Human Factors in Diving

Posted in education on January 1, 2023 by Paul Armstrong ‐ 18 min read

Human Factors in Diving

I recently completed The Human Diver’s 10 week Level 1 webinar series. After reading Under Pressure and integrating some of that into the way I dive and teach, I was looking for new material to integrate beyond just hard technical skills. There seemed to be a significant number of additional skills to be acquired in the human factors realm, so I decided to take the Level 1 class.

Gareth has a long history of human factors and Just Culture knowledge, stemming from time in RAF and the adoption of these approaches by the aerospace industry. This course aims to bring all of that knowledge to the dive industry, to improve our processes and practices.

The course is 10 classes, one per week, each 1.5 hours long. After each sub-section, Gareth asks each attendee to list the key items that stood out to them or thoughts they had and there’s then a short discussion. There’s also weekly homework to help solidify the knowledge and an extensive reading list for those looking for more. The class is one of the most well structured I’ve come across in a while (and a particularly refreshing upgrade from TAFE courses).

Below, I summarise parts of the course as it was presented. Note that I’m leaving out significant detail (including entire topics) and the course is revised regularly. Like any good course, feedback is rolled into the next iteration.

My hope in writing this is to provide readers with a good understanding of what the course contains and why it’s so valuable to attend. I’ve long considered Under Pressure to be mandatory reading for professionals and strongly suggested reading for all divers. After taking this class, I believe it’s similarly critical education for dive professionals.

Disclosure: As of writing this, I am not currently affiliated with The Human Diver and am not being compensated for this post. I intend to become an instructor for this material in the future as I believe it is incredibly valuable.

Introduction, Human Error and Non-Technical Skills

The course starts with an outline of both the content and the expectations of students. It is clear from the beginning that this course is in depth education rather than a tick the box certificate.

Next the discussion goes through the class of events commonly attributed to human error and some models for how human error is thought about. How do errors occur, what encourages and discourages them, what and how can we learn from them. For example, classes of conditions which lead to human error include the work environment, the individuals capability, the demands of the task and human nature. There is also the all important discussion of work as imagined vs work as done.

If you are a manager or system designer, this is a particularly important concept. We design workflows and then we imagine that people are following them. How work is actually done may differ drastically and then it’s up to us to work out what’s causing that. For example, prioritising efficiency over thoroughness.

The last section of the first class goes over human factors and non-technical skills. The discussion starts by going over where non-technical skills fit into the bigger picture of dive outcomes and then digging into the relationship between them. The outcome of a dive is a factor of technical skills, context, randomness and non-technical skills. So, while we all like to focus on our technical skills, they’re only a small part what goes into a successful dive.

Just Culture and Psychological Safety

Week two goes into what psychological safety and a Just Culture are is and how to promote them.

Psychological safety is, in short, the feeling that:

  1. You are included
  2. It is safe to learn
  3. It is safe to contribute
  4. It is safe to challenge the status quo

And that all of this can be done without being embarrassed, marginalised or punished.

Most of us have experienced a psychologically unsafe environment. It’s where you self censor or otherwise decide not to contribute because you’re worried that you won’t be taken seriously and that there will be backlash.

In contrast, a psychologically safe environment is one where you feel trusted and supported.

In diving, the difference is often seen as to whether a team is willing to cancel a dive. A psychologically unsafe team will hound someone who believes it should be cancelled until they change their mind. Or, they’ll needle them after the fact. A psychologically safe team will support the decision to cancel the dive.

This is why I iterate time and time again when I teach that the second rule of diving is any diver can cancel any dive at any time for any reason. And I mean it.

The discussion continues with the four stages of psychological safety: inclusion, learner, contributor and challenger. These build on top of each other and it’s not possible to reach higher levels without the foundation. If you’re part of a diversity and inclusion team, this is probably sounding very familiar right now. Inclusion is the minimum.

Following on, we move to Just Culture.

Just Culture, for those not familiar, is one where people are not punished for their actions, omissions or decisions which are expected of someone with their experience and training. As you would expect, negligence, wilful violation and destruction are unacceptable.

Where there is a Just Culture, people look to understand the systems involved and what caused the actions to make sense at the time. No one goes on a dive and says to themselves “today I’m going to breath 100% oxygen at 20 meters”. For those who aren’t familiar with oxygen, the safe limit for 100% oxygen is 6 meters. Instead, we have a set of events and systems which lead to the diver selecting the wrong gas at depth. For example, perhaps the gas is handed to the diver and the social norm is to accept the label as written, rather than checking it themselves. They look at the label, which says 50% and then they’re unknowingly breathing 100% at 20 meters.

Now, some people will jump up and down about how the diver should have checked the gas themselves. That’s technically true. It completely ignores the question of what caused it to make sense to the diver not to self-check the gas. On the face of it, we have a social culture of trusting the label. It’s likely that gas testers are not easily available (or may be completely unavailable) in such a social environment; after all, no one needs them.

When looking at the events after the fact, we need to look at the whole system. This is only possible when people expect to be treated fairly and that honest mistakes and unintentional violations will be treated as learning experiences. Be curious, not judgemental.

And, before this gets written off as a hypothetical, I’ve upset more than one dive operation by insisting on checking my gas. There’s a couple of large operations, which are rather well regarded in Australia, who do not require divers to check their own gas. They also make it difficult to do so for those who ask to. It’s really not hard to see a lot of less experienced divers accepting the dive leader telling them that they don’t need to. Frequently, when challenged on the requirement to test gas, dive leaders have cited time pressure or dive shop workflow to me as the main reason for trying to get divers to skip it.

Situational Awareness

This section discusses what makes for situational awareness. Our ability to notice things, think about them and anticipate what affect they will have on the future. As one might expect at this point, the impact of system design also comes into the discussion.

When we are focussing on one thing, it’s very hard for us to process other inputs. In order to get a feel for exactly how susceptible we are to influences on our situational awareness, I highly recommend watching these videos by Chabris and Simons.

The course involves some other videos and extensive discussion about situational awareness in diving. The discussion continued into the categories of distractions: dangerous, interesting, pleasurable and important; including how to notice or avoid the loss of awareness.

If you’ve ever told someone to “pay more attention” the discussion on how infeasible that is during an event and hindsight bias will be illuminating. This section also covers the reduced cost of attention as we become more skilled at a task. This is why repetition is key, especially when it comes to our infrequently used emergency skills.

To round out the discussion, we talked about how team awareness works and ways to enable greater awareness across the team. Of course, Just Culture and psychological safety are key components.

Decision Making

Decision making seems pretty straight forward, until you think about a diver ripping off their mask and spitting their regulator at 30 meters.

Popularised in Thinking Fast and Slow, one of the models we can use to think about decision making is System 1 vs System 2 thinking.

System 1 is where all the shortcuts are made. This is what makes us efficient. It’s also where biases and stereotypes come to play. Often, we talk about these in negative terms. They are a large part of how we operate so efficiently on a day to day basis though. This is not to say that we shouldn’t be careful with them, just that they’re not all bad. System 1 is also where our brains simplify things when it hits limits such as having too much info, not enough meaning, not enough time or not enough memory.

System 2 is active thought. This is where our brains go when we need to be methodical and logical. That thoroughness comes at the cost of time, energy and focus.

For example, system 1 thinking may tell us that a diver using split fins is a newbie diver who didn’t know any better when buying gear. System 2 is where we think about the potential advantages and disadvantages of split fins and, noticing a limp when the diver is on land, realise that split fins reduce the pressure on some joints, making them useful for people with leg injuries or weak muscles.

The discussion then went into skills, rules and knowledge. Skills take a lot of time to build up (through repetition), but have low error rates. Rules, such as procedures, offer a middle ground of error rates. Knowledge requires significant active thought and is thus quite error prone. Following on, there’s a discussion of naturalistic decision making, mental models and revisiting errors and violations in this context.

Next comes one of the most important concepts to take away from human factors education: the normalisation of deviance. This is where we deviate from a standard and, as nothing goes wrong, our brains normalise that deviance as the new standard. This can be seen on dive boats all over the world. Divers put on their gear, skip their pre-dive checks and jump in the water. Sometimes, they find that their gas is off or some other critical failure has occurred. More often, nothing goes wrong and the divers brain records this as an efficiency they can make next time.

Where this goes wrong is when multiple things stack up. For example, the diver skips their pre-dive check, so enters the water with their gas turned off. Only this time, they’re diving a thicker wetsuit and have put on too much weight to compensate. Now they’re headed to the bottom of the ocean without a breathable source of gas.

This is where standards, briefings, debriefings, accountability and psychological safety all come into play. It’s an inbuilt and important part of human nature, so it takes active effort to avoid.


There’s no assumption as dangerous as assuming that we have been understood.

This section of the course covers effective communication. Barriers, such as distraction, fear of retribution or focussing on response rather than listening. Enablers such as questioning techniques and closed loop processes.

For example, when doing a gas switch the dive leader points to the next diver to do the switch (so they know the communication is aimed at them) and then give the gas switch signal and the gas percentage. The diver will then reply by giving the gas switch signal and the gas percentage. This closes the loop so that the leader and the diver are both sure that the other knows what has been communicated.

Questioning techniques are next. Learning to ask open ended questions is a valuable skill. They drive engagement, understanding and verification of communication. As noted by Cialdini in Influence: Science and Practice word choice is important, because we are so tuned to certain words (see what I did there). Using and instead of but and what or how instead of why also help open up the conversation.

Think about the difference between someone asking you why did you do that? and what lead that to being the most sensible option at the time?. Often the first one will illicit defensive feelings and an appropriately defensive response. The second acknowledges that what was done seemed sensible at the time and shows an attempt to understand.

To finish this lesson, we covered the PACE model (Probe, Alert, Challenge, Emergency) and the broad array of probabilities that people will assign to probabilistic words. For example, saying that an event is likely vs probable.

Adjusting how we communicate is, in my experience, one of the hardest skills to master. This is particularly true in stressful situations and because it necessarily involves other people. As with everything else, repetition is key and having a psychologically safe environment where others can critique communication is incredibly helpful.

As an example, just having this post proof read came up with a few communications surprises. I had thought that elided was a fairly common word. Now I know it’s somewhat less common than I thought. There are also a very wide variety of English dialects around the world. Just because you speak English and your audience speaks English, doesn’t mean that you’re talking the same language. We can see this in simple terms in places such as using cylinder vs tank. They both mean the same item, the preference for their use shifts based on location and someone familiar with one term may not be familiar with the other.

More egregiously, and dangerously, we still see some people using feet and pounds. Confusion caused by divers using different measurement systems can and does cause fatalities. This is why I strongly recommend all divers use metres and bar exclusively.

Leadership and Followership

Just as important as being a good leader, is being a good follower. This module discusses both.

Starting out with what leadership is, the module covers performance vs trust, models of leadership and the transfer of control. This is where we get to think really hard about the kind of leader we want to be and how to achieve that.

There’s also a very solid discussion about the challenges of leadership in diving. Unlike many other activities, it’s largely a discretional activity and there aren’t that many good role models. This is, of course, not particularly helped by diving being often seen as a solo or near-solo activity. Just getting people to listen to the dive brief can be a challenge.

Along with being a good leader, is being a good follower. Depending on the situation, we can be either and it’s important to actively choose our role. Being a good follower is more than just not trying to take control. Constructive dissent is key and, with that, we once again get back to psychologically safe environments. Even in hostile environments though, it’s important for followers to speak up when something is dangerous.

To put it all together the module ends up with a discussion of the relationship between leaders and followers.


Many agencies eschew solo diving, but few do so by specifically calling out the values of teamwork. Often, a buddy is just a considered a “backup brain” or, even worse, “emergency gas”. Actual team work allows us to get a lot more from diving, from more effective learning to a shared sense of achievement.

Effective teams provide complementary skills, a shared mental model and mutual accountability for a common purpose to be much more effective than a group of individuals. This can be seen in formula 1 racing, where pit stops are often only a couple of seconds and obstacle courses where teamwork is needed to scale particularly high walls.

Tuckman’s model of team development is then discussed, along with the leadership styles that best fit each. From there, the discussion moves into how to build teams by connecting to people and motivating them.

Next comes briefing and debriefing, each with their own mnemonic.

Briefing: UNITED

  • U - Understand task, goal and objectives.
  • N - Notify the team of the roles.
  • I - Identify resources needed, risks, dependencies and threats.
  • T - Test the plan including go/no-go points and limits.
  • E - Establish emergency and contingency plans.
  • D - Determine the time and place of debrief.

Debriefing: DEBrIEF

  • D - Define the aims and goals of the dive, discuss if they were achieved.
    • Define the length of the debrief.
  • E - Set an example for learning and vulnerability by discussing something that didn’t go to plan or can be improved upon (notably, something that the leader could have done better).
  • B - Discuss the basics. Including planning, preparation and the briefing.
  • r - Review the dive timeline. This is a lower case r as a reminder that it’s a minor part of the debrief and to avoid going into detail. Keep it to important points and events.
  • I - Internal learning. What did I do well and why? What do I need to improve and how?
  • E - External (team) learning. What did the team do well and why? What does the team need to improve and how?
  • F - Follow up. What needs to be followed up or fixed before the next dive?
    • File incident reports if necessary.

I picked DEBRIEF up from reading Under Pressure and they’re part of how I dive. Even if my dive buddies aren’t interested in doing a debrief, I sit down after the dive and write up notes based on this model. I strongly encourage everyone to do this as it’s transformational.

Performance Shaping Factors

This module looks at stress and the factors behind human performance, utilising the WITH (or TWIN) model.

The discussion of how to mitigate errors, including point, touch, verbalise and peer checklists was quite useful. While we often have pointing and calling out the item as part of our checklists, especially in training, the value has never been explained to me before. Specifically, focussing on the check by pointing at the item to be checked, verbalising the check and then verbalising that the check is OK/not OK, reduces errors by 85%. Additionally, when checking items that can be physically touched (such as indicators or switches), touching them to confirm is helpful.

Following is a discussion on stress and the difference between eustress (positive) and distress (negative) along with their side effects (both positive and negative). Perception also often plays an important role in how we perceive stress and whether we panic or feel euphoric. Of course, no discussion of stress would be complete without a discussion of how to manage it.

Importantly for dive leaders, there’s also a discussion in how to identify stress and a model for checking in: HALT

  • Hungry or thirsty
  • Anxious or Angry
  • Late or Lonely
  • Tired

The module closes with a discussion of fatigue, what causes it and how to manage it. Tip: get good sleep, practice good ascent profiles and don’t rely on nitrox. Sleep is particularly important, going from 8 to 7 hours sleep cuts about 5% off our baseline performance, dropping to 5 hours cuts it down by 15% and only getting 3 hours sleep drops by over 40%. Even worse, it only recovers to 80% of baseline when given adequate sleep for 3 days after the fact. Not getting enough sleep has serious lag effects.

Incident Reporting and Checklists

The aeronautical industry has used both checklists and a comprehensive incident reporting system to sharply reduce incidents. We have the opportunity to do the same.

There are a few impediments to setting up a useful incident reporting system. Firstly, there needs to be a Just Culture in place. If people have a choice between omitting facts or being yelled at, they’ll almost always choose to omit details which they believe may cause them to be punished. Even more so if their job is on the line.

Secondly, we need to stop focussing on lawsuit mitigation. A lot of incidents don’t get reported (or details are left out) due to a fear of lawsuits. If we can’t collect all the relevant information, it’s much harder to learn. Ironically, many of the agencies have incident reporting systems, but they’re black holes from which neither learning nor action emits.

The module starts off by discussing what incident reporting is and why we should care. As you can probably tell from the last two paragraphs, I believe incident reporting is a critical component to improving the dive industry and we need something centralised where incidents are properly studied and the industry benefits from the learning that comes for this analysis.

Then comes a thorough discussion of checklists. How to make good checklists, when to use them, what are the pitfalls of checklists. They are, without a doubt, excellent for reducing error rates when used properly. Checklists are, generally, great for getting us to move from system 1 thinking to system 2 thinking by creating a barrier that slows us down and gives our brains time to think.

Goals and Solidification

The last week is about setting goals for how you will use the knowledge and discussing your goals with the rest of the class.