[Adrian]

Blackouts can happen at any depth. It can happen on the surface, after coming up from a dive when you've gone past your limit. Check out the BO threads in the safety forum, lots of info there. Spit is great, just work up a good gob of it, spread it well around and rinse it off before putting the mask on. Sometimes new masks have a protective layer of silicone(?) wax(?) that has to be washed off before you can effectively defog.