title: Measured removal rates of chrysotile asbestos fibers from air and comparison with theoretical estimates based on gravitational settling and dilution ventilation.
abstract: BACKGROUND
  Industrial hygiene assessments often focus on activity-based airborne asbestos concentration measurements, but few empirical data exist regarding the fiber removal rate from air after activities cease.
  
  
  OBJECTIVE
  Grade 7T chrysotile indoor fiber settling (FS) rates were characterized using air sampling (NIOSH Method 7402).
  
  
  METHODS
  Six replicate events were conducted in a 58 m(3) study chamber (ventilation 3.5 ACH), in which chrysotile-contaminated work clothing was manipulated for 15 min followed by 30 min of no activity. The fiber concentration decay constant and removal rate were characterized using an exponential decay model based on the measurements.
  
  
  RESULTS
  Breathing zone airborne chrysotile concentrations decreased by 86% within 15-30 min after fiber disturbance, compared to concentrations during active disturbance (p < 0.05). Estimated mean time required for 99% of the phase contrast microscopy-equivalent (PCME) fibers to be removed from air was approximately 30 min (95% CI: 22-57 min). The observed effective FS velocity was 0.0034 m/s. This settling velocity was between 4.5-fold and 180-fold faster than predicted by two different particulate gravitational settling models. Additionally, PCME concentrations decreased approximately 2.5-fold faster than predicted due to air exchange alone (32 versus 79 min to 99% decrease in concentration).
  
  
  CONCLUSIONS
  Other measurement studies have reported similar airborne fiber removal rates, supporting the finding that factors other than gravitational settling and dilution ventilation contribute measurably to PCM fiber removal from air (e.g. impaction, agglomeration).
  
  
  CONCLUSIONS
  Overall, the scientific weight of evidence indicates that the time necessary for removal of 99% of fibers greater than 5 μm in length (with aspect ratios greater than 3:1) is approximately 20-80 min.
authors.affiliation: a Cardno ChemRisk , Boulder , CO , USA .
authors.forename: J
authors.initials: J
authors.lastname: Sahmel
authors.affiliation: a Cardno ChemRisk , Boulder , CO , USA .
authors.forename: H J
authors.initials: HJ
authors.lastname: Avens
authors.affiliation: b Cardno ChemRisk , Pittsburgh , PA , USA .
authors.forename: P K
authors.initials: PK
authors.lastname: Scott
authors.affiliation: b Cardno ChemRisk , Pittsburgh , PA , USA .
authors.forename: K
authors.initials: K
authors.lastname: Unice
authors.affiliation: c Cardno ChemRisk , Brooklyn , NY , USA .
authors.forename: A
authors.initials: A
authors.lastname: Burns
authors.affiliation: a Cardno ChemRisk , Boulder , CO , USA .
authors.forename: C A
authors.initials: CA
authors.lastname: Barlow
authors.affiliation: d Cardno ChemRisk , Aliso Viejo , CA , USA .
authors.forename: A K
authors.initials: AK
authors.lastname: Madl
authors.affiliation: e Cardno ChemRisk , Sanibel , FL , USA , and.
authors.forename: J
authors.initials: J
authors.lastname: Henshaw
authors.affiliation: f Cardno ChemRisk , Jackson , WY , USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Paustenbach
mesh_terms: D000393:Air Pollutants / Q000737:chemistry*; D017632:Asbestos, Serpentine / Q000737:chemistry*; D002274:Carcinogens, Environmental; D004784:Environmental Monitoring; D006112:Gravitation; D008962:Models, Theoretical; D014691:Ventilation
chemical_list: D000393:Air Pollutants; D017632:Asbestos, Serpentine; D002274:Carcinogens, Environmental
keywords: Asbestos; concentration decay; exposure modeling; fiber removal; fiber settling; particulate removal