Worker Protection, Safety, and Health
Exposure control architecture
OSHA 29 CFR 1926.1101 sets a PEL of 0.1 f/cc as an 8-hour TWA and an excursion limit of 1.0 f/cc averaged over 30 minutes. The employer must conduct an initial exposure assessment, and negative exposure assessments are permitted only under defined conditions. Class I work (most friable removal, e.g., thermal system insulation and surfacing material) carries the strictest requirements; Class II (nonfriable removal) and Class III (repair/maintenance) have tailored rules. Required elements include a regulated area with signage, respiratory protection per a written program, protective clothing, decontamination (equipment room, shower, clean room), medical surveillance, and training with annual refresher.
Traps
Questions often present a respirator as the first line of defense; engineering controls and work practices come first. Another trap: assuming a half-mask is adequate for all Class I work - required protection escalates with exposure. Watch for confusion between the PEL (0.1) and the excursion limit (1.0), and between the 8-hour TWA and short-term sampling. Also expect questions on hygienist/competent person roles and on the requirement that the regulated area be demarcated and limited to authorized persons.
Rule of thumb
Know the two numbers: 0.1 f/cc TWA and 1.0 f/cc 30-minute excursion. Worked example: a sample averages 0.6 f/cc over 30 minutes - it exceeds the excursion limit even if the 8-hour average is below 0.1.