A massive apartment building explosion in Silver Spring will be ruled accidental, officials said Monday, after investigators concluded that a maintenance worker mistakenly cut through a gas line in a basement utility room while addressing a plumbing problem.
A subsequent gas buildup was ignited by an unknown source, causing the blast Thursday morning at the Friendly Garden Apartments just north of D.C. Fourteen people were injured. Two residents remained hospitalized on Monday, one in critical condition, Goldstein said.
That the blast erupted at 10:30 a.m., when many residents were away at work or in school, likely prevented deaths. An extensive search of the rubble has left firefighters “confident and comfortable” that no victims got trapped inside, Goldstein said.
For days, officials have cited the errant plumbing project as a leading theory to what went wrong. On Monday, they offered details and conclusions.
It started with the maintenance worker trying to fix a clogged drain in a first-floor unit. He inserted a snake tool into a line to try to get at the clog, Goldstein said, before heading to a basement utility area directly below the unit. The line that he mistakenly cut, officials said, was 1½ inches in diameter.
Even after cutting through it, there is no indication the worker realized what he had done. After cutting the pipe, he placed a cap over the hole. But that cap was designed for a plumbing line not a gas line, Goldstein said.
The pipe was not labeled, officials said. And because it was relatively wide, and because it was located at a point in the building’s system that had forced its pressure to be reduced, any sudden outflow of gas might not have be heard.
“You’re not going to hear a loud hissing, and you’re not going to have a rush of gas coming out of even an inch-and-a-half gas pipe,” Goldstein said.
The maintenance worker returned to the upstairs apartment, where one of the occupants was home. A sudden fireball erupted, which injured the apartment resident.
“The maintenance worker came to that resident’s aid, and then they both began to exit the building,” Goldstein said. “They were in the process of exiting the building, and were in the stairwell of the building — back stairs, specifically — when the significant explosion occurred.”
It’s unclear if there were two separate ignition sources — one causing the fireball and one causing the explosion — or if something charred or smoldering from the fireball led to the explosion.
In any event, that blast destroyed four levels, including the basement, and was followed by a much longer-lasting fire that engulfed the structure.
Investigators spoke to the maintenance man, who officials have described as cooperative. They confirmed his account with evidence found in the rubble, such as the snake, ladder and tools near the gas line, according to Goldstein.
The spark or flame that set off the flash fire and the explosion probably will never be known.
“Could be a pilot light. Could be a cigarette,” Goldstein said. “Could be the simple flick of a light switch. Could be a motorized tool. All kinds of components could be that ignition source.”
Montgomery County Executive Marc Elrich (D), the jurisdiction’s top elected official, said he was concerned the gas line wasn’t labeled and — as part of an older building — apparently didn’t have to be.
“We can require that we believe,” Elrich said. “And we’re going to look to be doing that. There shouldn’t be anybody going into a room and thinking they’re doing maintenance work and not knowing that they’re working on a water pipe or gas pipes.”
He also questioned what kind of training the apartment complex’s management required.
A representative for the nonprofit group that manages Friendly Gardens did not immediately respond to a request for comment Monday.
After the blast and fire, investigators were able to account for all residents in the building as either being away from the building at the time of the blast, not seriously hurt or hospitalized. Still, there was concern that an unknown building visitor — a delivery person, perhaps — was dead under the debris.
Firefighters led specially trained dogs to react to the smell of deceased humans across the debris pile. One of the dogs “alerted” to such a scent Thursday, and a different dog alerted on Friday. But dogs working the debris pile later Friday and Saturday detected no such odors, Goldstein said.
The explosion destroyed a section of the apartment complex. It also damaged units in nearby buildings, such that about 120 residents will have to live elsewhere for the foreseeable future. Goldstein said many of those residents, with firefighter escorts, were able to go back into their units over the weekend to retrieve critical items. He expects more residents to be escorted to their units Tuesday morning.