OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

May 28, 1998

Lawrence J. Keefe
Chairman, Tunnel Task Force
Underground Contractors Association
3158 River Road, Suite 135
Des Plaines, Illinois 60018

Dear Mr. Keefe:

We are in receipt of former Underground Contractors Association (UCA) Executive Vice President Gary L. Dowty's letter of April 12, 1995, and your letter of June 18, 1996, regarding the Occupational Safety and Health Administration (OSHA) standard on underground construction, codified at 29 CFR 1926.800. Because of the significance of UCA's questions and suggestions, we assembled a task group to make recommendations. The group included compliance officers from various OSHA Regions who are experienced in tunnel inspections. On May 14, 1997, you met with the task group to provide the group with additional material on pipejacking and microtunnel construction. The present response addresses all of the concerns raised in the letters.


The first part of Mr. Dowty's letter raised the issue of the scope of §1926.800, the tunneling standard. UCA offered definitions for several key terms as a way of clarifying the situations in which the standard applies. The definitions suggested for "boring pit," "pipejacking," and "tunnel" make coverage of the standard dependant on whether employees in the pit "normally" enter the horizontal excavation.

The basic premise of these suggested definitions is that OSHA did not intend the standard to apply to employees working outside the opening of the portal in an open pit. UCA cites a passage from a sentence in the preamble of the final rule of June 1989 in support of this proposition: "...if an employee is working outside the opening of the portal in an open pit...then this section [§1926.800] does not apply."

The quoted passage is from the last sentence of the following paragraph:

OSHA also intends to apply these rules [§1926.800] to certain pipejacking operations, based on the location of the employees performing the work. For example, if an employee is working underground, then this section applies, regardless of whether the ground support is advanced by pushing pipe or is fabricated within the heading. However, if an employee is working outside of the portal in an open pit (for example, operating horizontal boring and pipejacking equipment) and is not exposed to underground construction hazards, then this section does not apply.... (54 FR 23826) (emphasis added)

Taken in its entirety, this paragraph reflects OSHA's intent that the standard does apply to certain pits involved in tunneling operations where an employee works only outside the portal.

There are two circumstances in which a pit will be covered by the standard: First, it is foreseeable that employees in the pit will enter, or they do in fact enter the horizontal excavation; or second, the pit is connected to a horizontal excavation and typical underground construction hazards are present in the pit.

Several of the definitions UCA suggested tie coverage of the standard to whether employees in the pit "normally" enter the horizontal excavation. The likelihood of entry into the horizontal excavation is relevant only to the first category of coverage -- where it is foreseeable that employees in the pit will enter the tunnel.

The likelihood of entry into the horizontal excavation is not a factor in coverage under the second category -- whether typical underground construction hazards are present in the pit. If OSHA had intended employee presence in the horizontal excavation to be the only factor for determining coverage, then we would have stated that, as long as the employee works outside of the portal, there is no coverage. But we stated that open pits would fall beyond the standard's coverage where the employee works outside "and is not exposed to underground construction hazards...." In this second category the touchstone for the standard's coverage of a pit is whether the employees, while in the pit, are exposed to underground construction hazards.

Typical underground construction hazards are those found in shafts, where depth, configuration, and limited horizontal dimensions constrain an employee's ability to move and avoid hazards from loads overhead and from the operation of mechanical equipment. These hazards may also be present in pits that are physically connected to horizontal excavations. Because of limited space, hoisting pipe sections, spoil, muck, and other material can present crushing, caught in-between and struck-by hazards. Such hazards may also stem from hoisting boring equipment or from the use or maintenance of equipment. In microtunnel work, drive/entry shafts and pits are the center of much of the construction activity. Workers in the shafts and pits receive material and weld or join pipe section collars. The depth of a pit can make egress difficult and restrict air flow, which is especially dangerous where there are atmospheric hazards. Other examples of hazards that may be found in a pit are explosion and atmospheric hazards stemming from a tunnel classified as potentially gassy or gassy and engulfment hazards.

On May 14, UCA provided material to support its contention that the industry differentiates between trenchless excavation methods as either worker-entry or non-worker-entry. We have reviewed the material and appreciate that this distinction has significance to the industry. However, microtunneling now encompasses tunnel bores large enough to permit worker entry. We note that a June 1997 draft of the American Society of Civil Engineers (ASCE) Standard Guidelines for Microtunneling (accredited by American National Standard Institute to develop standards) does not refer to worker-entry as a distinguishing feature in its definition of microtunneling. These ASCE draft guidelines explain that while the term microtunneling originally related to the limited size of the tunnel diameter, there is no longer an upper limit for microtunnel diameters (1.0, Scope, and 3.0, Definitions).

In addition, the Agency continues to receive information about construction employees entering small-dimension microtunnels for limited periods to perform work such as repairing or maintaining equipment and removing intermediate jacking stations. In such instances, the rulemaking record for the underground construction standard clearly indicates the Agency's intent to apply §1926.800 to cover workers who enter a tunnel under construction.


The standard does not define several significant terms used in the preamble and the standard itself. We define the terms below as follows:

Shaft -- (1) A passage made from the surface of the ground to a point underground, the longer axis of which makes an angle greater than 20 degrees to the horizontal; or (2) a pit in which there are employees, and it is foreseeable that they may enter (or they do in fact enter) the horizontal excavation; or (3) a pit that has typical underground construction hazards and is connected to a horizontal excavation.

Tunnel -- An excavation beneath the surface of the ground to a point underground, the longer axis of which makes an angle not greater than 20 degrees to the horizontal. (This is the definition used in the American National Standard for Construction and Demolition --Tunnels, Shafts, and Caissons -- Safety Requirements, ANSI A10.16-1988, which is unchanged in the current 1995 revision.)

Consensus standards do not yet exist for the other terms mentioned in UCA's letter. While the term "pipejacking" is not used in the standard itself, it is used in the preamble to the standard. OSHA defines the term as follows:

Pipejacking -- A method of installing pipe or other lining where the section of lining is installed at the opening of the excavation and is jacked or otherwise forced towards the advancing face.

The remaining term does not appear in the standard or the preamble. The following is our understanding of its meaning as it applies to the standard:

Boring pit -- An excavation made for access to a level where or from which a horizontal excavation is to be dug (usually by an auger or boring machine).

Access and Egress

UCA's second point relates to the application of the work station access and egress requirement in §1926.800(b)(2). The letter explains that the smaller the tunnel, the more difficult it is to comply with this provision; employers should be allowed to implement a site specific plan instead of complying with the terms of the regulation. As an example, UCA suggests a work rule prohibiting entry or exit on foot while haulage machines are moving.

Paragraph (b)(2) of §1926.800 requires the employer to "provide access and egress in such a manner that employees are protected from being struck by excavators, haulage machines, trains and other mobile equipment [emphasis added]." This provision is written in performance language, so the employer may choose any effective method for protecting the workers from this hazard. One problem with the example in the letter is that it addresses only the hazard from haulage machines, while the standard requires protection from excavators, trains and other mobile equipment. Note: Although paragraph (b)(2) is written in performance language, there are specific requirements in paragraph (b)(3).

Reversible Ventilation

This part of UCA's letter addresses the application of the §1926.800(k)(4) reversible ventilation requirement to shafts and tunnels. With respect to shafts, the letter states that most contractors use a flexible bag line to provide ventilation to the shaft to prevent damage from clam buckets and other material, and because it is safer to install due to the fewer number of supports needed. When using this type of line, "reversibility is impractical...since reversed flow will suck the bag into [the] fan."

With respect to tunnels, the letter states that "it would be impossible to determine where all employees are at the time of a fire." Consequently, UCA suggests that reversing the flow in a fire could fatally trap more workers than would be saved.

The requirement for reversible ventilation is an important, long-standing safety requirement. This requirement was the product of the rulemaking procedure, and during that process, the Agency provided the following explanation in the preamble of the proposed rule:

The ventilation system must be able to pull air from the tunnel bore as well as supply air to the work area. After blasting, or in an emergency such as a fire, smoke, gas or fumes must be exhausted from the underground area through the vent line to protect the employee from exposure. (48 FR 35790)

This provision was in the predecessor standard (§1926.800(c)(2)(i) (1988)), and was redesignated in the June 1989 final rule. The OSHA standard is consistent with ANSI, California standards, and Michigan standards. Removing this requirement could only be done by changing the standard through the rulemaking procedure. We are unaware of changes in tunneling practices or experiences since the standard was first promulgated that would suggest that the provision should be removed.

With regard to the use of a flexible bag line, we are looking into whether approved bag lines that will not get sucked into a fan are available.

Approved Equipment

Paragraph (k)(10)(ii) of §1926.800 requires mobile diesel-powered equipment used underground (in atmospheres other than gassy operations) to be either approved by MSHA (30 CFR part 32), or demonstrated by the employer to be fully equivalent. The letter raised several objections to this provision. First, UCA stated that most equipment used in large diameter tunnels is not suitable for mines and therefore has not been approved by MSHA. In this regard we assume that UCA's concern is that, as a practical matter, the employer will have to demonstrate equivalency for most of its equipment. Second, UCA asserted that had this been a performance standard, rather than a specification standard, the ventilation requirements of paragraph (k) alone would be sufficient to ensure air quality -- there would be no need for the equipment to comply with MSHA criteria.

During the rulemaking for the revised underground construction standard, OSHA received and considered comments challenging the need for MSHA certification and asserting that a performance standard was preferable. When the revised standard was promulgated, OSHA gave the following explanation:

Several commenters objected to the incorporation by reference of 30 CFR Part 32, arguing that MSHA certification and approval is a complicated and time-consuming process. Instead, they urged that OSHA promulgate performance standards prescribing air quality requirements. (54 FR 23836)

In explaining the decision to retain the MSHA incorporation, the Agency stated that:

OSHA has carefully reviewed 30 CFR Part 32...Mr. Joseph Hadden, with MSHA, stated that 30 CFR Part 32 was developed through significant research and effort and he did not believe that OSHA needed to duplicate that research and effort to develop independently new standards governing the design and use of diesel-powered equipment underground.... 30 CFR Part 32 is also the nationally recognized standard for underground diesel equipment: OSHA's current standard, at §1926.800(c)(2)(vii), has for years incorporated Schedule 24, and both the ANSI A10.16 and Michigan standards also contain this reference. Moreover, the MSHA standards are widely recognized by the underground equipment industry and are widely available to any interested person.... (54 FR 23837)

OSHA specifically declined to adopt a standard that relied solely on a performance-based ventilation requirement:

30 CFR Part 32 is comprehensive in its requirements: OSHA believes that air quality performance standards alone would not provide a level of safety comparable with that provided by 30 CFR Part 32 at this time. Therefore, reference to 30 CFR Part 32 has been retained.... (54 FR 23837)

Having addressed this issue in the rulemaking, the standard would have to be changed through the rulemaking process to institute the policy UCA suggests. We do not consider that an advisable course now for the same reasons we adopted this provision when the standard was promulgated. During the discussion with UCA on May 14, a suggestion was made that MSHA be contacted to see how manufacturers are meeting the certification requirements. We are now discussing this matter with MSHA and will keep you informed of our findings and any further developments.

We would also point out that one of the reasons a ventilation-only approach is insufficient is that it does not account for air flow direction and local effects of the emissions. While aggregate air flow may be adequate, workers directly downstream of the emissions and proximate to the emission source could have significant exposure while workers upstream would be unaffected.


Under §1926.800(l)(2), only explosion proof portable lighting may be used within 50 feet of blasting areas. The letter stated that this provision was written when electric blasting caps were normally used, and the intent of the provision was to prevent premature ignition. UCA recommended that this provision be limited to areas where electric caps are being used, since most contractors now use non-electric caps.

When the current standard was proposed, OSHA received comments recommending the same limitation that UCA offered. OSHA decided against that approach because the Institute of Makers of Explosives (IME), the safety association of the U.S. commercial explosives industry, recommended in its guidelines that only explosion proof lighting be permitted around all explosive materials, not just electric detonators:

Some comments urged that [explosion proof lighting] ...only be required where electric detonators are used...OSHA consulted publications of the Institute of Makers of Explosives (IME). OSHA recognizes IME as an authoritative source on the subject of safety with explosives and accords great weight to its recommendations.... The IME Publication Number 17... states that 'where portable lights are needed around explosive materials, only approved electric flashlights or electric lanterns should be permitted.' The IME Publication Number 12...defines 'Explosive Materials' to include, but not be limited to, dynamite and other high explosives; slurries, emulsions, and water gels; black powder and pellet powder; initiating explosives; detonators (blasting caps); safety fuse; squibs; detonating cord; igniting cord; and igniters. Therefore, the IME clearly intends the requirement for approved lighting to apply to all explosive materials, not just electric detonators. (54 FR 23837)

Since the IME considered it important to use approved lighting equipment around all types of explosives, we do not believe the diminished use of electric blasting caps warrants a change in the standard.

Anti-Two Block Devices

The letter recommended that the §1926.800(t)(2) requirement that cranes be equipped with anti-two block devices only apply when moving employees: "In clamming or drilling operations, the cables slapping together will trip the device leaving the load suspended over the shaft and greatly reducing production for no gain in safety."

While we recognize the problem UCA describes, it is essential that employees be protected from two-blocking, a hazard well-recognized in the industry and documented in the rulemaking record. However, if no employees were exposed to that hazard, then there would be no violation of the standard if the cranes did not have anti-two block devices. We stress that this is an option only during the time that no employees are exposed to the consequences of a two-block. An example of this would be where there are no employees in a shaft or pit or any other area of two-block hazard exposure during clamming operations.

Lifting On Loadlines During Personnel Platform Lifts

Except for pile driving operations, §1926.1431(k)(11)(i) prohibits lifts on another of a crane's loadlines while the crane is suspending personnel on a platform. Because of this rule, a second crane is needed to supply materials to employees on the platform. The boom tips of the two cranes come very close together, creating a danger greater than using two load lines on a single crane. This provision was discussed during rulemaking for the cranes and derricks in construction standard, and OSHA determined that the requirements of §1926.1431(k)(11)(i) would serve several purposes. First, it prevents platform tipping due to entanglement with other load lines or loads. Second, it reduces the chance the equipment could be overloaded. Third, when hoisting personnel, it is essential that the operatorâ¿¿s full attention be devoted to the hoisted personnel; use of another load lone necessarily diverts the operatorâ¿¿s attention.

Consistency of Inspections

The letter states that because the number of tunnel projects in the U.S. is very low relative to other types of construction, UCA believes that OSHA's compliance officers lack expertise. Specifically, the letter asserts that standards are interpreted differently in different OSHA regions. Consequently, UCA suggests that OSHA appoint an official who would be well trained in tunneling to oversee all tunneling inspection activities.

OSHA agrees that construction expertise and consistency in interpreting standards is most important. However, we do not agree that OSHA lacks expertise in tunneling although that may be true in isolated cases. You should feel free to inform us or the Regional Administrator when you believe that to be the case in a specific instance. We will attempt to achieve greater consistency in the application of construction standards by continuing to develop expertise in the Directorate of Construction in the National Office and making that expertise available to the field staff for consultation as needed.


The letter expressed two concerns with respect to variances: (1) it takes too long for variance requests to be acknowledged and processed, and (2) when granted, a variance applies only to the employer that requested it, rather than to the whole industry; "if variances could be issued to an industry, then we would not need to go through the laborious process of amending the standards."

We regret that some requests have taken a long time to process. The Occupational Safety and Health Act provides that a variance can only be granted where the employer demonstrates "by a preponderance of the evidence" that the proposed alternative means or method is as safe or safer than what the regulation specifies. This usually requires that the employer provide, and we analyze, detailed information about its situation and the alternative safe practice it proposes.

We are required to publish the application in the Federal Register, allow a minimum of 30 days for the public to comment and request a hearing, and provide a hearing if requested. If a hearing is held, the public has the opportunity to provide testimony. We must then consider all submitted comments and testimony. We may then need to work with the employer to revise its variance application in light of the comments and testimony. The final ruling on the variance is then drafted and published in the Federal Register.

Many of the applications initially lack the detail necessary to make the statutorily mandated findings. OSHA works with each of those applicants to obtain the additional information that is needed. Unfortunately, this can be a time consuming process.

There is no statutory provision allowing industry-wide variances. Nor do we consider violations of the standards discussed above to be de minimus violations.

The "laborious process of amending the standards" is a corollary to the statutory requirement that all interested parties be given an opportunity to be heard when a standard is promulgated or altered. It is well worth that effort when it can be shown that there is a less costly means of accomplishing equal or greater safety.

When a variance request is granted, the variance is published in the Federal Register. This gives notice to other employers with the same fact situation of an alternative means of compliance that may be available to them as well. We are able to process fairly quickly subsequent variance requests from such employers proposing to use the approved alternative.

Joint Ventures

The last issue raised in the letter relates to citations issued to joint venture contractors. UCA states that typically the first named contractor is actually responsible for constructing the project, and the remaining contractors provide only bonding power, financial backing or equipment. UCA's concern is that, "some areas cite all parties of a joint venture individually exposing each non-participating contractors to repeat violations on their own projects even though they have nothing to say about the management of the [joint venture] job."

Identifying the correct party for citation in cases of violations found during an OSHA inspection is a legal issue. In general, the joint venture is a legal entity in and of itself. The agent for the joint venture (usually the first-named contractor) is normally the appropriate party for a citation.

If you need any additional information, please contact us by fax at: U.S. Department of Labor, OSHA, Directorate of Construction, Office of Construction Standards and Guidance, fax # 202-693-1689. You can also contact us by mail at the above office, Room N3468, 200 Constitution Avenue, N.W., Washington, D.C. 20210, although there will be a delay in our receiving correspondence by mail.


James G. Maddux, Director
Directorate of Construction

cc: Paul Lawent, Executive Director, UCA
George Kennedy, Safety Director, NUCA

Amended: June 18, 2014