OC Transpo is working to fix an engine issue that caused diesel fumes to leak into some of its new double-decker buses on Wednesday, causing one driver to get sick.

In a memo, OC Transpo general manager John Manconi said a gasket seal failure in the engine’s exhaust was to blame, with new seals coming from the engine supplier.

He said there is a temporary fix in place and the system using that gasket has been shut down on all buses, stopping the issue from happening again.

Ottawa's transit union said a driver was treated for elevated levels of carbon monoxide after feeling sick and pulling his empty bus over.

"An operator was taken off the bus, was feeling ill, was taken to hospital for observation," said Sharon Bow, VP of ATU 279.

"We're all concerned when things like this happen, we all have a concern for the members as operating staff, the equipment staff, and also the public."

Bow said at least three other drivers have also complained of fumes while driving the new buses.

The bus company said the buses are safe to operate and there are no risks to the drivers, passengers or bus itself.

Transit users said they don't feel reassured.

"The city shouldn't be buying those," said Richard Boyling. "They should be tested before they're sent out."

"I won't ride them. I'll wait for another one," said Kim Caesar.

Manconi said all buses will be inspected for leaks, with the repairs covered under their warranty.

With a report from CTV Ottawa's John Hua