It’s a morbid subject to talk about however it has to be discussed. Most accidents and deaths occur due to one or more of the following (these are in order of number of deaths):
Exceeding your training or not having the correct training for the environment that you are diving in. There are countless stories of Open Water divers heading into caverns or caves and thinking that because the visibility looks awesome that they won’t have any problems getting out. Obviously this is wrong. There are also cases where trained cave divers have exceeded their training, such as carrying stages or using DPVs when they have not been trained to do so. Certain dive sights also require a level of experience, this should be exceeded before diving in those sights.
A continuous guideline back to the surface means that you is your life line. It must always be placed with the primary tie-off in open water and the secondary tie-off at the start of the cavern zone. This is the second most common cause of deaths.
Not following the rule of thirds is the third most common reason for deaths in caves. Calculate the adjusted turn pressures for each diver and then stick to it. Whoever reaches their turn pressure first calls the dive.
Exceeding your rated depth. Cavern divers are only allowed to dive to 100ft and no recreational cave dive should exceed 130ft.
It started off just being lights but it also is about have the required equipment for your level of training. This equipment should be functioning and well maintained. Modern scuba equipment doesn’t fail often if it is kept maintained.
Most deaths occur when divers ignore the rules and limitations out on. They feel that those restrictions don’t apply to them and that they can just ignore them. Unfortunately, ignore these rules at your peril and your buddies’. It is better to thumb a dive, there is nothing inside a cave that is worth dying for.
A nice mnemonic to remember these is Two Girls All Day Long. If you prefer you can always swap the girls for guys 😉