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Assessing Whether a Dive is Safe

One of the things that non-divers "know" about diving is that it is a dangerous sport. I have always disagreed with this assessment, arguing that diving is not dangerous but hazardous. The difference, within my definition, is that if hazards are correctly identified and planned for in advance they can be managed. Hazards only become dangers if they are not dealt with correctly. Obviously, while any diver can make his sport dangerous simply by not thinking about what he is doing, I like to believe that within the UK’s club based training systems we teach divers to think and to stay safe.

The above, points to a need to assess dives before they take place and to ensure that the divers involved are competent to carry it out. Obviously, the level of planning required will vary according to the nature of the dive. I do not propose to go into all the ins and outs of planning a challenging dive but simply to explain the system that I use before jumping into the water. If I am acting as dive marshal I use the same approach for each diver and buddy pair as I use when making the decision to dive myself.

The simple approach I take has a maximum of four stages:

  1. Assess the dive (for each diver)
  2. Assess the individual divers
  3. Compare the diver ratings to the dive
  4. Compare the buddy pair ratings to the dive

Stages 1 and 2 simply consist of "hazard rating" the dive/diver/buddy pair, stages 3 and 4 are the decision steps, let me explain:

1. Assess the dive.

As a basically simple soul, I have an easy way to do this; count the hazards. By hazard I mean any of the following factors that applies to the dive:

  • Is the dive unusually cold?
  • Is it deep?
  • Is the visibility bad?
  • Is it going to be dark down there?
  • Is there a strong current?
  • Is the sea rough?
  • Is the site going to present any specific hazards in the prevailing conditions?

This list is not exhaustive and the answers to these questions will vary according to the individuals involved. For instance, a dive to 30m is pretty trivial to a diver with several years’ experience diving to depths of 40m+ but would be very hazardous for a novice on his first sea dive. One divers idea of bad visibility may also vary immensely from another’s and good visibility at one site may be quite unacceptable at another, this also needs to be allowed for when rating dives. (If you are wondering why the definition of good / bad visibility changes from site to site consider diving a wreck like the Dakotian in Milford Haven. This is a large cargo ship lying upright in about 20m; the holds have large, open, deck hatches. In good visibility it is very interesting to drop into the holds for a poke around but in poor visibility it can be even more interesting if you begin your ascent and discover a roof in your way because you have unknowingly worked your way into a hold!).

2. Assess the individual divers.

This is where we start to have fun! I rate each diver according to the number of hazards that I believe (s)he can handle simultaneously. Everyone I dive with has a rating, and no, I do not reveal ratings to anyone, I can’t afford the litigation!

Ratings are not based on qualification but on ability, experience and a personal "warm feeling factor". However, as a starting point for rating divers the following listing may help:

BSAC Novice Zero

BSAC Sport Diver / SAA Club diver One

BSAC Dive Leader Two

BSAC Advanced Diver / SAA Dive Supervisor Three

BSAC 1st Class Diver / SAA Dive Master Four

It is important to remember however that you are rating a divers ability, not qualification, and therefore the above is simply a starting point. The rating is adjusted to take account of many other factors, for instance:

  • A very experienced diver who is out of practise and/or unfit may merit a lower rating than someone who is less experienced but is well "dived up";
  • A relatively unqualified diver with abilities way beyond those that his qualification suggests;
  • An experienced diver who tends to err on the side of caution (a good failing) may be less able to handle multiple hazards simply due to reduced practice or to a tendency to worry.

When rating divers, bear in mind that a divers rating will change over time so you cannot rate your buddies and then just keep using the same list. There will also be occasions when short term adjustments are needed to a divers rating, a diver trying out new toys, a different cylinder configuration, buoyancy compensator and drysuit would be an example of this.

3. Compare the diver ratings to the dive

If each diver has a higher rating than the dive there should not be any problem and it is reasonable to go ahead. In this case there is no need to continue the assessment.

The problem arises however if one of the divers is rated lower than the dive. It may still be reasonable for the dive to continue provided the low rated diver has a buddy who is competent to look after him in the prevailing conditions. To assess this we need to continue through step 4.

4. Compare the buddy pair ratings to the dive.

This is slightly more complicated but should not tax the brain too much. The idea is that a diver who has surplus hazard credits can use the "spare capacity" to look after a less capable diver. However as it is always harder to do things for another diver than it is to look after yourself I only allow half the value of the surplus credits.

To make things clearer let’s look at an example: Freda and Bert are to dive together. Freda has been diving many years and although she is a dive leader I have rated her as a three-hazard diver because of her experience and proven ability. Bert, however, has only just started diving; he has dived twice at Stoney Cove and done a couple of sea dives to a maximum depth of about 15m. The plan is to dive the James Egan Layne, at a depth of 20m.

First we assess each divers rating against the dive (Freda is on the left, Bert on the Right)

Dive Assessment 1 1

Diver Rating 3 0

"Surplus" 2 -1

Carry Over

Effective Rating

Clearly Bert is not up to this dive but Freda has the ability to deal with additional task loading. If we allow half of Freda’s "surplus" to be used for Bert this will provide him with an effective rating (within this buddy pair) of 1 (see table below), so the dive should be safe for this pairing.

Dive Assessment 1 1

Diver Rating 3 0

"Surplus" 2 0

Carry Over 2/2=1 1

Effective Rating 1 1

For this approach to be acceptable Freda needs to be the sort of diver who will look after her buddy, not just carry out her own dive with him in tow. But then I hope you would not consider putting an inexperienced diver in the water with an inappropriate buddy.

In conclusion, there are many ways to decide if a dive is reasonably safe or not. This is the method I use, it may not be the best but it works for me. If you have another way of assessing dives, why not write it up? I’d like to know about it. Conversely if you feel unhappy about this method let’s have your comments, who knows, we may all learn something.

This article was originally written for and published in "Mouthpiece" the magazine of Slough Sub-Aqua Club.