[Note: I know dust collection and the safety of dust is a contentious topic around here. I was concerned about using a shop vac instead of a dust collector with my tools and set out to try to figure out how much of a price I may be paying by not having room to setup a larger dust collector and giant air scrubber. I do not wish to start any wars, just report my findings which I find somewhat reassuring and may be reassuring to those of you using shop vacs as well.]
Background: My shop is in my basement. I have a Ryobi BT3K, a small Inca (8-5/8" wide but short bed) jointer/planer, Inca 9-1/2" bandsaw, A Ridgid oscillating belt sander, and a router table with downdraft box. I use a Ridgid shop vac with 2-1/2" flex hose network for "dust" collection (along with a separator).
All my tools have 2-1/2" or smaller ports. I have a couple of different dust collectors but I don't use them because I just can't run 4" piping (perhaps some day I will figure out a way to do this--my shop is TINY). My shop vac gets about 150-160 CFM w/o separator. With the separator and network I get about 125-CFM. Absolutely not enough for collection of fine dust.
So the more I read Bill Pentz's site (among others) the more concerned I've gotten that I'm breathing boxcar loads of super-fine dust. That, this dust never settles and every time I enter the shop I breath more of it.
I realize my setup is sub-optimum, but the question is, how much of a price am I paying for it?
Recently I stumbled upon a particle counter that is really geared towards homeowners. It uses a laser to count particles in two sizes.
From the manual:
The meter comes with a table to help interpret the readings:"Small particles are all particles detected by the DC1100 right down to its detection limit--typically below 1-micron. Large particles are all particles detected above the large particle threshold which is typically around 5 microns."So I got this thing and plugged it in in my basement and let it settle for a half hour or so. I had not used any tools for at least 24-hours.0 - 25 Excellent Air Quality
25 - 50 Very Good
50 - 100 Good
100 - 350 Fair
350 - 1000 Poor
1000 + Very Poor
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).
So I switched on the vac and started to cut some MDF. I basically cut the edge off a 3/4" thick piece of 24" long MDF, taking about six swipes. This type of cut (where the blade isn't buried in the wood but rather the left edge of the blade is exposed) seems to generate the largest amount of visible dust above the saw.
I then switched off the saw and watched the meter spike. Approx. one minute after I was done cutting, the meter hit a max of 1955/515. So 195,500 particles (down to 1-micron) and 51,500 larger than 5.0 microns. Nearly twice the 1000+ reading that garners a "poor" rating from their table.
Subsequent readings:
+3 minutes (from peak): 1001/223
+9 minutes (from peak): 499/91
+46 minutes (from peak): 54/2 (now, it could have been low for a while, I had to go upstairs and wasn't paying super-close attention to the meter).
I'm taking for granted that the meter does, in fact, measure down to under 1-micron. However, I will say that the meter is extremely sensitive. Just moving around in the area (within six feet of the meter) causes readings to climb.
Some interesting factors: Above the saw is a vent from the furnace. The furnace has a Honeywell electronic air cleaner. When I close this vent, and let the [new] fine dust air cleaner (down to .3-micron) filter run for just fifteen or so minutes, the meter gets down to 18/1. With the vent reopened the meter almost immediately climbs to 50ish/3-4ish. So my take on this is that, with the vent open, the air from the rest of the house dilutes the super dirty air the table saw creates as I cut. So after cutting the #'s peak, but then fairly quickly start to drop again.
It is too early to make any real generalizations. I hope to use the meter to improve dust collection/filtering in my shop, home, and office (where we service PC's that are full of dust--similar issues to home wood shop).
BTW, the black thing is the meter, the big thing sitting on the floor is my new fine air filter.