Page 1 of 5 12345 LastLast
Results 1 to 15 of 61
  1. #1
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default Testing mask filter media

    Some of you will know I don't think much of masks as a first line defence for regular wood workshop situations but I'll put that to one side for now.

    Back in 2016 I made up a simple test rig to attempt to measure total dust in air in a workshop where a fine filter was weighed before and after pumping dusty workshop air through the filter for many hours. It looked something like this.

    The pump on the LHS pulled air though the lunch box in which a fine will filter was mounted internally so all the pump pulled dust ladened air though the filter.
    COMPSETUP1.jpg


    The rig had a few problems; like, needing to know the efficiency of the filter material, but more importantly having enough dust in the air so it would change the weight of the filter but I was not prepared to contaminate my workshop with enough to test it out so like a lot of my projects the rig and pump went back into my stash.

    Some of you may also know that SWMBO has been making masks for SARS-2/COVID19 use and I watched a few youtube vids where all sorts of claims are being made about the filtration efficacy of various materials and one thing I noted was that the testing was not being done under expected flow conditions.

    The usual method is to measure dust background levels and then cover the end of a particle counter with a filter material and remeasure counts. This method does not take into account the amount of air that needs to pass through the filter doing normal breathing. Of course fewer counts will be detected if the filter medium restricts the air flow and this will produce a high than expected filter media efficiency.

    After thinking about various ways of doing this I remembered the pump and rig I used in 2016. I decided against using the rig from 2016 as its not easy to replace the filter media and it would not allow for a complete mask to be tested. So I decided to make up a new test box and here is the complete shebang.

    MC is the arduino microcontroller. It the same one I use for my wearable dust monitor.
    The MC is USB connected to the laptop so the data comes out as text in a window on the laptop which I can copy and paste into a spread sheet.
    S is a sealed test box (connected to pump P) and also contains a particle counter that connects by bluetooth to the MC, so MC and S do not have to be next to each other as shown.
    P is a 70L/min pump that sucks air through the test box.


    IMG_4324.jpg

    Below a close up of test box S
    D is a small Dox containing a particle detector.
    Air carrying dust enters through the hole at the top of the test box and exist at P which is attached to the pump.
    Som fo the air enters the side of the small inner box at A in direction shown by the arrow,
    L is a Li-ion battery and V is a Voltage regulator.
    The large hole in the the top of the box is where the filter material is located for testing
    IMG_4329.jpg

    The filter media (in this case a piece cut from a P2 mask) being tested is placed over the hole in the test box and weighted down with a piece of thick walled steel tube to provide a reasonably tight seal.

    IMG_4327.jpg

    The background dust levels are measured with and without the filter media and the ratio of the two give an approximate assessment of the filter media efficiency at different particle sizes.

    My main problem is having enough background dust across all particle size ranges to perform statistically meaningful measurements as the inside house dust levels are currently very low (<1 ug m^3), outside is better but its starting to get warn outside and I'd rather work inside.

    I have done some preliminary measurements on P2 filter media and will post those shortly. I am also going too experiment with burning small incense sticks to see if that makes enough fine dust to work with.

  2. # ADS
    Google Adsense Advertisement
    Join Date
    Always
    Location
    Advertising world
    Posts
    Many





     
  3. #2
    Join Date
    Aug 2007
    Location
    Saskatoon, SK, Canada.
    Posts
    1,436

    Default

    Bob I applaud you for where you are heading with your tests.

    Would a large box or barrel with a hose to your cylinder of steel in which you blast in a measured amount of a known media, maybe a teaspoon of icing sugar, with compressed air work?

    If you get it going would you mind testing two layers of Swiffer Sweeper cloth and if you have one, a piece cut from Miele vacuum cleaner bag? My wife is a nurse and has made a test mask with a pocket in it to hold the filter media for herself if the hospital she is working in runs out of masks. The swifter is cheap and easy to come by and the Miele bag media looks to be even better. She could take a number to work and change them as needed, toss the filters and then launder the masks with the nursing clothes, put in new filters and repeat the next day. I'm not a believer in the "mask made from a T-shirt is better than nothing crowd".

    Pete

  4. #3
    Join Date
    Mar 2014
    Location
    NZ
    Posts
    157

    Default

    BobL, do you know the size of the Covid-19 virus particles? Also considering that Covid-19 particles are spread in moisture droplets, will that make a difference to your tests?
    Very interested in your results.
    Ian

  5. #4
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    Quote Originally Posted by QC Inspector View Post
    Bob I applaud you for where you are heading with your tests.
    Thanks

    Would a large box or barrel with a hose to your cylinder of steel in which you blast in a measured amount of a known media, maybe a teaspoon of icing sugar, with compressed air work?
    Thanks for the idea but I'd rather not pass anything that could absorb water and then become sticky through the dust detector as this will eventually damage the detector. I've been experimenting with solder fumes, and incense. with the latter proving slightly better but I know these fumes are also sticky to some extent. Wood dust would be one of the best as its relatively dry and does not stick quite as easily. This is my biggest problem at the moment so keep the ideas coming.

    If you get it going would you mind testing two layers of Swiffer Sweeper cloth and if you have one, a piece cut from Miele vacuum cleaner bag? My wife is a nurse and has made a test mask with a pocket in it to hold the filter media for herself if the hospital she is working in runs out of masks. The swifter is cheap and easy to come by and the Miele bag media looks to be even better. She could take a number to work and change them as needed, toss the filters and then launder the masks with the nursing clothes, put in new filters and repeat the next day. I'm not a believer in the "mask made from a T-shirt is better than nothing crowd".
    Here are some preliminary results - let me stress they are PRELIMINARY as I cannot control the input dust levels anywhere near as well as I would like.
    The results for the P2 and the Surgical mask are about what I would expect and have seen in the past.
    The cloth mask is made from a medium density flannel but even though it has been washed it could still be emitting bits of material (as could the vac bag) so I need to pump for a longer time to see if I can clear its self generated dust.

    I should state the surgical mask tested is not just a generic mask - it is a "Made in Japan" PM2.5 mask surgical mask as used in government Pathology labs.


    Screen Shot 2020-04-11 at 7.09.51 am.png

    At this stage, if you have some I would be giving a wood working P2 mask to your wife in place of any cloth mask. Fortunately I bought a couple of packets of these masks to clean up MILs place last year. I also have my Triton P2 cartridge full face helmet although going into supermarket wearing one of these might raise a few concerns. Still if it goes totally pear shaped I will wear it in extreme situations.
    Attached Images Attached Images

  6. #5
    Join Date
    Aug 2007
    Location
    Saskatoon, SK, Canada.
    Posts
    1,436

    Default

    Thanks Bob. I could send you a 20 litre pail of MDF dust if you like.

    I do have a couple dozen P95 masks (pretty much the same as your PM 2.5s) and some full face respirators if push came to shove. The problem with them is that if the wife needs them to work in they won't last long hence the search for a home made setup. I looked at a Trend Airshield Pro but ruled it out because of the weight, needing a second set of batteries to get through a 12 hour shift, the difficulty cleaning the innards properly and the high cost of replacement filters. The difference between N95 and P95 masks is the P95s are rated for oil mist as well as the dust.

    The health region is collecting the used N95 masks in the hospital and getting them "cleaned" using some kind of hydrogen peroxide vapour system and supposedly testing them to make sure it works. We don't know if they test every mask or just a sample. The company doing the cleaning say they can do it 10 times and the health region says they are going to limit it to 5 times. I have read a 3M paper that doesn't approve any cleaning method including this one for disposable masks because of degradation of the filter material etc.

    When I go shopping I put on a P95 mask (3M 8271) and nitrile gloves. Also have alcohol hand sanitizer in my pocket and disinfecting wipes in the car. If I have to I'll wear the full face. One store I went to for dog food was spraying every customer's hands with alcohol sanitizer as you walked in. Most are stores are closed and the supermarkets are limiting the numbers of people in the store and clean the conveyer and anything you touch as well as the shopping cart you use. Better to stay 2 metres apart instead of 2 metres under.

    Pete

  7. #6
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    Thanks Pete,

    The problem with handling any bulk wood dust (even sanded MDF) is that ~95% of it is typically >5microns that just gets in the way as it's not what I'm measuring and don't really what I want to be dealing with in my study. The ideal stuff would be the stuff that comes thought a vac cyclone but even though would make a mess. I'm going to persist with the incense even though the study and attached lounge is starting to really reek of patchouli oil.

    BTW I should add that none of my mask material testing deals with the Achilles heel of most face masks and that is how well they seal around the face especially for people with beards. I suspect this reduces the efficiency of a lot of masks that use even high efficiency material to being not that much better than cloth masks.

  8. #7
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    Quote Originally Posted by Flintlock View Post
    BobL, do you know the size of the Covid-19 virus particles? Also considering that Covid-19 particles are spread in moisture droplets, will that make a difference to your tests?
    Very interested in your results.
    Ian
    The size of the SARS-2 virus is supposedly less than 100 nm but apart from ultra high viral load environments, like a ward full of people with raging COVOD-19 where workers wear positive pressure full body suits, its size is almost irrelevant.

    A lone virus say 2m above the ground may be breathed in by a healthy person and is almost certainly going to be breathed back out again. Lone viruses act like <0.3 micron dust particles in that they behave more like an air molecule than a tiny bullet. They don't rattle their way down a respiratory tract/lungs but ride the air current and as such are unlikely to even touch the walls. They then are likely to be expelled out when you breathe out. In open air (ie not attached to surfaces) viruses will not last long.

    Unless you are seriously compromised health wise your immune system should also be able to cope with a few lone viruses - it's when the initial viral load is high and the immune system cannot respond fast enough is probably most likely when you will catch it. Interestingly it also appears to be a "kill mechanism" in that when an infected persons immune system eventually tunes into there being a problem (ie we're being invaded by aliens) that the immune system can flood the body with too many immune response chemicals too quickly (cytokine storm) which can easily kill the patient.

    Im familiar with this as I have an autoimmune disease (sarcoidosis) spread throughout my whole body and for which I take Hydroxychoroqine. It's not a cure - it basically dampens my immune response and reduces the chances of my own immune system over reacting to the disease.

    As you suggest droplets are a different thing. For the average person the greatest viral loads are likely to in droplets expelled by infected persons. The droplets are not a specific size for a couple of reasons. One being the force with which they are expelled (eg a sneeze expels more and bigger droplets) and the air temperature and movement eg breezes with make the droplets evaporate down to smaller sizes. The bigger the droplet the greater the possibility of larger viral load and the greater the chance of impacting and sticking to the respiratory tract

    Regular breathing seems to expel droplets in the <2.5 micron range but exercising, singing, shouting, talking loudly etc will increase the sizes significantly. From what I can tell we should be focussing on stuff similar to wood dust (ie 1-2.5 micron range) since these may contain enough of a significant viral load and if a filter can filter these then it will usually do even more for >2.5 micron droplets.

    Most folks don't realise that exhaling is a whole new-complex ball-game even for very high efficiency mask.

    Super fine dust particles breathed in may inadvertently become larger when breathed out by adhering to fine droplets in exhaled air. So a <100 nm virus going straight through the mask on the way in, may stick to a 1 micron moisture droplet going out while may be trapped on the inside of the mask. Over time this may build up a significant viral load on the inside of masks - this is anther reason why masks should be changed or cleaned/washed often. I'd say wearing any mask for more than a couple of hours at most is asking for trouble - more so in a high SARS-2 environment. Cloth masks can be cleaned/washed. SWMBO cleans her mask after every supermarket visit by spraying it to saturation with an Alcohol/water mix and letting it dry our. I am not allowed into a shopping centre.

  9. #8
    Join Date
    Aug 2007
    Location
    Saskatoon, SK, Canada.
    Posts
    1,436

    Default

    Quote Originally Posted by BobL View Post
    Thanks Pete,

    The problem with handling any bulk wood dust (even sanded MDF) is that ~95% of it is typically >5microns that just gets in the way as it's not what I'm measuring and don't really what I want to be dealing with in my study. The ideal stuff would be the stuff that comes thought a vac cyclone but even though would make a mess. I'm going to persist with the incense even though the study and attached lounge is starting to really reek of patchouli oil.

    BTW I should add that none of my mask material testing deals with the Achilles heel of most face masks and that is how well they seal around the face especially for people with beards. I suspect this reduces the efficiency of a lot of masks that use even high efficiency material to being not that much better than cloth masks.
    I was joking about sending a bucket of dust. I think your Customs folk would have a fit given the way they react to regular wood.

    I'll have to talk to the wife about shaving her beard but I'm pretty sure it will be a resounding No! I'll take a picture of the back of the mask I use in the morning. You'll see why I think it is one of the best disposables around.

    Here is a mask I'm working on. What do you think?

    IMG_4577.jpg

    Pete

  10. #9
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    It could hold a lot of sputum. Reminds me of a Young Ones episode called “Cold”.

  11. #10
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    I remeasure some of the filter materials and a couple of new ones

    P2 is a P2 dust cartridge.
    TJK = Thick Jersey knit. Its the best of the cloth materials I've tested so far BUT it's the the most difficult fabric to breathe through and would cause too much air to be drawn in from around the edges of the mask
    I also tested out some washed T-shirt fabric but it produced more dust than it filtered so I could not determined how much it was filtering.

    Screen Shot 2020-04-11 at 5.06.52 pm.png

  12. #11
    Join Date
    Apr 2001
    Location
    Perth
    Posts
    10,810

    Default

    Bob, I am not aware of this question coming up, but cannot imagine that it has not ...

    How do our woodworking masks rate? I have a Elipse P100 with a choice of P100 filters and P2R nuisance filters (with charcoal), and a 3M 7502 series also with P100 filters.

    I believe that P100 filters to a higher degree than N95 (yes?), and should be helpful for Covid-19 containing spray. Yes, no?

    And are the filters washable?

    Of course, the mind boggles what others might think if one walked through a supermarket wearing one of these masks!

    Regards from Perth

    Derek (busy with Telehealth now).
    Visit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.

  13. #12
    Join Date
    Aug 2007
    Location
    Saskatoon, SK, Canada.
    Posts
    1,436

    Default

    Derek here is a little information about the NIOSH rating system for masks. To the best of my knowledge the filters are not washable.Dust Masks, What's in a Rating | N95, P95, N100 etc.Bob here is a picture of the type of disposable mask I think is the best. The soft rubber seal pretty much stops leaks around the edges when correctly adjusted and worn.Pete
    Attached Images Attached Images

  14. #13
    Join Date
    Apr 2001
    Location
    Perth
    Posts
    10,810

    Default

    Thanks QC

    The reality is that the masks you link to are unavailable, and will be so for some months (I have masks on order, but who know when). So we look at what we have. While searching your link, I came across this ...

    Are N95 Masks Really Effective against the flu?

    A little online research will reveal that the flu virus is .17 microns in size. Clearly smaller than even N100 masks can filter out. However, it is critical to understand that the flu virus does not float in the air by itself. The flu virus is transported from patient to patient on droplets of excretions from sneezing and coughing. These particles are typically 5 microns or larger. When a sick patient wears a respirator, the respirator can be very effective at preventing infectious material from leaving the patients body, and when worn by healthy individuals, it prevents inhalation of said material. More importantly, wearing a mask is a excellent way of preventing the user from rubbing or touching their mouth or nose, which is a very high risk factor. At the end of the day will an N95 mask guarantee to protect you from the Flu? No. But it can substantially reduce your risk or receiving or transmitting the disease.


    Now it occurs to me that if 5 microns is the safe limit, then a mask I have in my workshop, one I have not liked and set aside, may have a use as it is washable. This is the Dustbeegone mask, which the website rates at 3 microns.

    Thoughts?

    Regards from Perth

    Derek
    Visit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.

  15. #14
    Join Date
    Aug 2007
    Location
    Saskatoon, SK, Canada.
    Posts
    1,436

    Default

    Regarding the Dustbegone. The two questions I have are how and who determined that the mask filters down to .3 micron? The second question would be how many washings does it take before there is a degradation of the filtration to where it isn't effective anymore? Kind of the same reason I am sceptical of the RZ type products. Once they achieve a rating from a certifying body I'll consider them.

    It would be nice if the entire world used the same destination system for rating breathing protection.

    Pete

  16. #15
    Join Date
    Apr 2001
    Location
    Perth
    Posts
    10,810

    Default

    Pete, I agree with you. This is the information on the Dustbeegone site ..

    Q. How long will the Dust Bee GoneTM Dust Mask last?

    A. With reasonable care your Dust Bee GoneTM Dust Mask should last three to five years if worn 6 to 8 hours a day.

    Link:
    Dust Mask FAQ's




    Now it would be very nice is this mask was useful for visits to the Supermarket (if so needed). I discarded it for use in the workshop as it only filtered 3-5 microns, and the Elipse and 3M filter to 0.03 microns.

    My interest is driven by my vulnerability. While I am healthy, the reality is that at 70 I fall into the at-risk group. A recent dose of allergy-driven mild asthma convinced me to stop seeing psychotherapy patients face-to-face and turn to Telehealth.

    Regards from Perth

    Derek
    Visit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.

Page 1 of 5 12345 LastLast

Similar Threads

  1. Carbatec pleated filter, new filter element?
    By fletty in forum DUST EXTRACTION
    Replies: 17
    Last Post: 21st November 2019, 12:30 PM
  2. Clearvue CV1800 - to filter or not to filter??
    By Sandy Taylor in forum DUST EXTRACTION
    Replies: 12
    Last Post: 17th June 2019, 05:14 PM
  3. Another media beat-up
    By Shedhand in forum NOTHING AT ALL TO DO WITH WOODWORK
    Replies: 13
    Last Post: 5th December 2009, 05:14 PM
  4. Charcoal Filter for Room Type Dust Filter
    By bitingmidge in forum HAND TOOLS - POWERED
    Replies: 10
    Last Post: 10th December 2008, 04:36 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •