As someone who is an officer in the fire service and is also marine firefighter qualified I can confidently say that most liveaboards I've seen have a lot of highly combustible furnishings etc in them. A liveaboard with a steel hull and superstructure is slightly better than some other construction types, but as a rough guess I would say that if a fire on a liveaboard isn't extinguished in the first 60 seconds then it will be beyond the capabilities of the crew and firefighting equipment onboard to extinguish.