When the holes line up in the cheese

I have heard the analogy about holes in the cheese several times and it pretty much sums up the incident pit.

I’ve been diving rebreathers for quite a while now, teaching them for nearly a decade and I have always been interested in rebreather diver incidents. There are many internet forums with sections dedicated to incidents where the person survived and that person can give a full account of what happened and why. Then there are the other sections of the forums where you read about diver deaths and almost certainly never get any details and a lot is left to supposition.

The reluctance to give known facts on diver fatalities stems from the respect to the families and the diver. The families do not want to read about how their loved one died and also if the diver made mistakes, friends do not want them to appear incompetent. From what I have read, there is almost never a catastrophic incident that takes the diver, it is always a series of events.

Personally I train hard, I teach CCR full time and I’m always practicing my skills as I’m demonstrating them. I occasionally do make mistakes, human error. It is possible and happens to us all at one time or another. Now when I look at my mistakes it is normally a series of events that ends with me thinking that I was lucky and that I had learned something.

“I was lucky”. I think that this statement is key. I have survived an incident. I am well trained, well dived and well disciplined, but why have I survived? Pure bloody luck!

Having read the reports of rebreather diver deaths, or where details have been available from someone who was present, I can see that the deceased was a victim of a series of events that eventually lead to their death. Each event was manageable but when added together they were devastating. This is where the Swiss cheese comes in. In Swiss cheese there are many holes but every now and again the holes line up to make a route through the piece of cheese.

Some time ago I read with interest the reports given by a manufacturer who attended a recent coroner’s inquest. One of the buddies had a Go Pro camera mounted to his head so could record the incident. The manufacturer stated that the diver had a hose blow. BOOM! He heard it and was in a host of bubbles. He shut down the bail out cylinder that he was carrying on his left side. This didn’t stop the bubbles so the diluent cylinder was closed. With the stress, he has leaked more loop gas than was prudent and with no diluent to make up the volume he added a little O2. He would have seen the oxygen percentage in the loop increase and the HUD would be flashing and a buzzer sounding. The stress would be increasing and he started venting gas from the mask. This caused more loss of loop volume and he added more O2. This continued until the oxygen percentage in the breathing loop was at 1.6 and on a rebreather this is considered a maximum level.

The diver reached for the regulator on the bail out cylinder. Once in his hand he spat out the mouthpiece of the breathing loop without closing it and started to sink as the loop lost gas. He started finning to retain buoyancy and was trying to open the valve on the cylinder. Then he looked at the divers with him, shrugged and finned to the surface.

The cause of the loss of gas was the wing inflator. Some years earlier the diver had removed the one that the manufacturer fits which had a breathable second stage fitted into it. This had been replaced with another one that didn’t supply gas to the diver, just the wing. It was also the wrong size and had been fitted with force. It worked well for an estimated four years before this malfunction.

The diver was with two others and on their dive they found the dead body of another diver from their boat. They found him dead on the bottom and this would have increased the stress levels of all three of the divers. This also led to an extra 20 minutes of unplanned bottom time. There was nothing they could do so they decided to leave him. This would have a massive impact on the mental state of anyone.

Now let us say that we had a big bag of “what if’s” and a time machine. If you look at any factor on this dive and changed one, there would more than likely have been a different outcome. “What if he had not changed the inflator?” He would likely still be here. “What if he had not found the dead diver?” The hose would have bust and it is more likely that he would have managed it better as he wouldn’t have been as stressed. Add a “what if” to any of the series of events and you would most likely change the outcome.

When you read about this, and other diver deaths, and about the narrow escapes of divers who have lived to tell the tale, you can see the holes in the cheese. It never seems to be one thing.

It is really easy for me, sat at my desk to come up with all of the solutions, but I also know what it is like to be in the incident pit. The difference between me and every other well trained and well-disciplined diver who hasn’t made it back is most likely due to luck.

I often see divers changing their habits They finish a training course all disciplined, doing everything that they have been taught and then they go off and change things. They pick up bad habits and ignore protocols.

A great example of this is pre dive checks. How many use a check sheet when first trained then get into the habit of doing it without? How many jump into the water and do a bubble check and a bail out check? Well I see folk doing it on their course then some time later I am diving with them and the checks are a distant memory.

How many are advised by their CCR manufacturer that the scrubber limit is X minutes but extend that time? I know the answers to these questions is many. And you what? You don’t die! Each time you do it and do not have an incident, the more you re-enforce it to be the norm. Now what you are doing is getting away with it. You will get away with it right up until the point that you don’t. When you do not, you enter into the incident pit and hopefully the holes in the cheese do not line up.

This was not the first time that they had re-used their lime. It was a standard practice and they did get away with it until one day they didn’t. If you look through the incident it could have had a very different outcome. What kept that Sky News Cameraman alive? It wasn’t his team, it wasn’t his skills, just pure luck.

The thing with trusting to luck is that there is good luck and bad luck. The more that you deviate from what you were taught in training, the more that you reduce your chances of survival. When you finish your course that is not the end of your training, this is just the beginning. We as Instructors can only teach you what you need to survive. It is up to you to practice and maintain those skills. Experience helps but you can only get this for yourselves, you can’t buy it but hopefully you can learn from the experiences of others.

Never give up and never trust to luck, you will need as much of it as you can get but please don’t come to rely on it.