NTSB/PAB-00/01

E P LU R IB U S UN UM

N AT I O N A L T R A S P O R TA T IO N

B O A R D

S A F E T Y

N

National Transportation Safety Board

Washington, D.C. 20594

Pipeline Accident Brief

Accident No.: DCA-99-MP-004

Type of System: Natural gas service line

Type of Accident: Rupture, explosion, and fire

Location: Bridgeport, Alabama

Date and Time: January 22, 1999, 10:02 a.m. CST

Owner/Operator: Utilities Board of the City of Bridgeport

Property Damage and Losses: $1.4 million

Fatalities: 3

Injuries: 6

Material Released: Natural gas

Pressure: 35 psig

Type of Failure: Excavation damage

Component Affected: 3⁄4-inch steel gas service line

The Accident

On January 22, 1999, while digging a trench behind a building at 406 Alabama

Avenue, a backhoe operator damaged a 3⁄4-inch steel natural gas service line and a 1-inch

water service line. This resulted in two leaks in the natural gas service line, which was

operated at 35 psig. One leak occurred where the backhoe bucket had contacted and

pulled the natural gas service line. (See figure 1.) The other was a physical separation of

the gas service line at an underground joint near the meter, which was close to the

building. Gas migrated into the building at 406 Alabama Avenue, where it ignited about

10:02 a.m. An explosion followed, destroying three buildings: 404, 406, and

408 Alabama Avenue (see figure 2). Other buildings within a two-block area of the

explosion sustained significant damage. Three fatalities, five serious injuries,1

 and one

minor injury resulted from this accident.

 1

 According to the Jackson County Coroner, on March 23, 2000, 14 months and 1 day after the

accident, one of the seriously injured persons died as a result of injuries sustained in the explosion. In

accordance with 49 Code of Federal Regulations (CFR) 830.2, his injuries continue to be classified as

“serious” for reporting purposes. Title 49 CFR 830.2 defines fatal injury as “any injury which results in

death within 30 days of the accident.”
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Figure 1. Damaged section of the gas service line to 406 Alabama Avenue.

(Arrow shows leak location. Note how the bowed area corresponds with the width of a

backhoe bucket.)

Figure 2. Damage to 404, 406, and 408 Alabama Avenue
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Preaccident Events

The owner of R&B Construction (R&B) told investigators that the owner of 408

Alabama Avenue had hired R&B to dig a trench from an electric pole behind 404

Alabama Avenue to his building for an underground electric service cable. (See figure 3.)

The owner of R&B told investigators that he had not planned beforehand to dig the trench

to 408 Alabama Avenue on the morning of the accident and that he did not call the

Alabama Line Location Center, Inc.2 However, when a part-time employee, who had

operated a backhoe for R&B in the past, arrived at the R&B office the morning of January

22 looking for work, the owner of R&B decided to have the employee dig the trench that

day.

Figure 3. Schematic of accident area

The owner of R&B was a full-time employee of the Utilities Board of the City of

Bridgeport (Utilities Board) at the time of the accident.3 He and a Utilities Board

coworker, who was the acting supervisor of the Utilities Board field personnel on the

morning of the accident, told Safety Board investigators that on the way to work that

morning, they located and marked the gas and water service lines for the trenching

 2

 Since the accident, the Alabama Line Location Center has been redesignated Alabama One Call.

3

 The Utilities Board owns and operates Bridgeport’s water and natural gas distribution systems.
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activity. The owner of R&B told investigators that blue paint was used to mark both

service lines because that was the only paint that they had.4

 Upon their arrival the day

after the explosion, Safety Board investigators could not find any blue or other line

markings on the ground at the accident scene. Representatives from the Alabama Public

Service Commission and the Alabama State Fire Marshals Office also did not observe

any markings on the ground when they arrived at the accident scene within hours of the

explosion.

The owner of R&B and the acting supervisor left the excavation site about

8:15 a.m. to go to the Utilities Board shop. They told investigators that, before they left,

they had asked the owner of 408 Alabama Avenue to watch the backhoe operator. The

R&B backhoe operator arrived at the excavation site some time after 8:15 a.m. While

digging the trench, the backhoe operator damaged the underground gas and water service

lines to 406 Alabama Avenue, resulting in leaks in the water and gas service lines. About

9:15 a.m., the owner of 408 Alabama Avenue went to the Utilities Board office at

513 Alabama Avenue and reported the excavation damage. He then returned to the

excavation site. The General Manager of the Utilities Board said the owner of

408 Alabama Avenue reported that the water line and possibly the gas line were

damaged.

The Utilities Board paged its field personnel between 9:18 and 9:22 a.m. Shortly

afterward, five Utilities Board employees responded to the excavation site from three

locations to locate and repair the leaks. One of the Utilities Board employees told Safety

Board investigators that upon his arrival at the accident scene, the R&B backhoe operator

showed him where he had wrapped black tape over the leak in the gas service line. In

addition, he and other Utilities Board employees noticed that water was running on the

ground. They could hear the hissing of leaking gas and smell a strong natural gas odor in

the general area.

The Utilities Board employee who was the acting supervisor turned the water off

so that field personnel could excavate and locate the leak. The acting supervisor could

see a portion of the pulled gas service line above ground and said that he suspected that

the gas service line was severed at some point. Though the acting supervisor could hear

the gas blowing and see the gas bubbling from the water in the excavated ditch, he did not

know the direction in which the gas was blowing. He told investigators that he “was

hoping” that the line was pulled off at the main and that the gas was blowing up into the

air. He added that he believed the leak was routine and the situation was safe. The

Utilities Board employees did not check for gas migrating underground or accumulating

in buildings and did not stop the flow of gas. After the acting supervisor turned off the

water, a Utilities Board employee started digging to remove water and soil from the

trench with a backhoe. By this time, the owner of R&B, because he was a Utilities Board

employee and was paged, had arrived at the excavation site.

 4

 The Superintendent of the Utilities Board told Safety Board investigators that the Utilities Board uses

yellow paint to mark gas lines and blue paint to mark water lines.
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Shortly after the Utilities Board backhoe operator started digging, the building at

406 Alabama Avenue exploded. The owner of 408 Alabama Avenue, the R&B backhoe

operator, and a Utilities Board employee received fatal injuries. Five other people,

including a bystander, received serious injuries, and one person received a minor injury.

The Alabama State Fire Marshals Office determined that the likely source of

ignition for the accumulated natural gas was a gas-fired heater at 406 Alabama Avenue,

which had an active pilot light at the time of explosion.5 The Superintendent of the

Utilities Board estimated that within 5 to 10 minutes after the explosion he had closed

two valves on the 4-inch natural gas main feeding the natural gas to the broken service

line.

R&B Construction

R&B is a small construction company that employs part-time employees. At the

time of the accident, it did not have employee qualification and training records or written

procedures for excavating near underground utility lines.

Recognizing that damages to underground facilities are usually preventable, and

most frequently occur due to a breakdown in the damage prevention process, Government

and industry have been working to identify and validate existing best practices for

preventing damage to underground facilities. The resulting Common Ground study of

one-call systems and damage prevention best practices6 discusses, among other best

practices, the need to “call before you dig.” The study recommends, “Unless otherwise

specified in state law, the excavator calls the one-call center at least two working days

and no more than ten working days prior to beginning excavation.”7 It also recommends

that an excavator observe a “tolerance zone” that includes the width of the facility plus 18

inches on either side and asks that excavators exercise reasonable care when excavating

within the tolerance zone to protect the underground facilities.

 5

 Although the gas line had separated underground, the compacted earth surrounding the line would

have provided a path that allowed continued gas flow sufficient to have fueled the pilot light.

6 Common Ground: Study of One-Call Systems and Damage Prevention Best Practices, U.S.

Department of Transportation, Research and Special Programs Administration, Office of Pipeline Safety,

Washington, D.C., August 1999. The Common Ground study, as authorized by the Transportation Equity

Act for the 21st Century (TEA 21), was prepared by more than 160 individuals representing a wide range of

interests, organizations, and viewpoints on preventing damage to underground utilities. A nonprofit

organization, the Common Ground Alliance, has been formed to implement the best practices discussed in

the Common Ground study.

7

 Alabama State law is similar to this recommendation.
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Bridgeport Utilities Board Procedures for Responding to

Pipeline Emergencies

The Utilities Board’s written emergency procedures in effect at the time of the

January 22, 1999, accident instruct service personnel to “...evaluate the extent of the

emergency, request assistance as needed, and inform the manager if necessary.” The

procedures further direct service personnel to:

Evacuate and secure the area if necessary. Actions should be directed

towards protecting people first and then property.

...If, in the opinion of the person in charge, the emergency is so severe that

immediate shutdown is imperative, he may do so without clearance from

the Manager.

However, the procedures do not instruct employees responding to a reported leak to

consider the possibility of multiple leaks, check for gas accumulation in nearby buildings,

and, if necessary, to take steps to promptly stop the flow of gas.

During its annual inspections of the Utilities Board, the Alabama Public Service

Commission did not identify any deficiencies in the Utility Board’s emergency

procedures. Since the accident, the emergency procedures have been changed only to

update the names, addresses, and phone numbers of contact persons and employees.

Probable Cause

The National Transportation Safety Board determines that the probable cause of

the accident was the failure of R&B Construction to establish and follow safe procedures

for excavation activities, resulting in damage to a 3⁄4-inch natural gas service line, and the

failure of the Utilities Board of the City of Bridgeport to provide appropriate emergency

response to the resulting natural gas leak.

Adopted: November 28, 2000