My 17 yr old son did his first crit (Cat 4/5 combined) last weekend. I warned him of the initial surge and told him if he is struggling, he should just focus on hanging on for one more lap. He said in this case, the start wasn't that bad, and that it just got gradually harder as the 30 min went on, with the last couple laps being really hard. And, there were zero crashes in the race (it was a wide open, non-technical course).