Not to be an alarmist, but I wouldn't do this kind of training with nobody around. If you push yourself a little too far with hypoxic training, you black out and drown.
we always have 2 guards on and i let them know what i am doing. i always get a weird look when i do it haha. doing things like this really enforces the surfing is a lifestyle idea. all the gurds i work with dont surf and they think i am crazy for surfing in the winter and holding my breath and swimming like i do.