Dust Collection Performance using Dylos Meter

[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

[John Stevens]

I think "respirable fraction of dust" refers to dust particles on the order of 1 micron in diameter or so.

Hi, Dr. Pan. I have a question, if you don't mind the imposition. What does the term "respirable" mean? Can non-respirable airborne wood dust cause serious illness? (By "serious illness," I mean something more than sniffles or a little rash on the skin.)

I only ask because I'm wondering if we might be over-emphasizing concern over respirable particles and under-emplasizing concern over non-respirable airborne particles. Thanks in advance for once again sharing your expertise here.

Regards,

John

[Wilbur Pan]

Hi John,

Actually, the opposite is true.

As most people know, the respiratory tract starts with your windpipe, divides up into the two bronchi that lead to each lung, which then divides into smaller and smaller airways, until you get to the alveoli, which are very tiny thin sacs that are so thin that oxygen simply diffuses right through them and into the blood, while carbon dioxide diffuses from the blood through the alveoli where it is exhaled out. The respiratory tract protects itself primarily through the production of mucus, which traps particles that get into the lungs, and cilia, which are little hairs that line the larger airways of the respiratory tract that move in such a way that they bring the mucous up and out of the lungs, so that you can either hock a goober or swallow it.

Here's a picture of this part of the respiratory tract.

A "respirable" particle is one that can get into the smallest airways of the lungs. A "non-respirable" particle is one big enough that it will get trapped in the cilia or mucous of the larger airways and be carried out of the respiratory tract. After reading through some more sources, it looks like respirable particles are considered to be 5 microns or smaller.

The reason smaller particles are more of a health issue than larger particles is that the smaller particles are the ones that will make it to the smallest airways of the lungs. These airways also are the least protected. They do not make much mucous, they have no cilia to move foreign particles out, and they are very delicate so they get damaged easily.

Here's a picture of the alveoli. You can see that they are much more delicate compared to the larger airways. To put things to scale, a 1 micron dust particle is probably about the size of the white space inside the letter "o" in the word "alveolus" in the picture, so you can see how such a small particle can get down to this part of the lung.

As I mentioned above, larger particles tend to get trapped by mucus in the upper parts of the respiratory tree, and are cleared out by the cilia. On the other hand, airborne particles 1 micron or less are just the right size to get down to the delicate small airways of the lungs. This is also why asbestos is so bad for your lungs: asbestos fibers are also just the right size to get down to the small airways of the lungs and cause damage. The same thing is true for cigarette smoke.

Once particles get down to the small airways, the only thing your body can do to try to remove them is to generate an inflammatory reaction to destroy or break down the particles. Unfortunately, this will also further damage the small airways of the lungs, namely destruction of the walls of the alveoli. (Look at the picture labelled "Emphysema".) This is why this will lead to lung disease like COPD (emphysema). If the particle can't be destroyed, which is the case if it is made of something tough like asbestos or cellulose (sawdust!), it will tend to sit there causing more inflammatory damage.

In a nutshell, I really don't think you can overestimate the potential for damage that respirable dust can do to your lungs. The fact that these dust particles are too small to see and that for the most part, the lung damage occurs slowly over a period of time only adds to the tendency to dismiss this problem.

Wilbur

[Wilbur Pan]

By the way, since I worry that I keep hijacking this thread, I'd like to ask a question that's more relevant.

What units of measurement are used on the Dylos units? I looked at the Dylos website and couldn't figure it out. So when Rob said that his Dylos read 85/5 with his shop not in use, does that mean a concentration of 85 particles per some amount of air volume, or 85 total particles detected by the Dylos from wherever it was sitting?

[Lee DeRaud]

Seems like it's just like real-estate: location, location, location. Plus there's a strong dose of activity, activity, activity added to the mix.

I've got the 0.5/5.0um unit. Just to baseline it, I stuck it on a bookshelf in a room that doesn't get much traffic and put it in 'monitor' mode (samples for one minute every hour). I'm seeing 10:1 variations in the readings over a 24-hour span...when I asked the Dylos tech guy about it, he said that 50:1 was not unusual depending on activity in the area and variations in any outdoor air getting into the room.

(I also discovered it can see fog: got an outdoor reading over 10000 early yesterday morning.)

I'm starting to think these widgets are more valuable for checking long-term trends than this turn-the-saw-on-and-off business.

[Steve Leverich]

Dr. Pan, this from Phil's first post on the Dylos -

"On returning to the shop, it was reading 53/4. You have to add "00" to the end of the readings, so 53/4 translates to 5300 particles total (per cubic foot), with 400 of them being larger than about 5 microns. So far, so good (looking at the table my reading was considered good)."

Here's the thread -

http://www.sawmillcreek.org/showthread.php?t=73486

I'm surprised this info isn't on the Dylos site, although I'm getting the impression it's a small organization - I'd asked Roger about a PDF manual in an email a while back, and he answered that it wasn't on the site yet - still isn't.

HTH... Steve

[Tim Marks]

I see that Dylos has raised the price to $200 each. Guess it is the law of supply and demand... SMC has cleared out their inventory for the forseeable future...

[John Newell]

In a nutshell, I really don't think you can overestimate the potential for damage that respirable dust can do to your lungs. The fact that these dust particles are too small to see and that for the most part, the lung damage occurs slowly over a period of time only adds to the tendency to dismiss this problem.

How much does it matter what the composition is? Is, say, clay dust better than maple dust better than cocobolo dust better than asbestos? Is there a hierarchy, and what factors govern how bad different materials of the same size are?

[Rob Blaustein]

How much does it matter what the composition is? Is, say, clay dust better than maple dust better than cocobolo dust better than asbestos? Is there a hierarchy, and what factors govern how bad different materials of the same size are?

Well we certainly know about asbestos--it tops that list--but the wood dust is trickier to know about. There are many substances the effects of whose inhallation have been fairly well established (e.g. exposure to silica dust causing silicosis), but my sense is that the data for wood dust, particularly different species, are much less available.

--Rob

P.S. Can we go back to calling Dr. Pan, Wilbur? Otherwise we open the floodgates and will soon be using Sir, Professor, Commander, Your Highness, etc...