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The Cause Of The Accident? Loss Of Situation Awareness.

Because of our innate biases, it’s easy to blame an individual for causing an adverse event, even if that individual made good choices. In fact, according to research, in the majority of adverse events, individuals make good decisions informed by incomplete information and NOT the other way around. As Human Factors coach Gareth Lock explains, if we want to improve our outcomes, we need to understand how decisions or choices are made and how “situation awareness” fits into this. Mr. Lock proceeds to lay out his case.



Text by Gareth Lock. Images courtesy of G. Lock. Note that The Human Diver is a sponsor of InDepth.

The title of this blog comes from the numerous reports I have seen attributing the cause of an accident to be a loss of situational awareness. This could be a direct statement like the title, or it could be something like ‘they should have paid more attention to…’, ‘they didn’t notice they had drifted off the wreck/reef’, ‘they weren’t focusing on their student’s gas remaining’, ‘they hadn’t noticed the panic developing’, or one of the most prevalent, ‘it was obvious, the diver/instructor just lacked common sense’.

How many times have you heard or read these sorts of statements?

The problem is that it is easy to attribute causality to something after the event, even if it is the wrong cause! In the recent blog on The Human Diver site, a number of biases were explained that makes it easy to blame an individual for the cause when, in fact, there are always external factors present that lead those involved to make ‘good choices’ based on their experiences, skills, and knowledge, but those choices still led to a ‘bad outcome’.

Previous research has shown that the majority of adverse events are not due to ‘bad decisions’ or ‘bad choices’ with ‘good information’, rather they are ‘good decisions’ informed by incomplete information. If we want to improve the decision making of divers, we need to understand how decisions or choices are made and how situation awareness fits into this. You might notice that I have used situation awareness instead of the more common situational awareness. The reason is based on language – you can’t be aware of ‘situational’ but you can be aware of the situation.

Mental Models, Patterns and Mental Shortcuts

Our brains are really impressive. We take electrical signals from our nervous system, convert these into ‘something’ which is interpreted and matched against ‘patterns’ within our ‘memory’, and then based on memories of those experiences, we tell our bodies to execute an action, the results of which we perceive, and we go through the process again.

What I have described above is a model. It approximates something that happens, something that is far more complex than I can understand, but it is close enough to get the point across. Data comes in, it gets processed, it gets matched, a decision is made based on experiences, goals and rewards, and I then do something to create a change. The process repeats.

Models and patterns allow us to take mental shortcuts, and mental shortcuts save us energy. If we have a high-level model, we don’t need to look at the details. If we have a pattern that we recognise, we don’t have to think about the details, we just execute an action based on it. Think about the difference between the details contained within a hillwalker’s map, a road map and a SatNav. They have varying levels of detail, none of which match reality.

The following example will show how many different models and patterns are used to make decisions and ‘choices’.

Entering the Wreck

A group of three divers are swimming alongside an unfamiliar wreck and one which is rarely dived. They are excited to be there. The most experienced diver enters the wreck without checking the others are ok, and the others follow. As the passageway is relatively open, they do not lay a line. They start moving along a passageway and into some other rooms. As they progress, the visibility drops until the diver at the back cannot see anything.

The reduced visibility was caused by two main factors: 

  1. Silt and rust particles falling down, having been lifted from the surfaces by exhaled bubbles 
  2. Silt stirred up from the bottom—and which stayed suspended due to a lack of current— caused by poor in-water skills, i.e. finning technique, hand sculling, and buoyancy control.

The divers lose their way in the wreck. Through luck, they make their way back out through a break in the wreck they were unaware of.

This story is not that uncommon but, because no one was injured or killed, it likely doesn’t make the media, thereby possibly allowing others to learn from this event. Publicity or visibility of the event is one thing, learning from it is another.

They Lost Situation Awareness in the Wreck

We could say that they lost situation awareness in the wreck. However, that doesn’t help us learn because we don’t understand how the divers’ awareness was created or how it was being used. Normally, if such an account were to be posted online, the responses would contain lots of counterfactuals – ‘they should have…’, ‘they could have…’, ‘I would have…’ These counterfactuals are an important aspect of understanding situation awareness and how we use it, but they rarely help those involved because they didn’t have the observer’s knowledge of the outcome.

Toward a Theory of Situation Awareness in Dynamic Systems. Endsley. 1995.

Our situation awareness is developed based on our experiences, our knowledge, our learnings, our goals, our rewards, our skills, and many other factors relating to our mental models and the pattern matching that takes place. Our situation awareness is a construct of what we think is happening and what is likely to happen. Crucially, it does not exist in reality. This is why situation awareness is hard to teach and why significant reflection is needed if we want to improve it.

The Mental Models and Patterns that were Potentially Matched on this Dive

As described above, our brains are really good at matching patterns from previous experiences, and then coming up with a ‘good enough’ solution to make a decision. The following shows a number of models or patterns present in the event described above.

  • “the divers are excited…” – this reduces inhibitions and increases risk-taking behaviours. Emotions heavily influence the ‘logical’ decisions we make.
  • “the most experienced diver enters the wreck…” – social conformance and authority gradient. How easy is it to say no to progressing into the wreck? What happened the last time someone said no to a decision?
  • “passage is relatively open…” – previous similar experiences have ended okay, it takes time to lay line, and time is precious while diving. We become more efficient than thorough.
  • “diver at the back cannot see anything.” – the lead diver’s visibility is still clear ahead because the silt and particles issues are behind them.
  • “exhaled bubbles…poor in-water technique…” – none of the divers had been in a wreck like this before where silt and rust particles dropped from the ceiling. Their poor techniques hadn’t been an issue in open water where they could swim around or over the silting. They had never been given guidance on what ‘good’ can look like.
  • “they lose their way…” – they have no patterns to match which allows them to work out their return route. The imagery when looking backwards in a wreck (or cave) can be different from looking forward. They laid no line to act as the constant in a pattern.

I hope you can see that much of the divers’ behaviours were based on previous experiences and a lack of similar situations. The divers didn’t have the correct matching patterns to help them make the ‘good’ decisions they needed to. Even if they did have the patterns for this specific diving situation, was there the psychological safety that allowed the team members to question going into the wreck, or signal that things were deteriorating at the back before the visibility dropped to almost zero?

As described in the recent article, ‘Challenger Safety’, team members will look to see if learner safety is present before pushing the boundaries. Learner safety is where it is okay to make a mistake; this could be a physical mistake or a social one.

Staying ‘Ahead’ of the Problem

The following three models from David Woods (Chapter 3, Cognitive Systems Engineering, 2017) show how we can think about how a diver deals with an incident as it develops. Each incident is not one thing, it involves multiple activities that need to be dealt with in a timely manner. If they aren’t dealt with, there is a potential that the diver is trying to solve an old problem when the situation has moved on.

The image above shows how we used to think people dealt with problems. There was a single diagnosis to the problem, and the operator would start to align their thoughts and actions with ‘reality’ based on the feedback they were receiving. 

This second image shows how a ‘perfect’ operator would track the changes as an incident developed and adapt their behaviour as a consequence. There would still be a lag, but the problems would be dealt with.

However, this image shows what happens when the operator falls behind the adaptation process, often still trying to solve an old problem, or they don’t have the models/patterns to pick up the changes then track more closely to the issue. 

Consider how this would apply to the divers in the wreck penetration scenario above. Accidents and incidents happen when those involved lose the capacity to adapt to the changes occurring before a catastrophic situation occurs. 

Divers holding a pre-dive briefing at the EDGE 2.0 workshop in Vancouver Island. Photo by Gareth Lock.

Building Situation Awareness

If situation awareness is developed internally, how do we improve it?

  • Build experience. The more experience you have, the more patterns you have to subconsciously match against. This means you are more likely to end up with an intentionally good outcome rather than a lucky one.
  • Dive briefs. Briefs set the scene, so we understand who is going to do what and when. What are the limits to ending the dive? We understand the potential threats and enjoyable things to see. Dive briefs also help create psychological safety, so it is easier to question something underwater.
  • Tell stories. When things go well and when they go not so well, tell context-rich stories. Look at what influenced your decisions. What was going on in your mind? What communication/miscommunication took place?
  • Debriefs. Debriefs are a structured way of telling a story that allows team members to make better, more-informed decisions the next time around. They help identify the steps within the events that lead to capacity being developed.

Can We Assess Situation Awareness during Dives or Diver Training?

The simple answer is no, not directly.

As described above, situation awareness is a construct held by individuals, even when operating as a team, with the team model being an aggregation of the individual’s models. The goal of The Human Diver human factors/non-technical skills programmes is to help divers create a shared mental model of what is going on now, what is going to happen, and update it as the dive (task) progresses so that the ‘best’ decisions are made.

In-water, we can only look at behaviours and outcomes, not situation awareness directly. We can observe the outcomes of the decisions and the messages being communicated which are used to share individual divers’ mental models with their teammates. This means for the instructor to be able to comprehend and then assess the ‘situation awareness’ behaviours/outcomes displayed by the team, the instructor must have a significant number of patterns (experiences) so that they can make sense of what they are perceiving. The more patterns, the more likely their perception will match what is being sensed in front of them and that their decision is ‘good’. Those patterns are context-specific too! An instructor who is very experienced in blue water with unlimited visibility will have a different set of patterns from a green water diver with limited visibility, or a recreational instructor compared to a technical instructor.

The best way to assess how effective situation awareness was on the dive is via an effective debrief which focuses on local rationality. How did it make sense for you to do what you did? What were the cues and clues that led you to make that decision? Cues and clues that would have been based on experience and knowledge. Unfortunately, a large percentage of debriefs that are undertaken in classes focus on technical skill acquisition and not building non-technical skills.


Situation awareness is a construct, held in our heads, based on our experiences, training, knowledge, context, and the goals and rewards we are working toward. It does not exist. You cannot lose situation awareness, but your attention can be pointing in the ‘wrong direction’. You are constantly building up a mental picture of what is going on around you, using the limited resources you have, adapting the plan based on the patterns you are matching, and the feedback you are getting. Therefore to improve, you must learn what is important to pay attention to and how you will notice it. It isn’t enough to say, “Pay more attention.” We should be looking for the patterns, not the outcomes.

If we want to improve our own and our teams’ situation awareness, i.e., the number of, and the quality of, the patterns we hold in our brains, we need to build experience. That takes time, and it takes structured feedback and debriefs to understand not just that X leads to Y, but why X leads to Y, and what to do when X doesn’t lead to Y. The more models and patterns we have, the better the quality of our decisions.

Gareth Lock has been involved in high-risk work since 1989. He spent 25 years in the Royal Air Force in a variety of front-line operational, research and development, and systems engineering roles which have given him a unique perspective. In 2005, he started his dive training with GUE and is now an advanced trimix diver (Tech 2) and JJ-CCR Normoxic trimix diver. In 2016, he formed The Human Diver with the goal of bringing his operational, human factors, and systems thinking to diving safety. Since then, he has trained more than 350 people face-to-face around the globe, taught nearly 2,000 people via online programmes, sold more than 4,000 copies of his book Under Pressure: Diving Deeper with Human Factors, and produced “If Only…,” a documentary about a fatal dive told through the lens of Human Factors and A Just Culture. 


Hal Watts: Plan Your Dive

Known for his deep air diving exploits back in the day, 86-year-old Hal Watts, aka “Mr. Scuba,” is one of the pioneers of early scuba and credited with coining the motto, “Plan Your Dive. Dive Your Plan.” He founded the Professional Scuba Instructors Association International (PSAI) in 1962, which eventually embraced tech diving, but never relinquished its deep air “Narcosis Management” training. Italian explorer and instructor Andrea Murdock Alpini caught up with Watts and teased out a few stories from the training graybeard.




Interview by Andrea Murdock Alpini 
English text by Vincenza Croce

Hal Watts, Terrence Tysall, and Bill Stone in March of 1993.  This was the last stop in the U.S. for a test dive of the Cis-Lunar Mk-4 rebreather prior to Stone’s San Agustin expedition (1994) for its first real sump dive.

“Plan your dive, dive your plan,” is a common refrain in diving, but it’s easy to forget the meaning of this phrase has changed over time.

The underwater explorers of the early days learned to plan their dives with watches, depth gauges, and US Navy tables. Back then, decompression tables were the Bible for divers—something miraculous, halfway between alchemy and physiology. Those trail-blazing divers defined what it meant to “plan” a dive.

But, at the time, the term “technical diving” did not exist; divers breathed air on the bottom as well as during decompression. Only after many years was oxygen added, followed by the famous jump into the hyperbaric chamber.  

Later came new innovations after a few decades of experiments: hyperoxygenated binary mixtures, the NOAA tables, Heli-air (i.e. the addition of helium in tanks loaded with air), the change in the speed of ascent, new molecules to be studied, new physiological and narcotic effects, and their consequent impacts on humans and their psyches.

In a very short time, diving traditions underwent a metamorphosis. The spool and the coral tank became a proper reel, the ascent bin and the plastic bag disappeared in favor of the buoyancy control device (BCD), the surface marker buoy appeared—and then, even later on, wrists were adorned with underwater computers instead of decompression slates.

Divers later renewed and revolutionized a niche discipline, transforming it into a sporting phenomenon and a vocation. Faced with imminent change, there is often nothing that can be done when an anomalous wave arrives; you cannot stop its irresistible force with the wave of a hand. And thus was the American revolution of underwater technique, where the means of exploration—read mixed gas and scooters—have become the end.

The self-proclaimed originator of the “plan your dive, dive your plan” motto was 86-year old Hal Watts, the founder of American didactic Professional Scuba Association International (PSAI) and a diving pioneer who once held the Guinness Book of World records for deep diving. Though the use of trimix grew in popularity, Hal continued to believe in deep air, in the ancient technique of coral fishermen. He supported wreck and cave diving—with decompressive mixtures and new configurations through PSAI; but, above all, he believed (and continues to believe) that deep air, if properly practiced, is a discipline with unique logistics, hidden dangers, and irresistible charms that can take you to a parallel world.

Hal Watts speaking at aquaCORPS tek.93 Conference

First of all, Hal, what was the dive that changed your way of seeing scuba diving? I mean, a dive that was like an epiphany, a dive which changed your point of view on a technical matter?

Hal Watts: Wow, you sure are really trying to test my old man memory. Now I’ll have to review some of my old logbook entries. 

The first scuba dive that really got my attention as to just how serious and dangerous scuba diving can be was on December 2, 1962. I was diving with Bob Brown, co-owner of Florida State Skindiving School in Orlando, Florida. I was a member of a dive club in Orlando known as Orlando Sport Diving Club. Bob and I had heard of a sinkhole in Ocala known locally as Zuber Sink as well as Blue Sink. Years later, I later leased the property and renamed it as Hal Watts’s 40 Fathom Grotto, and I eventually purchased the Grotto in mid-1979.

We had never talked to anyone about the sinkhole; therefore, we had no idea about the visibility or the depth. Up to this point, I had constructed my favorite BCD, using a large white Clorox plastic jug, which we tied to our twin tank system. We put air into the BCD from our “Safe Second Stage” mouthpieces. 

Bob and I tied our safety line to a tree on the bank of the sink and reviewed our dive plan. I am reminded of the motto I came up with, many moons ago—Plan your dive, dive your plan. 

We all know that motto. I didn’t realize that it was you who coined it.

It was back in the 1960s when I was writing course manuals for NASDS [National Association of Scuba Diving Schools] and opened up my Mr. Scuba dive shop.

Mr. Scuba’s Magic Bus!

But back to the dive at Zuber. I’ve failed to mention the fact that neither of us had been doing any dives below 30 m/100 ft. We followed the cave line down slowly, not paying enough attention to our depth. Before we realized it, we had hit the bottom, stirred it up, and had no clear water.

Lucky for us, I kept the cave diving reel in my hand, and Bob kept his hand on the line. I couldn’t see; however, I could feel Bob’s hand, squeeze his fingers tight on the line, grab his thumb, and give it the “thumbs up” signal. I don’t know how we managed it, but we were both able to use our NASDS safe second stages and add air into the Clorox “BCDs.” We were actually fated to begin an uncontrolled, too-rapid ascent. All of a sudden, we hit an overhead wall, which stopped our ascent at a depth of 9 m/30 ft. 

We looked at each other, and gave the OK hand signal. While decompressing, following the old Scubapro SOS mechanical computer, I started to pull up the loose line until the dive reel appeared. Wow, we sure had an awful lot of loose line floating around us. Were we extremely lucky? Of course, we were. Our problem was that we never planned our dive, and consequently, were unable to dive a plan.

After that dive, I worked with Scuba Pro and Sportsways to create the “Octopus,” or “safe second.” A while later, the octopus appeared for the first time in Scuba Pro catalogs. I was also the first to add a pressure gauge along with the Octopus.

Hal Watts set the world deep air record to 120m/390 ft in 1967

Ah yes, the “Safe Second.” That’s what NASDS called backup second stages, right? Sheck Exley (1949-1994), the legendary cave explorer with whom you were friends, was also credited with fitting a redundant second stage reg with a necklace. I want to ask you more about Exley, but first, I want to know: What are the best wrecks you ever dived?

This is really very hard to answer. I’ll have to list four, in the order that I dived them: the USS Monitor, Andrea Doria, Japanese wrecks located in Truk Lagoon, and the Lusitania in Ireland.

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The most important would have to be the USS Monitor, a submarine used during the Civil War. A group of well-known USA divers applied to the National Oceanic and Atmospheric Administration (NOAA) for a permit to dive the Monitor, as she was located in protected waters. In addition to myself, the group consisted of: Gary Gentile, attorney Peter Hess, and several other well-known expert divers. At first, NOAA refused. Then, Peter Hess filed proper papers asking that we get the NOAA permit. To that end, we presented my Deep Air training material to the concerned NOAA group. I appeared as an expert witness and provided NOAA staff and their legal representatives with my internationally accepted training material and my record of training several world record deep air divers. Our deep air training has been accepted worldwide with zero diving deaths. After that, we received the permit. 

Other than the Monitor, my favorite deep wreck dive would be the Lusitania, which is a very personal and proud story for me. The main reason is because venture capitalist Gregg Bemis owned the diving rights to the Lucey at the time. Gregg had contacted me requesting that I train him on PSAI Narcosis Management Level V, on air—which is 73 m/240 ft—and then train him on trimix so he and I could dive to 91 m/300 ft on the Lusitania lying off the coast of Ireland. 

When word got out that I had enrolled Gregg in my Narcosis Management Course, a well-known international course director (a personal friend of mine) called and told me, “Hal, do not teach Gregg deep diving.” 

PSAI’s ad in aquaCORPS Journal circa 1994 offering deep air training.

He told me that he had been training Gregg at his facility, and that he was a “train wreck.” “He is from a very well-off family in Texas, and if you cause him any injuries, you will be sued and put out of business,” my friend said. Well, guess what? Gregg completed the 240 Level V Deep Air course, then our PSAI Trimix course. My wife, Jan Watts, Gregg, and I went to Ireland to dive the Lusitania. He and I made an awesome 91 m/300 ft trimix dive to the deck.

Diving on the Andrea Doria with Tom Mount, Peter Hess, and several great wreck divers was also an awesome dive. Last but not least was a great trip to Truk to dive on some of the Japanese wrecks.

Please tell us about Sheck.  What was your relationship with him like?

Sheck and I became friends and made several dives together, and one of my favorites happened when Sheck, his Mary Ellen, my wife Jan, and I were diving at 40 Fathoms. Sheck wanted to practice gas switches during descents. Sheck was practicing, getting ready for a planned very deep dive (I think in Mexico with Jim Bowden). The four of us swam to the east side of The Grotto, slowly following the wall during our controlled descent, watching Sheck practice gas switching. 

Sheck Exley and Hal Watts at a NSS-CDS conference

After reaching our planned depth of 73 m/240 ft, we began our controlled ascent up to our first planned deco stop. During our last deco stop on our 4.5 m/15 ft platforms, I noticed that Sheck had a funny look on his face and was messing with his drysuit between his legs. I remembered then that he had told me that he had an attachment installed in the drysuit that would allow him to pee underwater. He was clearly in a bit of discomfort and Mary Ellen, Jan and I just floated nearby and watched.

I’ve heard that Sheck later used diapers, or just cut it loose in one of his old neoprene drysuits on his big dives, so evidently he didn’t get that early p-valve to work. What about your friendship and job collaboration with Gary Taylor, your brother-in-arms and a co-owner of PSAI?

Andrea, get comfortable, since this question will take some time to properly answer.

I first met Gary in Miami, which is where we became friends when I was staying in his home and taking Tom Mount’s nitrox course.  I have a photo of Tom, Gary, and me gas blending on the floor of Tom’s garage. During the course, Tom was still using his worn-out hand written paper flip charts as his notes.

Gary was impressed with my deep air program and offered to put together an updated slideshow presentation for me to teach with. PSAI still uses an updated version of this system to date. Gary stayed with Tom until Tom thought he had sold IANTD [International Association of Nitrox and Technical Divers] to another individual. After that sale came about, Gary contacted me wanting to get more involved with PSAI. Being smarter than folks thought I was, I jumped at the chance to have Gary on the PSAI Team. Tom’s deal fell through, but Gary was totally involved with PSAI, and now is a partner and president of our agency. Thanks to Gary and Tom. 

Many, many years ago I was still taking some type of classes—I think regarding mixed gasses, maybe with Rebreathers—at Tom’s house. In fact, I was one of Tom’s instructors who did the final proofreading of one of Kevin Gurr’s manuals. Too far back to recall much about this mixed gas stuff—remember my reputation for being a deep air diver.

Tom Mount and Gary Taylor mixing up some trimix in the garage.

Speaking of the people with whom you’ve dived, was the aim of The Forty Fathom Scubapros Club?

Before I invested in a sinkhole in the Ocala, Florida, area—which was locally referred to as Blue Sink or Zuber Sink, and is now referred to as 40 Fathom Grotto—several diving buddies whom I had dived with and trained for extreme deep air diving—as well as cave exploring—got together and planned to dive The Grotto at least one Friday night per month. Within a short period of time, several other buddies joined our group, which eventually became known as The 40 Fathom Scubapro’s dive club. Each diver had to meet my requirements of training. 

Forty Fathom Grotto aka Zuber Sink
An early Sheck Exley mix course at Forty Fathom Grotto
An Eric Hutcheson drawing of Forty Fathom Grotto

Eventually, our group set specific personal requirements—being a good person, supporting our club safety rules, and making at least one 40 Fathom Grotto dive per month. We set a limit of 14 or 15 members. Three 40 Fathom members eventually set World Records for deep air: I was one, A. J. Muns, and Herb Johnson set ocean records, and later I set the air depth record for cave diving. Naturally, as time passed and we got older, our membership got smaller. It is notable that none of our club members have died during any scuba dive.

Finally, what led you to create the iconic motto, “Plan Your Dive. Dive Your Plan?” 

I used to be a private pilot, and we used to say, “Plan your flight, fly your plan.” This was back in probably 1961 when I had just started diving and there were so many instances where all the other divers would get in the water without saying anything. I’ve seen so many incidents and fatalities that could have been avoided through proper planning.

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Dive Deeper

ScubaGuru: LXD 029 : Hal Watts – Record Deep Diver & Technical Diving Pioneer

Netdoc: Netdoc chats with Mr Scuba, Hal Watts

InDEPTH: The First Helium-based Mix Dives Conducted by Pre-Tech Explorers (1967-1988) by Chris Werner

Alert Diver.Eu: Rapture of the Tech: Depth, Narcosis and Training Agencies

Professional Scuba Association International: PSAI History

Andrea Murdock Alpini is a TDI and PSAI technical trimix and advanced wreck-overhead instructor based in Italy. He is fascinated by deep wrecks, historical research, decompression studies, caves, filming, and writing. He holds a Master’s degree in Architecture and an MBA in Economics for The Arts. Andrea is also the founder of PHY Diving Equipment. His life revolves around teaching open circuit scuba diving, conducting expeditions, developing gear, and writing essays about his philosophy of wreck and cave diving. He published his first book, Deep Blue: storie di relitti e luoghi insoliti (2018) and IMMERSIONI SELVAGGE, the new one is on the way, out on fall 2022. 

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