When a utility worker caused a major natural gas explosion in Springfield last week, he was using a simple probing device that's often used in such situations. A similar probe was also a key factor in a Massachusetts explosion five years ago.
The tool can be essential in finding gas leaks, but new techniques may make it safer.
It's called a probe bar, or a "bang bar," and it's just a long, handheld tube with a thin metal bar within that can extend to punch holes in soil, concrete and, sometimes, gas pipes.
Bob Ackley, an engineer who studies gas leaks for private groups, demonstrated how it works.
"It's a piece of steel rod about a quarter of an inch to half-inch in diameter, with a weighted shaft," he said. "So what you do is drive the pin into the ground so you can take an air sample from out of the ground."
That's what state investigators say a worker for Columbia Gas was doing in Springfield on Friday when searching for the source of a reported gas leak. Relying on old and inaccurate utility markers as a guide, they say, he accidentally punched the bang bar right into a high-pressure, plastic-lined steel pipe. The gas it released ignited, flattening a building, and injuring 20 people.
A similar accident happened in central Massachusetts five years ago. State records show that when a utility contractor was investigating a low-level leak in Groton, he punctured a high-pressure line with a probe, and the resulting explosion destroyed a nearby house.
Ackley says the danger is real but infrequent.
"This is used thousands of times a day all across the state," he said. "It's just a rare occurrence, but when you see a building go up and people get hurt it reminds you of how dangerous things can be."
Ackley says modern mapping systems are coming online that can more precisely identify underground lines, and show workers where not to use probe bars. National Grid, which brings gas to much of Greater Boston, now has the ability to transmit detailed electronic maps to technicians in the field. Columbia Gas, which serves Springfield, is working on it.
"We're in the process of updating our maps and systems now," Columbia Gas spokeswoman Sheila Doiron said. "We've been in business in the Springfield area for more than 165 years, so there are some pretty old records but there are some pretty new ones as well."
The state Department of Public Utilities is investigating the Springfield explosion. A key question will be why the painted line markers proved to be inaccurate.
This program aired on November 27, 2012.