Today my office received from the National Transportation Safety Board their preliminary report on the Over-pressure of a Columbia Gas of Massachusetts Low-pressure Natural Gas Distribution System.
Here is the Executive Summary of the report:
Executive Summary
The information in this report is preliminary and will be
either supplemented or corrected during the course of the investigation.
On September 13, 2018, about 4:00 p.m. eastern daylight
time, a series of explosions and fires occurred after high-pressure natural gas
was released into a low-pressure gas distribution system in the northeast
region of the Merrimack Valley in the state of Massachusetts.1 (See figure 1.)
The distribution system was owned and operated by Columbia Gas of Massachusetts
(Columbia Gas), a subsidiary of NiSource. The system over-pressure damaged 131
structures, including at least 5 homes that were destroyed in the city of
Lawrence and the towns of Andover and North Andover. Most of the damage was a
result of structure fires ignited by gas-fueled appliances. Several structures
were destroyed by natural gas explosions. One person was killed and at least 21
individuals, including 2 firefighters, were transported to the hospital. Seven
other firefighters received minor injuries.
Fire departments from the three municipalities were
dispatched to address the multiple fires and explosions. First responders initiated the state’s fire mobilization plan, that included
mutual aid from other districts in Massachusetts, New Hampshire, and Maine.
Emergency responders asked residents to evacuate from the
impacted area to four evacuation centers. At the request of emergency
management officials, National Grid shut down electrical power in the affected
area to remove a source of ignition. Nearby roads were closed, and freight and
passenger railroad operations were suspended. Columbia Gas also shut down the
low-pressure, natural gas distribution system.[2]
The cast-iron, low-pressure distribution system was
installed in the early 1900s and had been partially improved with both steel
and plastic pipe upgrades since the 1950s. The low-pressure distribution system
in the affected area relied on 14 regulator stations to control gas at the
required pressure into structures serviced by the system, unlike high-pressure
gas distribution systems that place an individual regulator to reduce pressure
at each customer service.[3] Each of the regulator stations reduced the
pressure from about 75-pounds per square inch gauge (psig) natural gas main
pipeline to 12 inches of water column (about 0.5 psig) for delivery to
customers.
Prior to the over-pressure event, a Columbia Gas-contracted
work crew, which included a Columbia Gas inspector, was performing a Columbia
Gas-designed and approved pipe-replacement project at a nearby intersection
(South Union Street and Salem Street) in South Lawrence. The contracted crew
was working on a tie-in project of a new plastic distribution main and the
abandonment of a cast-iron distribution main. The distribution main that was
abandoned still had the regulator sensing lines that were used to detect
pressure in the distribution system and provide input to the regulators to
control the system pressure. Once the contractor crews disconnected the distribution
main that was going to be abandoned, the section containing the sensing lines
began losing pressure.
As the pressure in the abandoned distribution main dropped
about 0.25 inches of water column (about 0.01 psig), the regulators responded
by opening further, increasing pressure in the distribution system. Since the
regulators no longer sensed system pressure they fully opened allowing the full
flow of high-pressure gas to be released into the distribution system supplying
the neighborhood, exceeding the maximum allowable pressure.
Columbia Gas developed and approved the work package
executed on the day of the accident. The work package did not account for the
location of the sensing lines or require their relocation to ensure the
regulators were sensing actual system pressure. The work was performed in
accordance with steps laid out in the work package. In light of this accident,
Columbia Gas implemented a safety stand-down for all employees who perform work
related to low-pressure natural gas systems for NiSource subsidiaries.[4]
Minutes before the fires and explosions occurred, the
Columbia Gas monitoring center in Columbus, Ohio, received two high-pressure
alarms for the South Lawrence gas pressure system: one at 4:04 p.m. and the
other at 4:05 p.m. The monitoring center had no control capability to close or
open valves; its only capability was to monitor pressures on the distribution
system and advise field technicians accordingly. Following company protocol, at
4:06 p.m., the Columbia Gas controller reported the high-pressure event to the
Meters and Regulations group in Lawrence. A local resident made the first 9-1-1
call to Lawrence emergency services at 4:11 p.m.
Columbia Gas shut down the regulator at issue by about 4:30
p.m. The critical valves of the involved natural gas distribution system were
closed by 7:24 p.m. Beginning about midnight, crews consisting of two Columbia
Gas technicians escorted by two emergency response personnel began shutting off
the meters at each house to isolate the homes from the natural gas distribution
system. All meters were shut off by the following morning.
National Transportation Safety Board (NTSB) Chairman Robert
Sumwalt and Member Jennifer Homendy led a 19-member NTSB team on scene. Parties
to the investigation include NiSource, Columbia Gas, Pipeline and Hazardous
Materials Safety Administration, Massachusetts State Police, and Massachusetts
Department of Public Utilities. In addition to the on-scene work, investigators
interviewed multiple people including two Columbia Gas Supervisory Control and
Data Acquisition controllers from Columbus, Ohio.
According to Columbia Gas, all cast iron and bare steel
piping in the affected neighborhoods will be replaced due to system integrity
concerns. The new system will consist of high-pressure plastic mains with
regulators at each service meter to reduce the line pressure from the main to
the required pressure. The Massachusetts Department of Public Utilities is
providing oversight of the new system installation to ensure that all work
complies with state and federal safety regulations.
The NTSB’s investigation into this accident is ongoing.
Future investigative issues include the coordination between the emergency
responders and Columbia Gas; an analysis of the engineering work package
preparation and execution, including the design documentation; and a review of
construction packages for constructability and safety.
1. Title 49 Code of Federal Regulations (CFR) 192.3 defines
a low-pressure distribution system as “a distribution system in which the gas
pressure in the main is substantially the same as the pressure provided to the
customer.” The Massachusetts Natural Gas Pipeline Safety Code, Title 220 Code
of Massachusetts Regulations (CMR) 101.06, further defines a low-pressure
distribution system “as any system in which the gas pressure in the main is
equal to or less than two psig (pounds per square inch gauge).”
2. Columbia Gas delivers natural gas to about 320,000
natural gas customers in southeastern Massachusetts, including the Merrimack
Valley.
3. Title 49 CFR 192.3 defines a high-pressure distribution
system as “a distribution system in which the gas pressure in the main is
higher than the pressure provided to the customer.” The Massachusetts Natural
Gas Pipeline Safety Code, 220 CMR 101.06, further defines a high-pressure
distribution system “as a system in which the pressure in the main is greater
than 60 psig, but equal to or less than 200 psig.”
4. A safety stand-down is an organized break from work by
which employers hold discussions with their employees. They are often taken as
occasions to discuss safety topics while also reinforcing the organization’s
policies regarding safety in general.
The full preliminary report can be found here:
https://www.ntsb.gov/investigations/AccidentReports/Pages/PLD18MR003-preliminary-report.aspx
Below are a few photos provided by the NTSB:
