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Particle Sizes

The size of dust particles, pollen, bacteria, virus and many more.

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The size of contaminants and particles are usually described in microns, a metric unit of measure where

  • one micron is one-millionth of a meter
  • 1 micron = 10-6 m = 1 μm

In imperial units

  • 1 inch = 25400 microns
  • 1 micron = 1 / 25400 inch

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.

Particle Sizes
ParticleParticle Size
(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
Carbon Dioxide 0.00065
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
Dot (.) 615
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
Glass Wool 1000
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
One inch 25400
Oxygen 0.0005
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
  • one micron is one-millionth of a metre
  • 1 micron = 10-6 m
  • 1 micron = 1000 nano metre

Airborne particles

Airborne particles are solids suspended in the air.

Larger particles - larger then 100 μm

  • terminal velocities > 0.5 m/s
  • fall out quickly
  • includes hail, snow, insect debris, room dust, soot aggregates, coarse sand, gravel, and sea spray

Medium-size particles - in the range 1 to 100 μm

  • sedimentation velocities greater than 0.2 m/s
  • settles out slowly
  • includes fine ice crystals, pollen, hair, large bacteria, windblown dust, fly ash, coal dust, silt, fine sand, and small dust

Small particles - less than 1 μm

  • falls slowly, take days to years to settle out of a quiet atmosphere. In a turbulent atmosphere they may never settle out
  • can be washed out by water or rain
  • includes viruses, small bacteria, metallurgical fumes, soot, oil smoke, tobacco smoke, clay, and fumes

Hazardous Dust Particles

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.

Inhalable Dust

Airborne particles which can enter the nose and mouth during normal breathing. Particles of 100 microns diameter or less.

Thoracic Dust

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.

Respirable Dust

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)

  • 50 μg/m3 (0.000022 grain/ft3) - allowable exposure per day over the course of 1 year
  • 150 μg/m3 (0.000022 grain/ft3) - allowable exposure over 24 hours
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    Material properties of gases, fluids and solids - densities, specific heats, viscosities and more.

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