Measured removal rates of chrysotile asbestos fibers from air and comparison with theoretical estimates based on gravitational settling and dilution ventilation.

CONTEXT: 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). MATERIALS AND 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). DISCUSSION: 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). CONCLUSION: 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.

Evaluation of take-home exposure and risk associated with the handling of clothing contaminated with chrysotile asbestos.

The potential for para-occupational (or take-home) exposures from contaminated clothing has been recognized for the past 60 years. To better characterize the take-home asbestos exposure pathway, a study was performed to measure the relationship between airborne chrysotile concentrations in the workplace, the contamination of work clothing, and take-home exposures and risks. The study included air sampling during two activities: (1) contamination of work clothing by airborne chrysotile (i.e., loading the clothing), and (2) handling and shaking out of the clothes. The clothes were contaminated at three different target airborne chrysotile concentrations (0-0.1 fibers per cubic centimeter [f/cc], 1-2 f/cc, and 2-4 f/cc; two events each for 31-43 minutes; six events total). Arithmetic mean concentrations for the three target loading levels were 0.01 f/cc, 1.65 f/cc, and 2.84 f/cc (National Institute of Occupational Health and Safety [NIOSH] 7402). Following the loading events, six matched 30-minute clothes-handling and shake-out events were conducted, each including 15 minutes of active handling (15-minute means; 0.014-0.097 f/cc) and 15 additional minutes of no handling (30-minute means; 0.006-0.063 f/cc). Percentages of personal clothes-handling TWAs relative to clothes-loading TWAs were calculated for event pairs to characterize exposure potential during daily versus weekly clothes-handling activity. Airborne concentrations for the clothes handler were 0.2-1.4% (eight-hour TWA or daily ratio) and 0.03-0.27% (40-hour TWA or weekly ratio) of loading TWAs. Cumulative chrysotile doses for clothes handling at airborne concentrations tested were estimated to be consistent with lifetime cumulative chrysotile doses associated with ambient air exposure (range for take-home or ambient doses: 0.00044-0.105 f/cc year).

Voice source changes of child and adolescent subjects undergoing singing training--a preliminary study.

Many vocal practitioners have strong beliefs regarding the age at which singing training of a child should begin, and the different ways in which male and female children should be treated. These beliefs are not substantiated by any scientific research, leading to considerable dispute between vocal coaches and choral directors. The singing voices of over 127 child singers and non-singers aged 8-18 were analysed using electrolaryngographic measures. Analysis particularly concentrated on the laryngographically derived vocal fold closed quotient (CQ). Results indicated that the voice source characteristics of subjects could be divided into groups according to age, gender and the level of vocal training received. Female subjects in particular exhibited a marked development of voice source production according to the length of training received, while male subjects exhibited patterning according to both age (and related pubertal development), and training received. It was concluded that the process of training a young voice has a quantifiable effect upon the singing voice production of the child, and in particular on the female voice, while pubertal development also creates measurable effects on the voice source production of the male child.