Open Loop in Lawrence, Massachusetts—Cause of the Columbia Gas Disaster

Every profession has its inside lingo, expressions that mean something only to practitioners.  In the disciplines of electrical and mechanical engineering, one such expression is to "go open loop."  The loop referred to is a feedback loop, a concept that control systems of all kinds use to regulate quantities such as speed, flow rate, and pressure.  A well-designed feedback loop works as a clever automatic hand on a control valve to maintain constant pressure in a gas supply line, for instance, in the face of variations in demand for gas or delivery pressure from the high-pressure gas main.  But in order to work, the feedback loop must be closed, or complete, all the way from the regulator that controls the pressure, say, through supply pipes to the sensor that tells the system what the pressure is, back to the regulator.  If the information flow is interrupted anywhere in the loop, the regulator usually goes to an extreme and jams, which can lead to dire consequences.  So if you ever hear an engineer talking about a person who lost control of his temper as "going open loop," that's where the expression comes from.

On Sept. 13 of this year, dozens of people were injured, one was killed, and over a hundred structures were damaged in and around Lawrence, Massachusetts, when a natural-gas supply line's pressure soared and turned pilot lights into blowtorches and stove gas burners into towering infernos.  The National Transportation Safety Board has released its preliminary report on the cause of the disaster, and it looks very much like it was a classic case of open loop.

That afternoon, work crews were in the final stages of performing a tie-in to connect a new set of plastic gas-distribution pipes to the system, and to decommission a set of old cast-iron pipes that dated back to the early 1900s.  While many modern gas distribution systems place individual regulators at each customer's location, the older systems such as the one in Lawrence used low-pressure gas (about 0.5 pounds per square inch gauge, or psig) in the distribution pipes.  To regulate this pressure, control-system sensors were placed on the pipes and fed their data back to regulators at the junctions between the high-pressure transmission pipes and the low-pressure distribution pipes.

The instructions to the work crews did not say anything about what to do with the sensor  signals coming from the old cast-iron pipes when the gas was switched over from the old system to the new plastic one.  So when the crews shut off the manual valve that fed the old pipes, the sensors in them were still connected to the regulator that was now feeding the new plastic pipes, which were connected to most of the homes in the affected area. 

It's easy to see that cutting off the valve broke the feedback loop.  The control system saw pressure falling in the old pipes, so it opened up the regulator.  But the higher pressure wasn't being sensed, because the crews hadn't been told to switch the sensor signals at the same time they switched the pipes. 

Pressures are monitored constantly on the system, but only at Columbia Gas headquarters back in Columbus, Ohio.  Overpressure alarms went off shortly after 4 PM at the monitoring center, but the dispatchers there had no way of shutting off the system.  All they could do was to try getting in touch with the technicians in Lawrence to tell them to shut off the gas.  Even though that was done about a minute after the alarms went off, it wasn't until 4:30 that the regulator supplying the overpressure gas was shut off.  By then most of the damage had been done. 

An article in the Boston Globe last week describes the anguish of Lawrence residents who are still waiting for Columbia Gas to restore gas service.  Many homes in the area are unlivable without gas heat, and as cold weather intensifies the situation is getting intolerable.  The company's self-imposed deadline of mid-November for having all customers back on line recently slipped to Dec. 16, and there are many complaints about poor communication regarding repair-work schedules and shoddy workmanship once the crews arrive.  Columbia Gas is going to be paying for this mistake for a very long time, as are the affected residents of Lawrence.

The behavior of Columbia Gas approaches a poster-child status of how not to run a utility.  You can bet that when the gas company was locally owned and operated, the monitoring center in Massachusetts probably also had the ability to shut off the gas.  But when consolidator Columbia Gas purchased the system, the move of the monitoring operation to Ohio was probably done to save money, money which was not spent on a corresponding control system to allow Ohio monitors to shut off regulators and valves remotely. 

Work-crew training and planning also came up short in this disaster.  It's sometimes hard to say exactly how much knowledge technicians and their immediate supervisors should have about the technology they are working on.  There's no need for every lowly tech to know enough to design the entire system, for example. That's what engineers are for.   But on the other hand, you would hope that the person in charge of the work crew would know enough to realize that if the sensor signals were not swapped at the same time as the pipe systems they were connected to, there could be trouble.  Presumably the company has done this sort of thing before successfully, so it may be a case of an isolated incompetent worker rather than a systemic issue.  But clearly, more explicit instructions and better training are needed.

Finally, Columbia Gas hasn't exactly covered themselves with glory in the public-relations department.  Gas utilities are by nature local monopolies, and it is easy for them to act like what they are, namely the only gas company in town.  Unfortunately, in misleading their customers as to when gas would be restored, they have created a lot of ill will that more careful and cautious scheduling could have avoided. 

Let's hope for Lawrence's sake that it's a mild winter in Massachusetts, and that everybody gets their gas lines working again before it's too much colder.  And for all you other gas utilities out there:  don't act like Columbia Gas.

Sources:  I referred to the article "Merrimack Valley residents voice frustration with recovery effort" which appeared on the Boston Globe website on Oct. 28, 2018 at https://www.bostonglobe.com/metro/2018/10/27/residents-voice-frustration-with-recovery-effort/dY3LvbGLsqqWj3feaeLS3O/story.html.  The preliminary NTSB report on the incident is available at https://www.ntsb.gov/investigations/AccidentReports/Pages/PLD18MR003-preliminary-report.aspx.  I blogged on this disaster on Sept. 17, 2018.

The Massachusetts Gas Disaster

Being one of the longest-settled regions of the U. S., the Commonwealth of Massachusetts has been home to gas utility companies for close to a century and a half.  Unfortunately, some of the pipes installed in the 19th century are still in use in older parts of the state, notably around Lawrence, Andover, and North Andover in the Merrimack Valley north of Boston.  So earlier this month, Columbia Gas of Massachusetts, the gas utility serving the area, announced that it was going to start replacing some older gas lines. 

On Thursday afternoon, Sept. 13, residents of these towns would have been justified in thinking that they had suddenly been transported into the midst of a bad horror movie.  House after house exploded and caught fire.  The Massachusetts State Police logged over 30 calls reporting fires, and by Saturday authorities counted over 60 suspected gas fires in the area.  When one house exploded, its chimney toppled over onto a car, and one teenager in the car later died of his injuries.  Twenty-five people suffered injuries, some serious.

As soon as the scope of the disaster was known, authorities shut off gas and electric utilities to the areas affected and ordered an evacuation, which lasted in some cases until Saturday.  Citing Columbia Gas’s lack of cooperation, Massachusetts Governor Charlie Baker said he was replacing Columbia Gas with another utility, Eversource, to lead recovery efforts, and declared a state of emergency in the region. 

A thorough understanding of what went wrong in Lawrence will have to wait for the results of investigations by local, state, and Federal officials, including members of a National Transportation Safety Board team that were dispatched to the scene.  Nevertheless, similar incidents have happened before, and their history is better known.

In the early days of gas utilities, gas was manufactured typically by the destructive distillation of coal and stored in large accumulator tanks at close to atmospheric pressure.  Only enough pressure to send it through distribution pipes and gas meters was used, and the delivered pressure was so low it was measured in inches of water, rather than pounds per square inch (PSI).  About 7 inches of water was the standard delivery pressure then, and it remains so today—equivalent to about 0.25 PSI.  Such a low pressure reduces requirements on residential piping and means that even a wide-open pipe is not going to leak enough gas to form anything more than a moderate flame.  I have seen a gas utility worker at a work site in my neighborhood street leave a delivery pipe open and unattended for a few minutes, with no apparent concern.

But by the same token, systems designed for such low pressure behave badly if by some mishap a higher transmission-line pressure reaches them.  For transmission over long distances, pressures ranging in the 50 to 100 PSI range are used to deliver gas to substations, where pressure regulators lower the pressure to the low levels needed at customers’ houses. 

Experts agree that somehow, a pressure greatly in excess of the normal 0.25 PSI was mistakenly connected to the distribution system in Andover, North Andover, and Lawrence.  The exact effects on each home depended on what kind of appliances were connected and operating at the time.  Fortunately, the weather was mild—highs in the 70s, lows in the 60s—so probably few domestic heating systems were being used.  Still, older furnaces and stoves use pilot lights, and one official was quoted as saying with enough pressure, a pilot light can turn into a torch.  Minor flaws in piping that would withstand 0.25 PSI may give way under higher pressures, resulting in major leaks of gas that can be triggered by an electric spark, a burning candle, or other source of ignition.  Out of the many hundreds of homes serviced by Columbia Gas in that region, some 60 or so suffered either major leaks or fires and explosions as a result.

When I lived in Massachusetts for a time after growing up in Texas, I noticed a rather widespread prejudice against gas for domestic heating, as opposed to either electricity or heating oil.  I encountered more than one person who said they would never buy or rent a place with gas, simply because of the danger.  Having grown up in a house heated with gas floor furnaces and space heaters (most of which would be too dangerous to install in new construction today), this attitude struck me as strange.  But Columbia Gas has not done its industry’s reputation any good by first allowing this accident to happen, and then by failing to take quick, decisive public actions to mitigate the disaster.  Columbia Gas’s parent company NISource saw its stock price fall 12 percent on the Friday following the disaster, an unusual occurrence for a generally conservative investment such as a fully-regulated utility firm. 

Environmentally speaking, the use of natural gas for domestic heating is more efficient than electric heating, even if natural gas is used to power the electric generation plants.  It can be argued that in making so many new natural-gas discoveries over the past decade, the U. S. has done more in recent years to replace higher-carbon-emission oil with natural gas than any other nation, thus decreasing the world’s carbon footprint. 

But these arguments will not console those who have lost loved ones or property in the Massachusetts gas explosions.  I wouldn’t blame them if some of them return to what is left of their homes and rip out all the gas lines completely.  I can also imagine the troops of lawyers who must be descending upon the region to file lawsuits against Columbia Gas and anyone else with deep pockets who might have been involved.  There is justice in compensating victims for their losses to the extent possible.  A trust has been betrayed when a utility’s normally benign facilities suddenly turn into engines of fire and destruction.  It will be interesting to learn what combination of mechanical failure, lack of understanding, and management errors led to this tragedy.  But even if we learn everything there is to know, that won’t fix the death and damage that resulted from it. 

Sources:  I referred to articles carried by CNN on Sept. 14 at https://www.cnn.com/2018/09/14/us/massachusetts-explosions-fires/index.html, the Boston Globe at https://www.bostonglobe.com/metro/2018/09/13/explosions-cause-unclear-but-specialists-point-gas-pressure/1EyRYFCahN7rZbqodpSxBM/story.html, and Fortune (a Bloomberg News story) at http://fortune.com/2018/09/14/gas-explosion-massachusetts/, as well as Wikipedia articles on natural gas and Lawrence, Massachusetts.