TransLink is blaming human error for a service disruption that halted the Expo and Millennium SkyTrain lines for hours Monday afternoon.

The transit provider said an “experienced technician” was installing a circuit breaker for the under-construction Evergreen Line at a power distribution panel when he inadvertently caused the shutdown.

“He accidentally tripped the main breaker feeding the critical systems at SkyTrain’s operations centre, causing a system-wide shut down of train controls,” TransLink said in a statement.

“The power outage halted trains and impacted TransLink’s ability to communicate with customers over SkyTrain’s PA systems.”

Monday's incident, which lefts thousands of riders either trapped on trains or waiting at stations, had nothing to do with a similar shutdown that halted service on the same two lines last Thursday, TransLink said.

The technician involved has been suspended.

On Tuesday afternoon, the unidentified worker’s union fired back, arguing the electrical panel shouldn’t have been worked on during peak hours and that it’s wrong to lay blame on a single employee.

“Management directed our member to do the work on an electrical panel despite knowing the panel’s poor design and high risk of failing while it was live,” said Tony Rebelo of Cupe 7000.

To apologize for the outages, TransLink is offering free transit on BC Day – a statutory holiday on Aug. 4 when many Metro Vancouver residents won’t be going to work.

COO Doug Kelsey called two major disruptions in a single week “unprecedented.”

“Our trains are reliable 95% of the time, but we do know this is little consolation for customers who are delayed for hours,” Kelsey said in a statement.

Not everyone is satisfied with the apologies, however, including Vancouver Mayor Gregor Robertson, who is calling for an independent investigation into what went wrong.

“You’ve got to wonder what contingency plans were in place, what backups and safeguards didn’t exist,” Robertson told reporters.

Monday’s disruption started during the noon hour, stopping all trains on the tracks, and the system stayed completely offline for more than three hours.

Staff walked onto the SkyTrain guideways, opened the train doors and let passengers walk to the nearest stations. A few riders went rogue and exited the trains before TransLink employees could arrive.

TransLink also provided bus-shuttle hubs at busy stations, with 42 buses dispatched to clear crowds.

Canada Line service wasn’t affected in either shutdown.