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 Le...