The boat's DM made sure that all divers had buddies, and I ended up in a group of three, with the guy sitting next to me on the very crowded boat and another guy on the other side of the boat. I quickly saw that the guy next to me was very experienced. When we met the other guy, we learned that he was visiting America from Europe and was doing only this day's diving, with all equipment rented locally. He seemed confident, and we were all using an appropriate nitrox mix for the two deeper NDL dives (about 110 feet/33 meters max) we were about to do.
The dive went well. We stuck together appropriately as we explored the wreck. About halfway through I checked the European's gas supply, and he did not know how to answer because he was thinking in bars and his gauge was in PSI. I saw he was doing very well--no concerns about gas supply. As we got reasonably near NDLs, we started up the ascent line, with the European going first. At safety stop depth, I saw him looking at the computer in his rented console, and he seemed puzzled. I looked, and I saw that he had 4 more minutes of required decompression to do. I don't know what brand of computer it was (I am not very knowledgeable about current computers), but I could plainly see that he was in deco. He had apparently not realized that he had violated NDLs during the dive.
Back on the boat, we explained it all to him. He had never seen a computer of any kind in deco. We told him that because of what had happened, his next dive would be shortened, and we told him to stay well above us throughout. He did indeed stay well above us throughout the dive, but when started the ascent, we could see that he still had not understood the computer NDL information and had not ascended early enough--he was already well into deco. The other buddy did not have enough wetsuit and was freezing, so I stayed with him throughout his long deco stop.
Back on the boat, it was obvious what had happened. The rental facility he had used had advised him on the proper nitrox mix for the dive, but they had then handed him an unfamiliar rental computer and not told him a damned thing about it. I asked him about the nitrox setting, and he had no idea how to do it. I am sure it was set to air. There is no way he could have been that far into deco with the mix he had.
It can be very hard--borderline impossible in some cases--to set the oxygen percentage on an unfamiliar computer. I have a friend who has more than 200 dives but only does trips once a year, and she has to get out the manual and teach herself how to do it on her one-button computer before every trip. I had never seen this guy's computer before, and I would have had no idea how to do it. I cannot imagine how a shop can tell someone to use a certain percentage of nitrox on a dive and then not make sure the rental computer was properly set. It could have been much worse. What if he had been on air and using a computer previously set for nitrox?
So here are the questions for newer divers reading this.
The dive went well. We stuck together appropriately as we explored the wreck. About halfway through I checked the European's gas supply, and he did not know how to answer because he was thinking in bars and his gauge was in PSI. I saw he was doing very well--no concerns about gas supply. As we got reasonably near NDLs, we started up the ascent line, with the European going first. At safety stop depth, I saw him looking at the computer in his rented console, and he seemed puzzled. I looked, and I saw that he had 4 more minutes of required decompression to do. I don't know what brand of computer it was (I am not very knowledgeable about current computers), but I could plainly see that he was in deco. He had apparently not realized that he had violated NDLs during the dive.
Back on the boat, we explained it all to him. He had never seen a computer of any kind in deco. We told him that because of what had happened, his next dive would be shortened, and we told him to stay well above us throughout. He did indeed stay well above us throughout the dive, but when started the ascent, we could see that he still had not understood the computer NDL information and had not ascended early enough--he was already well into deco. The other buddy did not have enough wetsuit and was freezing, so I stayed with him throughout his long deco stop.
Back on the boat, it was obvious what had happened. The rental facility he had used had advised him on the proper nitrox mix for the dive, but they had then handed him an unfamiliar rental computer and not told him a damned thing about it. I asked him about the nitrox setting, and he had no idea how to do it. I am sure it was set to air. There is no way he could have been that far into deco with the mix he had.
It can be very hard--borderline impossible in some cases--to set the oxygen percentage on an unfamiliar computer. I have a friend who has more than 200 dives but only does trips once a year, and she has to get out the manual and teach herself how to do it on her one-button computer before every trip. I had never seen this guy's computer before, and I would have had no idea how to do it. I cannot imagine how a shop can tell someone to use a certain percentage of nitrox on a dive and then not make sure the rental computer was properly set. It could have been much worse. What if he had been on air and using a computer previously set for nitrox?
So here are the questions for newer divers reading this.
- If you rent a computer, would you know how to set the oxygen percentage?
- Would you know how to tell if your NDL is getting low in time to ascend?
- Can you recognize when your rental computer is telling you how to do required decompression stops?
