Particle Sizes

Sizes of airborne particle as dust, pollen bacteria, virus and many more

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

There are

  • 25400 microns in one inch

The eye can see particles to about 40 microns.

The size of some contaminants and particles are indicated in the table below.

Particle Particle Size
(microns)
one inch 25400
dot (.) 615
Eye of a Needle 1230
Glass Wool 1000
Spanish Moss Pollen 150 - 750
Beach Sand 100 - 10000
Mist 70 - 350
Fertilizer 10 - 1000
Pollens 10 - 1000
Cayenne Pepper 15 - 1000
Textile Fibers 10 - 1000
Fiberglass Insulation 1 - 1000
Grain Dusts 5 - 1000
Human Hair 40 - 300
Human Hair 60 - 600
Dust Mites 100 - 300
Saw Dust 30 - 600
Ground Limestone 10 - 1000
Tea Dust 8 - 300
Coffee 5 - 400
Bone Dust 3 - 300
Hair 5 - 200
Cement Dust 3 - 100
Ginger 25 - 40
Mold Spores 10 - 30
Starches 3 - 100
Red Blood Cells 5 - 10
Mold 3 - 12
Mustard 6 - 10
Antiperspirant 6 - 10
Textile Dust 6 - 20
Gelatin 5 - 90
Spider web 2 - 3
Spores 3 - 40
Combustion-related - motor vehicles, wood burning,
open burning, industrial processes
up to 2.5
Fly Ash 1 - 1000
Milled Flour, Milled Corn 1 - 100
Coal Dust 1 - 100
Iron Dust 4 - 20
Smoke from Synthetic Materials 1 - 50
Lead Dust 2
Face Powder 0.1 - 30
Talcum Dust 0.5 - 50
Asbestos 0.7 - 90
Calcium Zinc Dust 0.7 - 20
Paint Pigments 0.1 - 5
Auto and Car Emission 1 - 150
Metallurgical Dust 0.1 - 1000
Metallurgical Fumes 0.1 - 1000
Clay 0.1 - 50
Humidifier 0.9 - 3
Copier Toner 0.5 - 15
Liquid Droplets 0.5 - 5
Insecticide Dusts 0.5 - 10
Anthrax 1 - 5
Yeast Cells 1 - 50
Carbon Black Dust 0.2 - 10
Atmospheric Dust 0.001 - 40
Smoldering or Flaming Cooking Oil 0.03 - 0.9
Corn Starch 0.1 - 0.8
Sea Salt 0.035 - 0.5
Bacteria 0.3 - 60
Bromine 0.1 - 0.7
Lead 0.1 - 0.7
Radioactive Fallout 0.1 - 10
Rosin Smoke 0.01 - 1
Combustion 0.01 - 0.1
Smoke from Natural Materials 0.01 - 0.1
Burning Wood 0.2 - 3
Coal Flue Gas 0.08 - 0.2
Oil Smoke 0.03 - 1
Tobacco Smoke 0.01 - 4
Viruses 0.005 - 0.3
Typical Atmospheric Dust 0.001 to 30
Sugars 0.0008 - 0.005
Pesticides & Herbicides 0.001
Carbon Dioxide 0.00065
Oxygen 0.0005
  • one micron is one-millionth of a meter

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 syntetic 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

Related Topics

  • Material Properties - Material properties - density, heat capacity, viscosity and more - for gases, fluids and solids

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