Dive certifications explained: agencies, levels and specialties

Scuba diving needs knowledge and skills that are not obvious: how pressure affects your body and your gear, how to manage buoyancy and gas, and what to do when something goes wrong. A certification card shows a dive center that you have been trained to a recognized standard, which is why reputable operators ask to see one before renting you gear, filling a tank or taking you on a dive.

Certifications do not expire in most systems, but skills do fade. Most dive centers will suggest a refresher if you have not been in the water for a year or more, and that is good advice regardless of what the card says.

Several organizations write training standards and certify instructors. PADI and SSI are the largest worldwide. NAUI, SDI, RAID and BSAC are well known too, and CMAS is a federation of national bodies that is especially common in Europe and Latin America. Technical training is often done with TDI, IANTD or the technical branches of the recreational agencies.

For recreational diving, the agencies largely recognize each other's entry-level cards, and the core skills are very similar. What matters most is the instructor and the quality of the training, not the logo on the card.

Names differ between agencies, but the path usually looks like this.

Open Water Diver is the first full certification. It qualifies you to dive with a buddy, without a professional, to about 18 meters in conditions similar to those you trained in.

Advanced Open Water, or an equivalent, adds experience in different kinds of diving, often including a deep dive and navigation, and usually raises the recommended limit to about 30 meters.

Rescue Diver focuses on preventing and handling problems, both your own and other divers'. Many divers say it is the course that made them most confident.

Divemaster is the first professional level, followed by instructor ratings. These courses have prerequisites that include a minimum number of logged dives, which is one more reason to keep your log complete.

Specialties teach one area in depth. Enriched air nitrox is among the most useful, because it extends your no-decompression time on many recreational dives. Deep diving qualifies you to around 40 meters. Peak performance buoyancy, navigation, night diving, drysuit and underwater photography are other popular choices.

Pick specialties for the diving you actually do. If your next trip is a liveaboard with several dives a day, nitrox will make a real difference. If you dive cold lakes at home, a drysuit course will change how much you enjoy them.

Dive centers usually ask for your highest certification and, for some dives, a specialty card such as nitrox or deep. Plastic cards get lost and many agencies now issue digital cards, which are easy to forget about until you are at the counter.

Frey Dive keeps all your certifications in one place, with the agency, level, date, number and a photo of each card. You can scan a card with your phone to fill in the details, and the most recent certification shows up in your statistics so you can see how far you have come.