Dust Collection Performance using Dylos Meter

[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

[Rob Will]

I have my Dylos meter set up in the shop.
One of my employees had cleaned up in there this afternoon.
When I went in the shop about 4 hours later, the reading was about 165/35. At that point, I turned on my furnace fan and the particulate count quickly (in about 5 minutes) dropped to 35/1.

The machine room area is 32 x48 16 and my furnace moves about 1200 cfm. This means that the furnace fan would take about 20 minutes to change the air in the shop. If the clean air from the blower disperses evenly within the shop then that means that every 20 minutes I am actually only filtering half of the air. At the end of one hour, I have filtered 7/8 of the air in the shop (???).

So here's the weird part: Why does the reading from the Dylos meter drop so quickly --- when at the end of 5 minutes, I have actually only filtered 25% of the air in my shop?

One possibility would be if my Dylos meter was positioned on the opposite wall from the furnace registers and I am sending over a "curtain" of clean air that washes down the wall and across the meter (?).

One of the tractor companies is sending me to the Daytona 500 this weekend !!! so I don't have time to test this. In the meantime, I would be interested in your thoughts on this and if the meter's location within your shop makes a difference (??).

Note: my woodshop furnace is equipped with a purpose-built two-stage air filter and I intend to monitor the negative pressure within the blower compartment (to guard against a clogged filter creating temperature rise problems). So far the furnace based system seems to be many times more effective than my ceiling mounted air cleaner (Delta 3-speed) -- and a lot easier to service.

Rob

[Greg Funk]

So here's the weird part: Why does the reading from the Dylos meter drop so quickly --- when at the end of 5 minutes, I have actually only filtered 25% of the air in my shop?

One possibility would be if my Dylos meter was positioned on the opposite wall from the furnace registers and I am sending over a "curtain" of clean air that washes down the wall and across the meter (?).

Rob,

I suspect something similar in my shop. I went in the shop today and just ran the dust collector for a while. The count dropped from about 100 down to 40. I then shut it off and left it and the count climbed back up to 80 over a 2 hour period. I suspect there are air currents that take a while to settle down.

Do you have a 1/5 or the .5/2.5um version?

Greg

[Rob Will]

Rob,

I suspect something similar in my shop. I went in the shop today and just ran the dust collector for a while. The count dropped from about 100 down to 40. I then shut it off and left it and the count climbed back up to 80 over a 2 hour period. I suspect there are air currents that take a while to settle down.

Do you have a 1/5 or the .5/2.5um version?

Greg

Greg,
I have the 1/5 version
Rob

[Will Blick]

I wonder if the speed of the particles effects the readings? This could account for the lower readings.... the particles are there, but the Dylos can't see'em above a certain speed?

Like every tool, lots of experimentation is in order :-(

[Rob Will]

I wonder if the speed of the particles effects the readings? This could account for the lower readings.... the particles are there, but the Dylos can't see'em above a certain speed?

Like every tool, lots of experimentation is in order :-(

I thought the Dylos uses a fan to draw air through ??
I wondered about this as well.

Rob

[Will Blick]

It does have a fan.....but maybe that is the only accurate air speed it will read the particles. if the inlet has induced air, the total air speed will increase over the sensing device.... just a thought, I see some strange movements also.

Ceiling fans also stir up dust....arggggg.... I can drop a rooms particle count by 50% by turning off the ceiling fan...

[Rob Will]

I went back out to the shop and moved my meter closer to the furnace air intake rather than on the opposite wall where "clean" air blows directly on it.

It seems that I get smoother data with the Dylos on the end of the room by the air cleaner intake (not too close). This is probably more representative of the overall particle count in the room. The air has had more time to mix and some of the turbulence from the blower has settled down.

On a different note here is my air:
Start - empty shop - no recent activity: 85/5
Furnace blower on for 3 minutes: 75/2
Furnace blower on for 40 minutes: 20/0
Furnace blower off: 29/1
Wait 5 minutes, furnace blower back on: 29/1
Stomp feet to other end of shop and back - blower on - peak reading 3 min later at 1080/138 then started to drop quickly.

Note the 1 micron level at start: 85
After changing the air twice (40 minutes) 1 micron level = 20

If 1 air change = 1/2 of the air gets cleaned....
and two air changes = 3/4 of the air gets cleaned.....
then the "85" count dropping off to about 20 or 30 seems about right.

I'm guessing that the 1 micron level in my shop would never drop below 15

Rob