Er,
You are at home, having a couple of beers with your family and you suddenly get told over the TV to leave your home immediately due, e.g. a bush fire alert.
You grab everyone, mum and the kids, and sprint for the car.
Stopped by the police. Drunk? Yes. Force majeur? Most probably.
You may very well be found 'guilty' of DUI, but the question is whether you are treated as a 'vanilla' drink driver when it comes to the judgement.
I think you would be cool but I could be wrong.
Sympathy to anyone who has been in the bush fire situation without the beers, let alone someone who needed to drive when they had absolutely no intention of driving when they opened the first beer.