What is the concept of failure points?

Technical divers refer to any part of your diving equipment that can break or go wrong as a “failure point”.

On a regulator, failure points include the o-rings at both ends of your intermediate pressure hose and the cable tie on your second stage mouthpiece. On your mask, the most significant failure point is the strap.

The concept of failure points is rarely discussed in mainstream scuba diving, but it is nevertheless highly relevant. Here is a story that shows how important it can be.

Ian back-rolled into the water in the warm waters of eastern Indonesia and dropped quickly down the reef wall to 20m. He reached for his inflator to halt his descent. However, when he pressed the inflator button, all he did was send a stream of air bubbles directly into the ocean.

His inflator mechanism was connected only to the low-pressure inflator hose. The corrugated hose was nowhere to be seen. He had no means of adding air to his BCD.

He continued to drop. He tried finning upwards but this just slowed his descent. It didn’t stop him going down. He couldn’t drop any weights because he wasn’t carrying any. He was using a wing and harness BCD with a 7kg stainless steel backplate and, with the thin skin suit he was wearing, this gave him all the negative buoyancy he needed. Actually, as he was now learning, it gave him more than enough. He looked down. All he saw was a dark blue void fading into black. There was no seabed in sight.

Luckily, a couple of other divers were nearby and, seeing that Ian was in difficulty, they swam over and helped him get to the surface and back on the boat.

How did this happen?

Ian had never considered the possibility that his BCD might malfunction during a dive. However, all BCDs have multiple potential failure points and can quite easily stop working properly, as he had just discovered. For example, the bladder can get torn or a dump valve can shear off.

This is why, however you choose to configure your BCD, you must always make sure that, if necessary, you can reach the surface and stay afloat there without the help of your BCD. If you don’t have easily removable weights, this may be very difficult.

The problem with Ian’s BCD was that his corrugated hose had only been connected to the BCD pump mechanism by a single cable tie and this cable tie had broken. It had either just snapped or, more likely, it had disappeared some time ago and Ian had not noticed.

BCD cable ties are notorious failure points, which is why all good systems have either TWO cable ties or a permanent heavy-duty screw fitting at EACH end of the corrugated hose. Check your BCD to see how yours is constructed. There are TWO cable ties so that, if one breaks, the other one will still do the job. Of course, both cable ties must be in place before the dive for this built in redundancy system to work. You have to check.

Good BCDs also have some sort of permanently fixed bridging or wrapping device connecting the corrugated and inflator hoses. This device is there so that if the corrugated hose does come off the pump, it will still be hanging next to the inflator hose. In an emergency, if it comes off you can then reattach it to the pump and hold it in place manually while you inflate your BCD.

Ian’s BCD had no such connecting device, so, when his corrugated hose came off, it just floated away behind his back and out of reach.

Some BCDs have fewer potential failure points than others. For instance, some have an internal air cell to keep the wing functional even if the external casing gets torn or the material around the dump valves gets worn. Others have double cylinder straps instead of a single strap to ensure the cylinder never falls out.

What can you do?

Consider every item of dive equipment you own. Identify the failure points and make sure you know what to do if something breaks during a dive.

Check frequently that all o-rings, cable ties, connectors, straps, buckles and snaps are in good shape and replace anything that is torn and worn. If you notice during a dive that bubbles are coming out of a hose or gauge, fix it or replace it before the next dive.

And when you are buying new dive equipment, compare the options with the concept of failure points in mind.

Learn more about this in Scuba Exceptional - Become the Best Diver You Can Be