rebreather Diving: Caustic Cocktail

Rebreather Diving: The Caustic Cocktail

A cautionary tale of my personal experience with this dreaded mixture.

Rebreather divers are open to incur a few additional risks than regular open water scuba divers. These include potential exposure to dangerous levels of CO2, going hypoxic (not enough oxygen), and going hyperoxic (too much oxygen). And then, there is the dreaded caustic cocktail. This occurs when the absorbent material (Sofnolime and Intersorb are the most common), used to remove CO2 from the breathing gas, is inundated with water. The most common causes of water intrusion are poor connections in the loop hose or a DSV left in the open position when not in the diver’s mouth. But the more extreme case is when a hose is cut or the connection comes undone, opening the loop entirely to immersion.

When any significant amount of water comes in contact with the absorbent medium, it creates a highly corrosive alkaline-based liquid containing calcium or sodium hydroxide. And when you experience a catastrophic flood, as I did, a caustic cocktail can turn a good day into a really ugly one.

Not my first rodeo

My own experience with rebreathers started with a Drager Dolphin in 2000. Back then, this particular model SCR was the most readily available and affordable rebreather. The Dolphin was a solid unit, but it had it’s share of problems. Mine had a nasty habit of leaking through the lid of the scrubber canister, and on one occasion the leak was large enough to deliver a nasty caustic cocktail. The amount of chemical-laden liquid that came in with my next breath was enough to make me instantaneously cough and gag.

Internal exposure with this corrosive alkaline-based liquid can be life threatening, as it will cause a chemical burn to all tissues it contacts. Depending on the strength of the alkaline solution, this can trigger a series of complications. The most serious reaction takes place in the upper laryngeal airway and/or lower bronchial airway, where exposure can cause a spasm reflex that can hinder breathing to the point of asphyxiation. And if the lungs are also exposed to the caustic mixture, there is a risk of developing chemical pneumonitis or prolonged respiratory distress.

My dive buddy later remarked that I sounded like some old clunker where the engine was having trouble turning over, and instead only sputtered and backfired. While I don’t remember if I kept the mouthpiece in or not, I do remember that it felt like an eternity before I was able to grab for my backup second stage regulator. As it turned out, the exposure was mild by most standards. I was left with a mild scratchy throat, and food tasted strange for two days.

Caustic Cocktail – Event Redux

That early experience with the ugly realities of mixing water and sorb further reinforced habits I’d honed though years of using underwater camera housings. I make sure every piece of equipment I own is properly maintained, properly assembled, and thoroughly checked before getting in the water. As a result, after 15 years of rebreather diving, I have never had to abort a dive due to an equipment failure.

Never, that is until August 29, 2015. That was the day when the phrase “famous last words” came up against two most prophetic words in the English language: “shit happens!” It was a beautiful Saturday morning, and the plan was to dive the Mizpah wreck, a local dive site off Palm Beach, Florida. It is a site that I have done many times, and the intention was to look for the goliath groupers gathered there, as it was the mid stage of their spawning season.

Before departure, my KISS Classic rebreather was subjected to all the usual pre-dive validations: POS and NEG checks, O2 flow rate confirmation, cell calibration. Everything was performing, as it should. Once on site, we started the drop 700 feet up current of the wreck as the flow was quite strong this day, and we wanted to allow plenty of time for an easy descent without overshooting the wreck.

During my descent, I stopped momentarily at a depth of 20 feet to ensure everything was working properly. In addition to gauging my work of breath on the unit, this involved listening for any gurgling noises or escaping gas. I even rolled over on my back, looking for any noticeable bubble streams coming off the rebreather. Satisfied, I preceded downward and leveled off a few feet from the bottom. Gliding in with the current, my O2 set point was in the green at 1.2 PPO2. Then, as I was making some last-minute adjustments to my camera system, there was a very audible sound of gas leaving the loop as I exhaled. Such a sound can be an ominous warning that things are not in proper order. I first thought that something was allowing breathing gas from the loop to escape through the overpressure relief valve (OPV) mounted atop the head on the unit. I had it adjusted to the lowest setting to allow easier venting, but it should not be venting while I was at a stable depth, and not adding diluent. I figured that something must have become lodged in the valve. With the next exhalation, there was once again a sound of gas releasing into water. Obviously, something was not right.

One of the most fundamental safety protocols on the KISS Rebreather is the use of the BOV for crisis management. During training, students are taught to switch their BOV from closed circuit mode to bailout mode at the first sign of trouble. This includes cases where the loop goes hypoxic or hyperoxic, or when the diver becomes hypercapnia (excessive amount of CO2). A significant part of the instruction process involves repeated performances of this bailout drill, to the point where it becomes embedded in the student’s muscle memory. This way should a situation arise, the action is automatic.

Over and over, I’d told students, ‘if something doesn’t feel right, sound right or look right – switch to bailout, ask questions later.” But on this day, I didn’t follow my own advice. Instead, I tried a more clinical assessment, reaching behind my head to check the OPV. Big mistake! My next inhalation was accompanied by a mouth full of liquid. Congratulations Stearns! You just received a caustic cocktail, and you are 85 feet from the surface.

Compared to that other caustic cocktail I experienced nearly 15 years ago; this was far more unpleasant; my throat felt as if it was on fire. At that point, my muscle memory kicked into overdrive. I slammed the lever on my Shrimp BOV to full bailout, closing off the loop while at the same time forcibly exhaling every ounce of fluid I could back through the mouthpiece. Before giving into my instinctive response to take another breath, I took the mouthpiece from my lips while manually depressing the purge button underneath the BOV, flushing any residual liquid before returning it to my mouth.

As mentioned earlier, internal exposure to this corrosive alkaline-based liquid can trigger a reflex spasm that makes breathing difficult or impossible. I inhaled. Despite the extremely unpleasant sensation of having cold dry air pass over chemical burns in my throat, I was still able to breathe. Good!

After catching a few sanity breaths, I looked around and realized I was on my own, as the dive group had moved down current. While the pain in my throat was intense, I was not having difficulty breathing. Knowing I had plenty of bailout gas, there was no need to rush things during my ascent. In mid water, I made my first stop to deploy my SMB so that the dive boat captain would know where I was, and that I was coming up.

Because my breathing was not labored, I opted to spend another 3 minutes at 20 feet before surfacing. If I were to require medical attention, no need to include a trip to the chamber. When I look back, I am amazed that during the entire event, from descent to getting back on the boat, I was carrying a large DSLR camera housing with two Sea & Sea YS-250 strobes in my hands.

Out of the water, but not out the woods

During those short but agonizing minutes spent returning to the surface, I’d had the presence of mind to remove the BOV several times and swish a bit of saltwater around in my mouth. This purged some but not all of the residual alkali liquid. Beyond that, there wasn’t much I could do. Immediate first aid responses for the ingestion and inhalation of alkaline burns associated with a caustic cocktail are limited.

In contrast to acidic burns, which can be treated by immediately flushing with freshwater, alkaline burns require far more action over a longer time period. The foremost recommendation is try to spit as much of it out as possible while at the same time flushing your mouth with water as soon as possible. That includes seawater.

Once at the surface, I alerted the captain and deckhand to the problem, and began flushing vigorously with fresh water, and sipped a can of Coke™.  The reason for the Coke is that, though you cannot “flush” your esophagus, you can achieve some neutralization from the carbonated beverage. Should a small amount of alkali get ingested, it is pretty much neutralized once it hits the acidic environment in the stomach. As long as you are not feeling nauseated, it is advised to attempt to drink some Coke or Pepsi™.

My mouth and throat felt like total crap, but my real concern was respiratory issues. Depending on the potency of the solution and the extent of the exposure, this liquid can trigger severe swelling and/or spasms in the esophageal airway, making breathing difficult to impossible. When the latter happens, the inflicted diver will need to be intubated by an EMS and administered O2.

Twenty minutes out the water, I was not experiencing spasms or any other signs of respiratory distress. My throat was still burning badly, but I was functioning well enough to turn my attention to my rebreather and investigate what went wrong. One look told the story. The hose coupling in the exhalation side had come completely undone from the head of the unit. Calling what happened a catastrophic flood would be putting it mildly. I had the whole damn ocean inside my rebreather. Everything from the scrubber to both counter lungs and loop hoses was filled to the top with a milking fluid. 

Later analysis determined that I had likely turned the locking collar the wrong direction, giving me a false lock. A slight pull on the hose would have revealed that. Human error is a bitch, and I now have one more item to add to the pre-dive checklist.

The aftermath

In most textbooks, one of the first things advised following a caustic cocktail is to seek medical help. My first course of action was to speak with Doug and Alan, two fellow rebreather divers. In addition to having experienced similar situations, both are in the medical field – one a cardiologist, the other an ER trauma nurse. Among the short list of things, they advised was to avoid taking pain remedies like Ibuprofen (i.e. Motrin, Advil), Naproxen (Naprosyn), Diclofenac (Voltaren) or Aspirin. Instead, the preferred alternative was Tylenol by day and Tylenol PM (sparingly) by night to aid sleep.

Fro the rest of the day, the discomfort in my mouth and throat escalated slightly. It felt like a cross between having the world’s worst case of strep throat and having just eaten a potent jalapeno pepper. To reduce the discomfort of swallowing, most of my day was spent sucking throat lozenges containing benzocaine; that and continuing to drink plenty of water. Both Doug and Alan felt that my exposure was likely limited to only my mouth, upper throat, and esophagus, and based on their own experiences, said I should start feeling better in 3 or 4 days. There were no apparent respiratory issues, but I was now coughing up quite a bit phlegm.

A secondary concern with alkaline chemical burns associated with caustic cocktail is liquefactive necrosis, should the chemical burn go deeper into the tissues. Seeing a little bit of red in the phlegm the morning the third day, I decided to walk into the ER of my neighborhood hospital. There, I was run through the usual battery of tests, chest x-ray and ultrasound, checking vitals, blood cbc, and so forth. Although they could not find anything significant, they still wanted me to stay overnight for observation.

By day four, back at home, the discomfort in my mouth and throat was about on par with what might remain shortly after vomiting. While this rate of improvement was a great sign, my vocal cords took longer to recover, and I talked at a whisper for over a week. Little more than two weeks from the day of the incident, I felt fit enough to return to the water, which I did with no issues.


Could this mishap been avoided?

In addition to following your training, you plan for the worst and hope for the best, and deal with what comes. Because nothing is infallible and nobody is perfect, and Mr. Murphy has a way coming along for the party when you least expect it.

I am sure there will be plenty who after reading this will have their options as to how “would-a, should-a” could have been handled. But the bottom line, when you are diving closed circuit and something does not feel, sound, or look right, the best solution is to bail out. And if your rebreather does not have a BOV, get one as soon as possible. It could save your life, and don’t let anyone tell you it is not needed.

You can read more on what I have to say about BOV’s by flipping over to “To BOV, or not to BOV?”

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