Imagine your wife is 39 weeks pregnant and you think you may have to take her to hospital and you think you may well not make it if you stick to the speed limit.
That one's easy. You count as an ambulance for that particular trip, provided that you don't actually hit anything. If you do hit something you're in trouble, just as an ambulance driver would be. (After all, giving birth in a car at 39 weeks isn't that big a deal, it happens every day; running over someone else's child also unfortunately happens every day but
is a big deal.)