Actual O2 Tox at 1.4 PPo2?

[Charlie99]

An unusual facet of the incident is that the seizures continued on up from 147' all the way to the 40' and 30' stop and continued at the shallow depths for 10+ minutes.

After remaining 3-4 minutes at depth (147-150ft) we began an ascent to our deco stop at 40 feet.

Upon reaching 40 feet, Elizabeth was still in a full seizure. We continued to try to push the regulator in her mouth, and frequently free-flowed the regulator in front of her mouth. ....... As we proceeded with our deco and struggled with her inflated drysut, Elizabeth was still seizing at 30ft, 12-15 minutes after she began.

Very strange.

 

[Jim Lapenta]

The Deco Stop this thread as well. Jeff was well known to the tech community here. Even though I did not know him I was actually on an Erie trip with him during my heliotrox checkout dives. I posted to the link in which I responded but if you read the whole thread his ppo2 was around 1.26. This was a safe, meticulous, person. He actually knew what was happening and tried to respond as did his teammate. It was not succcessful. As a result of this incident our tech instructor is now mixing for 1.26 ppo2 and recommending his students do the same. This is after consulting with Jeff's instructor and NAUI's director of tech training. It may mean a few more minutes of hang time but everyone is different. Some may be fine at 1.4 but why take the chance. This is still not an exact science. I have no problem with lowering the threshhold.

 

[Dr Deco]

Hello Readers

I do not have any personal knowledge about the depth limits. I thank those who responed to this query.

Dr Deco :doctor:

 

[DeepSeaExplorer]

A PO2 of 1.6 has been proven to be perfectly safe for recreational diving, evidence probably millions of safely conducted dives. I would not replace what is tested and true based on one isolated incident where the diver was using medications and had symptoms of a previously undected health problem. Though they be over the counter, many of these drugs have unknown, or little known, side affects - especially when it comes to diving. There has never been a confirmed case of of Tox at 1.6 for recreational dives, at least none without other more likely explanations.

 

[lamont]

I look at it as each person has their own po2 limit and then medications of all types and other factors effect that limit rising or lowering it. I do want to say that I am not an expert on hyperbaric medicine nor a tech diver. TDS has a lot of information on this though; it would be a great source to gain more understanding along with that link.

TDS doesn't really have a lot of good information on this.

People are still speculating based on the external symptoms that it was oxtox, there's no real way to do an autopsy and confirm that the symptoms were triggered by O2, so the useful available information is fairly low. Everyone assumes oxtox based on the symptoms without any proof.

And since there's a spectrum of susceptibility to seizures and people do not know if they have an undiagnosed seizure disorder until they have seizures, then what is an acceptable level of risk for O2 and seizures and what is an acceptable level of fatalities across the whole community? We can probably chase ppO2 limits from 1.4 to 1.2 to 1.0 to 0.8 and where does it end and we draw a line saying that reasonably prudent people believe that the level is 'generally safe'?

And at what level do we start simply measuring noise? You're going to get some level of seizures in the population even if everyone was running CCRs with a setpoint of 0.21. I find it odd that we've had two possible cases so closely together in the cave diving community, but in the OW community we have no idea of how many fatalities that started with buddy separation were due to seizures...

 

[Charlie99]

People are still speculating based on the external symptoms that it was oxtox, there's no real way to do an autopsy and confirm that the symptoms were triggered by O2, so the useful available information is fairly low. .

Actually, it was stated pretty clearly that the seizure lasted 10+ minutes even after moving up to 40' or shallower --- ppO2 of less than 0.6ata.

In all other reports I've seen of oxtox, there might be another brief seizure while ascending or after going to a lower FO2 gas, but continued seizures for 10 minutes at ppO2 of less than 0.6ata seems very unusual and makes me suspect that it wasn't really a normal oxtox situation at all.

I for one am not going to adjust my ppO2 levels based upon this incident.

Charlie Allen

 

[z3r0c00l]

You're going to get some level of seizures in the population even if everyone was running CCRs with a setpoint of 0.21.

Or air!

 

[TSandM]

Charlie, I'm not sure you can say there was anything strange about the fact that the seizure continued. Seizures are strange things; the majority are brief (1 -2 minutes), but if the electrical impulse gets into a circular path, arrhythmias and seizures can be persistent and very hard to break. It doesn't necessarily require an anatomic abnormality to do it, either.

New onset seizures in otherwise healthy adults are not common, although they do occur. Sometimes it's a single event, and no cause is ever proven. Sometimes it's the initiating episode of a seizure disorder. But it's far more common for seizure disorders to begin in childhood.

 

[Charlie99]

Charlie, I'm not sure you can say there was anything strange about the fact that the seizure continued. Seizures are strange things; the majority are brief (1 -2 minutes), but if the electrical impulse gets into a circular path, arrhythmias and seizures can be persistent and very hard to break. It doesn't necessarily require an anatomic abnormality to do it, either.

I'm wasn't referring to seizures in general, but instead was referring to oxtox related seizures. Does your comment "but if the electrical impulse gets into a circular path, arrhythmias and seizures can be persistent and very hard to break. " apply to oxtox initiated seizures also?

In all of the cases I've heard about, going to lower ppO2 resolved the seizure in a couple of minutes. I was pointing out that the reported seizure wasn't following this common pattern, and her seizure lasted 12-15 minutes, with 10+ minutes of that at less than 0.6ata ppO2. The gas was 24/26 at a max depth of 147'.

The question I'm trying to resolve is whether or not Divers4Life | Liz & Tim's Adventures is a warning to us to further reduce ppO2, or whether it was caused by something else and therefore tells us nothing about ppO2. We aren't using this incident to decide that we should keep the FHe below 0.26 or the partial pressure of helium below 1.4ata.

Should we really be using this incident to set our ppO2 limits?

 

[limeyx]

I'm wasn't referring to seizures in general, but instead was referring to oxtox related seizures. Does your comment "but if the electrical impulse gets into a circular path, arrhythmias and seizures can be persistent and very hard to break. " apply to oxtox initiated seizures also?

In all of the cases I've heard about, going to lower ppO2 resolved the seizure in a couple of minutes. I was pointing out that the reported seizure wasn't following this common pattern, and her seizure lasted 12-15 minutes, with 10+ minutes of that at less than 0.6ata ppO2. The gas was 24/26 at a max depth of 147'.

The question I'm trying to resolve is whether or not Divers4Life | Liz & Tim's Adventures is a warning to us to further reduce ppO2, or whether it was caused by something else and therefore tells us nothing about ppO2. We aren't using this incident to decide that we should keep the FHe below 0.26 or the partial pressure of helium below 1.4ata. Should we really be using this incident to set our ppO2?

For me it ends up being quite a simple solution.
There is basically zero benefit to me to push the PPO2 to 1.4 on a decompression dive.

So anything deeper than 100 feet (or shallower than 100 that involves mandatory deco) is averaged to be 1.2 PPO2 or less on the bottom. Pushing to 1.4 does not shorten deco or give me anything else except maybe slightlyless He in the mix which (if I paid for He by the cft which I do not) a slightly cheaper mix for a given depth.

Thankfully this means I can easily use just two bottom mixes deeper than 110 feet
25/25 to 130 and 18/45 to 200 feet.

For recreational dives, there are some cases where I end up pushing it to 1.3 (32% @ 100 feet) but generally most dives average less than 100 feet so the PPo2 is less.

Recreationalk dives between 100 and 130 are always on 25/25 for END reasons.

The one interesting thing that makes me less confident of pushing to even 1.3 on a recreational dive is that with a tech dive, I generally will expect the tox risk to be on deco, which means I have a lower PPO2 mix (back gas) to switch to to lower the PPO2 in a tox case.

For recreational diving the only way to lower the PPo2 is to ascend.

I dont see a huge benefit to pushing to 1.4 on a recreational dive honestly.