I'm no expert but would suggest that "emergency arrangements" can be printed on the back of visitor passes, delegate name-cards etc. The course leader (at a training event etc.) will usually ensure latecomers details are entered or ticked-off on the delegate list. This is more to do with issuing of certificates/updating records but may also be relevant to local roll-call requirements. Interrupt a session to run-through housekeeping again? No way!

I was thinking of a reminder after the tea break, if there were lots of latecomers.

I suggest repetition is way over the top in most cases. The type of events you refer to where strangers are present are typically in extremely low-risk environments, and so the full range of emergency actions isn't covered - only where to go if the evacuation alarm sounds. As long as the majority are aware of what to do and the event leaders act appropriately, a few latecomers will readily 'go with the crowd'. Of course, if risks are higher or if individuals are going to be alone, then that's a different case. Even then, I've never been verbally taken through the emergency actions in any hotel where I'm sleeping - and the general fatality rate for hotel guests in UK and elsewhere doesn't suggest that needs improvement. Again, it's a bit different if your 'hotel' is a ship or an offshore installation - for these there are typically regular familiarisation practices. IOSH policy is that our responses to risk should be proportionate. I suggest worrying about latecomers in vey low risk environments is disproportionate? Same goes for printing out the instructions - it's an unreliable way to communicate if the information is important (but OK if there's a verbal briefing too), and I suggest the average UK hotel which runs exhibition events and/or is open for meals has many hundreds of 'strangers' in the building every year who are completely unbriefed -so your latecomers are no different?