Rebreather Pro

Keeping warm during your dive

Why it is important to keep warm throughout your dive?

When we have adequate thermal protection, we tend to enjoy our dives much more than when we are cold, but adequate thermal protection goes far beyond comfort. Let’s envision a typical deep diving scenario and look at what happens to the human body during that exposure. Even in the coldest water, we seems to be able to tolerate the descent and bottom time adequately. We are working hard on that segment of the dive and moving enough to maintain good circulation. During decompression, our body chills because of inactivity and exposure time. When the body chills, the brain sends a signal to the extremeties to shut down the circulation and put an emphasis on maintaining core temperature. Just when we need to be off-gassing the entire body, our brain is sending a message to prioritize circulation to the body core. If we further chill during a long decompression, the circulation is prioritized to a smaller and smaller, more critical body core and brain.

If you feel that your hands and feet are getting chilled, then that is a signal that they are not just cold, but perhaps not off-gassing properly. Exit the water, move around, and you may be sending a nice cascade of trouble to the rest of your body. This is not an argument for heating the body on decompression though, it is actually a call to keep better constant thermal regulation through both the bottom time AND the decompression.

Its not just about comfort. It is critical to good balanced decompression.

CLICK HERE for an Advanced Diver Magazine feature about Jill's Antarctic cave diving exploration. 

-- Jill Heinerth

Rebreather CO2 Incident

 

CO2 Incident

I’ve posted this video link before, but I want to highlight it again, because there is so much to learn from this incident:

http://www.hse.gov.uk/diving/video/co2video.htm

This time you view it I would like you to consider bailout volume and scrubber ratings. Many people look at the scrubber rating that is verified through CE testing and say, “yeah, but that was in really cold water and at a ventilation rate that only an Olympian could maintain.” The ventilation rate of the diver in this video while using bailout was estimated to be over four times the rate that is tested by CE standards.

It is a terrible cascade when CO2 begins to elevate in the diver. Bailing out as soon as possible is critical or the cascade can lead to the point of unconsciousness… essentially suffocation by over ventilation as this diver experienced.

At some point, any scrubber design can be over-breathed. They all have their extreme limits.

This video is a terrific learning tool and I am grateful to the participating divers and manufacturer who realized it was more important to send a safety message to the community than to worry about the embarrassment of being a part of an incident. -- Jill Heinerth

 

Grant Graves: Precision Diving

I'm sure that many of us in the technical diving community can benefit from the wealth of information by freediving guru Grant Graves on his great new blog, Precision Diving. He gave some amazing presentations at this year's Oztek conference. Check it out here.

Bent - Ensuring the Best Outcome for Divers with Decompression Illness

Approximately a decade ago, I experienced a decompression illness hit while exploring The Pit in Mexico’s Yucatan Peninsula. Since that time, I have tried to share my experiences openly to help other divers understand that getting bent is a sport’s injury that we should be talking about. Not to belittle the serious of some DCI hits, I just think that we can all learn from each others’ experiences.

To begin with, there are two important things to ensure when you are technical diving. You should have supplemental oxygen available for treatment and a means to reach out to the emergency medical service and DAN or its equivalent.

I haven’t been bent in America, but I have taken plenty of fellow divers out to the local chamber for treatment. Having done this before, I can offer some other simple logistical advice if you live in or are visiting America, a country lacking a medical safety net for its citizens.

PREPARATION
Tell your buddy how to find your car keys, wallet, DAN card, health insurance information and emergency contact information. Share any medical issues that might be pertinent to diving risk assessment or treatment.
Ensure there is a way to call EMS and/or DAN. Know how to reach the closest hospital and local chambers.

Rebreather Pro Tech Tip: Nitrox Diluent

I was recently questioned again at a cave diving site about why I had Nitrox in my diluent tank. Some instructors teach their students that only air can be put in a diluent tank, but they have not fully considered the situation that occurs in cave diving.

Many caves have roller coaster bottom profiles that roll up and down over subtle and dramatic depth changes. When air diluent is used, it means that gas is frequently dumped to adjust for buoyancy changes. Soon after, the diver drops again, diluent is added to make up for the pressure increase, thus diluting the mix, and causing oxygen to be injected in the system. Volume increases result in more gas dumping and so on. Buoynacy becomes more challenging and gas use increases significantly.

If the diver uses Nitrox in their diluent tank, they can choose a mix that closely resembles their planned PO2 for maximum depth. I like to choose a diluent mix around1.0 and sometimes as high as 1.2.  I run my rebreather at a set point of 1.2. In this situation, my gas use decreases, buoyancy control is easier and I still have adequate ability to flush down hyperoxic scenarios, flush up more effectively from hypoxic situations and flush with diluent to confirm oxygen cell readings.

Still others will criticize me for selecting a diluent as high as 1.2 arguing that I cannot flush down hyperoxic situations very well. Every dive has a specific risk assessment. Most caves I dive have hard bottoms where I am unlikely to be capable of exceeding a particular depth. I feel my risk of hypoxia is greater than hyperoxia. I have enough room in the water column to shift up and down in depth to confirm cell verification flushes.

I also challenge every diver to see just how much diluent it takes to flush up or down to relieve hyperoxic or hypoxic scenarios and make them safe to breathe. The moment you discover a dangerous mix, you should be bailing to safe offboard open circuit gas supplies until the problem can either be solved or you abort the dive. In the event that the problem is fixable, such as an inadvertently closed slider valve, then the loop can be flushed appropriately with whatever gas is onboard.  Jill Heinerth

Rebreather Summit: Carbon Dioxide

Carbon Dioxide – Actual Case Discussed at Summit

Sponsored by the NACD, this year’s CCR Cave Summit was held at Camp Kulaqua last weekend. The expert’s roundtable is always the most popular part of the day, offering the audience a chance to ask all their burning questions. This year, the audience was divided with approximately one third being aspiring CCR cave divers and the balance already owning and actively participating in the sport. Beyond basic merits of individual units, the crowd was extremely interested in the topic of carbon dioxide and how it may be responsible for contributing to the deaths of CCR divers. As I have discussed previously in this blog, it is not something that can be determined as a contributing factor at the time of autopsy unless there was some sort of obvious mechanical failure in the rebreather or its preparation. Jeff Gourley shared a personal account about when a mushroom valve folded up in his mouthpiece, causing rapid carbon dioxide build-up that almost cost him his life. Literally moments into his dive, he detected that something was wrong and bailed to open circuit. He described difficulty in getting the mouthpiece into his mouth. After a few sanity breaths, he switched back and almost passed out. Luckily, his advanced training and well-practiced skills got him to the surface on open circuit. The interesting aspect of this incident was that he described the “hangover” as something that lasted all day long with a slow, delayed return to lucid thought.
I am grateful for divers such as Jeff who feel comfortable sharing their worst dives for the benefit of the community. We can all take away several lessons from this incident. Proper pre-dive checks will prevent most of these sorts of failures. Getting off the loop and staying off the loop are critical when you feel that something isn’t right. For the dive buddy or emergency provider – realize that a diver recovering from an incident of high carbon dioxide or low oxygen may be impaired for many hours afterwards. They may be walking and talking, but their brain and body chemistry will take a long time to recover.  Photo: Jill Heinerth and Richie Kohler on a recent Sentinel rebreather dive in Florida.

Ask Jill: The O2 Toxicity Debate

Ask Jill: A number of us were discussing your book last night over conversation and things crossed into the whole O2 Toxicity thing. While we know it is bad, and in fact more likely fatal than Narcosis and such, much of it seems to be speculative outside of the rebreather community.

Are there cases being reported of O2 Tox on Open Circuit? It seems that there are two schools. Those who say “It’s a rebreather problem” and those, like myself, who just plan for it, just in case. I know that, while in Coco View, diving 5 times a day with EAN, my OTU’s clearly exceeded safe recommendations, enough so that I moved to Air diving by Wednesday.

My answer:
When people say "it's a rebreather problem" they are likely referring to Pulmonary Toxicity which is caused by long exposures of PO2's as low as .5. That is what you are counting with OTUs. When you count OTUs you are not walking close to the edge of a precipice that will result in a symptom that will result in drowning. Not at all. You are keeping track of a number of units that will leave room for you to have a chamber run if needed. Chamber runs give you a very high dose of oxygen. If you had already dived aggressively in Coco View for a week and not heeded the OTU count and then got bent, they could still treat you, but you might start to suffer symptoms of Pulmonary Toxicity. You might experience substernal irritation, difficulty getting a full breath and something that feels like the heaviness of a bad cough. If you needed further treatments, they could be delayed or canceled because of the potential lung damage and loss of vital capacity. This type of toxicity knows no equipment boundaries. It can occur from open or closed circuit diving that is lengthy, especially when long decompression is involved. More likely than not, individuals will not experience it unless they are diving aggressively for a week or more. Most people use the "Repex" Method to county Oxygen Toxicity Units (OTUs).

The other type of oxygen toxicity is CNS (Central Nervous System) Oxygen Toxicity. This is the one that can cause symptoms that result in drowning. It can and does happen to open circuit and closed circuit divers equally. Essentially, there are two ways to get CNS toxicity. You can breathe a mix too deep or stay too long at a high partial pressure. Anecdotally, some experts argue that there may be pre-disposing factors to an individual’s likelihood of having CNS toxicity. Specifically, they argue that some drugs heighten your chances of having an oxygen toxicity convulsion. One could argue that if your medication has side effects that are similar to the list of symptoms of CNS toxicity, then effects could be additive (I get to say this stuff, because I do NOT have a medical degree). An argument in support of this comes from many incidents of death where there seemed to be no reason for the underwater convulsion, yet the diver(s) had prescriptions or Sudafed in their systems and used marginal to hot mixes for their dives and were otherwise healthy and young.

So what are the symptoms of “oxtox?” Visuals disturbances (like seeing spots), hearing disturbances (like ringing), tingling, nausea, irritability, dizziness and convulsions are all symptoms, but may not occur before convulsions resulting in drowning and death.

You can keep track of your “CNS count” using a CNS clock. This is a 24-hour clock that tracks how much extra oxygen you are putting into your system. Think of your body like a campfire. If you keep putting a few logs on the fire, they get slowly consumed and then end result is just a little ash. If you throw a bunch of gasoline on the fire, everything burns super hot and creates a lot of ash, smoke and flame. Your body is similar. It can tolerate a little extra oxygen and will use it in normal metabolism. Eventually you hit a threshold of how much oxygen the body really needs and you start creating extra byproducts that we call free radicals. Our amazing body can tolerate and manage a certain amount of those, but if we throw gas on the fire, like extremes of partial pressures for a long period we reach a tipping point. The body cannot tolerate the additional free radicals and starts to have symptoms. Eventually the body is overwhelmed and convulsions may occur.

That is a much longer answer than you might have expected, but I hope it illustrates a good general picture of oxygen risks. I will finish this answer over the next several posts.

Rebreather Carbon Dioxide Monitoring

Many people have been asking me about the various ways that the Sentinel rebreather monitors carbon dioxide levels. The new Sentinel Expedition offers a gaseous CO2 monitor that is the world’s first commercially available carbon dioxide sensor proofed and designed for operation in high humidity, high oxygen rebreather breathing loops.

The Sentinel Expedition CO2 monitor actively measures carbon dioxide while the diver is breathing on the loop. It is capable of real time monitoring that enables the diver to see rising levels and warns the diver in time for them to complete a dive, reduce activity levels or bail out.

The alarm thresholds have been set at  5mB and 10mB. Although the diver may not detect any symptoms as they begin to rise above 5mB, it is prudent to wrap up a dive. It is generally agreed, that levels of 15-20 mB are capable of inducing unconsciousness in a diver, therefore the 10mB threshold is realistic bail out alarm level.

The monitor consists of a combination of filters and sensors that can survive within the high humidity of the rebreather loop and is powered from the unit’s onboard rechargeable battery.

In the my next blog post, I will outline the other ways carbon dioxide is monitored in the Sentinel LSS.  Jill Heinerth

National Geographic Expedition Diving Science

All is well on the Bahama Blue Hole shoot for National Geographic. The science keeps rolling in. Some of the conditions are very challenging with high concentrations of hydrogen sulfide and low or no visibility. We're using Megalodon rebreathers for collections of stygiobitic life and sampling of bio-mats. Now that we have arrived in Andros, we will be recovering some human Lucayan bones from Sanctuary and Stargate caves. Brian Kakuk, Kenny Broad and I will also search for and recover a deep speleothem from Stargate in order to date previous sea level stands. One brought out of Dan's cave has been dated up to 350,000 years old. The climate data within this sample can show what topside conditions were like in almost year by year accuracy. These samples have already revealed that several massive warming events in the past occurred extremely rapidly. Its a thrill being a part of such fascinating science, but I can't do it justice. Stay tuned next summer for National Geographic Magazine and NOVA Television.  Jill Heinerth  Pic: Dr. Tom Iliffe with cave biology sample (JH)