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  1. #1
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    Default DRAFT: FAQ - Dust Extraction (Theory)

    This FAQ has been created to provide some guidance for new woodworkers. At the time of creating this thread the forum had determined there was a need to clearly state some facts to alert those entering the field there are a number of dangers and misconceptions. What follows is hopefully brief and easy to read.

    Wood dust becomes a potential health problem when wood particles from processes such as sanding and cutting become airborne. Breathing these particles may cause allergic respiratory symptoms, lining of your lungs and non-allergic respiratory symptoms, and cancer.

    Gunnaduit's Wiki Work
    One of our forum members has commenced work on an authoritative wiki, if you are looking for citations then you need to go here:
    Wikipedia talk:Articles for creation/Health hazards and exposure control of wood dust - Wikipedia, the free encyclopedia

    Stuff about dust. (looking for a place to put this stuff)
    The primary objective with dust is to get it out of the shed if you can.
    Not all woodworking dust is the same. Different timbers have different levels of risk to health, but it is probably true to say that none are good and some are very bad.
    Dust collector, cyclones and any other filtering device should, where possible be placed externally to the workshop and preferably in a way that the air to the workshop is not drawn in from that direction. A small lawn locker or similar will suffice to house a DC providing it has itself sufficient ventilation. Space constraints will still make this difficult for some woodworkers.
    Some people will be more susceptible to wood dust than others particularly in the area of allergic reactions. This is similar to, say, the allergy caused by hay fever. Not everybody is affected. If you experience adverse reactions from any woodworking, stop and do something about it.
    Dust in the workshop comes from two sources.
    1. Initially the use of machinery.
    2. Residual dust that has not been successfully collected. This is the most insidious as it is fine, sometimes invisible and potentially the most likely to create health problems.
    Dust cannot in practical terms be eliminated; Only minimised.
    A fan that blows will always create more problems than it solves. Look towards an exhauster mounted in the wall. An extraction fan if you prefer.

    Can I believe what I read in the Dust Extraction Forum?
    Not always. Some of the information is incorrect and may well prove dangerous over an extended period. It is up to you, the reader, to do your research and identify reliable sources. Ask questions and compare answers.

    Bill Pentz.
    If you are considering learning about dust in the woodworking environment then you should start here. Bill Pentz is widely recognised as an authority on dust collection for recreational woodworkers and has written an excellent article in his blog on Dust Collection Basics.
    Note: Bill is trying to improve his website and is seeking any constructive feedback for improvements. As his site provides a significant resource to woodworkers worldwide you are encouraged to send him an email with your comments. (As his work is unpaid you may also wish to help support his work).


    Bob Loss.
    Another great write up by our very own forum member BobL can be found here - http://www.fwwa.org.au/Art005_WoodDust_c1.pdf

    Is wood dust hazardous to my health?
    YES. Suggest you read this. Here is a snippet "peer reviewed medical research clearly shows every fine invisible dust exposure causes a tiny but measurable respiratory capacity loss and some of this loss becomes permanent, so all exposed to fine invisible dust develop respiratory damage and capacity loss". Further reading here and here.

    Dust vs Chip collection.
    There is a lot of confusion about machines called "dust collectors". These are mostly better called chip collectors, as the more dangerous particles escape and get into your lungs. The most dangerous dust is largely invisible. Further reading.

    From the Pentz site: " typical small shop workers including hobbyists that vent their dust collectors and cyclones inside receive more fine dust exposure in a few hours of woodworking than full time professionals that vent their dust collection outside receive in months"

    If I get perfect air filtration am I safe?
    NO, whilst the risk of inhaling dust is removed, dust coming into contact with your skin can cause dermatitis and other allergic reactions.

    Some Practical Examples and Q's about cost effective dust solutions
    Although not exhaustive and being revised continuously, the aim of this page is to provide the amateur weekend woodworker with some readily available, cost effective advice that can reduce the inhalation of fine dust.

    It is by no means exhaustive, and reflects only the opinions of those that contribute to these Woodwork forums. Some will be irrelevant to your type of woodwork, but the aim is to provide tips and information for those with a basic knowledge of things wishing to learn further.

    Misconceptions about dust masks
    Some may consider they are a simple cheap complete solution for woodworkers. Someone using an ROS for a hour in the shed fills the shed and coats everything in the shed with fine dust. A mask can be worn and continued for 30 minutes thereafter but unless the wood worker changes their clothes and wash themselves they will continue to breathe fine wood dust for as long as they wear the dusty clothes and remain unwashed. It is not good enough to just test the air in the shed, the air under the woodworkers nose has to be tested.

    Even if the woodworker does remove their clothes and wash, the risk has not gone. All the surfaces in the shed are covered in fine dust. Subsequent moment which does not itself create dust, such as dropping a sheet good, starting a non-woodworking power tool like bench grinder, or even having a stereo up loud will continue to fluff the fine dust of the coated surfaces for weeks until all that fine dust has been removed. Wind gusts that minutely change the pressure outside and inside a shed will also fluff dust up in side the shed. We have done tests that show the mere act of opening or closing a door will fluff up dust from surfaces inside a room. If one is worried about fine dust and their only solution is to wear a dust mask this means wearing the mask permanently in a wood working shed whether making dust or not.

    Masks are very useful as a back up to other fine dust removal devices that will remove as much of it as possible it from the shed while it being made. This is especially the case when very large amounts of dust are made, for example a full face air mask in addition to an externally vented DC, and have the front door and window open when ripping larger pieces of wood with something that generates a lot of dust eg tablesaws. Because some of the dust is being continually removed while being made, if other good ventilation equipment or dust collection practices are in place and are kept running after the dust making activity has ceased, the dust mask need also only be worn for a few minutes after heavy dust making has ceased.

    If all you can afford or have on hand is a mask then so be it, it does reduce exposure and is better than nothing at all, but don't be fooled into thinking masks are a total solution to fine woodwork dust.

    Eye protection and skin protection
    Avoidance in the first instance by capture of dust at source is the best solution. For eyes, goggles are an uncomfortable option and unless sealed will still allow some exposure. Full face air shields are much better but they still have limitations (insert reasoning here).

    For skin, regular clothing that covers all skin area provides a small benefit but don't forget the human body covered in anything other than skin and air tight clothing acts like a set of bellows. Just reaching out and picking up a tool compresses the clothing against the skin and blows air out of cuffs and necklines etc. Then relaxing the arm creates a small vacuum inside the sleeve and air (containing dust) is sucked into the cuff and collar regions. In clean rooms garments with elasticised cuffs and collars are used to prevent human dust getting out. These are not always that comfortable to wear particularly if one wishes to do something relaxing like woodwork.

    Skin irritation can also be as simple as touching an offending species, or in dust, shavings, sap, bark or complete form. Some examples may include those (insert some eg’s here) such as Silky Oak.

    Is there a benefit in moving machinery outdoors?
    Yes. However the misconception can be that no dust is then being generated. A good quality mask and ensuring contaminated clothing is removed after is likely still be necessary.

    Mobile bases are readily available in kit form, or can be made with a few locking castor wheels and some hardwood rails.

    What about a room air filter or pedestal fan to blow dust towards an opening to outside eg door, garage opening?
    While it's better than nothing, one small pedestal fan is not going to much other than stirring up the are in the vicinity of the fan. More than double the benefit is achieved by using two fans, one fan blowing into and one blowing out of openings in opposite walls and preferably one inside stirring up the air so the dust doesn't. However by now it's starting to get noisy.

    Some useful links to WW Forum Threads on these topics
    Dust extraction choices
    BobL's Dusty setup
    http://www.fwwa.org.au/Art005_WoodDust_c1.pdf

    Misconceptions about dust/chip collectors

    Do not under any circumstances place a chip or dust extractor in the same workspace as yourself unless it can filter down to at least .5 micron. If the collector is placed in such a way that the exhaust either through the bag or the filter is returned to the workplace and not filtered to .5 or better you are breathing and recirculating the invisible dust. It is a good rule of thumb to say that the machine should be outside the workshop or if within it should be totally isolated and exhausted in such a way to the outside that the dust cannot return to the building through windows or doors.

    Machine Port Requirements for Good DE Performance

    Al ports should be 150mm/6" for maximum effectiveness. Some machines may require two ducts to the machine such as a table saw and it is best that both at least equal 150mm so as not restrict the main six inch duct that is mandatory for good dust extraction.

    All cabinet based machines must have an air inlet into the cabinet at least equaling the extraction port. If this inlet port is a lesser size than the extraction port the air speed in the cabinet will fall to what can be drawn through the air inlet and the dust could fall out of the air stream. Band saw lower cabinets are particularly poor in this regard. It is always necessary to modify these cabinet based machines as none of them have adequate porting either in size or number.

    How Big Must My Dust Extractor Be?

    If your dust extractor will not support 1000 CFM air flow through a 150mm duct it is too small to collect the fine dust that causes us woodworkers the most issues. Note the 1000cfm is for a configured system, a stated specification may reduce significantly once installed.

    Contributors to this FAQ
    Bill Pentz
    BobL
    Bushmiller
    Groggy
    Gunnaduit
    Mini
    Nickb00
    sjt
    Last edited by dai sensei; 15th July 2013 at 10:17 PM. Reason: added another link to BobL's pdf paper

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  3. #2
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    Default

    While this FAQ is in draft please add comments or criticisms as short posts, use a single topic per post so I don't have to unpick a 200 line single paragraph with 30 topics. As I action them I will DELETE THEM from view.

    When finished this thread will have only one post - the FAQ.

  4. #3
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    Default

    Guys, I am not an expert, just the cut-and-paste guy - give me something I can put in there instead.

    If there is too much (more than a paragraph) make a very short summary and put the rest in another post labelled (for example):

    FAQ - Dust Extraction: Dust masks

    Then link to that post in the short summary. If I put those big chunks in the FAQ people are unlikely to read it.

  5. #4
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    Default

    Please - do not change the font type, size or colour in any submissions, it takes ages to sort it out!

    Hyperlinks, Bold and underline are ok.

  6. #5
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    Default Dust Extraction "Pressure and Flow" graph

    The following graph has been adapted from the graph on this webpage in The Engineering toolbox website and is mostly the same as the one I have been using in many of my posts regarding air flow and

    It shows the pressure losses (in inches of water per 100 ft of smooth bore duct) as a function of flow rate (in CFM) for that smooth bore duct with different diameters. It can also be used as a guide for expected flows resulting in changes of resistance pressure in a system. Because of turbulence effects etc the only way to be certain of flow rates under specific pressures is to measure actual flow rates.

    Compared to the original, this graph has been extended on the right hand side to cover vacuum cleaner pressures 30" +, and I have extended the red lines for the 2, 4 and 6" ducting to these higher pressures - if you need other sizes I'm sure you can work these out for yourself. It also covers higher volume flows which members with bigger DCs might find useful.

    Hopefully the mods will put this into the Dust extraction sticky thread so we can more easily refer to it as needed.
    Flowratesx.jpg

    If you are happy use equations () this will enable you to determine the flow to be calculated at any pressure.

    For 4" ducting the relevant equation is
    Flow (in CFM) = EXP(0.5491*(LN(Press in inches of WC))+4.80052)
    If you uses Excel you can use the equation " =EXP(0.5491*(LN(X))+4.80052)" , where X is the Press in inches of WC
    So at 10" of WC the flow is EXP(0.5491*(LN(10))+4.80052) = 430 CFM

    For 6" Ducting the equation is
    Flow (in CFM) = EXP(0.5358*(LN(X))+5.9365)
    So at 10" of WC the flow rate is 1300 cfm and at 12" it is 1433 cfm.

    Please note this is the MAXIMUM flow rate for smooth bore ducting and will only give you an approximation of the flow rates.

  7. #6
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    Default

    There ya go.

  8. #7
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    Thanks,

    Done this mean I can keep adding to this thread every now and then and it will keep it "addable to"?

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