Case study2

O R I G I N A L A R T I C L E

Insights to the Columbia Gas Explosions Lawrence and North Andover, MA September 13, 2018

Ronald J. Willey

Department of Chemical Engineering,

201C CN, Northeastern University, Boston,

Massachusetts

Correspondence

Ronald J. Willey, Department of Chemical

Engineering, 201C CN, Northeastern

University, 360 Huntington Ave, Boston,

MA 02115.

Email: [email protected]

Funding information

Practical Applications, Waltham,

Massachusetts

Abstract

On September 13, 2018 at approximately 4:00 PM EDT a series of emergency calls

were received by 911 operators working the Lawrence and North Andover region of

Massachusetts. The calls ranged from smells of “natural gas” to actual fires to actual

explosions (at least five recorded). A low-pressure natural gas supply system (0.5 psig

14 in. water column) “overpressurized” by at least one order of magnitude. Approxi-

mately 8600 customers were affected. Of these, 131 customers had some type of

“extended over pressure event” such as a release of natural gas within their basement.

This is a 1.5% failure rate on systems that should have been in place when over pres-

sure occur. Unfortunately, this 1.5% failure rate translated into a multimillion dollar loss

for the gas company, and the disruption of quality of life for 8600 residents, hundreds

of whom were displaced for over 6 months as their homes were rebuilt. One year later,

full recovery is still in progress for the area. The root cause traces back to a failed

“management of change” system. With proper a hazard analysis/safety review and

communication, this event could have been prevented or at least mitigated.

K E Y W O R D S

case history, natural gas

1 | INTRODUCTION

1.1 | Author's note

Much of the information in this manuscript was obtained from the

NTSB final report on the incident first issued in September 2019.1

The author made a personal visit to the site of the incident taking

photographs. Also, the author interviewed several people who had an

interest in this event.

1.2 | Abstract from the NTSB report

On September 13, 2018, about 4:00 PM local time, a series of structure

fires and explosions occurred after high-pressure natural gas was released

into a low-pressure natural gas distribution system in the northeast region

of the Merrimack Valley in the Commonwealth of Massachusetts. The

natural gas distribution system was owned and operated by Columbia

Gas of Massachusetts (CMA), a subsidiary of NiSource, Inc. CMA delivers

natural gas to about 325 000 customers in Massachusetts. One person

was killed and 22 individuals, including three firefighters, were trans-

ported to local hospitals due to injuries; seven other firefighters incurred

minor injuries. The fires and explosions 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 occurred from

fires ignited by natural gas-fueled appliances; several of the homes were

destroyed by natural gas-fueled explosions. Fire departments from the

three municipalities were dispatched to the fires and explosions. First

responders initiated the Massachusetts fire-mobilization plan and

received mutual aid from neighboring districts in Massachusetts, New

Hampshire, and Maine. Emergency management officials had the electric

utility shut down electrical power in the area, the state police closed local

roads, and freight and passenger railroad operations in the area were Originally Prepared for American Institute of Chemical Engineers 2020 Spring Meeting and

16th Global Congress on Process Safety.

Received: 4 September 2020 Accepted: 12 September 2020

DOI: 10.1002/prs.12195

Proc Safety Prog. 2020;e12195. wileyonlinelibrary.com/journal/prs © 2020 American Institute of Chemical Engineers 1 of 9

https://doi.org/10.1002/prs.12195

suspended. CMA shut down the low-pressure natural gas distribution

system, affecting 10 894 customers, including some outside the area who

had their service shut off as a precaution. The National Transportation

Safety Board made new recommendations to the Pipeline and Hazardous

Materials Safety Administration; the 31 states with an industrial

exemption for natural gas infrastructure projects; the Commonwealth of

Massachusetts Executive Office of Public Safety and Security; and

NiSource, Inc (Ref. 1, p. iii).

2 | BACKGROUND

2.1 | The location

The location of the natural gas pipeline replacement project was in

Lawrence and North Andover, Massachusetts. Figure 1A,B shows the

geographical location of the city. Population of Lawrence Massachu-

setts is approximately 76 000 and North Andover is approximately

30 500.2,3 Lawrence was one of the first industrial centers of the

United States and is located along the Merrimack River.

Shown in Figures 2 and 3 are the approximate street location

where the regulator vault and sensors were located. Approximately

six blocks of cast iron piping, dating back to the 1900s, were being

replaced with new pipe polyethylene pipe.

2.2 | The pipeline replacement project

CMA, a subsidy of NiSource, Merrillville, Illinois, began plans for a

low-pressure gas pipeline replacement project in 2016. After some

delay, in 2018, Feeney Brothers Associates, a subcontractor specializ-

ing in pipe main construction, was hired to replace 7595 ft of 90 year

old of 8 in. cast-iron gas mains with 4845 ft of polyethylene pipe.

These pipelines supplied low-pressure natural gas to homes and com-

mercial customers (ca. 8600) in the Lawrence and North Andover

regions. Supply pressure ranged from 0.25 to 0.5 psi or 7 to 15 in.

water column.

2.3 | The initiation

Around 4 PM, September 13, 2020, Feeney brothers closed the feed

to a segment of the cast iron pipeline being replaced and brought on

line new replacement pipeline. Pressure within the old fell. The sen-

sors attached (see Figure 4) sent a signal of pressure decreasing from

about 0.5 to 0.0 psi. The regulator valves opened, and remained open,

as the replacement pipe pressure continued to build beyond the 0.25

to 0.5 psi to estimates of 10-fold. The problem was that the pressure

sensor was not relocated from the old pipeline. The old pipe, because

it was isolated was not increasing in pressure. Yet the control system,

sensing low-pressure, continued to keep regulator valves open.

2.4 | Fires, explosions, and odors

From 4 PM to 6 PM that day, due to a higher than normal pressure distri-

bution line, localized customer gas equipment failed. Some gas appli-

ances did not hold the increase of pressure, even at 6 psi, and the gas

leaked into basements and other areas of many homes. These areas

filled with natural gas. Pilots and electrical shocks provided the ignition

FIGURE 1 A,B, Geographical location of Lawrence and North Andover Massachusetts [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 2 This intersection is near the regulator station and sensing valves [Color figure can be viewed at wileyonlinelibrary.com]

2 of 9 WILLEY

sources. An example house destroyed in the explosion is shown in

Figure 5. A chimney on the right side of house collapsed (see bricks on

the right side). Leonel Rondon, 18, was killed while sitting in a car when

the chimney fell upon the car. Figure 6 shows the 134 locations that

have an over pressure event followed by a leak, fire, or explosion.

2.5 | Aftermath

It took nearly six months to completely re-pipe the whole area

(as many as 10 000 gas customers received completely new service)

and return gas service to all customers in the area. The cost is still

being assessed; however, one reported settlement was at 143 million

dollars, and the total losses are reported at 1 billion dollars for

NiSource.4

3 | A CLOSER LOOK AT THE LAYERS THAT FAILED

3.1 | Questionable qualifications of the engineer- in-charge

The engineer responsible for this project lacks a Professional Engi-

neers' License. This was possible under the industrial exemption that

public utilities hold. Based on the description in the report, this person

had and engineering-in-training certificate; however, the person had

not completed the P. E. examination. This would indicate that the

experience of this engineer is around 4 years or less.

As time moves on, the available documentation of any original

project become harder to find and assemble. In this case, the 800 cast

iron pipeline was installed in the early 1900s. Then, a control system

consisting of a sensor and control valves were probably added around

the 1970s or 1980s. Then, the company changed hands with new

owners.

How can we expect a young engineer to find previous informa-

tion, that may have been under the previous ownership, for review in

upgrade projects? Maybe, we are expecting too much? As was written

in the NSTB report (Ref. 1, p. 29)

FIGURE 4 Schematic of the sensor, control valves, and pipelines (Ref. 1, p. 15) [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 3 Possible location of the regulator vault, see also Figure 4 [Color figure can be viewed at wileyonlinelibrary.com]

WILLEY 3 of 9

“The documents prepared for the South Union Street pro-

ject were signed by a degreed engineer who had an

engineer-in-training certificate, which is held by individ-

uals preparing to take the P.E. examination. However, he

was not yet eligible to take the P.E. examination because

he had not satisfied the work experience requirement.”

(Ref. 1, p. 29)

An outcome of this oversight was this recommendation by the NSTB,

nationwide. (Ref. 1, p. 29)

On November 14, 2018, the NTSB issued Safety Recom-

mendation P-18-5 to the Commonwealth of Massachu-

setts that addressed the removal of a P.E. licensure

exemption for such public utility work, along with a

corresponding Safety Recommendation P-18-6 issued to

NiSource, the parent company of Columbia Gas of Massa-

chusetts, recommending P.E. approval natural gas pipeline

projects within NiSource (NTSB 2018). As described more

fully in section 2.1, Massachusetts acted to satisfy Safety

Recommendation P-18-5 less than 2 months after it was

issued. Subsequent to this recommendation, the NTSB

contacted two independent organizations seeking expert

information on the current state of P.E. license oversight

and the industrial exemptions among the United States

and territories for major infrastructure projects. (Ref. 1,

p. 30)

P-18-5 To the Commonwealth of Massachusetts Elimi-

nate the professional engineer licensure exemption for

public utility work and require a professional engineer's

seal on public utility engineering drawings (Ref. 1, p. 33)

P-18-6 To NiSource: Revise the engineering plan and con-

structability review process across all your subsidiaries to

ensure that all applicable departments review documents

for accuracy, completeness, and correctness, and that the

documents or plans be sealed by a professional engineer

prior to commencing work. (Ref. 1, p. 34)

The Commonwealth of Massachusetts' exemption for the require-

ment of registered Professional Engineer (P.E.) to perform industrial

and public utility work limits the opportunities for competently trained

and experienced engineers to uncover system design and work pro-

cess deficiencies. By eliminating the exemption, especially for systems

involving inherently dangerous materials such as natural gas distribu-

tion systems, companies, workers, and the public are provided greater

safety assurance that competent and qualified engineers, who are eth-

ically bound to work only on projects within the scope of their exper-

tise, will review, assess, and execute the requisite work activities

according to best engineering practices and with expected safeguards.

(Ref. 1, p. 33).

Why required a P.E.? The answer is that a qualified P.E. generally

has the experience, the knowledge, and just enough hesitancy, to ask

the right questions as projects go forth. They understand that protec-

tion of the public is paramount to the profession and is within a code

of ethics for engineers. They also understand that old systems always

have surprises. They will ask the questions such as “where is the con-

trol system and what does it consist of?” in a replacement project.

When a P.E. affixes their stamp to a set of drawings, they understand

that there is a code of ethics behind that stamp, a requirement that

what they are stamping must withstand, to the best of their ability,

safe construction, and operation.

3.2 | Inadequate documentation

NiSource engineering plans used during the construction

work did not document the location of regulator sensing

lines.

The field engineer responsible for the South Union Street

Project largely relied on GIS to develop work packages.

He also had access to isometric drawings containing sche-

matics of the pipes in the regulator vaults as well as the

piping and valve configurations. Sensing lines, however,

were not included in the isometric drawings or GIS. (Ref.

1, p. 41)

I note to this audience the OSHA regulations that cover our chemical

industry: OSHA PSM 1910.119(d)(3)(i)(B).5

Piping and instrument diagrams (P&ID's); need to be up to date.

However, I further advocate that we must ask the question, and verify

independently. Has someone “walked the line?” during a MOC review6?

Have we located all of the key controllers and sensors? Even it is buried,

most likely a vault will be apparent wherever sensors or regulator valves

are located. Open up these vaults and inspected before the job begins.

Same goes for any controllers or sensors on any lines or vessels that

have to be considered in any process safety management function. We

verify the information that we are working from. NiSource had over

FIGURE 5 Front view of a house in which natural gas leaked to due to over pressure distribution line (Ref. 1, p. 3) [Color figure can be viewed at wileyonlinelibrary.com]

4 of 9 WILLEY

2000 low-pressure regulator runs. I would not be surprised if a major oil

refinery or chemical plant also have this many on any large site. This

accident reminds us why we need to ask in verify important ancillary

equipment that may be attached to our processes.

3.3 | Management of change procedure lacking

NiSource did not perform an adequate management of change analy-

sis for the pipeline replacement.

NTSB investigators found that NiSource did not use man-

agement of change (MOC) procedures for managing main-

tenance and construction changes to pipeline operations.

The company did not conduct separate risk assessments

for each construction project, critical components of a

PSMS program. MOC procedures require an analysis of

implications [hazard identification or process hazard

analysis],1 among several other elements. Additionally, a

risk identification and assessment are necessary to estab-

lish the appropriate prevention and mitigation measures

to reduce the likelihood of consequences should an inci-

dent occur. CMA failed to perform such an analysis and

failed to establish appropriate controls to mitigate the

risks of the work that was being performed. Had NiSource

adequately performed MOC, it could have immediately

addressed the issue and mitigated the consequences of

the event. (Ref. 1, pp. 35 and 36)

There was a delay in the project of 1.5 years. This resulted in loss of

organizational memory, specifically where the sensors were located.

The safety review dated January 16, 2017 was signed by engineering

FIGURE 6 Map of the damaged structures in the area impacted by the overpressurization (Ref. 1, p. 2) [Color figure can be viewed at wileyonlinelibrary.com]

WILLEY 5 of 9

and construction. Measurement and Regulation within the company

did not sign off on this safety review. Sign off was not required in the

original NiSource policy.

There was a nearly complete turnover in project personnel

[ between initiation and implementation]. CMA did not

effectively transfer the knowledge its 2016 construction

personnel had about the status of the project sensing

lines to its 2018 construction personnel. (Ref. 1, p. 41)

The NTSB issued a recommendation:

Apply management of change process to all changes to

adequately identify system threats that could result in a

common mode failure. (P-18-8) (Ref. 1, p. 36)

After this recommendation from the NTSB, NiSource implemented

their Gas Standard 1680.010, “Tie-Ins and Tapping Pressurized

Pipelines,” that incorporate management of change.

3.4 | Pressure regulator(s) lacking downstream pressure relief

Note the plural. That is because there are two regulators in series

such that if one failed open, a second one would continue to con-

trol. Normally, these regulators must have downstream over pres-

sure relief as specified in US Code of Federal Regulations

(CFR) 49.

For example, CFR 49 section 192.195 is as follows: Protection

against accidental overpressuring

(a) General requirements. Except as provided in §

192.197, each pipeline that is connected to a gas source

so that the maximum allowable operating pressure could

be exceeded as the result of pressure control failure or of

some other type of failure, must have pressure relieving or

pressure limiting devices that meet the requirements of

§§ 192.199 and 192.201. (b) Additional requirements for

distribution systems7

FIGURE 7 A typical gas regulator now required on services to prevent overpressurization (Figure adapted from Reference 9) [Color figure can be viewed at wileyonlinelibrary.com]

6 of 9 WILLEY

In other words, at or near the regulator feeding the customer gas sys-

tem exceeds a threshold supply pressure, the regulator relieves to the

surroundings. An example of this detail is shown in Figure 7. Code fur-

ther requires that a pressure regulator between a distribution line and

a customer service must be placed outside with some exceptions such

as a high-pressure gas distribution within the building and specific gas

meter rooms.

Gas meter piping supplying gas to a building at a pressure

in excess of 1/2 psig (3.4 kPa gauge) shall be provided with

a regulator that will reduce the pressure of the gas to 1/2

psig (3.4 kPa gauge) or less prior to entering the gas distri-

bution piping in the building, except where the use of higher

pressure is permitted. Where gas distribution pressure in

excess of 1/2 psig (3.4 kPa gauge) is permitted, it shall be

regulated not to exceed the maximum pressure level as per-

mitted by the code or the commissioner. (NYC code 8)

With the system 100 years old, some systems may not have had external

regulators. Further, modern regulators are designed to vent should over

pressure downstream occurs. Shown in Figure 7 is an example cut away

of a regulator with overpressure ventilation capability (Itron9). Three

colors are shown. The red is the supply line. The blue is the downstream

low-pressure feed to the service. Within this specialized regulator valve

is the ability of the center pressure balance to lift further should the

downstream pressure exceed a limit pressure. Then, the excess gas flows

through the yellow area of the valve. Generally, this is straight to the sur-

roundings. Natural gas is lighter than air and will eventually disperse

upward from the point of release. Codes require that these regulators be

placed away from any areas that may be ignition points.8

3.5 | Layers of protection at the customer service point

One of the expectations of natural gas distribution systems at the cus-

tomer end point is prevention of leaks within the customer's business

or home should an over pressurization supply line event occurs. In this

case approximately 8450 of 8600 customers had no leaks during the

overpressurization event. However, approximately 150 customers had

an incident. Why? The following three subsections offer explanation.

3.6 | Lack of, or failure, of an outside pressure relief regulator at the customer service point

Grandfathering occurs in gas line distribution systems. Meaning that

customers were connected in 1900s, others in 1910s, and others

later. Early installations may not have been upgraded when codes

change. This is called “grandfathering” in existing set ups. Although

current codes require new connections to have over pressure protec-

tion at the customer service, older customer's may be missing this reg-

ular/relief system. For example, Figure 8 shows a customer regulator

with over pressure protection. Not all services connected to the sys-

tem may have had this type of regulator because they were installed

before code requirement. Thus, if an over pressure event occurs, one

of the layers, an outside regulator valve with over pressure relief at

the customer service point, may not have existed.

3.7 | Grandfathering of internal appliances lacking over pressure protection

The national fire code, NFPA 54 section 8.1.4,10 has some specific

requirements that new services undergo pressure tests of not less

than 3 psi and be stressed by no less than 1.5 times the working pres-

sure, holding over 30 minutes. Many appliances regulators now hold

up to 25 psig or higher. Early 20th century appliances did not have

this protection and may not even had a regulator between the low-

pressure gas supply and the appliance. These were grandfather in

meaning that they were installed in the 1940s or earlier. Gas appli-

ances with regulators came onto the market in the 1960s and later.

Thus, an old gas stove pilot, may be directly piped to the low-pressure

gas line. It can be a source of gas entering into a building. As of this

writing, this detailed has not appeared in the press or any report. It is

from the author's background of living in New England, and in older

residences that connected to gas service many years ago.

3.8 | Grandfathering of inside gas meters

Current codes and guidelines11 require that gas meters be placed out-

side of a home or commercial property. Figure 9 shows an example of

FIGURE 8 Example of a regulator, Itron Series B42, with excess pressure relief. Photograph by R. J. W. taken in Lawrence shortly after the incident [Color figure can be viewed at wileyonlinelibrary.com]

WILLEY 7 of 9

an inside gas meter in the author's home. The gas meter was gra-

ndfathered under earlier codes and standards (ca. 1960). Presently,

there is no requirement to move it outside. These meters have relief

systems within to prevent total catastrophic failure. The relief, should

an overpressurization event happen, goes straight into the surround-

ings, such as a basement.

4 | CONCLUSIONS AND OUTCOMES TO DATE

4.1 | Summary from the NTSB report

In this accident, when the cast iron main with the sensing

lines attached was isolated from the distribution system

and abandoned in place, both regulators responded to the

decreasing pressure, detected by the sensing lines, by fully

opening. Both regulators were disabled simultaneously by

the single event of isolating the cast iron main, which

eliminated the redundancy of using dual regulators. In this

accident and the earlier accidents discussed above, the

overpressure occurred as the result of a single failure. In

engineering analyses, such a situation is referred to as a

common mode failure. Therefore, the NTSB concludes

that the multiple overpressurization accidents investi-

gated by the NTSB over the past 50 years demonstrate

that low-pressure natural gas distribution systems that

use only sensing lines and regulators as the means to

detect and prevent overpressurization are not optimal to

prevent overpressurization accidents. Thus, the NTSB rec-

ommends that PHMSA revise 49 CFR Part 192 to require

overpressure protection for low-pressure natural gas dis-

tribution systems that cannot be defeated by a single

operator error or equipment failure.

Less than 2 months after the safety recommendation was

issued, on December 28, 2018, Bill H.5005, requiring that

licensed P.E.s review and approve engineering plans devel-

oped by or on behalf of natural gas companies, to ensure

the safe construction, operation, and maintenance of nat-

ural gas infrastructure, was passed by the Massachusetts

House of Representatives. The act applies to engineering

work or services on natural gas distribution systems that

could pose a material risk to public safety, as determined

by the DPU, performed by or on behalf of a natural gas

company. Moreover, the act requires any engineering

plans or specifications for engineering work or services

that could pose a material risk to public safety, developed

by or on behalf of a natural gas company, to bear the

stamp of approval of a licensed P.E.39 After the Massa-

chusetts Senate passed the act, it was signed by the gov-

ernor on December 31, 2018, as Chapter 339 of the Acts

of 2018. (Ref. 1, p. 33).

4.2 | The value of process safety as a part of the undergraduate chemical engineering curriculum

The author is reminded about recommendations from the US Chemi-

cal Safety Board from the T-2 Accident12:

American Institute of Chemical Engineers

2008-03-I-FL-R1

Work with the Accreditation Board for Engineering and

Technology, Inc. to add reactive hazard awareness to bac-

calaureate chemical engineering curricula requirements.

2008-03-I-FL-R2

Inform all student members about the Process Safety Cer-

tificate Program and encourage program participation.

Accreditation Board for Engineering and Technol-

ogy, Inc.

2008-03-I-FL-R3

Work with the American Institute of Chemical Engineers

to add reactive hazard awareness to baccalaureate chem-

ical engineering curricula requirements

This recommendation should be extended to mechanical engineers

who train for pipe design and process design type positions.

For the AICHE, audience keep in mind that Process Safety certifi-

cation CCPSC is available from the CCPS. Another resource for

FIGURE 9 An example of a gas meter inside a Northeast US home. Newer installations place these outside. (R. J. W. photo) [Color figure can be viewed at wileyonlinelibrary.com]

8 of 9 WILLEY

process safety engineering to consult is the CCPS Risk Based Man-

agement Book (the “Red Book).13 Another suggestion/recommenda-

tion is to extend OSHA PSM to cover utilities handling flammable

gases and liquids. Finally, if buildings are utilizing natural gas, should

flammable gas detectors be installed?

ACKNOWLEDGMENTS

The author acknowledges partial financial support for this his

investigation of the accident from Practical Applications, Waltham,

Massachusetts. Mr John Murphy is also acknowledged in reading the

draft manuscript and provided further suggestions for improvements.

Helpful discussions with Dr Laurence Britton is also much appreciated.

ORCID

Ronald J. Willey https://orcid.org/0000-0001-8491-9302

ENDNOTE 1 The bracketed statement added by R. J. W. after review by John

Murphy.

REFERENCES

1. National Transportation Safety Board, Pipeline Accident Report Over-

pressurization of Natural Gas Distribution System, Explosions, and

Fires in Merrimack Valley, Massachusetts September 13, 2018; 2019,

73, https://www.ntsb.gov/investigations/AccidentReports/Pages/PA

R1902.aspx

2. Population of Lawrence Massachusetts; 2020. https://suburbanstats.

org/population/massachusetts/how-many-people-live-in-lawrence,

Accessed January 21, 2020.

3. North Andover, Massachusetts Demographics Data, https://www.

towncharts.com/Massachusetts/Demographics/North-Andover-town-

MA-Demographics-data.html, Accessed 4 February 2020.

4. Columbia Gas reaches $143 million settlement for Merrimack Valley

explosions, https://www.boston.com/news/local-news/2019/07/29/

columbia-gas-settlement-merrimack-valley-explosions, Accessed 4

February 2020.

5. OSHA, 1910.119 - Process safety management of highly hazardous

chemicals, https://www.osha.gov/laws-regs/regulations/standardnum

ber/1910/1910.119, Accessed 13 February 2020.

6. Forest JJ. Walk the line. Process Saf Prog. 2015;34:126-129. https://

aiche.onlinelibrary.wiley.com/doi/abs/10.1002/prs.11724

7. United States Government Printing Office, Part 192 Transportation

of natural and other gas by pipeline: Minimum Federal safety

standards.

8. NYC Fuel Gas Code 2014 > E Meters and Gas Service Piping > E.2

Gas Regulator and Gas Regulator Vent Outlets https://up.codes/s/

gas-regulator-and-gas-regulator-vent-outlets, Accessed 7 February

2020.

9. Itron, B42 Series Residential Regulator, http://deaconind.com/

Customer/DEINSU/specpages/B42.pdf, Accessed 7 February 2020.

10. National Fuel Gas Code, National Fire Protection Association and the

American Gas Association, NFPA 54-2018, ANSI Z223.1-2018; 2018.

11. InspectAPedia: Gas Meter & Piping Clearance Distance Codes &

Specifications, https://inspectapedia.com/plumbing/Gas_Meter_

Clearances.php#Codes, Accessed 7 February 2020.

12. T2 Laboratories Inc. Reactive Chemical Explosion https://www.csb.

gov/t2-laboratories-inc-reactive-chemical-explosion/, Accessed 13

February 2020

13. Center for Chemical Process Safety. Guidelines for Risk Based Process

Safety. New York, NY: John Wiley & Sons; 2007.

How to cite this article: Willey RJ. Insights to the Columbia

Gas Explosions Lawrence and North Andover, MA September

13, 2018. Proc Safety Prog. 2020;e12195. https://doi.org/10.

1002/prs.12195

WILLEY 9 of 9