Dust Collection Performance using Dylos Meter

[Greg Funk]

For a person who will be exposed to the dust for up to ten hours a day, and up to 40 hours a week, the "permissible exposure limit" for "total dust" is 15mg/m^3. If you limit the dust to what is called the "respirable fraction," the limkt is 5mg/m^3, still five times the figure stated in the earlier thread. OSHA also gives these exposure limits as particle numbers as measured by "impinger samples counted by light-field." These particle number limits are 50 million particles/cu.ft. for total dust and 15 million particles/cu.ft. for the respirable fraction of dust.

John,

Thanks for that very informative post. Do you have any idea what particle size they were talking about for those impinger samples. Those limits seem quite high relative to the numbers I have been seeing where the highest reading is was about 50,000/cu ft. Perhaps they measure smaller particle sizes.

Greg

[John Stevens]

Do you have any idea what particle size they were talking about for those impinger samples.

Hi, Greg. Unfortunately, I don't have any more info. Maybe I'm just missing it, but I can't find any info on particle size for wood dust, which falls under the category of "nuisance dust" in the applicable OSHA regulation. This is odd, because the same table in the same regulation gives sizes for quartz dust. If I'm correct that the reg does not specify particle size for nuisance dust, then my guess is that the specific info on the particle sizes is contained in some document that is available to the public somewhere, but I don't know where, because administrative law ain't my bag. I'd also guess that lots of info on which particle sizes ought/ought not to be measured was presented to OSHA at the time it made its regs, and all such evidence has been incorporated into an official "record" that is available to the public for inspection, again, somewhere.

The info I got was from OSHA's web site, which in turn is quoting OSHA's regulation that's published in the Code of Federal Regulations (CFR). FWIW, the citation is 29 CFR 1910.1000, tables Z-1 (see footnote "(f)" in that table) and Z-3 (see footnote "d" in that table). These tables can be found online at:
http://www.osha.gov/pls/oshaweb/owad...ARDS&p_id=9992
and
http://www.osha.gov/pls/oshaweb/owad...ARDS&p_id=9994
respectively. Unfortunately, the text doesn't say anything about particle sizes.

By the way, I have to add an important qualifier to my last post. From poking around the internet and reading correspondence between a guy at the CDC (Centers for Disease Control) and another guy at NIOSH, there's apparently a lot to know about the various ways of collecting dust particles for counting, the point being that some ways are much more accurate than others.
http://www.osha.gov/pls/oshaweb/owad...ONS&p_id=21109
I should have noted that in my earlier post, because I think that by failing to do so I gave readers a false sense that the particle counts made by us "lay people" would be the same as those made by NIOSH personnel. BTW, NIOSH is a branch of the CDC, and does the testing for OSHA: http://www.cdc.gov/niosh/about.html

Again, sorry for the long, boring post, but I hope this helps somewhat.

Regards,

John

[John Newell]

There is more to this than just particle size, though, no? Some woods produce toxic reactions wholly apart from the issues of having particles lodged in your lungs. That is a non-professional observation from my own experience...but I think it's correct.

[Greg Funk]

There is more to this than just particle size, though, no? Some woods produce toxic reactions wholly apart from the issues of having particles lodged in your lungs. That is a non-professional observation from my own experience...but I think it's correct.

Certainly some woods like cedar and tropical woods are more likely than others to cause problems with certain people. And you can develop an allergy to a few or all types of wood dust. Myself, I haven't really noticed sensitivity to any of the wood species I normally work with so I am concerned with wood dust in general.

Greg

[Wilbur Pan]

It was reported in an earlier thread on this forum, that the OSHA standard is 1mg dust per cubic meter. (http://www.sawmillcreek.org/showpost...&postcount=113) I did a little digging (google "osha wood dust) and found that this is incorrect.

I guess I should apologize for the error, since I was the one that made that post.

[John Stevens]

I guess I should apologize for the error, since I was the one that made that post.

Hi, Dr. Pan. For what it's worth, I think that it was a very understandable mistake, considering that your figure was consistent with the NIOSH and ACGIH recommendations...and administrative law ain't your bag, neither.

I also want to take this opportunity to say that although I haven't agreed with everything you've written on this topic, I've still gained a lot from your contributions, and I'm grateful for your continuing participation in threads like these. I apologize if my link to your earlier post seemed to single you out. I tried to avoid that by not mentioning your name, but I did want to give people a fast way to go back and check the figure that had been given earlier for OSHA standard so that any confusion in that regard would be cleared up.

Regards,

John

[Wilbur Pan]

For a person who will be exposed to the dust for up to ten hours a day, and up to 40 hours a week, the "permissible exposure limit" for "total dust" is 15mg/m^3. If you limit the dust to what is called the "respirable fraction," the limkt is 5mg/m^3, still five times the figure stated in the earlier thread. OSHA also gives these exposure limits as particle numbers as measured by "impinger samples counted by light-field." These particle number limits are 50 million particles/cu.ft. for total dust and 15 million particles/cu.ft. for the respirable fraction of dust.

Thanks for that very informative post. Do you have any idea what particle size they were talking about for those impinger samples. Those limits seem quite high relative to the numbers I have been seeing where the highest reading is was about 50,000/cu ft. Perhaps they measure smaller particle sizes.

Just to put some real world values on these numbers:

I think "respirable fraction of dust" refers to dust particles on the order of 1 micron in diameter or so. If you do the conversion, 1 cubic micron is 6.1 × 10-14 cubic inches. 15 million dust particles/cubic foot would mean a total volume of 0.000000915 cubic inches of wood dust/cubic foot. A typical shop size is 20' x 20' x 10', or 4000 cubic feet, which allows you 0.00366 cubic inches of respirable dust in your entire shop.

Now, the Forrest Woodworker II table 10" saw blade comes with 3/32" and 1/8" kerfs. (I'm not picking on Forrest, I just wanted to pick a table saw blade that anyone would want on their tablesaw.) If you make a cut 3/32" wide in 3/4" thick stock, you'll only need a cut of 1/20" long to make that 0.00366 cubic inches allowed in your shop. Of course, not all the wood in that saw kerf will be pulverized into 1 micron particles. But even if only 0.1% of the wood gets converted into 1 micron particles, and this is a highly conservative estimate, a 52" cut will get you to the same point, or just a bit more than ripping one 4'x8' sheet of plywood in half.

And since I was the one that made the mistake before, I'll amend my previous analysis by saying that if limiting your exposure to 15 mg/m3 of hardwood dust is your goal, 6.6 inches of sawing with a Lie-Nielsen dovetail saw in 3/4" stock will get you there, assuming complete conversion of the wood in the kerf to dust particles. If you are making dovetails in 3/4" stock, and for simplicity assume that each side of a pin or tail is 3/4" (it actually will be 0.756" for a 1:8 dovetail angle), that's just under 9 cuts, or not even enough to finish a dovetail joint with 3 pins/tails.

My main point is that regardless of what the exact numbers or limits you set on wood dust exposure, it doesn't take all that much wood cutting to get you there, which is why having good dust management is key.

[Greg Funk]

Now, the Forrest Woodworker II table 10" saw blade comes with 3/32" and 1/8" kerfs. (I'm not picking on Forrest, I just wanted to pick a table saw blade that anyone would want on their tablesaw.) If you make a cut 3/32" wide in 3/4" thick stock, you'll only need a cut of 1/20" long to make that 0.00366 cubic inches allowed in your shop. Of course, not all the wood in that saw kerf will be pulverized into 1 micron particles. But even if only 0.1% of the wood gets converted into 1 micron particles, and this is a highly conservative estimate, a 52" cut will get you to the same point, or just a bit more than ripping one 4'x8' sheet of plywood in half.

Wilbur,

Interesting analysis but I don't think you have a good basis for your assumption that .1% of the wood gets converted to 1um particles. Based on literature I have seen the bulk of the fine particles are >10um in size. The vast majority of the output of a saw cut is in the form of shavings or chips. Of the small portion that gets converted into fine dust there is a much smaller portion that gets converted into respirable particles.

One data point I would provide is that based on the measurements I took where I saw 500,000 particles/cu-ft 1um or smaller and assuming for the worst case that all particles were 1um in diameter, my calculations would indicate that the 1um particles contribute .005 mg/m^3 to the dust load. For the larger particles it is more difficult as I believe the meter counts all particles larger than 5um. If you assume the average larger particle size is 20um then you would get a load of just over 7mg/m^3 from the larger particles.

In any case I agree with your conclustion regarding the importance of good dust collection.

Greg

[Wilbur Pan]

Interesting analysis but I don't think you have a good basis for your assumption that .1% of the wood gets converted to 1um particles. Based on literature I have seen the bulk of the fine particles are >10um in size. The vast majority of the output of a saw cut is in the form of shavings or chips. Of the small portion that gets converted into fine dust there is a much smaller portion that gets converted into respirable particles.

Take a look at the Report on Carcinogens Background Document for Wood Dust, from the December 13 - 14, 2000 Meeting of the NTP Board of Scientific Counselors Report on Carcinogens Subcommittee, which was prepared for the U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program.

Table 2-6 on page 20 of this report measures the distribution of particle size from various woodworking operations involving oak, ash, beech, and particle board. The percentage by mass of 0.65–1.1 μm particles is 0.5-3.0%, which makes my guesstimate of 0.1% not unreasonable.

This set of data lumped dust particles 9 μm and larger in one category. The percentage of all particles less than 9 μm from these woodworking operations ranged from 27.4-55.6%.

[Greg Funk]

Take a look at the Report on Carcinogens Background Document for Wood Dust, from the December 13 - 14, 2000 Meeting of the NTP Board of Scientific Counselors Report on Carcinogens Subcommittee, which was prepared for the U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program.

Table 2-6 on page 20 of this report measures the distribution of particle size from various woodworking operations involving oak, ash, beech, and particle board. The percentage by mass of 0.65–1.1 μm particles is 0.5-3.0%, which makes my guesstimate of 0.1% not unreasonable.

This set of data lumped dust particles 9 μm and larger in one category. The percentage of all particles less than 9 μm from these woodworking operations ranged from 27.4-55.6%.

OK I'll read the paper.

You may also want to look at a paper - "Comparison of wood-dust aerosol size-distributions collected by air samplers" from the Journal of Environmental Monitoring (http://www.rsc.org/publishing/journa...p?doi=b312883k) in particular have a look at figure 2.

Greg

[Greg Funk]

Table 2-6 on page 20 of this report measures the distribution of particle size from various woodworking operations involving oak, ash, beech, and particle board. The percentage by mass of 0.65–1.1 μm particles is 0.5-3.0%, which makes my guesstimate of 0.1% not unreasonable.

Wilbur,

They are referring to the % (by mass) of particles that are airborne not the % of total wood released by the sawing operation. You may be correct but the article you cited doesn't provide any indication of the amount of wood released as airborne particles.

I suspect you may be close if you were talking about a sanding operation where a much higher percentage of the wood becomes airborne. I know from personal experience that it doesn't take much hand sanding before the environment becomes filled with dust and unpleasant.

Maybe I'll run another test this afternoon with some hand sanding...

Greg

[Will Blick]

I think Wilburs example is a good one..... regardless if his estimate of .1% is accurate, its a moot point, cause even if its .01%, just 10x the small cut size he based his calcs on, and you get to the same place. Add some sanding, and you probably 10x this again... etc.

We all run the risk of becoming overly analytical with these tools, I am no exception....but I am trying hard to simply use the meter as a benchmark or a reference to comprehend what is going on in terms of dust...specially before, during and after certain shop operations. I am just as interested in the household air, and the ambient air in my city as it compares to others I am not discouraging posts by any means...

I just got my .5/2.5 unit.... As with most meters, I am dumbfounded by the results. First, my house is reading 800/20. Obviously lots of fine particles, not happy about that... I suspect its from carpeting... a vacuum cleaner is a huge dust generator.... I may consider a super hepa system like a Miele...

My shop, which has been idle for a week, registered 100/20... amazing, has more fine particulate than my shop. I will monitor my shop and report back....but I exhaust my Cyclone outside, and I run a continous exhaust.... so I don't fear too many problems, other than while in the process of sanding, cutting, etc. Bill Pentz made a lot of great contributions to this field, but the one that is the most obvious and effective is to use a cyclone and exhaust outside, and/or leave the work space open to the outside, give the dust a place to move. Of course, wearing a good respirator is the most important factor.

But back to results.... I checked outside, a windy day here in the desert... 1800/50... WOW! Its safer to be sanding wood! This can certainly explain a lot of the headaches on windy days....

Whats really interesting is.... i run an expensive .3 micron air filter in my bedroom, huge filter, probably 7 sq ft of media 3" thick... however, the results are no better the the rest of the house. EDITED AND CORRECTED WITH POST BELOW

What I would love to rig up this experiment .... take my 3m respirator filters and force air through them, with the exhaust air feeding the meter..... I am curious how effective these filters are.

Well, lots of experimentation to do....sure wish this thing had a batter pack option... i may rig up one...

As for previous comments regarding the type of particles. I think its obvious, certain particles are allergens to some people, but not to others, just like pollens. Unfortunately, some wood types have a high "hit rate" as allergens. However, from what I have gathered, even if you are not allergic to the particles, high concentrations of any small particles can't be healthy.

[Phil Thien]

Whats really interesting is.... i run an expensive .3 micron air filter in my bedroom, huge filter, probably 7 sq ft of media 3" thick... however, the results are no better the the rest of the house. Makes me wonder about how substantiated some of the claims these makers have... this meter sure gives us "eyes" into seeing what is actually happening. Of course, I am assuming the meter is accurate.

Will,

Could your HVAC system be at play? Perhaps a forced air system that is changing the air in the room faster than the .3 micron filter can clean it?

For other results posters, it would be helpful to know what kind (if any) HVAC systems are in place where tests are performed.

Thanks,
Phil

[Will Blick]

> Could your HVAC system be at play?

Sorry, I should have mentioned, I have self contained HVAC system for the bedroom only.

However, I just learned something fascinating with the meter.... when you are full of dust (which it appears we can be, without even knowing it) you can't stand near the meter, cause you become the source of the dust. I was standing by the meter for a minute and hence the results I reported above.... then I left the meter plugged in, went back in 15 minutes and it has been reading 150 ever since.... so lesson learned - get away from the meter, let it settle. So, good news, really expensive air cleaners really work. I bought a new filter for it ($199), since this one has reached its life expectancy of 5 years. IIRC, this one filters down to .3 micron. Anyway, I always assumed it was best to have the cleanest air where you breathe the most, i.e. in your bedroom. Here is a link of the one I own

http://www.austinair.com/healthmate.php

Next I am curious about the effectiveness of HEPA vacuum cleaners. I am convinced most house dust comes from vacuums that stir the dust out of the carpet, the bag / cyclone catches the big particles and the rest shoots out the exhaust, and based on the post above, these particles float around for several weeks, which by then, we have vacuumed again.... carpets are huge dust producers, constantly shedding.... and the beater brushes on the vacuum just add to the problem... sheeeeesh....

[Rob Blaustein]

Some preliminary results with my 1um/5um unit.
Relevant info: Basement shop, about 13' x 19'. House has forced hot air, furnace/blower in a different room in the basement. I use a 3M ultra allergen 1200 pleated filter in the furnace.

Baseline shop reading fluctuates from 25/0 to 80's/5. If I run my Jet AFS 1000B filter (hanging from my 8 ft ceiling) at medium for 10 min, it gets down to 20/0. I am making some bookshelves and just cut up some 3/4" plywood. I made 6 cuts, each 5 ft long, so I cut about 30 linear ft of 3/4 ply in a 5-10 min period. My DC is a Jet DC1200 with a Wynn upgrade cannister filter, plastic bags below. I run a 4" diam flex hose to the base of the cabinet saw, and a 4" diam flex to my Excalibur overarm guard. The duct runs are quite short so I don't think there is much static pressure loss. Anyway, I was amazed at how good the dust collection was (note: I wasn't running the Jet air filter during the cuts, just the DC). The meter peaked at maybe 150/25 or so. Again, running the air filter for 10 min brought it down to 20-30/0-2. I then applied some edgebanding and noticed that after I ran some 220 grit along the edges to smooth them out, the meter hit the 300/50 range. So I generated more dust in the air with that little bit of sanding than by cutting up the sheet goods with the combined DC from below and above. At some point I'll also check what happens when I don't use the overarm guard DC. I also now want to check what happens in the rest of the house, particularly after the heat comes on. One thing I'm curious about: in the morning when the sun comes into our bedroom through a window above our bed, I can see the scatter from lots of dust--I wonder what the Dylos would read there. I'll keep you posted.
--Rob