The Defence of necessity had been attempted in imparied driving cases in Canada on numerous occassions. I say "had" because of the abject failure of the defence to that particular charge. I'm not saying that it has never been successful, but the elements of the defence are so stringent -that you believe your life or the life of another to be in danger - that the defence virtually never works. It just did. The Globe and Mail reports on a case from Sudbury:

A Sudbury man was cleared yesterday of drunk-driving charges after admitting he drove while impaired to seek mental-health assistance after a failed suicide attempt.

....

Mr. Desrosiers testified that he told the police he had attempted to kill himself with carbon-monoxide poisoning inside his garage.

The officer on the scene told court he became so concerned over the man's uncontrollable sobbing in the back of his cruiser that he wanted to transport Mr. Desrosiers to hospital, believing he was a risk to himself and others.

...

Judge Keast said he found Mr. Desrosiers "to have been a reliable and credible witness."

"He was expecting to die," he said.

He believed Mr. Desrosiers chose to drive while intoxicated rather than stay inside his home, where he was considering a second suicide attempt.

....

At trial, it was revealed Mr. Desrosiers spent two weeks in hospital under psychiatric care, was put under different medication and remained under psychiatric care almost one year after his arrest.

It is clear Mr. Desrosiers' mental health had deteriorated badly in the hours before his suicide attempt and his decision to drive after consuming alcohol was made by a man with serious mental-health issues at the time, the judge said.