How Dive Computers can have a negative impact on diver safety
It would be difficult to argue that dive computers have not made scuba diving a safer sport. Ascent, depth and no deco limit (NDL) alarms are a huge benefit that do a lot to keep divers from harm. What really concerns me as a dive instructor are the attitudes divers adopt when they, their buddies or guides are wearing them.
It’s quite common for divers to ask dive professionals for help and advice setting their computers, but what these requests often reveal is quite worrying, many people simply have no idea how their computers function. They are, for all sake and purposes, little boxes of black magic inhabited by scuba fairies.
It might be a little too much to expect your average diver to have opinions on which algorithm is the best choice and why, although that would not be a bad thing, but what your computer displays during a dive should be in no way mysterious.
A good example of how not having this knowledge could put a diver serious danger would be the information your computer displays if you enter a decompression phase. Recreational divers seek to stay within their NDL limits and avoid decompression, but accidents happen. This information, if understood, will in most cases get you safely back to the surface. Fail to interpret this data and you may find yourself in some very dire circumstances.
It may sound easy enough but a limited amount of space on your computers display requires the information to be presented in a very basic way, often a few arrows and lines accompanied by some numbers are what you will see. The prudent diver, who read the computers manual, will look at this and understand the difference between deco stop time, the stop ceiling and total time to surface.
Haven’t read the manual? Well now you have some potentially dangerous guess work to do and panic becomes likely. Make a point of researching what your computer will display in this situation, you may already be stressed, adding confusion to the mix will not help.
Slightly off topic, planning to deliberately go into deco without the right equipment and training is not technical diving, it’s just dangerous and foolish. Facing an unknown amount of deco time at the end of the dive, combined with an unpredicted and limited gas supply to facilitate it, is asking for trouble.
Technical divers measure their breathing rates and enter the water with the gas they need to complete the dive, furthermore to accomplish this they also plan the exact duration of the dive, deco stops and time swimming between them, your dive computer cannot do this. Technical diving is extremely rewarding, if it interests you, get the proper training, you’ll live longer.
Back on topic and back to basics, dive tables are not the most exciting part of an open water dive course, but arguably the most 
important aspect. Here you might ask if we discussing dive computers or dive tables? They are essentially the same thing, dive tables provide you with a maximum time at a predetermined depth. Dive computers do this on the fly and adjust for any change in depth, providing real time information throughout the dive.
Another table variation is a multi-level dive planner, these provide maximum bottom times for two or more predetermined depths. These give results which are closer to a computers dive profile than your standard single depth table. Multi-level diving is a good alternative for those who do not wish to invest in a dive computer, consider PADIs Multi-Level diver speciality. Get your dive tables out of the closet and practice, it’s very simple and does not take long.
Whilst dive computers make dive planning that much simpler, dive tables do go a long way to helping a diver understand how a computer does its job, and provide an excellent back up. Batteries only last so long and, unfortunately, they nearly always expire during a dive trip. When they do run out having your battery replaced often involves sending the computer away for service. This is not so easy in remote dive locations, trust me, I live in one.
Understanding your computer can also help you get a lot more from your dive trips. Remember dive tables do a great deal of rounding up. For example, can’t find your planned dive depth? Round up! Can’t find your planned bottom time? Round up! How long before you can get on a plane after diving? Depending on the table you are using it might be 12, 18 or even 24 hours.
All of these factors combined result in divers missing dives, a computer offers accurate results based on the time you spend at depth. Bottom time previously lost to rounding up can now be enjoyed underwater. Punch the days planned dives into your planner function and you get an exact no fly time and maybe squeeze in an extra dive as a result.
Activities such as Enriched Air Nitrox diving require a bit more knowledge about your computer. How does your computer track your O2 exposure, does it default back to air between dives, is your oxygen partial pressure (PPO2) set correctly and what alarms will sound if you get close to you gases maximum depth or PPO2?
Divers are taught during open water courses not to share computers. No matter how well disciplined a buddy team is no two dive profiles will be identical and if separated one is left without any knowledge of depth and time. A surprisingly common spin on this is blindly following a dive guide who has the only computer, dress it up how you will, this is still sharing a computer. A dive briefing, among other things, should include maximum depth and time information.
How then shall we put this into practise if we have no means of measuring it? A mechanical depth gauge and watch are fine for this, but not if the dive guide is using their computer and following a multi-level dive profile generated by it, once again you are diving blindly.
Following your dive guide in this way becomes even more problematic if you dive with someone else later that day, or even the next. You continue to off-gas and decompress for many hours after diving, tables will provide you with the information you need to account for this ,or your computer will monitor it, but that will not be possible if the computer is on someone else’s wrist diving elsewhere.
The presence of computers with the convenience of being able to jump into the ocean and have on the fly dive information instantaneously appear often presents another risk, the process of dive planning being neglected or omitted entirely.
Listen closely during dive briefings, if there is not an appropriate depth and time plan get one, make sure it accounts for any dives you have done previously. Finally make sure you have some means of measuring it, plan your dive then dive your plan. It is often the case that in a group some divers will have computers and other do not. Naturally those who have purchased a dive computer will feel a little put out if they are limited to table based dive times. In this case a Multi-Level dive plan will keep everyone under the water longer and happy.
Owning a computer is a good thing for any diver. Trusting your life to it without knowing how it functions, or how to interpret the instructions it provides is most definitely a bad thing, and could lead to serious injury. For the most part scuba diving has an excellent safety record, the incidents that do occur are typically attributed to omitted procedures. Ultimately your computer has one purpose, to keep you as safe as possible, this can only work if it is used correctly.
Stay safe, go and read your manual, most manufacturers have downloadable PDF versions of these, keep one in your inbox for quick reference during trips.
Savedra Dive Center (www.savedra.com) Panagsama beach, Moalboal, Philippines
