Managing Oxygen Toxicity Risks

[Akimbo]

We all know (or should) that breathing high oxygen levels underwater can be very dangerous and beneficial at the same time. High oxygen levels reduce decompression obligations. Decompression patients, commercial, and military divers are routinely exposed 100% oxygen at 60 FSW pressure equivalent in a chamber — a PPO2 of 2.82 ATA or more than twice the recommended MOD (Maximum Operating Depth) for recreational divers.

It is a safe and accepted practice because divers under close supervision and even the most dangerous OxTox (Oxygen Toxicity) symptoms are manageable — what the heck is that supposed to mean? Compared to in-water stops, here are the biggies:

• They can quickly be switched to air when any symptoms are suspected or observed
• They are far less likely to aspirate vomitus and/or drown
• They are far less likely to physically injure themselves and/or drown if they convulse
• They are under less physical and mental stress, can hydrate, and maintain thermal comfort… not sure what role dirty magazines play but it seems to be standard equipment.
• For hyperbaric treatments, a trained attendant is sitting next to you.

Hypothetically, what if you determine that exposing divers at water stops to higher levels of oxygen would outweigh the risks? All the reasons I can envision start with choosing to make dives without quick access to a treatment chamber. They include:

• Diving off a liveaboard, hours or days from an operational hyperbaric chamber and an aircraft to get you there. DCS risk is much higher doing 4-5 dives a day for a week than two dives every few Saturdays.
• Expedition dives. There are a large number of virgin wrecks that are deep, but in warm calm water… and in the middle of nowhere.
• Scientific and archeological surveys
• Let’s not forget my personal favorite, treasure hunts

What exactly could you use this “system” for? These conditions come to mind:

• Accelerating normal decompression to reduce thermal and/or elapsed time stress
• Increasing safety margin for normal decompression — use higher O2 levels than the decompression profile prescribe
• Prophylactic oxygen treatments — return “symptom free” for additional water stops without taking credit in your decompression profile. Useful when you can’t reliably return to the boat without surfacing.
• IWR (In-Water Recompression). Before everyone gets their underwear in a twist; let’s all agree that it is very dangerous, should only be performed under very limited conditions, and with only very competent people. You may well be choosing whether to die trying or not.

The question then becomes how can risks be minimized and/or mitigated (assuming you decide to dive there anyway and can’t afford the chamber and the vessel to put it on)? I contend that the answer is “not much” unless the diver can be brought under some level of supervision and have access to more gear than they can swim with. This may not be out of the question for divers that can reliably return to the boat or some other way-station.

What would it take? These random thoughts come to mind:

Supervision: As a minimum, that means two-way communications. That could mean a FFM with audio communications to a topside supervisor, which may as well be hard-wire. Considering how inexpensive TV cameras are today a camera may also be included.

Intervention: Supervision without intervention is useless. Ideally the supervisor must be able to switch the diver(s) between pure O2 and air. This automatically puts breathing gas management under topside control where logistics are more easily managed. Depending on the situation, a standby diver ready to jump in seconds and/or a safety diver tending the divers on O2 are necessary.

Barf Management: A FFM is much better than a mouthpiece for communications and comfort, but isn’t without risk since vomiting is a common OxTox symptom. A commercial diving helmet would be a big improvement, but switching to one underwater is challenging (aside from being very expensive and requires considerable training).

Convulsion Management: A convulsing diver is better off in a FFM, and even better off in a commercial diver’s hat. There is a high probability that they will recover after being switched to air, but the air-way obstruction risk remains. Commercial hats are pretty tight to offer assistance but at least the diver won’t drown as long as they are kept upright.

The last two issues got me thinking. Instead of a FFM or commercial diving helmet, what about an open-bottom hat/mini bell that is permanently rigged. Sort of a cross between an old Miller Dunn helmets and one of those tourist diving helmets.

Swim, up, stick head in, sit or snap harness in, and switch from your demand regulator or rebreather mouthpiece to an oxygen oral nasal. It could be pretty light-weight for transport, but would be in the 50-100 Lb range (per hat) with enough lead to sink it.

So why did I post this? Reality checks are always good, online design reviews are stimulating, and hopefully all of us will learn something. Besides, the diving here is lousy today.

 

[Rich Keller]

The first thing that comes to mind is a covered diving stage. The air pocket would be supplied with air from the surface and have an O2 mask with an overboard dump for treating a diver. Both divers standing in the air pocket, the diver being treated on O2 and another on air from the pocket supervising. If the treated diver has a problem the mask can be removed so he would be instantly be back on air just like they would if they were in a chamber. Trying to do this from the surface there would be a lag time between switching from O2 to air as the effected diver would still be on O2 until the air got all the way through the umbilical to him.

 

[Akimbo]

The “show-stopper” is very few dive boats have any lift capacity beyond a small boat davit. They also lack compressor capacity to keep it ventilated. Then there is the transport problem to a remote dive site and onboard. When it comes to logistics and budget, we commercial divers are really spoiled.

… Trying to do this from the surface there would be a lag time between switching from O2 to air as the effected diver would still be on O2 until the air got all the way through the umbilical to him…

My thought, though maybe not a good one, is to have an oral-nasal mask on an O2 hose and the hat ventilated by an air hose. Sure the hat would fill with high O2 from exhaust, but it could be almost immediately ventilated with no lag-time. Dumping diver exhaust outside of the hat is a possibility, but probably not too reliable or simple.

 

[tracydr]

Wouldn't it be easier to have a small hydobaric chamber on board than the bell thingy?

 

[Rich Keller]

A davit at the stern might be the answer. Big enough to lift the stage just far enough out of the water to set it down on a large swim platform. Air and O2 could be supplied from 300 cu/ft storage bottles from the surface. To scale it down a bit the supervising diver could remain on scuba, have a scuba tank on the stage that could supply the air pocket and an O2 bottle on the stage for the diver being treated. The overboard dump for the O2 mask is a simple thing that would not complicate the operation or allow an O2 buildup in the air pocket. There would also need to be a way for the supervising diver to view the diver being treated so he can remove the mask if the treated diver cannot.

 

[Akimbo]

It is hard to imagine how you could get something large enough for two people and keep the weight under a ton. You could drop a lot of weight from part of the bell that contains the bubble by using flexible materials so it inflates, but that would be a major PITA to handle through the air-sea interface. I “think” a solution that works on an unmodified boat in the 60'+ length range is needed.

Personal Prejudice Alert: I have never thought much of open bottom bells for military or commercial surface support operations — even before hats dominated. Too many handling problems for too little gain. Modern hats are too difficult to ditch and self-don. Does your experience differ? I’ve never actually used one.

Wouldn't it be easier to have a small hydobaric chamber on board than the bell thingy?

It depends on what you mean by small hyperbaric chamber. A commercially available “small” chamber weighs 2½-3 tons plus about that much again in compressors and O2 supplies to run it.

Hyperbaric Chambers - Aqua Air Industries

Here is a typical LP (Low Pressure) compressor needed to run it. Most commercial jobs have at least two.

Aqua-Air Industries,  Diving Equipment for the Professional

There are one-man “torpedo” chambers but are pretty limited and only useful for emergency DCS treatments. High O2 is really scary in them because there is no attendant… among many other reasons.

Here is a link to a commercially available open bottom bell:

Aqua-Air Industries,  Diving Equipment for the Professional

 

[Rich Keller]

Maybe something that can be towed behind the boat might work. Say a very small flat double hull aluminum boat with the dome for the air pocket attached by chains. Sink the boat so it will act as the stage platform and the weight needed to hold down the dome that would then be suspended above it. When you are done pump air back into the double hull bringing it back to the surface under the dome. This could be something like a jon or pontoon type boat.

 

[Akimbo]

That could work for local diving, but remote and expedition dives makes transport logistics expensive.

 

[dwhthediver]

What about something like those goofy helmets SeaWorld uses for their shark "dives"?

 

[Akimbo]

I have never seen the hats used at Sea World. Do they look like any of these?

tourist diving helmet - Google Search