Nearlythere has it about spot on there and, indeed, most fire safety officers think along the same lines. Problem solved.
However, a little caution does have to be exercised in certain circumstances.
Imagine, for example, a restaurant with an open kitchen and a theatrical chef who delights in extravagant flambeeing (spelling??). Well, that might be fine, but what if the restaurant has a lowish ceiling, say 2.5m, and it has a largish number of covers, a hundred or two say, and it has exits that, on a busy night, will cause queues before the last person leaves the restaurant 2 and a half minutes after the fire starts (a perfectly acceptable time). Well, that may or may not be good enough. In a kitchen there is likely to be the potential for rapid fire development (a frying range going up for example) and with a low ceiling there will be the potential for rapid lateral spread of smoke. Do you really want two hundred people queueing at exits when the smoke is passing over (and barely above) their heads?
It's unusual circumstances I've described, but it just illustrates that there are no hard and fast answers and each case must be judged on its own merits.
Stu