MikeFerrara:
In this country you can always be held liable for not ascting as a "reasonably prudent person" would act if it results in damages to another.
. . . IF you had a duty to perform the task AND the person who suffered damage relied on your assistance or expertise AND that reliance was reasonable. Of course, you can always be sued there as here, even if these elements are satisfied and the claim lacks merit. You just have a less expensive ordeal getting out.
I'm with McRae on this. The realistic risk of a claim is primarily born by the dive professional sponsoring or leading the risk.
One cannot exclude the possibilty that anyone might be sued for anything, and it is always possible that a dive buddy may be sued for injuries to a buddy (it doesn't matter that you did nothing. That is an issue for trial or motions practice).
I frankly don't worry about this much. With a DM who accompanies the group or the professionals or club sponsorig a dive, reliance is may be clearly 'reasonable' in the eyes of law--the pro has a greater duty than the rec diver, especially one with no professional certification. I don't practice dive law in Australia but I've been involved in defending professional claims there and believe they have essentially the same test for a duty, breach of duty and consequences applies as in the US and Canada.
My advice: Getting sued is like get hit by lightning--it can happen regardless of precautions or plans--but you're more likely to get sued for driving than diving. You might manage both risks the same way: with a rider of $1M or two on your insurance. You're not likely to be the most attractive deep pocket, but at least it'll fund the legal fees of your defense.
And always practice safe diving and, if possible, vet our dive buddies in advance and avoid those that seem like trouble (you'll usually know).