In imperial units
The eye can in general see particles larger than 40 microns.
Typical size of contaminants and particles are indicated below. Note that the values varies widely depending on how the products are processed. By example milling corn starch in 30 minutes can reduce the average diameter of starch particles from 10 to 0.3 microns (μm, 10-6 m). Further milling may produce particles even smaller than 0.1 microns.
|Anthrax||1 - 5|
|Antiperspirant||6 - 10|
|Asbestos||0.7 - 90|
|Atmospheric Dust||0.001 - 40|
|Auto and Car Emission||1 - 150|
|Bacteria||0.3 - 60|
|Beach Sand||100 - 10000|
|Bone Dust||3 - 300|
|Bromine||0.1 - 0.7|
|Burning Wood||0.2 - 3|
|Calcium Zinc Dust||0.7 - 20|
|Carbon Black Dust||0.2 - 10|
|Cayenne Pepper||15 - 1000|
|Cement Dust||3 - 100|
|Clay, coarse||2 - 4|
|Clay, medium||1 - 2|
|Clay, fine||0.5 - 1|
|Coal Dust||1 - 100|
|Coal Flue Gas||0.08 - 0.2|
|Coffee||5 - 400|
|Combustion||0.01 - 0.1|
|Combustion-related - motor vehicles, wood burning, |
open burning, industrial processes
|up to 2.5|
|Copier Toner||0.5 - 15|
|Corn Starch||0.1 - 10|
|Dust Mites||100 - 300|
|Eye of a Needle||1230|
|Face Powder||0.1 - 30|
|Fertilizer||10 - 1000|
|Fiberglass Insulation||1 - 1000|
|Fly Ash||1 - 1000|
|Gelatin||5 - 90|
|Ginger||25 - 40|
|Grain Dusts||5 - 1000|
|Gravel, very fine (0.08 inch)||2000|
|Gravel, fine (0.16 inch)||4000|
|Gravel, medium (0.3 inch)||8000|
|Gravel, coarse (0.6 - 1.3 inches)||15000 - 30000|
|Gravel, very coarse (1.3 - 2.5 inches)||30000 - 65000|
|Ground Limestone||10 - 1000|
|Hair||5 - 200|
|Household dust||0.05 - 100|
|Human Hair||40 - 300|
|Human Sneeze||10 - 100|
|Humidifier||0.9 - 3|
|Insecticide Dusts||0.5 - 10|
|Iron Dust||4 - 20|
|Lead, solder radiator manufacturing - mean value||1.3|
|Lead, battery and lead powder manufacturing||12 - 22|
|Lead Dust||0.1 - 0.7|
|Liquid Droplets||0.5 - 5|
|Metallurgical Dust||0.1 - 1000|
|Metallurgical Fumes||0.1 - 1000|
|Milled Flour, Milled Corn||1 - 100|
|Mist||70 - 350|
|Mold||3 - 12|
|Mold Spores||10 - 30|
|Mustard||6 - 10|
|Oil Smoke||0.03 - 1|
|Paint Pigments||0.1 - 5|
|Pesticides & Herbicides||0.001|
|Pet Dander||0.5 - 100|
|Pollen||10 - 1000|
|Radioactive Fallout||0.1 - 10|
|Red Blood Cells||5 - 10|
|Rosin Smoke||0.01 - 1|
|Sand, very fine (0.0025 inch)||62|
|Sand, fine (0.005 inch)||125|
|Sand, medium (0.01 inch)||250|
|Sand, coarse (0.02 inch)||500|
|Sand, very coarse (0.02 inch)||500|
|Saw Dust||30 - 600|
|Sea Salt||0.035 - 0.5|
|Silt, coarse (0.0015)||37|
|Silt, medium (0.0006 - 0.0012 inche)||16 - 30|
|Silt, fine||8 - 13|
|Silt, very fine||4 - 8|
|Skin flakes||0.5 - 10|
|Smoke from Natural Materials||0.01 - 0.1|
|Smoke from Synthetic Materials||1 - 50|
|Smoldering or Flaming Cooking Oil||0.03 - 0.9|
|Spanish Moss Pollen||150 - 750|
|Spider web||2 - 3|
|Spores from plants||3 - 100|
|Starches||3 - 100|
|Sugars||0.0008 - 0.005|
|Talcum Dust||0.5 - 50|
|Tea Dust||8 - 300|
|Textile Dust||6 - 20|
|Textile Fibers||10 - 1000|
|Tobacco Smoke||0.01 - 4|
|Typical Atmospheric Dust||0.001 to 30|
|Viruses||0.005 - 0.3|
|Yeast Cells||1 - 50|
Airborne particles are solids suspended in the air.
Smaller dust particles can be hazardous for humans. In many jurisdictions dust fractions at specified particle sizes in working environments are required to be measured.
Airborne particles which can enter the nose and mouth during normal breathing. Particles of 100 microns diameter or less.
Particles that will pass through the nose and throat, reaching the lungs. Particles of 10 microns diameter and less. Referred to as PM10 in the USA.
Particles that will penetrate into the gas exchange region of the lungs. A hazardous particulate size less than 5 microns. Particle sizes of 2.5 micron (PM2.5) are often used in USA.
The total allowable particle concentration - building materials, combustion products, mineral fibers and synthetic fibers (particles less than 10 μm) - specified by EPA (U.S. Environmental Protection Agency)
Material properties of gases, fluids and solids - densities, specific heats, viscosities and more.
Exposure limits for various air contaminants.
Air filters efficiency and arrestance.
The National Fire Protection Association (NFPA) hazard system for chemical materials.
Clean rooms virtually free of contaminants like dust or bacteria.
Clean room class limits according ISO Standard 14644-1.
Strainers and filters - mesh size vs. particle diameter opening size.
ppm - or parts per million - is commonly used as a unit of concentration.
Particle sizes for common products like coal, sand, ash and more.
Flow velocities in slurry transport systems to avoid settling of solids.
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