Two Hawaiian Electric Co. employees were injured yesterday, one seriously, when a blown circuit breaker caused an explosion that forced a steel door at HECO's Archer Lane substation to fly open.

The 4:45 p.m. incident briefly disrupted electrical service to 5,000 customers in the area around Ward Avenue, extending makai to Kaka'ako and Kewalo. Power was restored quickly to all but 60 customers as of 10 p.m., HECO spokeswoman Lynne Unemori said.

Some traffic signals in the area also were disabled, slowing rush-hour traffic.

One man was transported to The Queen's Medical Center in serious condition, said Emergency Medical Services spokesman Bryan Cheplic. The man was believed to have acid-type burns to his legs.

Unemori said another man was treated at the scene; she did not know the nature of his injuries.

HECO was performing switching work when the circuit break malfunctioned, she said.

Also yesterday, the police department began experiencing delays with its 911 system about 4:30 p.m. but it was not immediately known if that was related to the power outage. The problem did not affect response time to emergency calls and the malfunction was cleared up at 8:48 p.m., police said.

Reach Rod Ohira at rohira@honoluluadvertiser.com.