Doctors and nurses at the Montreal Children's Hospital donned biohazard suits and scrubbed down patients who had been exposed to an unknown chemical substance on Thursday morning.

Nobody was ever truly in danger though. The hospital was conducted a 'Code Orange' drill to practise dealing with a mass emergency, in this case the simulated impact of a train into a school bus full of children.

For the drill nursing students, medical students, and actors played the part of injured people and their relatives desperately seeking information.

Young women covered in fake blood and gore held dolls and pretended they were injured children. Actors limped and groaned their way to stretchers after being scrubbed down in case they were coated in a hazardous chemical.

Medical student Michael Homsy said all involved took the simulation seriously.

"Of course its always going to be a different factor when it's the real thing," he said.

The last time the Children's ran an all-hands-on-deck training exercise was in 2012, at their old location, and staff said it was a good idea to have a dry run at the new site before any real emergency actually happened.

"In a large disaster like this it would be many more patients that we would be expecting," said Dr. Ilana Bank. "We did however simulate 64 which is still a large number. This actually gave the opportunity to the staff to actually train and learn and improve their response in the future."

Large-scale disasters in Montreal are rare, and the most notable 'Code Orange' crises in this city were the result of mass shootings at schools.