A Nova Scotia man has beaten a drunk driving charge using the defence of necessity after he argued he had no choice but to drive an injured friend to the hospital last year.

According to an Amherst provincial court decision released on Tuesday, Roger Pleau and friend Eldon Deegan were drinking beer at Deegan's apartment in Upper Nappan on Oct. 4, 2012, while their wives went to bingo in Amherst.

They weren't allowed to smoke in the apartment, so Pleau and Deegan went outside for a cigarette. The apartment was on the second floor of a complex and Deegan stumbled down the stairs, gashing his scalp on an iron rail and sustaining a concussion.

The men were locked out of the apartment building and both keys for the building — the main and the spare — were with their wives. Neither man had a cellphone.

Deegan was incoherent and having difficulty breathing. Pleau, 54, from Maccan, panicked and drove his friend to the local hospital, according to court documents.

At the hospital, the nurse noticed Pleau appeared drunk so she called police. Pleau was found to have blood alcohol readings of 110 and 100 milligrams of alcohol per 100 millilitres of blood.

Amherst provincial court Judge Paul Scovil noted in his decision, "Obviously, if Mr. Pleau and Mr. Deegan were non-smokers none of this would have occurred."

"There are any number of reasons for individuals to quit the habit of smoking. This case outlines another one."

In acquitting Pleau on the drunk driving charge, Scovil said, "Mr. Pleau thought his friend was going to die. I accept what Mr. Pleau testified to. He gave evidence in a forthright and credible manner. No doubt credibility is key in cases like this.

"His inability to call 911, the panic of being locked out of the apartment building with someone in obvious medical distress would lead the accused to take the action he did."

Scovil warned his decision should not be taken lightly.

"This should not be taken as condoning impaired driving. Nor should the public think that the defence of necessity is an easy one to make out," he wrote.

"Rare is the case that such evidence would be accepted, but this is such a case."