The Ottawa Fire Services hazardous materials crews were called in to help deal with the oxygen, which is non-toxic, but can pose a fire and explosion hazard in the presence of ignition sources. (CBC)

The Royal Canadian Mint headquarters in Ottawa is operating normally again after a liquid oxygen spill prompted a weekend evacuation.

An Air Liquide tanker truck had been delivering oxygen to the mint on Sussex Drive when a valve malfunctioned on Sunday, Ottawa Fire Services reported.

Both the mint and the neighbouring Global Centre for Pluralism, housed in the former Canadian War Museum building, were evacuated. A section of Sussex Drive was closed between Guigues Avenue and Bruyère Street and the air conditioning and cooling systems were shut off in nearby buildings, including the National Gallery of Canada, as a precautionary measure.

The Ottawa Fire Services hazardous materials crews were called in to help deal with the oxygen, which is non-toxic, but can pose a fire and explosion hazard in the presence of ignition sources.

Up to 25,000 litres of liquid oxygen are believed to have spilled after a valve broke on the delivery tanker truck. (CBC)

Up to 25,000 litres are believed to have spilled, said mint spokesman Alex Reeves. However, because liquid oxygen has a boiling point of –183 C, it evaporates into oxygen gas as soon as it hits the air.

The liquid oxygen is used in the mint's silver smelting process, Reeves said.

It took crews hours to close the valve on the tanker. The closed section of Sussex Drive did not reopen until 6:30 p.m. At that point, a section of the mint remained off limits to staff while it was checked for possible ignition sources.

In the meantime, firefighters used fans and water vapour to ventilate the building and surrounding area.