Underground construction requirements

Yes — the check-in/check-out requirement applies even when a single employee is working underground. OSHA explains that provisions in Subpart S are not contingent on the presence of more than one worker and that the check-in/check-out system is meant to provide an accurate count of persons underground at any time, including lone workers (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• Make sure your check-in/check-out procedure always allows aboveground personnel to know whether any individual is still underground in case of an emergency.

You may stop using the check-in/check-out procedure only when the underground facility is sufficiently completed so that permanent environmental controls are effective and remaining work will not create environmental hazards or structural failure. OSHA specifically allows an exception in that situation (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• If any remaining construction activities could create hazards or compromise controls, the check-in/check-out procedure must remain in place.

Yes — self-rescuers approved by NIOSH must be immediately available to all employees at work stations in underground areas where employees might be trapped, including lone workers. OSHA reinforces that the requirement to provide self-rescuers applies to any employee working in those areas (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• Selection, issuance, use, and care of those respirators must comply with applicable respirator provisions referenced in the standard.

Yes — Subpart S covers cut-and-cover excavations only when they are physically connected to ongoing underground construction operations and are covered so as to create conditions characteristic of underground construction. OSHA explains this scope in the standard (1926 Subpart S).

• If a cut-and-cover excavation is independent (not physically connected) it may instead fall under Subpart P (excavations and trenching).

No — excavation and trenching operations are excluded from Subpart S when they are not physically connected to underground construction operations; such operations are covered by Subpart P of Part 1926 instead. This limitation is stated in the Subpart S scope (1926 Subpart S; see also the May 3, 2001 interpretation discussing scope).

No — underground electrical transmission and distribution lines are expressly excluded from Subpart S because they are addressed in Subpart V of Part 1926. The Subpart S scope lists that exclusion (1926 Subpart S).

The requirements apply when at least one employee is engaged in covered work; they are not contingent on having multiple employees. OSHA states that provisions using plural terms like "employees" are intended to apply to any and all employees, including lone workers (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• Treat all Subpart S duties as employer responsibilities whenever the work falls within the subpart’s scope.

The employer is responsible for maintaining the check-in/check-out procedure. Subpart S places the duty on the employer to ensure a system exists so aboveground personnel can determine an accurate count of persons underground (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• Employers should document the procedure and train relevant staff on how to use it in normal operations and emergencies.

An employer must be able to determine an accurate count of the number of persons underground and whether any specific individual is still underground. OSHA emphasizes that the check-in/check-out procedure must allow aboveground personnel to know if someone remains underground in emergencies (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• The system should be reliable enough to identify who is present underground at any time, not just the total number.

Yes — Subpart S explicitly covers underground construction, caissons, cofferdams, and compressed air work as part of its scope and title. Employers performing compressed air operations in covered underground construction must follow Subpart S requirements (1926 Subpart S).

Yes — while the standard specifically requires a check-in/check-out procedure and immediate availability of self-rescuers where trapping is possible, employers must ensure they can account for and respond to an emergency involving a lone worker. The May 3, 2001 interpretation stresses the employer’s obligation to know whether an employee remains underground, which implies reliable communication and emergency response systems are appropriate (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• Typical controls include radios, voice/visual check procedures, and rescue equipment positioned for immediate use.

The employer must provide self-rescuers that are approved by the National Institute for Occupational Safety and Health (NIOSH) and make them immediately available at work stations in underground areas where employees might be trapped by smoke or gas. OSHA cites this requirement in Subpart S and clarifies its application to any employees in such areas (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• Ensure selection, issuance, use, and care follow the respirator provisions referenced by the standard.

Yes — the check-in/check-out requirement applies during any shift when someone is underground, even if only one person is scheduled for that shift. OSHA explains the rule is intended to provide an accurate count at any time and would be defeated if it didn’t apply when a lone worker remained underground (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

No — an employer cannot rely solely on informal self-reporting if it does not reliably allow aboveground personnel to determine an accurate count of persons underground. OSHA requires a formal check-in/check-out procedure that provides that capability (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• The procedure should be reliable and documented so aboveground staff can act quickly in an emergency.

Yes — OSHA has confirmed that when Subpart S uses terms like "employees" or "persons," those terms are meant to include any and all employees, including a single worker. The subpart’s provisions therefore apply to lone workers as well (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

Yes — the standard requires measures such as a check-in/check-out system and availability of self-rescuers where employees might be trapped, and OSHA’s interpretation stresses that these provisions apply when one or more employees are working underground. Employers must therefore have appropriate rescue and personal protective equipment available for lone workers in trap-risk areas (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• Evaluate site-specific rescue procedures and ensure rescue equipment and trained personnel are ready if needed.

Yes — the employer’s check-in/check-out procedure must permit aboveground personnel to determine an accurate count of persons underground at any time, which includes accounting for workers who leave and then re-enter during a shift. OSHA’s requirement is designed to track who is underground during all phases of work (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• Use a system that updates entries and exits promptly (e.g., sign-in boards, electronic logs, radio check-ins).

The employer must maintain a procedure that ensures aboveground personnel can determine an accurate count and identify who is underground; the standard does not mandate one specific method, so a door log can be sufficient if it reliably provides that information. OSHA focuses on the outcome (accurate, timely accounting) rather than a prescribed format (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• Choose a method (paper roster, electronic system, radio check) that suits site conditions and ensures rapid emergency response.

Yes — Subpart S applies to tunnels and shafts connected to tunnels, and OSHA specifically discussed lone employees working in a tunnel or a shaft connected to a tunnel when explaining the scope and application of the check-in/check-out rule (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

The selection, issuance, use, and care of respirators and self-rescuers used under Subpart S must follow the respirator requirements referenced in the standard. OSHA’s interpretation points to the respirator provisions the subpart incorporates for proper selection and care (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• Ensure respirators/self-rescuers are NIOSH-approved and that your program covers fit, training, maintenance, and inspection consistent with the referenced respirator rules.

No — assumptions are not acceptable; the employer must have a procedure that provides an accurate count and identification of persons underground. OSHA warns that the requirement would be defeated if it ceased to apply simply because others left and one worker remained; the employer must know whether the lone worker is still underground (1926 Subpart S; OSHA letter of interpretation, May 3, 2001).

• Maintain the check-in/check-out procedure until the standard’s exception conditions are clearly met.