Aspokesman has defended Shell Canada's safety record at its Scotford plant after the companywarnedlocal residents about a gas leak for thesecondtime in less than a week.

Residents near the Shell plant in Fort Saskatchewan were advised Tuesday to stay indoors after hydrogen sulphide and sulphur dioxide were releasedat the heavy oil upgrader site at around 10 a.m.

Last Thursday, sulphur dioxide ignited on site, but in a different unit.

Shell spokesman Randy Provencal apologized to neighbours for the unpleasant incidents,but stressed the two were unrelated.

"I don't think this is reflective of our operational performance here at the plant site," said Provencal.

"The refinery's been here for 23 years and the upgrader's been here for almost four years and we do have a solid track record from an operational perspective and a safety perspective."

Alberta's Energy and Utilities Board gave Shell permission to nearly double the size of the plant two weeks ago. However, the board may now take a second look at the expansion.

"If we find incidents coming close together of very serious non-compliance, that is going make us take a look at a company's record and our decision to licence that company," said energy board spokesman Dave Sheremata.

Provencal said he hopes the board and neighbourslook at theplant's record over four years of operation.

"I hope they look at the long track record and not just the last few days here," he said.

No injuries

The gas release on Tuesday occurred in a hydrogen-cracking unit. An evacuation involved 1,400 workers from the facility and surrounding plants.

There were no reports of injuries, and the Alberta Energy and Utilities Board had staff on site to investigate.

The EUB said mobile air monitoring hadn't detected any hydrogen sulphide or sulphur dioxide beyond the plant, and residents were told it was safe to go outside by late afternoon.

Last Thursday, the company received complaints from residents who said they weren't warned until a few hours after the fire, which burned for several minutes before being contained.

About 600 employees were forced to leave after the incident, which is still being investigated.

Shell's Scotford upgrader processes bitumen from the Alberta oilsands into synthetic crude oil.

It's part of its Athabasca oilsands operation, which it owns along with Western Oil Sands (TSX:WTO) and Chevron Canada (NYSE:CVX).

The EUB recently agreed to a major expansion that almost doubles the size of the heavy oil upgrading plant.

With files from the Canadian Press