Dust extractor risks?

[Scrit]

I should have made the point before that the woodworking industry tends to burn only solid waste - dust is collected for use in producing chipboard/MDF or pressed into pellets for burning. Even Felder have a briquetting machine which goes onto their larger extractors, mind yoy they cost about £10k!

The other point I should have made is that commercial wood heating units such as the Talbott have an afterburner option where the flue gas is monitored and a secondary gas burner is used to fully combust any materials still in the exhaust. This reduces smoke production considerably and is a legal requirement in smokeless zones. The only approach one can take with a stove is to utilise a fire brick lining and a stove with an "air injector" design such as the Relax design sold by The Hot Spot where a "dampable" air tube extends into the base of the fire to promote higher combustion temperatures. I used to have an R6 and it worked quite well, although loading with sawdust could only be indertaken at the time I started it up for the reasons mentioned above.

Scrit

 

[Shadowfax]

Ok, with me fire officer's head on - anything will burn if it gets hot enough and the smaller the pieces the easier they will be to ignite. (Think firewood, shavings and one match. Which will get you a fire more quickly?)
Dust of any sort will burn easily, as some of you have discovered, and if it is already suspended in air there is a chance of rapid burning or what is generally termed an explosion.
Compact the dust and it will be very difficult to ignite. Exclude that air and the chances get even smaller.
Static electricity in a small extraction system is not worth considering and the idea of grounding the plastic parts even less so.
Sparks and embers in the dust and shavings, though, is a very different matter.
I would definitely agree that emptying the DX system bin should be done every day but I must admit I am guilty of not doing it! A real case of "do as I say, not what I do"! I must have a word with myself over that.
Cheers.

SF

 

[engineer one]

shadowfax i understand what you said, but it was my thought that
spontaneous combustion is easier when a lot of maybe different
shavings are crammed into a bag/storage facility, whilst
if you aerate them, it will be less easy for heat to build up
to the point where combustion could take place.

paul :wink:

 

[Shadowfax]

I see what you mean, Paul, and you do have a point but, generally, if there is enough air in any mixture there is a good chance that combustion will take place, given an ignition source.
If the mixture is compacted the chances of it supporting combustion will be reduced.
This is why it can be so difficult to extinguish a fire in a heap of dusty product such as coal or grain. Raking the stuff away from the fire allows air into the hot area and feeds the fire while leaving it untouched means that it is so compact that the water runs off rather than soaking in and cooling the hot area. You almost can't win! This is the reason for some fires apparently taking days or weeks to be put out.
There was a fire in a tyre dump that went on for years but the reasons for that were a bit more complex. In fact that is another story altogether and quite irrelevant but who cares!
The other point was auto ignition or self combustion. That is caused by an exothermic reaction in the material and depends on just the right amount of oxygen being present to start the reaction which then leads to the production of heat, the release of more oxygen and so on. Yes, spreading the material out a bit will probably prevent this but it might not be possible in an enclosed container to get enough air into the mixture to stop the reaction if there is going to be one.
Most wood chips will not produce this effect simply because it would most likely be the presence of resin in the mixture that might start the exothermic process. However, with the sort of dry timber that the woodworker needs if there was enough resin in the chippings to produce the reaction the timber would be too wet to work anyway.
Really sappy wood chips left in a pile could well get warm, though. and things could get exciting!
Does any of that make sense? I'm aware of the first rule of holes, here!

Cheers

SF

 

[DaveL]

Where did your cyclone come from then?

Nick,

If you look here you can see the making of it and here for the blast gates and start of the pipe work.
I have been running it without an output filter, not good but it still put less fine dust back into the shop than the dust collector as bought. Now large surface area filters can be had from an Ebay seller I will be adding a pair to the output to reduce the dust that the air filter has deal with.

Yes you may of noticed that I do spend far too much time making things for the shop instead of for the house, I have been reminded that the timber I bought over 2 years ago is still not desk shaped. [-(

 

[engineer one]

ah but dave in this world of safety you must make sure that
the atmosphere in the workshop is not likely to cause
you any more damage than it already has \/ \/

the best excuse is that you cannot yet see the desk shape in the
wood, and you do not want to provide something that is not
stylish enough :lol: :lol: :lol:

but like you i have miles to go before i sleep, and wood to change
into usable shapes. :twisted:

paul :wink: