I have brought a number of product liability lawsuits over the years in both state and federal courts for a wide variety of products. So I have a small amount of knowledge about this area.
In this instance, we don't know the real and full story.
But for purposes of our discussion, and applying Connecticut law as an example, the defective product is the contaminated air that was sold. You keep focusing on the defective product as possibly being the compressor. Perhaps it was and perhaps it wasn't. However, the straightforward case is a product liability action against the seller of contaminated air, which was the defective product which injured someone.
The plaintiff will not automatically name the manufacturer of the compressor. That would depend on whether there was a defect with the compressor.
Regarding jurisdictional and venue issues, you are generally correct, but it's also not that clear-cut. Simply by way of example, if a Florida dive operator advertises in Connecticut or solicits business in Connecticut, yet does not actually conduct business here, then the Florida dive operator might be subject to federal court jurisdiction venued here in Connecticut. All I'm saying is that there are a number of potential issues regarding venue and jurisdiction.
Either way, my overall point for posting is just that if a dive operator sold contaminated air, it sounds like a straightforward product liability lawsuit against the dive operator for selling a defective product, unreasonably dangerous to the user or consumer. In Connecticut, it would not be a negligence lawsuit, but rather, a product liability lawsuit. And the comparative or contributory negligence rules for negligence based lawsuits might be different for a product liability lawsuit in other jurisdictions as they are here in Connecticut.
Michael