Several components stand out to me as a safety risk:
1. There are senior students leading labs who may not have completed relevant OHS training that a listed employee would run. This is a no fly zone in any training scenario and is the most important point IMO.
2. The (fresher) students have commented on the remarkably high number of seniors in the class. This has a slightly less direct safety issue: a perceived power imbalance. If you have ever led a class you may notice that too many "big" personalities can cause less confident students to withdraw, and, crucially, ask less questions. This can lead to accidents (the seniors 'trying to lead' doesn't fix this in my experience).
3. The nature of the interactions itself is a distraction. If I am getting hit on, I am probably not thinking about the content of what is being said - I am thinking of the quickest way to excuse myself from that situation. Once again, this can increase risk.
While I'm here, I also have issues with this from a non-safety perspective.
4. While lecherous behaviour does not constitute harassment, it 'sets the bar' for student interactions and makes particularly socially ill-equipped students feel more confident in pursuing people. This just ends up making the environment less pleasant for the people being approached, as well as the onlookers.
5. Further, this is actually worse than flirting at, say, work ,or a social gathering, because college is expensive. Distracting students from a highly expensive experience designed to provide skills and challenge thinking is arguably wasting someone ELSE'S money. Which is just not cool.