Scuba-specific legal rules on the issue of a diver's duty to a buddy or other divers are not well developed by the appellate courts. We are starting to see some general rules emerge, though.
In Rasmussen v. Bendotti, 29 P.3d 56, 107 WashApp. 947 (2001), the Washington Court of Appeals held a scuba diver owes a duty to a buddy to act as a reasonably prudent diver. This duty includes, at the minimum, performing a buddy check and a self-equipment check before the dive.
However, that duty appears to be circumscribed by the risk a diver assumes by engaging in scuba diving. The most recent case on the issue is an unreported case from California entitled Yace v. Dushane, 2003 WL 22953762 (Cal.App.2.Dist.). The case was not selected for publication in the California reporters or the Pacific Reporter, so the California Rules of Court prohibits parties from citing to the case as authoritative. Nonetheless, the reasoning expressed in the case is enlightening.
In Yace, a diver died while diving near Santa Cruz island. The diver was apparently low on air, and her buddy had ascended to get his bearings. When he descended again, the buddy allegedly panicked, bolted for the surface, and did not assist the diver on the ascent or share air with her. Her children sued her diving buddy for negligence.
The Court of Appeals first held that the existence and scope of a duty of care in a sport depends upon the nature of the sport and the parties' genereal relationship to the activity. The California Supreme Court earlier opined that a participant in an active sport breaches a duty of care to a coparticipant only if the participant engages in conduct that is so reckless as to be totally outside the range of the ordinary activity involved in the sport. cf. Knight v. Jewett, 3 Cal. 4th 296, 320 (1992), Kahn v. East Side Union High School Dist., 31 Cal. 4th 990, 996 (2003). Accordingly, it is improper to hold a sports participant liable to a coparticipant for ordinary careless conduct committed during the sport. See Knight, supra, 3 Cal.4th at 318. Notwithstanding that general rule, there is a duty to use due care not to increase the risks to a participant over and above those inherent in the sport. See Knight, supra, 3 Cal.4th at 316. The Court of Appeals applied those rules to the Yace matter.
The Court of Appeals stated: "Unlike most sports, the possibility of a life-threatening emergency in scuba diving is apparent, and indeed anticipated. Just as an emergency problem with the air supply is itself an inherent risk of the sport, so also is the reaction to that emergency of one's diving buddy...a diver's panicked failure to assist a dive buddy in trouble cannot be characterized as either intentional or reckless...the mere conjunction of the words "negligence" or "recklessness" with "panic" suffices to demonstrate that no liability can exist in this case: we would have to say that a scuba diver has a duty to his dive buddy not to panic. That, of course, we cannot do."
Following the California Supreme Court's guidance in Knight, the Court of Appeals qualified its opinion by stating that "circumstances may arise in which a diver's negligent acts might 'increase the risks to a participant over and above those inherent' in scuba diving, thus giving rise to a duty of due care." 2003 WL 22953762 at 2.
Keep in mind that Rasmussen and Yace deal only with duties owed between buddies. I have not found any cases discussing the issue of duties owed by a diver to non-buddy third parties. Of course, instructors, divemasters, and other diving professionals who are responsible for the safety of other divers are outside the rules discussed in Rasmussen and Yace because they specifically assume a heightened duty of care (albeit attenuated by a waiver).
Also, if a person does undertake to assist another, the person assumes a duty to exercise reasonable care in rendering that assistance.
Although the instructor is mistaken, his comment should make you think about what duties you owe to other divers. The rules I've discussed are those that get applied after someone gets sued, and it's much safer to use broader rules in daily decision making. It's a double-edged sword if you think about it. Hope this helps.