Asbestos Class I work practices

A negative pressure enclosure (NPE) is a sealed work area that uses HEPA‑filtered exhaust to keep interior pressure lower than surrounding areas so air flows into, not out of, the enclosure; it may be used as an allowable control method for Class I asbestos work to comply with paragraph (g)(5)(i).

• The non‑mandatory appendix explains how NPEs may be erected and used as the control method authorized in 1926.1101(g)(5)(i) and provides detailed planning and construction guidance in 1926.1101 App F.

(See also the mandatory criteria in 1926.1101(g).)

You must conduct an exposure assessment before work begins that gathers information about prior similar jobs and the specific variables of the current job to plan controls and monitoring.

• The appendix recommends collecting a physical description of the work area, estimated amount of material, HVAC shutdown schedule, personnel hygiene procedures, personal protective equipment and clothing, local exhaust ventilation details and test plans, work practices, air monitoring plan, waste transport method, and dump site location (1926.1101(f)(1), 1926.1101 App F).

You should determine and document the usual elements of an asbestos removal plan before erecting an enclosure: a description of the enclosure, equipment, procedures, ventilation testing, air monitoring, and waste handling.

• The appendix lists recommended planning information including the work area description, approximate amount of material to be removed, HVAC shutdown/ sealing schedule, personnel hygiene procedures, PPE/clothing description, local exhaust system design and test procedures, work practices, air monitoring plan, waste transport methods, and dump site location (1926.1101(f)(1), 1926.1101 App F).

Essential items include 6‑mil plastic sheeting and strong adhesive tape, HEPA‑filtered vacuums, HEPA‑filtered portable ventilation (negative air) units, water sprayers with wetting agent, and shower/decon facilities.

• The appendix recommends at least 6 mil plastic for surface protection and two layers for sealing openings and ducts, HEPA vacuums with long hoses, HEPA‑equipped portable negative air systems (with replaceable filters), water sprayers that produce a fine mist and a wetting agent (about 15 mL per liter), backup power for ventilation, and mixed hot/cold showers and soap (1926.1101 App F).

• See respiratory protection and protective clothing requirements in 1926.1101(h) and 1926.1101(i), and signage in 1926.1101(k).

An enclosure must be airtight and watertight except for controlled openings, lined with two layers of at least 6‑mil plastic, supported so it won’t collapse, and divided into work, decontamination, and waste areas with airlocks on exits.

• The appendix states walls, ceilings and floors should be lined with two layers of 6 mil sheeting, seams overlapped and staggered, structural supports provided, openings limited and designed to direct airflow, and distinct work, decontamination, and waste storage areas separated by curtains/doors and airflow patterns (1926.1101 App F).

• These enclosure guidelines support the regulatory criteria in 1926.1101(g)(5)(i).

Maintain a negative pressure of at least -0.02 inches of water gauge within the enclosure (i.e., the enclosure must be at least 0.02 inches lower than ambient).

• The appendix specifies maintenance of -0.02 inches water gauge as a key criterion and notes design differentials typically range from 0.02 to 0.10 inches water gauge depending on enclosure size and conditions (1926.1101 App F; see also 1926.1101(g)(5)(i)).

Air flow patterns must be checked before work begins, at least once per operating shift, and whenever there is a question about enclosure integrity; static pressure must also be continuously or routinely monitored.

• The appendix requires smoke or visual flow tests before operations and at least once per shift, and it recommends manometers or pressure gauges (with alarms or chart recorders) to monitor static pressure within the enclosure (1926.1101 App F).

Use manometers or pressure gauges to monitor static pressure and consider attaching alarms and strip‑chart recorders to detect pressure loss and filter loading.

• The appendix specifically recommends pressure monitoring devices with alarms and strip chart recorders attached to each ventilation system at points identified by the design engineer (1926.1101 App F).

If pressure falls below the required differential, work must stop, the cause investigated and corrected, and airflow patterns retested before work resumes.

• The appendix directs that when manometers or gauges show a reduction below the required level, work should cease, the reason for the change investigated, appropriate changes made, and airflow retested prior to resuming operations (1926.1101 App F).

Shut off, deactivate, and lock out HVAC systems servicing the restricted area and seal all ducts, grills, ports, windows and vents with two layers of plastic unless the duct portion serving the restricted area is isolated and pressurized as described.

• The appendix requires sealing and locking off HVAC power and sealing all openings with two layers of plastic; if a duct must remain connected to other zones it must be sealed, caulked, pressurized, and the supplying fan locked on (1926.1101 App F).

You must provide an equipment room, shower room, and clean room as part of the enclosure; workers must remove contaminated items in the equipment room, step through decontamination, and shower before entering the clean room.

• The appendix describes a decontamination system where workers step into an equipment room to clean tools and remove gross contamination, then remove coveralls and proceed to the shower area before entering the clean room (1926.1101AppF). See the regulatory requirements for hygiene facilities in 1926.1101(j).

For Class I asbestos work, employers must provide full‑facepiece supplied‑air respirators (SARs) in pressure‑demand mode with an auxiliary positive‑pressure SCBA whenever exposures exceed 1 f/cc as an 8‑hour TWA; when exposures are at or below 1 f/cc, employers must provide either tight‑fitting PAPRs or full‑face SARs (unless a negative exposure assessment is demonstrated).

• The respirator requirements are set out in 1926.1101(h). OSHA clarified these requirements in the Letter of Interpretation on respirator selection dated January 4, 2024 (see https://www.osha.gov/laws-regs/standardinterpretations/2024-01-04).

• If a valid negative exposure assessment (NEA) is demonstrated, employers may select respirators consistent with Table 1 of 29 CFR 1910.134 but may not use filtering facepieces and must use HEPA filters for air‑purifying respirators (1926.1101(h); LOI: https://www.osha.gov/laws-regs/standardinterpretations/2024-01-04).

Design airflow so the enclosure volume is replaced roughly every 5 to 15 minutes; the exhaust rate must exceed makeup air and maintain negative pressure and air movement past each worker.

• The appendix states the volume removed should replace the container every 5 to 15 minutes and that exhaust must exceed makeup air to maintain negative pressure and flow past each worker (1926.1101 App F).

Position intakes and exhaust ports and HEPA vacuums to pull contaminated air away from each worker’s breathing zone, force relatively clean air past the worker toward an exhaust, and ensure the exhaust plume is away from people and HVAC intakes.

• The appendix recommends placement of intakes/exhausts and HEPA vacuums to remove air from the breathing zone, and locating the exhaust plume away from adjacent personnel and HVAC intakes (1926.1101 App F).

Waste must be bagged during or immediately after removal and kept saturated until sealed; double‑bagging is recommended, sharp waste must go into hard airtight containers, and waste should be stored in a worker‑controlled waste area.

• The appendix specifies immediate bagging, recommends double bagging and sealing in asbestos disposal bags, keeping material saturated, using hard airtight containers for sharp debris, and storing bags in a controlled waste storage area (1926.1101 App F).

Yes — asbestos work involving asbestos‑containing building materials performed by property remediation companies (including residential cleanup) falls under the construction asbestos standard, 29 CFR 1926.1101, not the general industry standard.

• OSHA confirmed in the November 14, 2024 Letter of Interpretation that remediation activities involving ACBM are covered by the construction standard (https://www.osha.gov/laws-regs/standardinterpretations/2024-11-14) and the regulatory requirements and planning elements are described in 1926.1101(f)(1).

Take air samples to demonstrate enclosure integrity, clean room and shower cleanliness, and HEPA filter effectiveness; use visual airflow checks (smoke tubes) at openings and worker positions and be cautious when sampling near ventilation exhausts.

• The appendix recommends smoke testing or visual methods to trace air currents, periodic air sampling for enclosure integrity and clean room contamination, and careful sampling near portable ventilation exhausts (1926.1101 App F).

Airlocks (vestibules/double doors or curtains) should be used at exits and between the equipment room and shower room, shower and clean room, and waste area and outside; airflow through these airlocks must draw air toward the work area and be verified with smoke tests.

• The appendix describes airlocks and recommends locating them between those rooms, using vestibules/double curtains where appropriate, and checking flows with smoke tubes to ensure air moves toward the work area without eddies (1926.1101 App F).

Yes — openings may be intentionally designed to direct airflow toward the interior; if negative pressure is lost, such openings should have HEPA filters or automatic trap doors to prevent asbestos dust from escaping.

• The appendix allows openings designed to direct air flow but requires they draw air into the enclosure under anticipated conditions and be fitted with HEPA filters or automatic trap doors in the event negative pressure is lost (1926.1101 App F).

If the clean room is shown to be contaminated, relocate the clean room to an uncontaminated area before resuming operations that rely on a clean room.

• The appendix explicitly states the clean room must be relocated to an uncontaminated area if contamination is detected (1926.1101 App F).

Use plastic sheeting with a minimum thickness of 6 mil and tape or adhesive strong enough to support the weight and stresses of the material for the entire project without detaching.

• The appendix requires at least 6‑mil plastic for covering surfaces and sealing openings and specifies that tape or adhesive must be sufficient to support material weight and stresses throughout the project (1926.1101 App F).

You must post required warning signs and labels for regulated areas and asbestos waste as described in [1926.1101(k)]; the appendix references 1926.1101(k) and recommends controlling access, bagging waste, and properly labeling asbestos bags and containers.

• The appendix points to the mandatory signage and labeling rules in 1926.1101(k) and recommends storing labeled bags/containers in a worker‑controlled waste storage area (1926.1101 App F).

Yes — HEPA filters should be designed to be replaceable as airflow is reduced by dust buildup, and pressure monitoring with alarms or chart recorders is recommended to indicate when filters need replacement.

• The appendix states filters should be replaceable when air flow is reduced by dust build‑up and recommends pressure monitors with alarms and strip chart recorders at points identified by the design engineer (1926.1101 App F).