First thanks for raising such an important subject. Boot and shoe makers often don’t consider their working environment enough.
All the comments made here are so valid and relevant. Perhaps I can add the odd one and expand on another.
Dust extraction systems have been around as long as we have had powered scouring/buffing machines. Most of the various plus and minus points are well known and understood. For example, dust extraction systems in footwear factories normally suck the dust through a curtain of water. This does two things. First the risk of fire is almost completely eliminated and the dust is easier to collect because it is in the form of a sludge and will not fly up into the atmosphere when disturbed. However, this does not stop the risk of fire in extraction pipes. If for some reason dust in crevices is ignited by a spark, it can very quickly catch fire because there is a plentiful supply of oxygen being drawn along the pipe by the extractor. It’s rather like using bellows on apparently dead embers in a barbecue.
It is this oxygen supply factor which makes it so important not to have anything which could cause a spark.
The reference to solvent fumes is equally important not just because of fire risk, which is quite rare except where people are being stupid with naked flames nearby. As already raised by Tex, the major concern is for your health. The important factor is that any extraction should remove fumes FROM THE WORK BENCH downwards and not upwards, as Tex and Larry both spell out. It does not matter where the pipe goes after it leaves the bench. The best system is where you have the air being sucked down through a hole in your bench covered with a grill to stop things falling in, as shown in the diagram.
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The numbers inside the dotted lines are parts per million of solvent on a typical workbench being used for more than two hours continuously, for sole/bottom cementing. Most small workshops never get anywhere near these figures but note the inward pointing arrows. These indicate the fresh air supply which is important if the flow down the pipe is to be maintained.
Just to repeat myself, I have seen a number of examples where workshops have been fitted with an extractor fan in a window above head height. In each case the worker was cementing on a bench against this wall and all the fumes were being dragged over his face to reach the extractor.
Thanks again Lisa for raising this discussion. Can I make a suggestion regarding cement fumes. Why not get rid of them by using water-based adhesives?