Gas leak leads to evacuations

Unique situation led to high chance of explosion

The Yuba City Fire Department responded to and helped evacuate residents as a result of a gas leak Wednesday that presented a unique situation with a significant chance of an explosion.

At about 4:15 p.m. Wednesday, the fire department was called out to a natural gas leak at Monroe Drive and Teal Hollow Drive in Yuba City after a 4-inch natural gas pipe was ruptured by work done by Comcast.

Currently, Comcast is expanding fiber optic cable infrastructure for a new subdivision on the east side of Royo Ranchero south of Monroe, Yuba City City

Manager Diana Langley said in an email Thursday.

Yuba City Fire Chief Jesse Alexander, in a letter to the city and city council members, said that while natural gas leaks are relatively common due to construction, this situation was

unique.

He said because natural gas is lighter than air, it normally rises and dissipates without much of an issue. However, what happened Wednesday was quite different.

“(A) telecommunication contractor also pierced the storm drain, which caused the gas to be forced into the storm drain and spread laterally instead of vertically,” Alexander said in the letter. “Since they were using a drill versus a backhoe, there was not a large hole for the gas to rise out and dissipate.”

He said because of these factors and because the 4-inch gas line is “very large and has significant pressure,” the department “started getting large

LEL (lower explosive limit) readings on our combustible gas indicators coming from the storm drains.”

Alexander said a 5 percent LEL reading is “considered immediately dangerous to life and death,” and a 7 to 15 percent LEL reading poses a “significant risk of ignition and possible explosion.”

At the site on Wednesday, the department was getting LEL readings of about 20 percent from approximately 200 feet away from the leak, he said.

Alexander said because of the unusually high LEL readings, evacuations of 21 residential structures with more than 40 evacuees took place around the area. He said the nearby senior center was established as a temporary evacuation center.

“As time progressed, the natural gas continued to spread laterally in the storm drain and increase in concentration,” Alexander said. “At one point, PG&E recorded an LEL of 40 percent approximately 300 feet from the leak site.”

He said in all his years dealing with gas leaks, he had never been at an incident where there was a recorded LEL reading of greater than 15 percent over 50 feet away.

“At this point, we removed the manhole covers to relieve the pressure and decrease lateral spread (Public Works responded to the scene and provided manhole cover hooks),” Alexander said. “Fire entered into Unified Command with PG&E, which activated a PG&E ‘Second Alarm’ response. Three holes were dug in an effort to mitigate the incident, which was clamped off at 8:15 pm.”

In his letter, Alexander said “PG&E contract crews will remain at the scene for most of the evening digging up the site to perform repairs.” He said because of the amount of natural gas in the storm drain, some people in the area may smell it for the next couple days.

“We confirmed no dangerous LEL readings were detected, but we encourage the public to call YCFD or PG&E if they become concerned about the smell increasing,” Alexander said.

Yuba City Councilman Marc Boomgaarden said as an ex-fire chief, he is continually impressed with the city’s fire department.

“Excellent work by Yuba City Fire (Department),” Boomgaarden said. “These kinds of things are signals to the preparedness of the city to deal with this kind of situation.”

The fiber optic work that is being done by Comcast is unrelated to the agreements recently made by Yuba City and Marysville with Sifi to install fiber optic infrastructure throughout the two cities.

Langley said the work that will be done by Sifi is different from Comcast because Sifi’s “trenching will be fairly shallow and there should not be issues with drilling into gas mains.”