moving 27L/min.
Whilst processing the blocks pushing them through with a push stick, I was getting some burn marks and the odd bit of smoke came off the tip of the tct blade where it was cutting through the bitumen on the bottom (uppermost) side of the blocks and occasionally the odd spark where I presume the bitumen had fragments of concrete oversite embedded...
I was down to my last 4 blocks when I noticed something smouldering between the gap in the table and the blade, so powered off/disconnected and poured a little water into the gap and took the screwed on side of the table off to take a closer look. Matted around the sides of the blade was a lot of wood fragments and stringy wood fibres so I cleaned these out and reassembled and proceeded to trim the last few blocks.
By this time the overriding smell in the workshop was of hot bitumen and as I turned around to turn off the dust exctractor - it's on a radio remote as the cyclone/drum is located in the far corner of my 4 x 5m shop, I noticed that there were what looked like furnace intensity flames visible through the perspex window cut in the drum as a level indicator...
Panicking I powered it off and gingerly felt the outside of the plastic drum which was noticeably warm but not yet hot, and as the only way to get the drum out is to lift off the motor/fan assembly which weighs ~35kg and is 1.5m off the ground - so shoulder height for me and so given the difficulty in demounting this safely with the drum contents on fire I pulled the whole assembly onto it's side - the drum was only maybe 1/4 full so the whole assembly was at this point decidedly top heavy... the motor and cyclone crashed to the floor and I then grabbed the top of the drum and hauled it outside and emptied the contents onto the lawn at a safe distance from my wooden workshop.
I then ran back into the workshop to check there wasn't anything alight inside - it was pretty smoky so I opened up all the windows and went back outside to deal with the smouldering heap.
It took 4 watering cans of water ~4 gallons to dampen it off!
Phew! that was a close call, I think throughout I was adrenaline powered and tbh only today as I write this do I realise how close a call this all was - the risk both to me and my workshop going up in flames does not bear thinking about.
The only casualty in all this is the cyclone which is fubar and a minor scratch on my hand so I think I got off pretty lightly given what could have a Darwin Award moment for me....

I am now pondering what fire protection I ought to have - a fire extinguisher has always been on my todo list but I somehow never got around to buying one, however now I question what I would/could have done even if I had one
Assembled with a fire in the drum there is no easy access to douse with either a powder or CO2 - I guess perhaps with the fan on I could have directed a powder one into the air intake but am not so sure enough would fall into the drum to smother the fire.
Equally with the amount of water required to dampen the drum contents and whilst assembled the lack of ability to effectively direct it a water based extinguisher would not have worked effectively either.

Grateful for any thoughts and advice from others on this forum as to how best to mitigate this, I certainly am giving it a lot of thought....
Stay Safe everyone!!
/Ed

 

[Spectric]

This is what happened to MAC timbers, a fire in there extraction system. In your case I would suggest that cutting pitch pine should have made you more cautious as to the potential hazzard, maybe checking or emptying the drum more than usual could have prevented the fire. I can see why people use those large bags and not enclosed containers as you can see what is going on, with your drum could you not have shut of the duct and starved the fire of oxygen.

 

[KingAether]

Glad you are safe and sounds, definitely a little luck on your side! I had a fire related close-call a few years back at the forge and it was scary..
You can get small auto-detonating fire extinguisher spheres; maybe worth seeing if it would be suitable to attach one to the inside of the drums lid just in case

 

[Droogs]

Have you considered having a large CO2 extinguisher fitted to the side of the drum with the nozzle fitted to vent into the system when the handle is pulled. this would deprive any fire in the bucket of air and give time to extract things safely. In this case I think it is mainly due to the excess amount of bitumen, perhaps a bit more diligence in cleaning off the source materiel in future.

 

[imageel]

Glad you are safe and sounds, definitely a little luck on your side! I had a fire related close-call a few years back at the forge and it was scary..
You can get small auto-detonating fire extinguisher spheres; maybe worth seeing if it would be suitable to attach one to the inside of the drums lid just in case
View attachment 135383

I just looked that product up - thanks that looks an ideal solution to this type of problem
/Ed

 

[Lazurus]

There appears to be several automatic fire extinguishers on the marked, I think I will be investing in one for peace of mind after reading the above. The powder filled ones appear very reasonable.

 

[--Tom--]

Lucky escape as the extractor will be fanning the flames with fresh air. I keep a powder extractor in the shop- and in that instance would have probably drilled a whole into the bucket to fit the nozzle and then dumped the contents in.
Planning the dust extractor design to help get it out of the shop is a good idea- if you rebuild could it be on castors?

You can get spark arrestors that go in line in the ducting to stop any sparks making it to the collector. They are expensive but cheaper than a fire.

 

[pe2dave]

Water/powder fire extinguisher near the door.

 

[davethebb]

My advice would be to ensure you have the ability to inject water into the dust collector. If you use a CO2/powder extinguisher etc. you will run the risk of disturbing the dust fines, creating a dust explosion before you have sufficient concentration of the extinguishing agent. This was my area of expertise for 30 years plus.

 

[pe2dave]

My advice would be to ensure you have the ability to inject water into the dust collector. If you use a CO2/powder extinguisher etc. you will run the risk of disturbing the dust fines, creating a dust explosion before you have sufficient concentration of the extinguishing agent. This was my area of expertise for 30 years plus.

good point Dave.
Do they / should they be earthed? Stop sparks igniting the dust inside?
Run an earth wire inside, tape to the sides?

 

[davethebb]

If the fines are small enough and dry enough static may be a risk but in this scenario, it is likely to be a small one (the fines to large particle ratio is also important). This fire started because the bitumen became hot and set a smoldering fire in the dust collector.

I would hope that the extractor/bin is earthed via the mains supply. However, the flexible hoses and plastic pipework unless they are made of conductive material could in theory potentially create a build-up of charge. If it was an industrial situation running all the time with long runs then it may be something to consider but in general, for domestic setups, it is a low risk.

 

[gmgmgm]

My advice would be to ensure you have the ability to inject water into the dust collector. If you use a CO2/powder extinguisher etc. you will run the risk of disturbing the dust fines, creating a dust explosion before you have sufficient concentration of the extinguishing agent. This was my area of expertise for 30 years plus.

Just in case anyone thinks a "dust explosion" sounds mild, it's not! Dust explosions are a form of fuel-air explosion, the same principle as the "thermobaric" bombs mentioned in the news recently in Ukraine. Have a look on youtube for "flour mill explosion" to see some examples, including the impressive explosion from a mere 50lb bag of flour.

(I certainly don't have 30 years of experience in this field, but thought it worth emphasising davethebb's point about the potential dangers here. I wouldn't have known CO2/powder would be a bad choice of extinguisher).

 

[TominDales]

My advice would be to ensure you have the ability to inject water into the dust collector. If you use a CO2/powder extinguisher etc. you will run the risk of disturbing the dust fines, creating a dust explosion before you have sufficient concentration of the extinguishing agent. This was my area of expertise for 30 years plus

Firstly you did the right things quickly getting the fire out and putting it out with water. So your quick thinking saved the day.
As for lessons learned.

I agree with this suggestion. Whilst recommend having a fire extinguisher in the shed/shop CO2 etc. Having the ability to pour water into dust collector is a good idea, its the simplest way to put this type of fire out.
I also agree with the recommendation that the container be a steel drum and have some earthed metal pipe toward the end before the cyclone to reduce static.
As @gmgmgm said, fine dust is easily ignited.
We have a client set their commercial vacuum on fire sucking up graphene and carbon black dust. the bag ignited. My father is a farmer and used to mill flower/cattle feed and he told me of several elevator/mill explosions in the 1950s/1960s

 

[MorrisWoodman12]

Water/powder fire extinguisher near the door.

I seem to recall being told that the fire extinguisher should be further into the workshop. If the fire is between you and the door you want to be able to grab it and fight your way through the fire using the FX rather than having to fight your way through the flames to safety and the FX.
Just a thought.
Martin

 

[okeydokey]

Some years ago I bought a used large Scheppach dust/chip collector from a retired fireman, came with a few metres of plastic/wire wound/encapsulated pipe. Everything had earthing cables connected and linked so there was no way he would get a static caused fire/explosion.

 

[Sachakins]

FX, one each end and one in middle. The one nearest the door is predominantly for someone coming in to help.

 

[Julie]

I was in my workshop yesterday processing my 2nd pallet load of Baltic pine woodblock flooring described here and found that with this batch I was getting ~25% wastage since these blocks had shrunk such that when viewed on end the block sides were almost v shaped top to bottom and by the time I had straightened one edge to 90 degree to the top the block overall was undersized by 2-3mm in comparison to my target finished width of 71mm.
So to salvage these I planned to trim the non-straightened edge by running through my table saw to take ~5mm off and then run them through the jointer to clean the face up and using strips from a sacrificial block laminate them back to the desired size.
This was a bit of a diversion from my prior workflow but I thought it worth the effort to save more blocks from the skip and whilst it was a mind numbingly repetitive process I thought tbh the whole job from start to end was similarly repetitive but with a good workflow was doable!
So set the fence on the saw and started processing the undersized blocks ripping the longer side with the other finished side against the fence. My table saw is a cheapo APTC model with almost farcical dust extraction so I had my 100mm chip extractor pipe taped up onto the factory fitted shroud encasing the blade and the excess merely extracting residual dust from the table saw body.
My chip extractor is a home-built one using a 220l oil drum sized plastic drum with a 450mm tall cyclone fabbed out of 2mm perspex in a routed frame the same diameter as the drum top and atop that a re-purposed Jet DC-1100a motor/fan unit moving 27L/min.
Whilst processing the blocks pushing them through with a push stick, I was getting some burn marks and the odd bit of smoke came off the tip of the tct blade where it was cutting through the bitumen on the bottom (uppermost) side of the blocks and occasionally the odd spark where I presume the bitumen had fragments of concrete oversite embedded...
I was down to my last 4 blocks when I noticed something smouldering between the gap in the table and the blade, so powered off/disconnected and poured a little water into the gap and took the screwed on side of the table off to take a closer look. Matted around the sides of the blade was a lot of wood fragments and stringy wood fibres so I cleaned these out and reassembled and proceeded to trim the last few blocks.
By this time the overriding smell in the workshop was of hot bitumen and as I turned around to turn off the dust exctractor - it's on a radio remote as the cyclone/drum is located in the far corner of my 4 x 5m shop, I noticed that there were what looked like furnace intensity flames visible through the perspex window cut in the drum as a level indicator...
Panicking I powered it off and gingerly felt the outside of the plastic drum which was noticeably warm but not yet hot, and as the only way to get the drum out is to lift off the motor/fan assembly which weighs ~35kg and is 1.5m off the ground - so shoulder height for me and so given the difficulty in demounting this safely with the drum contents on fire I pulled the whole assembly onto it's side - the drum was only maybe 1/4 full so the whole assembly was at this point decidedly top heavy... the motor and cyclone crashed to the floor and I then grabbed the top of the drum and hauled it outside and emptied the contents onto the lawn at a safe distance from my wooden workshop.
I then ran back into the workshop to check there wasn't anything alight inside - it was pretty smoky so I opened up all the windows and went back outside to deal with the smouldering heap.
It took 4 watering cans of water ~4 gallons to dampen it off!
Phew! that was a close call, I think throughout I was adrenaline powered and tbh only today as I write this do I realise how close a call this all was - the risk both to me and my workshop going up in flames does not bear thinking about.
The only casualty in all this is the cyclone which is fubar and a minor scratch on my hand so I think I got off pretty lightly given what could have a Darwin Award moment for me....

View attachment 135377

I am now pondering what fire protection I ought to have - a fire extinguisher has always been on my todo list but I somehow never got around to buying one, however now I question what I would/could have done even if I had one
Assembled with a fire in the drum there is no easy access to douse with either a powder or CO2 - I guess perhaps with the fan on I could have directed a powder one into the air intake but am not so sure enough would fall into the drum to smother the fire.
Equally with the amount of water required to dampen the drum contents and whilst assembled the lack of ability to effectively direct it a water based extinguisher would not have worked effectively either.

Grateful for any thoughts and advice from others on this forum as to how best to mitigate this, I certainly am giving it a lot of thought....
Stay Safe everyone!!
/Ed

Well, that was a disaster in the making, you were lucky, I have worked with industrial dust extraction systems, the ducting and the containers are almost always made of Metal, the exception to this being flexible hoses, but even these are protected by static elimination earthing, fire breaks which close if there is too much heat build up, fusible links which shut off the fans if a fire is present in the system, without all of this, and very strict guidelines on what timber you can process, it would be a game of chance, also we always had several fire extinguishers, ABC Dry Powder, and Water, and for High Voltage use CO2 as at 415v even Dry powder can carry a charge and earth out through you if your holding a metal bodied extinguisher

In my own workshop I have a twin bag extractor and a fine dust canister extractor, the latter is a metal bin, and it's regularly emptied, I always have a fire extinguisher to hand, one water and one ABC Dry Powder, this has been a rule since I started my workshop, even things you would not think of as a fire risk can be, I once had a Pressure Washer catch fire, and I was glad of my powder extinguisher that day!, so Fire safety first

You don't have to go to the lengths we did in a full scale wood processing workshop, but you should take precautions nonetheless, I would not recommend a Plastic Drum, mine is a 210l Steel one with a Snap Ring fitted lid, if you need to deal with a fire in it, then you just seal the inlet and outlet, this is easily done by closing the blast gates after switching off the fan, I also have a smoke detector in the shop, the drum is used as a dust separator you see, so as to avoid as much material as possible getting in to the actual extractor and clogging the filters

I would not mount a heavy fan/motor mech on top of the drum, put it to one side, connect with a length of tubing either metal or a low smoke flame plastic, have a Blast gate in the line, and another on the intake from the machine/s that way you can always isolate a fire in the system, and potentially if you have a good seal, snuff it, always remember the Fire Triangle Heat-Fuel-Oxygen, remove any of these and the fire dies, so Snuff it, by closing off the air, or with a Dry Powder Extinguisher, wet it if there is no electrical risk, this removes the fuel and reduces the heat so breaking two sides of the triangle

My bag extractor is no problem as it's mainly employed on my planer-thicknesser so doesn't see fine dust, which is the main fire and or explosion risk, I do also sometimes use a fine mist of water spray to keep the dust down

You should also take great care when processing Particle Board, as it's made from recycled material and often contains metal fragments from screws, nails and other bits of hardware which are simply merged in the material, Never put this through a Planer, you will need new blades almost certainly, also if this stuff gets in to your extractor it's very bad news as the hot metal fragments off the saw can start a fire in the extractor too!

I hope this is helpful

 

[aet1]

Just in case anyone thinks a "dust explosion" sounds mild, it's not! Dust explosions are a form of fuel-air explosion, the same principle as the "thermobaric" bombs mentioned in the news recently in Ukraine. Have a look on youtube for "flour mill explosion" to see some examples, including the impressive explosion from a mere 50lb bag of flour.

(I certainly don't have 30 years of experience in this field, but thought it worth emphasising davethebb's point about the potential dangers here. I wouldn't have known CO2/powder would be a bad choice of extinguisher).

Well, that was a disaster in the making, you were lucky, I have worked with industrial dust extraction systems, the ducting and the containers are almost always made of Metal, the exception to this being flexible hoses, but even these are protected by static elimination earthing, fire breaks which close if there is too much heat build up, fusible links which shut off the fans if a fire is present in the system, without all of this, and very strict guidelines on what timber you can process, it would be a game of chance, also we always had several fire extinguishers, ABC Dry Powder, and Water, and for High Voltage use CO2 as at 415v even Dry powder can carry a charge and earth out through you if your holding a metal bodied extinguisher

In my own workshop I have a twin bag extractor and a fine dust canister extractor, the latter is a metal bin, and it's regularly emptied, I always have a fire extinguisher to hand, one water and one ABC Dry Powder, this has been a rule since I started my workshop, even things you would not think of as a fire risk can be, I once had a Pressure Washer catch fire, and I was glad of my powder extinguisher that day!, so Fire safety first

You don't have to go to the lengths we did in a full scale wood processing workshop, but you should take precautions nonetheless, I would not recommend a Plastic Drum, mine is a 210l Steel one with a Snap Ring fitted lid, if you need to deal with a fire in it, then you just seal the inlet and outlet, this is easily done by closing the blast gates after switching off the fan, I also have a smoke detector in the shop, the drum is used as a dust separator you see, so as to avoid as much material as possible getting in to the actual extractor and clogging the filters

I would not mount a heavy fan/motor mech on top of the drum, put it to one side, connect with a length of tubing either metal or a low smoke flame plastic, have a Blast gate in the line, and another on the intake from the machine/s that way you can always isolate a fire in the system, and potentially if you have a good seal, snuff it, always remember the Fire Triangle Heat-Fuel-Oxygen, remove any of these and the fire dies, so Snuff it, by closing off the air, or with a Dry Powder Extinguisher, wet it if there is no electrical risk, this removes the fuel and reduces the heat so breaking two sides of the triangle

My bag extractor is no problem as it's mainly employed on my planer-thicknesser so doesn't see fine dust, which is the main fire and or explosion risk, I do also sometimes use a fine mist of water spray to keep the dust down

You should also take great care when processing Particle Board, as it's made from recycled material and often contains metal fragments from screws, nails and other bits of hardware which are simply merged in the material, Never put this through a Planer, you will need new blades almost certainly, also if this stuff gets in to your extractor it's very bad news as the hot metal fragments off the saw can start a fire in the extractor too!

I hope this is helpful

Perhaps you would put me straight on this regarding explosion risk - if there is a fair amount of fine dust then isn't a bag or filter style dust extractor the way to go so the dust is not left flying around in the air inside the can?

 

[davethebb]

Perhaps you would put me straight on this regarding explosion risk - if there is a fair amount of fine dust then isn't a bag or filter style dust extractor the way to go so the dust is not left flying around in the air inside the can?

The explosion risk for small workshop extraction systems is generally very small - otherwise, you would hear about incidents occurring. Although you may have an explosive atmosphere you typically do not have ignition sources sufficient to initiate the event under normal working conditions. The scenario given by the OP (fire) will initiate an explosion if there is an explosive atmosphere, and injecting any form of suppressant at the speeds fire extinguishers provide rouses the dust and creates the explosive atmosphere, hence the explosion risk. The fact the fines will be on the filter cartridge may in fact work against you as the fines will be distributed and not mixed homogenously with the larger particles. Hope this helps.

 

[aet1]

Thanks for this clarification Dave.