Allowable limits
OSHA wood dust is classified as a nuisance dust PEL is 15 mg / cubic meter
ACGIH (American Council of Government Industrial Hygienists) recommends
Hardwood 1 mg / cubic meter
Softwood 5 mg / cubic meter

Figuring an average density for wood of 500 kg / cubic meter

At 1 mg / cubic meter you are allowed this many particles

particle size - number
0.5 - 307,692,307,692
1 - 38,461,538,462
5 - 305,343,511

However the Dylos meter only counts particles of 2 sizes and there are many more particles of different sizes.

Here is how I did it.

Wood - seasoned & dry kg/cu.m
Afromosia 705
Apple 660 - 830
Ash, black 540
Ash, white 670
Aspen 420
Balsa 170
Bamboo 300 - 400
Birch (British) 670
Cedar, red 380
Cypress 510
Douglas Fir 530
Ebony 960 - 1120
Elm ( English ) 600
Elm ( Wych ) 690
Elm ( Rock ) 815
Iroko 655
Larch 590
Lignum Vitae 1280 - 1370
Mahogany ( Honduras ) 545
Mahogany ( African ) 495 - 850
Maple 755
Oak 590 - 930
Pine ( Oregon ) 530
Pine ( Parana ) 560
Pine ( Canadian ) 350 - 560
Pine ( Red ) 370 - 660
Redwood ( American ) 450
Redwood ( European ) 510
Spruce ( Canadian ) 450
Spruce ( Sitka ) 450
Sycamore 590
Teak 630 - 720
Willow 420


Reference 1
volume=4/3Άr3
A one micron particle has a .5 micron radius and a volume of 0.52 cubic microns
1 micron particle = 0.5 micron radius = volume of 0.52 cubic microns
0.5 micron particle = 0.25 micron radius = volume of 0.065 cubic microns
5 micron particle = 2.5 micron radius = volume of 65.5 cubic microns

Reference 2
1 cubic meter = 1.0 Χ 1018 cubic microns (10 followed by 18 zeroes)
10,000,000,000,000,000,000

500 kg / cubic meter density of wood – sort of an average - see chart

1 kilogram = 1,000,000 milligrams

500,000,000 mg / cubic meter density of wood – sort of an average - see chart

A solid cube of that is one cubic meter would have 500,000,000 mg. of wood in it and a volume of 10,000,000,000,000,000,000

If you are allowed 1 mg weight then you are allowed 20,000,000,000 particles of 1 micron volume

Reference 1 - http://grapevine.abe.msstate.edu/~fto/tools/vol/sphere.html

Reference 2 - http://www.google.com/intl/en/help/f...tml#calculator