Long Beach power outage: Vault explosions can be spectacular and deadly

Chris Kreuz was using his phone to video smoke coming from a manhole and witnessed one of the Long Beach electrical vault explosions  right at the moment it blew a heavy manhole cover into the street. He was standing only feet away from the fiery blast.

It's spectacular — you might have

, or perhaps

. Nobody was hurt in the Long Beach explosions of three electrical vaults, but these explosions can be deadly.

A Southern California Edison subcontractor was killed in a vault explosion in Huntington Beach in September, 2013.  Another Edison worker died in a vault explosion in 2003, according to federal Occupational Health and Safety Administration records.

It's unclear how many vault explosions have occurred within Southern California Edison's vast service area. Edison officials declined to be interviewed about past vault explosions while still dealing with the Long Beach incident. Parts of downtown Long Beach remained without power Friday afternoon.

The Public Utilities Commission, which regulates investor-owned utilities like Edison, could not immediately provide a list of vault explosions or fires. Edison is required to report only significant incidents that kill or hospitalize workers or that cause a certain amount of damage.

Cal/OSHA records only the incidents that occur in workplaces, and it organizes them by employer, so vault explosions that harm employees of a subcontractor working on an Edison project might not show up in a search of occupational injury records.

The area's other large power utility, Los Angeles Department of Water and Power, has seen five similar events in the past two years, none fatal, said Jay Puklavetz, interim director for power, transmission and distribution.

Those incidents include a vault explosion in May that blew a manhole cover skyward in Northridge. It landed on some cars and hurt three people.

In most cases, deteriorated cables are at fault, he said. The current flowing in the aluminum or copper core of an electrical cable can come into contact with the metal shielding on the outside of the cable when the insulation separating the two is damaged. "That's when you get the explosion, no different than if you were to stick a wire into your light socket," he said.

The other major cause of vault explosions is when a gas such as methane, collects in a vault and then ignites on a power source or spark.

The DWP created its own manhole cover retention system that uses springs or bolts to keep vault covers from blowing sky high. About half the DWP's manhole covers are fitted with the springs or bolts.

He said a vault explosion led DWP to develop the cover restraints. "Fifteen, twenty years ago we did have a lid that flew and damaged somebody's home," he said.