LONG BEACH (CBSLA) — Five utility workers were burned in an explosion in an underground vault in Long Beach early Tuesday.

The explosion happened just before 4:30 a.m. in an underground SoCal Edison vault near Golden Shore and Seaside Way in Long Beach. Five contract workers for SoCal Edison were working inside the vault at the time of the explosion.

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All five workers escaped from the vault on their own, according to Long Beach Battalion Chief Jim Arvizu said. Their injuries ranged from serious to moderate.

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Officials say 84 customers in the area, mostly businesses, were without power due to the explosion.

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The cause of the explosion is under investigation.