Dust is bad for you. How do you get rid of it?
Do dust extractors really work?
The difficulty for woodturners is that conventional dust extractor machines do not work too well for taking dust away from the lathe. It is quite easy to construct a casing around a bandsaw, for example, and connect the hose of a dust extractor so all the dust is whisked away. Not so with a lathe. You cannot put an enclosure around the lathe because that would get in the way of you and your turning tools. You can try putting the air intake of the extractor as close behind the wood as possible and if you have a really good airflow this will remove some of the dust.
The problem is getting enough airflow to take enough dust away. Even a large 2 horsepower machine will leave some fine dust hanging around for you to breath in. Try holding your finger close to the nozzle of a vacuum cleaner. You can feel strong air movement. Then try holding your finger four inches away - do you feel much happening? Try hoovering up some dust by holding the nozzle 6" off the floor and you will soon realize the extent of the problem.
One possible solution. . . If you do not mind sweeping up the dust and shavings from the floor a powered respirator such as the Trend may be all that you need. One of these will give you excellent protection. They are quiet and take up little space in the workshop. They also offer eye and face protection as a bonus.
DUST EXTRACTORSLow priced dust extractors are now widely available. There are two different designs used. One type of machine uses a robust centrifugal fan to suck air and dust directly through the fan blades (which are heavy cast or welded metal in case something solid is sucked in) into two bags which blow up like balloons when the motor is switched on. The lower bag collects most of the chips and can be plastic while the upper bag is cloth and acts as a filter.
The fine dust soon cakes onto the inside surface of the upper bag and this layer of dust itself contributes to the efficiency of filtering. Large particles fall down into the lower bag. The lower bag must be emptied periodically, preferably before it fills up to the top. The better machines have a cyclone separator. This means that the incoming stream of dust and air is made to follow a corkscrew path inside the machine before it gets to the collector bags. The centrifugal force generated by the violent spinning motion makes the heavy chips and large dust particles fly to the outside of the airstream and fall down out of the way before they can clog the filter bag. There is a variation on this design which uses only one large hanging bag. With this machine the upper part of the bag does the filtering and the bag must never be allowed to fill right up.
Shown here is the authors ancient bag filter machine. To reduce noise and dust it is positioned outside the workshop. You can see the 4 inch hose going through the wall.
The other type of machine works like a vacuum cleaner. The fan sucks the air into an oil drum shaped container and then through a filter. The debris does not go through the fan blades so a smaller and less robust fan can be used. These machines usually also make use of the cyclone effect to reduce the load on the filter.
PROBLEMS WITH DUST EXTRACTORSUnfortunately both types of machines have problems. The upper bag on the bag type machine will let very fine dust through. As previously mentioned, the layer of dust inside can perform as a fine filter and this works fine so long as the machine is on all the the time or the layer does not get so thick as to impede the passage of air. The general idea is to give the top bag a whack now and again to dislodge the dust and let it fall down inside to the lower container. Unfortunately, this action also liberates a large cloud of dust into the air. When the machine is switched off, the bags collapse or partially collapse. At the moment of switch-on they fill with air again and, oh dear, a huge cloud of dangerous fine dust is released into your workshop. So these machines are fine for removing most of the coarse particles but they are not so good at protecting your lungs from dangerous fine dust. It should be said that it is possible to buy improved bags with a finer weave which offers better filtration of fine particles. However I have found with my machine that it is very difficult to seal the bags and hoses perfectly to the frame of the machine and that as the inside is at a positive pressure, even a small leak results in a little stream of fine dust blowing through the gap.
The "vacuum cleaner" type of machine usually has a finer filter but the effective filter area can be much smaller than the bag type. This means in practice that the filter clogs up with fine dust and has to be cleaned frequently to maintain maximum suck. Cleaning the filter generally means taking the thing apart which is an enormous nuisance and should be done outside to prevent the dust getting back into the workshop. Fine if its not raining. The vacuum cleaner type of machine has a powerful suck but is not designed to shift a large volume of air. It will work fine if you have a duct closely fitted around the source of dust and they are ideal for most woodworking machines. Lathes are more difficult and you cannot get the normal collecting nozzle close enough to the lathe to take away all the dust and at the same time leave room for you to work.
To maximise the dust collection you should make special nozzles which fit around the workpiece as closely as possible. Many users find that modified drainpipe fittings are just the job. The type of hopper intended to join drainpipes to gutter can often be used and can be fitted fairly easily to the hose of the dust extractor. Ideally it would be mounted on some kind of tripod stand so it can be positioned close to the wood surface you are sanding or turning.
If you can, you should park your dust extraction system outside the building or even work in the open air to avoid a build-up of dust. The trouble with this is that you will get very cold in the winter.
What woodturners really need is a machine which moves a larger volume of air at lower speed - a breeze which wafts the fine suspended dust away from the lathe into an efficient filter. The only systems commercially produced so far as I know which get anywhere near the solution to this problem are those setups for paint spraying and welding which consist of a large three sided box built around the work area. Built into the rear of the box is an array of large powerful fans which suck all fine dust and fumes through suitably designed filters at the rear and recirculate the air. They work well because they move a very large volume of air. These are large and extremely expensive. It is time someone came up with a system specially for woodturners which hobbyists could afford.
To make airflow comparisons between products you often need to convert units with a calculator which is a nuisance but this may help
- 1 litre = 0.035 cu ft
- 1 cu ft = 28.3 litres
- 1 litre/sec = 2.12 cu ft/min
- 1 litre/sec = 3.6 cu m/hr
- 1 cu m/hr = 0.28 litres/sec
You must therefore use a good, close fitting, mask when sanding as well as employing a dust - or should we say chip - extractor. Masks are available in a huge variety of forms. The cheapest is the lightweight disposable dust mask. "Disposable" according to health and safety regulations means that the masks should be replaced after every shift of 8 hours. One design uses flat pads of filter material held to the mouth by a lightweight soft aluminum face-piece. One, or preferably two, elastic straps hold the mask on. This is cheap and effective but tends to get very sweaty and inhibits conversation because it touches the lips. The moulded disposable masks are more popular, they are shaped so as not to touch the lips and are very light and comfortable. They can be folded and stored in a pocket until needed. The very cheap variety of moulded mask is rated for "nuisance dust" and is only good enough for occasional use. One problem with these, is that it can be difficult to get a proper seal round the nose. This makes your specs or goggles steam up! You can glue a small amount of cotton wool around the top edge of the mask to improve the seal.
|Class||Filter penetration limit (at 95 L/min air flow)||Inward leakage|
|FFP1||Filters at least 80% of airborne particles||<22%|
|FFP2||Filters at least 94% of airborne particles||<8%|
|FFP3||Filters at least 99% of airborne particles||<2%|
The basic masks are a lot better than nothing but if a mask is your only protection you should use a good one. The table above shows the different grades of mask and the leakage. Even with the very best mask you could be breathing in 2% of the dust. If you have a beard there will be even more leakage because you will not get a proper seal. You can see that these masks will be no good if you have already developed a sensitivity to very small amounts of dust. If you are asthmatic or allergic to dust, you must use better equipment. Even the heavier rubber type mask with cartridge filter will not give 100% protection. The best one I have seen has a very soft pneumatic cushion-edge seal for the face. You can even adjust the pneumatic pressure to get the best seal. It has a remarkably good rating for inward leakage of 1.05%. The cartridge filter has a penetration of 0.5%. These are not as comfortable to wear as the others and with some types the cartridge projects forward so much as to interfere with a face shield.
POWERED RESPIRATORSIf you are very dust sensitive already or if you have a beard you have a real problem. A powered respirator may well provide the answer. These use a small battery powered blower which sends filtered air into a face shield which encloses your whole face. Because the inside of the face shield is under a slight positive pressure, dust will not enter even though the seal is not perfect. The shield provides good impact protection as a bonus. They are expensive but they can, in the long run, be actually cheaper than regular use of a superior grade of disposable mask. They are more comfortable than masks (which get sweaty after a short while) and can be used if you have a beard. They give excellent eye protection. They can be fitted with carbon filters as well as particle filters to remove solvent fumes or odours from certain timbers which may cause allergic reaction. Running costs are low and the rechargeable battery lasts for 8 hours continuous use. These units are perhaps the answer for the professional woodturner if they can be afforded. Trend Airshield Pro units are popular.
WALL MOUNTED FILTERSIt is possible to buy special filters which continously circulate the air in the workshop and clean the finest suspended dust out of the air. They will eventually reduce the dust to an extremely low level but they can only supplement the use of an efficient local means of dust extraction. To be any help, they must be powerful enough to change the entire workshop full of air within a reasonable period. There will be a delay between the creation of dust (eg the end of an intensive sanding operation) and its reduction to a safe level. One type is the electrostatic filter which is the most efficient form of filter you can buy. Electrostatic filters can remove the finest dust, even pollen and viruses, from the air. Small units can be obtained which may be O.K. for a small workshop and "hobbyist" duty for £200 or so. Industrial units cost £1200 plus. The elements need to be cleaned out regularly at intervals depending on the dust loading. The other type is a box containing a fan plus a heavy duty large capacity filter which has to be thrown away when full. Industrial capacity filter units cost well over £1000 and the replacement filters cost about £100 to replace. These filters would last a long time - they can take up to 3kilo of dust before they are full. You might have to invest in one of these if you have developed wood dust sensitivity. Remember - prevention is better than cure!
SO WHAT CAN THE HOBBYIST WOODTURNER DO ON A SMALL BUDGET?There is no perfect solution to the dust hazard as yet for us woodturners. The best solution at an economical cost is to... (a) Use a mask or powered respirator. (b) Use a powerful dust extractor with a suitable collector hood positioned so as to remove the maximum amount of dust. (c) In the summer, when heat loss is not a problem, position the dust extractor outside so fine dust is not returned to the workshop. (d) Minimize the sanding. Use sharp tools and develop your skill to the point where very little sanding has to be done. (e) Try using the wet sanding method which does not produce dust.
MORE ABOUT THE HEALTH HAZARD OF DUST
Fine wood dust is bad for you, especially if you have any respiratory problems. Even if you feel that dust does not bother you, it can have a cumulative effect eventually resulting, if you are very unlucky, in permanent damage to your health.
Power sanding is particularly good at filling the air with dust. The fine dust is the most dangerous and the most difficult to get rid of. The shavings and the large particles of dust are not much of a problem as most of it falls to the floor quickly and lungs have a built in mechanism which can eject relatively large particles. (If you smoke, the little hairs inside your lungs which do the work, may become damaged, so smokers are more vulnerable to wood dust.) Fine dust, however, hangs about in the air and if you breath it into the deepest parts of your lungs it can become trapped in there and cause all sorts of problems. The dust particles that cause damage are normally in the range of 0.2 to 5 microns in size (a micron is one thousandth of a millimetre) and are so small as to be invisible to the naked eye. They can remain suspended in the air for hours. Even if you cannot see any dust the atmosphere may still be harming your lungs. You are likely to breath 8 to 10 cubic metres of air during an 8 hour working day. If the dust in the air averages out to, say, 5mg per cubic metre during that period then you will suck in 50gm (2 ounces) of dust. Most of this will be dealt with by the body\'s own dust defence mechanism - the nasal hair and the mucus lined walls of the airways leading to the lungs. You will, in fact, swallow most of it. Only a very tiny percentage of the dust is permanently trapped in the lungs but it is this which causes the damage. 5mg/cubic metre is a very high concentration and is, in fact, the maximum exposure level allowed under the COSHH regulations. COSHH means "Control of substances hazardous to health regulations 1988". It applies to all businesses and self-employed persons. You would be wise to abide by its recommendations even if you are only a hobbyist. Dust from some wood can cause skin complaints such as dermatitis. You should avoid carrying dust out of the workshop on your clothes - leave your overalls in the workshop when you leave - wash your hands and hair frequently. Most species of wood including home grown timber can be harmful but some species (mainly tropical) are much worse. Avoid, if possible, monsoon, cherry mahogany, redwood, beech, South American boxwood, Western red cedar, satinwood. To give only a few examples, pine, afrormosia, mahogany, boxwood, chestnut, cedar, iroko, ebony, rosewoods, beech, ramin, walnut, larch, spruce, teak, padauk, yew, cherry and oak are known to cause dermatitis, conjunctivitis, rhinitis and asthma. Turning wood with cutting tools does not produce so much of the very fine harmful dust as the process of sanding. It follows that it is healthier to get the best finish from your tools rather than depend on heavy sanding. Sanding to shape should be avoided if at all possible. Scrapers produce a significant amount of dust especially if they are blunt, so you really ought to develop your skill with the gouges and chisels.