18.6 Asbestos, Lead, and Silica: Regulated Substance Programs

Asbestos, Lead, and Silica: Regulated Substance Programs

Three substances account for a large share of the industrial hygienist's regulatory workload, and each is governed by a comprehensive, expanded standard with its own limits, triggers, and programme elements. The exam tests these numbers directly, and it tests the differences between them.

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1. The Numbers at a Glance

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2. Asbestos

Exposure limits. 0.1 f/cc as an 8-hour TWA and 1.0 f/cc averaged over 30 minutes as an excursion limit. Both must be met.

Counting rules. Phase contrast microscopy counts fibres longer than 5 µm with an aspect ratio of at least 3:1. PCM cannot distinguish asbestos from other fibres, so a PCM count in a fibrous but non-asbestos environment overstates asbestos exposure; transmission electron microscopy provides speciation and counts thin fibres PCM cannot resolve.

Construction work classes. The construction standard assigns every job to a class, and the class drives the required controls:

Class I is the most stringent, requiring critical barriers, negative-pressure enclosures, decontamination units, and supervision by a competent person.

Regulated areas are required wherever exposure exceeds or can reasonably be expected to exceed a limit, with demarcation, restricted access, warning signs, and no eating, drinking, smoking, or applying cosmetics.

Presumed asbestos-containing material (PACM). Thermal system insulation and surfacing material in buildings constructed before 1981 is presumed to contain asbestos unless a rebuttal is established by a qualified person.

Notification: results of monitoring within 15 working days of receipt.

Clearance. After abatement, air clearance is commonly performed by aggressive sampling with PCM at 0.01 f/cc, or by TEM where higher confidence or regulatory requirement demands it.

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3. Lead

Exposure limits. PEL 50 µg/m³ as an 8-hour TWA; action level 30 µg/m³, which triggers exposure monitoring, biological monitoring, and training.

Biological monitoring and medical removal are the defining features of the lead standard:

Medical removal protection benefits preserve earnings, seniority, and benefits for up to 18 months, which is what makes removal practicable rather than punitive.

A crucial currency caveat. The OSHA blood lead triggers date from 1978 and are far above modern health-based guidance. The ACGIH BEI for lead is 20 µg/100 g, and public health bodies recommend removal from exposure at levels well below the OSHA figures. An exam item may ask for the OSHA regulatory number; professional practice should be guided by the lower health-based values.

Hygiene facilities. Change rooms with separate storage for street and work clothing, showers where feasible, and lunchrooms with filtered positive-pressure air. Employer laundering; no removal of contaminated clothing from the workplace by employees; no compressed air or shaking to clean clothing.

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4. Respirable Crystalline Silica

Exposure limits. PEL 50 µg/m³ as an 8-hour TWA; action level 25 µg/m³.

Two compliance routes in construction. The construction standard offers a choice:

1. Table 1 — specified exposure control methods. For eighteen named tasks (stationary masonry saws, handheld power saws, drilling rigs, jackhammers, walk-behind saws, rig-mounted core saws, dowel drilling, vehicle-mounted drilling, and others) the standard specifies engineering controls — typically integrated water delivery or a shroud with dust collection — plus work practices and, for some tasks and durations, respiratory protection. A fully compliant Table 1 employer need not perform exposure monitoring at all.
2. The alternative exposure control method. Assess exposure by monitoring or objective data and control to the PEL.

Table 1 is the reason the construction silica standard changed field practice so quickly: it converts an assessment problem into an equipment specification.

Programme elements. A written exposure control plan identifying the tasks, the controls, the housekeeping practices, and the procedures to restrict access; a competent person in construction to implement and inspect it; and housekeeping restrictions that prohibit dry sweeping and compressed-air cleaning where a safer alternative is available.

Medical surveillance must be offered to employees exposed at or above the action level for 30 or more days per year in general industry, and includes a chest X-ray read by a NIOSH B-reader, spirometry, and a tuberculosis test, repeated at least every three years.

Notification: within 15 working days after completing an exposure assessment.

Analysis. Respirable samples are collected with a cyclone at the 4 µm 50% cut point and analysed for crystalline silica content by X-ray diffraction or infrared spectroscopy — a bulk gravimetric result alone does not measure silica.

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5. What the Three Standards Have in Common

Every expanded health standard follows the same architecture, and recognising it lets you reason about a standard you have not memorised:

   Exposure assessment  ->  Regulated area / access control
            |                          |
            v                          v
   Engineering & work-practice controls first, respirators after
            |
            v
   Medical surveillance  ->  Removal / referral where triggered
            |
            v
   Hygiene facilities  ->  Training  ->  Recordkeeping (30 yr / duration + 30 yr)
            |
            v
   Written programme, competent person, and employee notification

The differences that matter for the exam are the numbers and the substance-specific twists: asbestos has an excursion limit and work classes, lead has biological monitoring and medical removal protection, and silica has Table 1 and a B-reader chest X-ray.