Scuba diver dies while exploring popular shipwreck, a third tragedy in the Florida Keys

[Nick_Radov]

I thought that I would share a first hand experience of an oxygen toxicty event, so that someone may benefit.

Several years ago, I was doing a decompression dive to 180 feet on x17/20 (17% oxygen, 20% helium). On ascending to 110 feet (1.4), I switched to my low o2 deco gas which was x32. I was very slightly negative on the ascent and was about to kick gently up to the first decompression stop. Shortly after switching to the x32, I had some minor issue that I wanted to resolve. While solving the problem, suddenly, I saw fireworks in front of my eyes (visual disturbance, oxygen toxicity symptom), saw that I was at 130 something (1.6), and immediate switched back to the x17/20. Within a few seconds, the visual disturbance went away and I resumed the ascent after staying on the x17/20 for several minutes.

What happened was, as I was solving the minor problem, I had stopped kicking and was actually, very slowly descending. In addition to the fireworks, I recall being very agitated at the time (irritability another CNS toxicity symptom).

I routinely do 1.6 ata for deco and was actually surprised that this had happened. I attribute the increased sensitivity to the activity that I was undergoing to resolve the minor problem.

Please be familiar with the VENTID symptons. There is no guarantee that you will have a symptom or that you will recognize it if it does occur. But, if you do know the symptoms and you do have a sympton, you might at least know what is going on and ascend enough to recover. I was fortunate enough to have the x17/20 and to be familiar with the symptoms and also to have a symptom prior to a CNS convulsion.

How do you know that those symptoms were due to oxygen toxicity and not hypercapnia?

 

[yle]

The instructor you are referring to did understand what the PPO2 limit does and how it effects your diving depth, MOD.

Oh, I see. Glad that you know the instructor and the full context of the conversation I had with him. Thank you for helping me understand.

Seriously... the instructor was telling a relatively new diver "ignore the prudent limits established by best practices for new divers, and manipulate your computer settings so that the computer will reassure you that exceeding those prudent limits is perfectly safe... because the computer said it's okay. Because you set the computer to say it's okay."

Did the instructor understand that a higher ppO2 setting would result in the computer displaying a deeper MOD? Oh yes, I am certain he was very aware of that correlation.

Was the instructor aware of the flaw in his advice he was providing to a newbie diver? I am convinced he was not. And it seems he's not the only one.

 

[scubaozy]

How do you know that those symptoms were due to oxygen toxicity and not hypercapnia?

Good question, the way it is presented, symptoms disappearing upon switching gas in seconds makes hypercapnia more likely.

I had enough common sense to understand the slippery logic he was using: that my computer would "allow" me to go as deep as I wanted if I just chose whatever MOD I wanted and then set the pp02 correspondingly high.

Well, I set my dc to 1.6 for rec diving because in the past my dc was annoying the hell off me beeping once I shortly exceeded the mod. Some dive computers assume penalties on your cns loading as much as 80%, so, if you exceed your conservatively set mod/pp02, for consecutive dives on a liveboard, you might have to listen to a peeping computer the whole week.

 

[crofrog]

I get what you are saying and it's still misleading advice by the instructor given to @yle . A diver's NDL will not be impacted by the PO2 setting on their computer. The NDL is the primary limiting factor on a computer along with ascent rate. I think more experienced divers ought to mentor less experienced ones either when asked a direct question or when unsafe practice is overheard or witnessed.

NDL will 100% be impacted by the pO2 of the gas they’re breathing, and the computer if set to a higher pO2 will provide a longer NDL for a given profile.

 

[Manatee Diver]

NDL will 100% be impacted by the pO2 of the gas they’re breathing, and the computer if set to a higher pO2 will provide a longer NDL for a given profile.

That setting is just changes the displayed MOD and the point at which the computer warns you about high PPO2.

It doesn't change the deco schedule.

 

[crofrog]

That setting is just changes the displayed MOD and the point at which the computer warns you about high PPO2.

It doesn't change the deco schedule.

I misread what he posted orginally, my precoffee brain thought he was saying that the inspired ppO2 wouldn't effect NDL.