Underground construction rules for an immersed tube tunnel

August 8, 2002

MEMORANDUM FOR:
K. FRANK GRAVITT

Acting Regional Administrator

FROM:
R. BRUCE SWANSON, Director

Directorate of Construction

SUBJECT:
Request for Interpretation Regarding the Applicability of §1926.800 to Fort Point Channel Crossing Immersed Tube Tunnel

The purpose of this memo is to clarify the applicability of 29 CFR 1926.800 to the portion of Boston Central Artery Tunnel construction project known as the Fort Point Channel Crossing Immersed Tube Tunnel project. This is in response to your memo of December 7, 2001 and subsequent conversations. I apologize for the delay in answering your memo.

Based on materials supplied in your memo and other information about this project, 29 CFR 1926.800 does apply to the Fort Point Channel Crossing immersed tunnel tube construction project.

Background: The Fort Point Channel (Channel) is a narrow body of water extending from Boston Harbor into South Boston. The Fort Point Channel Crossing is part of the Boston Central Artery Project designed to remove several major roadways from the downtown Boston surface roadway grid by putting them under ground. This channel crossing serves to extend the Massachusetts Turnpike to Logan Airport.

The Channel Crossing involves the construction of two concrete immersed tube tunnels (ITTs) side-by-side across the bottom of the Fort Point Channel. Each ITT, one for eastbound traffic and one for westbound traffic, is assembled from a series of concrete, shoebox-shaped sections constructed on land. They were then floated into place, sunk into the Channel, and landed on support structures and materials placed in Channel bottom. Once in place and connected, the concrete ITT sections were covered with 5 feet of gravel. The ITT sections form two long concrete tubes running at the bottom of the Channel to and from "cut and cover" tunnel sections at either side of the Channel.

From contract documents on the Internet, we understand that cut-and-cover tunnels will run several hundred feet beyond both ends of the Fort Point Channel tubes they adjoin. At the western extremity, the Fort Point Channel tubes are connected through several cut-and-cover sections to Interstate 90 and Interstate 93. At the eastern extremity the tubes connect through a cut-and-cover section that extends Interstate 90 through the Ted Williams ITT to Boston's Logan International Airport. There are several transitions to surface streets at both sides of the Channel crossing from the cut-and-cover tunnel sections. We note that the Channel crossing, as you describe it, is not undergoing any active blasting, drilling or earth hauling.

Section 1926.800(a)(1) sets out the scope of the Underground Construction standard: This section applies to the construction of underground tunnels, shafts, chambers, and passageways. This section also applies to cut-and-cover excavations which are both physically connected to ongoing underground construction operations within the scope of this section, and covered in such a manner as to create conditions characteristic of underground construction.

Discussion: The standard does not define "tunnel." However, there are numerous indications that the ITTs are considered by the industry to be "tunnels." The industry that builds ITT's refers to them as "immersed tube tunnels." In addition, they are referred to as tunnels in project contract documents. We note also that the descriptions on the project's Internet page describe the Fort Point Channel Crossing portion of the CA/T as "immersed tubes tunnels" and refer to the ITT portion of the project as "tunneling under the Fort Point Channel..."

One of the CA/T contractors, Modern Continental (in its letter dated May 3, 1999, to the attention of Brenda J. Gordon, OSHA Area Director, Braintree, Massachusetts) requested a variance from our underground construction ventilation standard, §1926.800(k)(4). In its request Modern Continental, contractor for the Fort Point Channel Crossing tunnel, explained its ITT ventilation system using "tunnel" to describe the ITT sections. This current perception of them as tunnels is consistent with the fact that, from both a construction and safety standpoint, they "create conditions characteristic of underground construction." In a January 31, 1978 letter to Mr. Lewis J. Baker, OSHA discussed the "problems germane to tunnel operations" in the following terms: "limit[ed] access or egress of employees, the movement of air, the amount of natural daylight illumination or...other problems germane to tunnel operations." ITT construction shares those hazards as well as the hazards which, under §1926.800(d), employers must address in instructing underground construction employees.

Your memo described a number of hazards common to underground construction and ITT tunneling:

Flooding

Oxygen deficiency

Lack of fresh air for workers at the workface (ITT section bulkheads) and other work areas; potential for accumulation of harmful accumulation of mists/dusts/fumes/gases/vapors (such as local concrete sawing)

Potentially explosive atmospheres

Lack of illumination

Fire

Limited means of access and egress; need for power-assisted emergency hoisting capability

Inability to use unassisted voice communications

Hazards posed by welding and cutting operations

Hazards posed by electrical equipment

Struck-by and caught-between hazards from diesel powered material handling equipment, hoisting/lowering in shafts and asphalt paving operations

These hazards are typical of underground construction.

In addition, by including "shafts, chambers and passageways," the Agency indicated that "underground construction" was to include the construction of a means of getting under or through an obstacle. "Underground" was used to differentiate "cut-and-cover" construction from construction completely enclosed in the media through which the construction passed. That media could be hard rock, shale, sand stone, clay, sand, silt, mud, muck, as well as water itself.

Water is a constant threat in tunnel construction in all but the driest of environments. The fact that OSHA requires underground construction employees to receive flood control training is because of the broad recognition of the magnitude of the hazards posed by water to tunnel workers.

In a letter dated May 28, 1998 to the Underground Contractors Association's Tunnel Task Force Chairman, Mr. Lawrence J. Keefe, OSHA used the following definition of a tunnel: "[a]n 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."1 The ITTs are covered with 5 feet of gravel and connect underground tunnels at either end of the channel. When considered in conjunction with the industry recognition of this type of construction as tunnels and the fact that the hazards they pose are typical of underground construction, the ITTs are "tunnels" within the meaning of the standard.

In sum, the installation of, and construction work in the Fort Point Channel Crossing concrete immersed tube tunnels is covered by §1926.800.

[1] The definition continues with a parenthetical explanation, "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." This parenthetical explanation is inaccurate. Neither the 1988 nor 1995 ANSI A10.16 definition includes the phrase "to a point underground." Therefore, the inclusion of the phrase "to a point underground" was in error. [ back to text ]