[boveus]

30 minutes is not arbitrary in the context of search and rescue. When someone has fallen overboard on a Naval vessel in most parts of the world's oceans their survival time is as short as 30 minutes: https://ussartf.org/cold_water_survival.htm

In rare circumstances the water can be much colder than average and this drops below 30 minutes, but for the most part the military operates in waters with survival time no lower than 30 minutes.

[thaumasiotes]

That makes no sense. If survival time is 30 minutes, and it takes 28 minutes just to get into the air, nobody will ever be successfully rescued.