Confined Space in Construction: OSHA Subpart AA Basics for Employers

If you work on construction sites, you must follow OSHA’s dedicated confined space rule — 29 CFR 1926 Subpart AA (Confined Spaces in Construction). It is NOT the same as the general-industry rule (1910.146).

This guide covers the key requirements: exact OSHA requirements, step-by-step procedures, roles, testing order, alternate procedures, and rescue rules.

What Is a Confined Space in Construction? (OSHA Definition – 1926.1202)

A confined space meets ALL three criteria:

1. Large enough for a worker to enter and perform work
2. Has limited or restricted means of entry or exit
3. Is not designed for continuous occupancy

Common construction examples:

• Manholes & utility vaults
• Storm/sanitary sewers
• Crawl spaces
• Storage tanks & process vessels
• Boilers
• Excavations with restricted access
• Pier caissons & pipelines

When Does It Become Permit-Required (PRCS)?

A space becomes permit-required if it has (or has potential for) ANY of these:

• Hazardous atmosphere (oxygen <19.5% or >23.5%, flammables above 10% LFL, toxic above PEL)
• Engulfment hazard
• Inwardly converging walls or floor that slopes downward and tapers
• Any other recognized serious safety or health hazard

Key Differences: Construction Rule vs. General Industry

Roles and Responsibilities on Multi-Employer Sites

• Host Employer – Owns the site, shares known hazards
• Controlling Contractor – Coordinates all entry operations, shares info (danger signs are posted, or an equally effective means used, by the employer who identifies the permit space, 1926.1203(b))
• Entry Employer – Develops permit program, issues permits, trains their people
• Entry Supervisor – Authorizes entry, signs permit, can cancel it
• Attendant – Monitors from outside; remains outside the space until relieved by another attendant
• Authorized Entrant – Wears harness with retrieval line where non-entry rescue applies (1926.1211(c)), follows permit

Step-by-Step Atmospheric Testing Order (Required by OSHA)

Test in this exact sequence with a calibrated monitor:

1. Oxygen first (19.5% – 23.5%)
2. Flammable gases/vapors (must not exceed 10% LFL for entry)
3. Toxic gases (CO, H2S, etc. – below OSHA PEL)

Test top, middle, and bottom in vertical spaces (stratification). Monitor atmospheric hazards continuously unless the employer shows continuous equipment is not commercially available or periodic monitoring is sufficient (1926.1204(e)(2)).

Ventilation & Alternate Entry Procedures (1926.1203(e))

You may use alternate procedures (no permit, no attendant) ONLY when:

• The ONLY hazard is atmospheric
• Forced-air ventilation alone keeps conditions safe
• You document the determination and monitoring data
• All physical hazards are eliminated or isolated
• A written certification is made
• Atmospheric hazards are monitored continuously unless the employer shows periodic monitoring is sufficient

Rescue Requirements

1. Non-entry rescue required unless retrieval equipment would increase overall risk or would not contribute to the rescue; chest or full-body harness with retrieval line; mechanical device available for vertical-type spaces more than 5 ft deep (1926.1211(c))
2. On-site rescue team OR pre-arranged local service that can arrive in time
3. Practice rescue at least once every 12 months, unless a real rescue in the same or similar space was properly performed in that time (1926.1211(b)(4))

Training & Refresher Requirements

Every person must be trained before initial assignment and whenever:

• Duties change
• Hazards change
• Program deficiencies are observed

Under 1926.1207, retraining is triggered by changes in operations, deviations from procedures, or inadequate knowledge; there is no fixed annual interval.

NSC Training Products for Confined Spaces in Construction

• Confined Space Entry: Construction Safety Training – training program
• Confined Spaces for Construction Training Booklets (pkg of 10) – employee booklets
• Confined Space in Construction Student Supplement (pkg of 10) – student supplement
• Confined Spaces Can Kill Safety Poster – poster

NSC does not sell signs, monitors, harnesses, retrieval equipment, or permit templates.

FAQ – Quick Answers

Q: Can we reclassify a PRCS to non-permit in construction?
Yes – only when a competent person determines all hazards are eliminated or isolated, with a written certification. Ventilation is not elimination (1926.1203(g)).

Q: Do we need an attendant with alternate procedures?
No – alternate procedures eliminate the need for permits and attendants.

Q: Is 10% LFL the hard limit?
Under alternate procedures, no hazardous atmosphere, including flammables above 10% LFL, may be present while anyone is inside (1926.1203(e)).

Q: Who can cancel a permit?
Only the Entry Supervisor.

Q: How long do we keep canceled permits?
At least 1 year (1926.1205(f)).

Stay safe out there.
National Safety Compliance Team