Dust extractor risks?

[Scrit]

Perhaps a dumb question, but how many of you routinely extract dust when sanding and thern don't empty the dust extractor/vacuum cleaner at the end of a session?

Scrit

 

[Scott]

ahem ...

 

[Adam]

Whats the risk Scrit? I do have it in a physically seperated "extractor" house which is a few feet from the workshop.

Adam

 

[Scrit]

Loose abrasive particles from sanding can "spark-off" when they contact metal, such as sheet metal ductwork, the steel impellor or its' housing in the extractor, etc. Those sparks can then smoulder and cause a fire in the waste sack many hours after the machine has been switched off. I was talking to a near neighbour yesterday evening who mentioned that he'd been out on a "shout" earlier this year caused by this happening in a home workshop (he's a fire officer) and I was curious to find out if people were aware of this peculiar risk.

As a point of interest it is normally a stipulated condition on commercial insurances (i.e. for trade users) that you empty extractors and vacuums at the end of each day/shift and remove the waste outside. As to whether or not people do it, well, that's anyone's guess.

Scrit

 

[Colin C]

Thanks for the heads up on this Srit

 

[Mike.C]

Yeah thanks for the heads up Scrit. I had no idea that i should empty it ever day.

Cheers

Mike

 

[George_N]

I had an 'incident' when routing an edge rebate in some plywood last year. I was using the router hand-held with the vac attached and the dust port got blocked with some long curly fibres from the edge of the board. I stopped the router as soon as I spotted the blockage and smelled the smoke but the dust was already starting to smoulder. Before I could stop the vac the little glowing cinder shot down the vacuum hose and into the dust bucket. it was relatively easy to put out but I dread to think what might have happened if I had missed that momentary whif of smoke or dismissed it as surface burning.

cheers

George

 

[Midnight]

canna be too careful with these things... I;ve seen fume extractors at work going up in smoke.. hellova fuss...

thesedays my DX only gets fired up to help cool the router when raising panels.. planes have rendered my sanders all but redundant...

 

[Paul Chapman]

Many thanks for the tip, Scrit. Could be a life-saver :shock:

Paul

 

[engineer one]

yes scrit as said, thanks, it is strange that we all now think about
extraction, but our old male habits of only throwing things out
when the bins are full may well get us ini trouble.

i have read many of the articles about extraction, and all talk about
sparks getting in, or spontaneous combustion, but you tend to feel
it will only happen when you are working, not whilst down the pub

so i guess we have to make efforts to deal with sawdust in the same way
as rags used for applying finishes.

i wonder how much of the problems could be stopped purely
by making the sawdust less compacted than they are in the
extractor, thereby getting more air in and making combustion more
difficult.

also i think we should take more care when cleaning the filters.
i know my trend 160 is great, but cleaning the filter kind of makes a
mockery of the extraction capability, since you have to do it
in the open and it is better if you use an air line to clean it??????? :? :?

but once again a reminder for all, but particularly those of us who
were lucky enough to be apprenticed, even if not in woodwork,
to spend a few minutes at the end of the day to clean up, and tidy up.
it is tempting particularly with woodworking, not least because we often
work alone, to keep going until you finish the job, whereas it might be
better to remember that as we tire we become less safe, and probably the
standard of our work deteriorates too.

paul :wink:

 

[DaveL]

Well this will probably make Scrit wince.
I don't empty the dust collector every day as I use the contents to heat the shop.


I have two bins so I can just wheel the full one across to the wood burner, in the other back corner, having replaced it with the empty one. During the summer I bag the shavings and dust and store it in the garage until the cold weather is back.

 

[Scott]

During the summer I bag the shavings and dust and store it in the garage until the cold weather is back.

"Spontaneous combustion" comes to mind Dave :!:

 

[Stoday]

I was in a DIY shop some years ago when the dust from the table saw caught fire.

 

[wrightclan]

i wonder how much of the problems could be stopped purely
by making the sawdust less compacted than they are in the
extractor, thereby getting more air in and making combustion more
difficult.



paul :wink:

Paul,

I think you'll find that getting more air in feeds oxygen to a fire and making combustion far more likely. If you take a shovel of fine sawdust and dump it quickly on a fire, some of it will burn quickly, and then it will dampen down a fire and smoulder away for hours. If, on the other hand you lightly sprinkly that same shovel of fine sawdust over a fire, you will see rapid bursts of flame shooting up your chimney; reminding us of the explosive danger of suspended sawdust in the air. Compaction makes combustion more difficult, but perhaps less easy to detect until hours later.

I have to admit, I don't empty mine as regularly as I should.

Scrit,

I wonder about your views, experiences on workshop stoves (woodburners). You seem to be the resident expert on safety (although we are at odds on the safety of fixed-base routers). My Dad says I shouldn't put one in the shop for safety reasons--explosion danger from suspended sawdust--even though he had one for decades in his workshop, and I and my brothers used it regularly.

Have you (or anyone else) known of instances of this occurring. My thoughts are that a woodburner draws air in, not out. Thereby causing any burning of suspended sawdust to occur inside the stove, not likely to cause an explosion in the workshop. I wonder if some explosions attributed to woodburners may have actually been caused by other factors, such as static electricity; and the woodburner is just an easy scapegoat. Any thoughts?

Brad

 

[Nick W]

Dave,

Where did your cyclone come from then?

 

[nickson71]

I think Dave built his own .........

 

[Scrit]

I wonder about your views, experiences on workshop stoves (woodburners). You seem to be the resident expert on safety (although we are at odds on the safety of fixed-base routers). My Dad says I shouldn't put one in the shop for safety reasons--explosion danger from suspended sawdust--even though he had one for decades in his workshop, and I and my brothers used it regularly.

Have you (or anyone else) known of instances of this occurring. My thoughts are that a woodburner draws air in, not out. Thereby causing any burning of suspended sawdust to occur inside the stove, not likely to cause an explosion in the workshop. I wonder if some explosions attributed to woodburners may have actually been caused by other factors, such as static electricity; and the woodburner is just an easy scapegoat. Any thoughts?

The term that you may be looking for (if I can spell it correctly) is "stochiametrically viable mixture". i.e. a mixture of air and fine, combustible particles where the volume of combustible material suspended in air in conjunction with the surface area of that material is such that in the presence of a spark or flame a chain reaction (explosion) will occur. In reality that takes a LOT of dust in the air (visibility would be impaired) and recent research has shown that static in plastic extraction pipes within small extraction systems is generally insufficient to cause a problem (commercial-size systems are, however, a different kettle of fish). Explosions do occur in industry, however, as sparking in the waste sacks can cause a minor explosion. Should an extractor explosion occur in a dusty shop which is not cleaned (e.g. dust on roof spars, etc) enough wood dust can be loosened and dropped into the air to produce large volumes of combustible mixture which can then be ignited by the first explosion....... apparently it isn't the DX explosion that kills, but the second more major one [Source: HSE]

I'd say that assuming the workshop is kept relatively clean (and that means vacuuming the ledges once a year or so) and there's an extraction "regime" in place on machines with the stove is properly physically protected, that the likelihood of problems is fairly slim. I was given a spec for a wood-burner many years back by an insurer: "stove to be positioned against a masonry or fireproof wall, on a raised fireproof base such as concrete with pygmy walls either side to further protect it." That came with an instruction to extinguish the fire at night (but NOT remove the hot ashes) and ensure that no combustible materials (sawdust sacks) were left in the workshop overnight, although there were no comments about keeping the unit clean or sweeping the flue regularly. Many woodworking manufacturers burn their waste to heat in units like the Talbott heater installed inside the building and the general requirement is generally just to protect the unit from collision damage with FLTs, pallet trucks, trolleys, etc

Problems attributed to wood-burners are more likely to come from flue fires (wood waste produces a LOT of soot and flues need to be swept once or twice a year), combustibles being left against the stove at night or the stove's fire hole being opened in extremely dusty workshops (the "stochiametrically viable mixture" scenario) than anything else, IMHO - all issues which can be resolved easily.

According to the my insurers one of the biggest source of fires in woodworking shops is sparking from loosened abrasives, the original drift of this thread.

Scrit

 

[woodbloke]

I seem to recollect a program on the box many years ago where it was demonstrated that any dust, if its fine enough and the conditions are correct, can explode. I particularly remember the demonstration of the exploding custard powder! Rob

 

[CHJ]

Paul,

I think you'll find that getting more air in feeds oxygen to a fire and making combustion far more likely. If you take a shovel of fine sawdust and dump it quickly on a fire, some of it will burn quickly, and then it will dampen down a fire and smoulder away for hours. If, on the other hand you lightly sprinkly that same shovel of fine sawdust over a fire, you will see rapid bursts of flame shooting up your chimney; reminding us of the explosive danger of suspended sawdust in the air. Compaction makes combustion more difficult, but perhaps less easy to detect until hours later.

I have to admit, I don't empty mine as regularly as I should.

Sorry to butt in at this late stage, further to the comments re sprinkling dust on a fire. I burn the contents of my chip/coarse dust collecting box in an open topped 200litre drum, a couple of weeks ago I had to scrounge a replacement drum after tipping said chippings mixture on top of burning debris and it ignited with enough force to send a fireball 2-3 metres upward, burst the side of the somewhat rusted drum and more disturbing, followed me and the now 'empty' box a metre or so back towards the shed. Obviously explosive mixtures can be created even in 'open air' situations.

I must admit to not emptying the bins/containers after each session but are particularly careful not to 'consume' oil/wax soaked rags, abrasives, etc. (accidental consumption of same enforces after session emptying)
Machines are always cleaned down especially the vicinity of the tool grinder after each session.

 

[wrightclan]

Obviously explosive mixtures can be created even in 'open air' situations.

My point was that more air increases combustion. Your example reinforces my point. when you dumped such a large amount, you initially released a large cloud of dust immediately above the fire. When I was talking about a shovelful being dumped rapidly, there is a short 'explosion' or rapid burning from the loose particles, before the bulk settles down and smoulders away. What you attempted is the same thing on a massively larger scale and with more air to boot.