US EPA

3584219 

Journal Article 

Rate of decline of asbestos fiber concentration in room air 

Moorcroft, JS; Duggan, MJ 

1984 

Yes 

Annals of Occupational Hygiene
ISSN: 0003-4878
EISSN: 1475-3162 

28 

4 

453-457 

English 

6529076 

10.1093/annhyg/28.4.453 

WOS:A1984ABN5100010 

Asbestos (1332214) fibers falling from the air were investigated. Air samples were taken from a north London school from which the amosite (12172735) ceilings had recently been stripped and the rooms had been cleaned. Samples were collected under conditions of no disturbance and when dust had been deliberately stirred up. All concentrations of asbestos measured without disturbance were less than 0.01 fiber per milliliter. After disturbance, asbestos concentrations increased up to 0.47 fiber per milliliter. Asbestos concentrations decreased from 0.01 to 0.004 fiber per milliliter after 30 minutes of no further dust disturbance. If the equivalent aerodynamic diameter of an asbestos fiber was considered to be 3 times the actual fiber diameter, the settling velocity could be calculated. It took 13 minutes for a 3 micrometer diameter fiber to fall 2 meters, and 480 minutes for a 0.5 micrometer diameter fiber to fall 2 meters. During periods of disturbance, there were very few asbestos fibers attached to dust particles, and there was a predominance of fine fibers. The factor by which the asbestos concentration fell was 1.7 from 30 to 90 minutes when no disturbance occurred, and 10 when there was air disturbance. The authors conclude that the reduction from gravitational settling and ventilation are not sufficient to account for the observed reductions in asbestos concentration. Many asbestos fibers must be intercepted by static charges on room surfaces such as walls and ceilings.