A senior health official says she is surprised that the Saskatoon Health Region has been charged in a carbon monoxide leak that contributed to three deaths at a seniors home.

The region faces 11 offences under Saskatchewan's Occupational Health and Safety Act related to a gas leak from a boiler at St. Mary's Villa in Humboldt in December 2010.

"Certainly, we knew it was a possibility, but we weren't expecting them," region vice-president Bonnie Blakley said Monday. "We've been working with the Department of Labour since the incident in December 2010 to respond to the contraventions.

"So ... we were a bit surprised to see them. On the other hand, we recognize that that was one of the things that Justice can use in terms of followup in those instances."

Staff initially thought seniors were getting sick because of a stomach virus, exhaustion due to the Christmas season, food poisoning or tuberculosis. Even as some workers got splitting headaches and double vision, they never thought gas poisoning was a possibility.

As the illness spread through the care home, a nurse called her manager to tell her about it. It was the manager's husband who overheard the conversation and first suggested it might be a gas leak.

A SaskEnergy dispatcher initially suggested staff open some windows instead of evacuating the building. Although some windows were opened, some were not equipped with the right handles to open and some people -- unaware of the danger -- closed the windows because they were cold.

When a SaskEnergy employee arrived at the centre and suggested an evacuation, it took an hour to start emptying the building.

Roman Schneider, an 89-year-old priest, died an hour after the evacuation began. Two other women, 94 and 98, died in the weeks that followed. Another 22 residents, five workers and two visitors were treated in hospital for exposure to the gas.

There were no carbon monoxide detectors in the seniors home. They were not required under the building code.

A government report found that staff at St. Mary's Villa did not initiate appropriate emergency procedures.

It also said there was no Code Brown -- the health region's response designation for hazardous spills or releases. The Code Brown emergency response plan did not include a recognition of carbon monoxide as a chemical substance that may be hazardous to the health or safety of a worker.

The charges include several related to the safe use and maintenance of a boiler.

"While the charges are being laid now, there's very much been an eye on what needed to be done to prevent incidents in the future," said Glennis Bihun, executive director with the Ministry of Labour's occupational health and safety division.

Blakley said the region has already addressed all of the problems.

"Probably the biggest one is that CO detectors are in all of our facilities now."

The matter is to be heard in Humboldt provincial court next Monday. A defence lawyer said it's too early to say how the region will plead.