OSHA has granted a permanent variance to McNally Tunneling Corp./ASI Marine, allowing the company to deviate from several federal compressed-air safety standards during construction of the Southerly Tunnel and Consolidation Project in Cleveland, Ohio. The variance took effect December 29, 2025, and will remain in place until the project is completed or OSHA revokes it.

Key Points

  • What: OSHA permanently exempts McNally/ASI Marine from three compressed-air safety rules for one specific tunneling project in Cleveland, Ohio.
  • Who: McNally Tunneling Corp./ASI Marine workers performing hyperbaric interventions inside a tunnel boring machine.
  • When: Effective December 29, 2025, through project completion.
  • Impact: Workers may now be exposed to air pressures up to 58 p.s.i. — nearly 20% above the standard 50 p.s.i. legal limit — under alternative safety protocols.

What Changed and Why

Under existing OSHA rules (29 CFR 1926.803), workers in compressed-air environments cannot be exposed to pressures exceeding 50 pounds per square inch (p.s.i.) except in emergencies. The company's tunnel boring machine (TBM) operates below the water table through soft soils and requires periodic worker entry into a pressurized chamber — at pressures up to 58 p.s.i. — to inspect and maintain the machine's cutting tools.

McNally/ASI Marine argued that modern tunneling technology has fundamentally changed compressed-air work. Unlike older caisson-style construction where entire tunnels were pressurized, their TBM only pressurizes a small forward chamber. This means far fewer workers are exposed to compressed air, and for shorter durations.

The company also uses newer oxygen-based decompression protocols — the process of safely reducing a worker's air pressure after a hyperbaric exposure — which it says are safer and more effective than the decompression tables OSHA's 1970s-era rules require.

OSHA's Decision

OSHA reviewed the application, published a preliminary approval in July 2025, and received zero public comments opposing the variance. Satisfied that the alternative measures provide at least equivalent worker protection, OSHA granted the permanent variance with conditions, including:

  • Maximum crew size of three workers inside the pressurized chamber
  • Twin man-locks allowing crew rotation during decompression
  • Specialized medical support and hyperbaric supervision on-site
  • Adherence to the company's project-specific Hyperbaric Operations Manual

This variance applies only to the Southerly Tunnel and Consolidation Project and does not set a precedent for future McNally/ASI Marine projects.

What You Should Do

This notice has no relevance to F-1 students, H-1B workers, or immigration matters. It is a narrow, project-specific OSHA safety variance for a construction company in Ohio. No action is required by our readers. If you are a construction safety professional or tunneling worker affected by this project, review the full variance conditions at regulations.gov under Docket No. OSHA-2025-0004.