This is a commonly held belief that I’ve never seen come true in my 10+ years of EMS experience or 20+ years total of emergency medicine experience.
If you’re not on the clock you have no duty to act (5ish states have laws saying bystanders must help, know your state laws)
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If you’re not on the clock you don’t have a large malpractice insurance policy covering you.
Both of those facts make the trained bystander a very unappealing target for a lawyer. Yes you can get sued. Anyone can sue anyone for just about anything.
None the less, you don’t even need a lawyer to fight that one. If you’re not on the clock you have no duty to act. Even if your state has a law requiring action I don’t believe any require you to place yourself in peril, like trying to rescue a drowning diver.
And since you don’t have a several hundred thousand to million dollar insurance policy covering you, lawyers know they won’t get any large settlement from the average Joe (if your a million dollar diver then YMMV), the lawyers will go after the parties with large insurance coverage.
I’ve been through malpractice suits, and I’ve been the Good Samaritan. I’ve never seen a Good Samaritan get sued, and I’ve never seen or heard of someone not responding getting dragged into the case.
With all of that in mind, operate however makes you comfortable. If I’m in a situation I don’t want to deal with the medical questions and someone asks what I do, I fix computers.
If I see a crash in town without EMS responders yet I drive right by. (If I witness the crash I may stop to be a witness, not render aid). EMS will be there soon enough.
If I’m driving cross country and see a crash, I’ll likely stop, as I know aid may be some time a way.
Thankfully as of yet I haven’t needed to intervene on a dive boat. If I did or not would likely revolve around how sick someone was and how far away help is.
(All of this applies in the United States. I have no knowledge of international duty to act requirements)