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 in general see particles larger than 40 microns.

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

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 0.1 - 50
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 - 0.8
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
Ground Limestone 10 - 1000
Hair 5 - 200
Human Hair 40 - 300
Human Hair 60 - 600
Humidifier 0.9 - 3
Insecticide Dusts 0.5 - 10
Iron Dust 4 - 20
Lead 0.1 - 0.7
Lead Dust 2
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
Pollens 10 - 1000
Radioactive Fallout 0.1 - 10
Red Blood Cells 5 - 10
Rosin Smoke 0.01 - 1
Saw Dust 30 - 600
Sea Salt 0.035 - 0.5
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 3 - 40
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 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

Related Documents

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