Risk Management and the role of FTA in dive planning
The approach of most divers to risk, when they are taught risk management at all, is to assess risk based on its likelihood of occurrence. If the system designed to avoid or mitigate the risk being assessed has an “acceptable” degree of reliability, and the diver is familiar with and fluent with that system, the risk itself is said to be acceptable.
Another approach, and one all of us should be aware of, makes an assessment of risk based on the magnitude of regret should the risk happen. Individuals falling into this grouping are most often unwilling to accept risk no matter how unlikely the event.
The second approach to risk is safe, the first is not!
And so, we arrive at the first rule that we need to accept as divers; certainly as technical divers. No form of diving is safe; and in real terms, no high-stress, high-risk, fun activity is. However, this does not mean divers are cavalier about personal safety or off-hand when it comes to risk management. Quite the opposite; the vast majority of experienced technical divers are risk adverse. They use any and every tool they can to help them identify, assess, avoid and mitigate the risks inherent in poking one’s head underwater and breathing compressed gas.
We are going to look at several tools to help us in this regard. First is something called Fault Tree Analysis. Here is a very simple example of a Fault Tree Diagram and how it can be used to analyze what went wrong and then to “fix” the problems.
The issue being analyzed is buddy separation. Based on actual experience or reliable feedback, the Fault Tree Diagram lists lost visual contact; divers swimming at different speeds; and divers swimming in different directions as most common causes. Each of these causes is a “stand-alone” in this diagram and is connected with the fault (buddy separation) by the graphic element that signifies an OR statement.
For each of the three causes of buddy separation, the diagram lists a couple of contributing causes or effects. For lost visual contact it highlights the dive team failing to keep close or not thumbing the dive as soon as it was apparent that the vis sucked.
Contributing factors to the cause swimming at different speeds, are shown as divers swimming in a single file formation, and divers conducting buddy checks too infrequently. This would be particularly true of the diver in the lead, wouldn’t it?
When divers swim in different directions, the diagram indicates that the team has ignored their dive plan, or have poor communications skills.
Cheap and Cheerful Analysis
As a result of this very simple Fault Tree Diagram, our Analysis of the situation and suggestions for managing the risk of buddy separation would run something like this.
To help lessen the risk of buddy or team separation, members should be mindful of losing contact because of poor visibility. If divers find the visibility poor during the dive, they should 1/ maintain close visual contact OR if visual contact is compromised 2/ abort the dive.
At all times, the team must swim at the same rate otherwise separation becomes more likely. Having the team swim side-by-side and conduct frequent buddy checks is the best strategy, but if swimming in single file is necessary, buddy checks must be made more frequently than usual.
One other issue is when a member of the team swims off in a different direction to his buddy(ies). A strong dive plan will only minimize this risk if it is followed at all times. Any mild deviation from this plan (for example, swimming “off track” to explore something that looks interesting), should only be made if all team members can agree on the change, which requires excellent communications (signs/notebook/slate).