🤿 Stuff Every Scuba Diver Should Know: Training Guide

Pressure Changes Underwater

As a diver goes deeper, water pressure rises. At the surface the air pushes with 1 atmosphere. Every 33 feet of seawater adds another atmosphere, so at 33 feet the total is 2 atmospheres, and at 66 feet it is 3 atmospheres.

Boyle's law says that when temperature stays the same, pressure and volume move in opposite directions. When pressure goes up, gas shrinks. When pressure drops, gas expands.

A balloon filled at the surface and carried down to 33 feet shrinks to half its size. Bring the balloon back up, and it returns to full size. The same squeeze affects body air spaces and gear.

The largest pressure change happens in the first 33 feet. From the surface to about 33 feet, pressure doubles. That is why ears, sinuses, mask and lungs face their toughest squeeze close to the surface.

Breathe Continuously

The first rule of scuba diving is to breathe continuously and never hold your breath. Training agencies teach this on day one, before a new diver breathes from a tank in a pool.

If you hold your breath and rise, air in the lungs expands. Without an exit, it can rupture lung tissue. This injury is called pulmonary barotrauma and can push gas bubbles into the arteries, an arterial gas embolism.

Lung injury depends on pressure change, not total depth. Even a breath-hold ascent from as shallow as 4 feet after inhaling tank air can tear tiny air sacs in the lungs. A sudden ascent from 15 feet can make lung air expand by about 50 percent.

Equalize Your Ears and Mask

Equalize your ears early and often on the way down. Waiting until it hurts can mean the ear tubes are already locking shut.

Without equalizing, ears may begin to hurt around 4 feet deep. At that point water pushes harder on the eardrums than the air behind them. By about 6 feet, the ear tubes can be locked shut.

If ears start to hurt on descent, ascend a few feet and try equalizing again. Do not push deeper. Foot-first, head up position helps air rise up the ear tubes and mucus drain down.

Never wear earplugs or swim goggles while scuba diving. They trap air you cannot equalize. A dive mask covers your nose so you can exhale into it, which helps avoid mask squeeze.

Before the Dive

The BWRAF pre-dive buddy check goes through BCD and buoyancy, Weights, Releases, Air, and Final check. The B stands for BCD and buoyancy, and buddies test the inflator and deflate valves.

Dive buddies should base their plan on the slower or less experienced diver. A plan built for the less experienced diver keeps the whole team inside its comfort zone.

Using the rule of thirds for air, turn back toward the exit after using one third. One third gets you out, one third gets you back, and one third stays in reserve for delays or emergencies. DAN calls this the safest rule when you must return to a set point, like a boat's anchor line.

Depth and Time Limits

Deeper dives have shorter no decompression limits because you absorb nitrogen faster at greater depth. The no decompression limit is the time you can stay at a depth and still go straight up without required stops.

Staying within dive computer limits lowers risk but is no guarantee. Dive computers run math models that predict, not promise. Adding safety stops and diving conservatively helps.

A newly certified PADI Open Water Diver is trained to a maximum of 60 feet. Local law can set a different limit, so know the rules where you dive.

Recreational scuba diving has a maximum depth of 130 feet. Advanced Open Water Divers age 15 or older are trained to 100 feet, and the PADI Deep Diver Specialty covers the full 130 feet. Each specialty dive can earn credit toward the related PADI specialty certification.

Ascending Safely

A slow ascent gives nitrogen time to leave the body and lets expanding air escape the lungs. The US Navy and NOAA use a rate of 30 feet per minute, the slower end of training agency recommendations.

At the end of a recreational dive, make a standard safety stop at 15 feet for 3 minutes. The pause lets the body release nitrogen slowly before the final, biggest pressure change near the surface.

Decompression Sickness

The nickname the bends first appeared among Brooklyn Bridge caisson workers. They came up from pressurized worksites hunched over in pain, like a fashion pose called the Grecian Bend.

The most commonly reported first symptom of decompression sickness is pain, especially near the joints. Numbness and tingling come next. Any of these after a dive means see a doctor.

Signs of DCS usually appear between 15 minutes and 12 hours after a dive. They can rarely appear as late as 36 hours. Many divers blame sunburn or tiredness, so watch yourself and your buddy.

The main first aid for DCS is high-concentration oxygen. Breathing it helps flush nitrogen and can ease symptoms, but the diver still needs medical evaluation even if they feel better.

The definitive treatment for DCS is hyperbaric oxygen in a recompression chamber. The chamber puts the diver back under pressure while they breathe pure oxygen.

Nitrogen Narcosis

Nitrogen narcosis at depth feels most like being intoxicated, with poor judgment. A diver may feel overconfident or anxious and make poor decisions.

Slowly ascending to a shallower depth usually clears narcosis within a few minutes. If a diver does not feel normal, end the dive and do not go deeper again.

Air Emergencies

If you run out of air and your buddy is close, signal out of air first, then use your buddy's alternate air source, often called an octopus. Hold onto each other, signal OK, and ascend together slowly. Running out of breathing gas is the most common dive incident, so watch your gauge.

Out of air with no buddy near and the surface close, a trained diver can use a Controlled Emergency Swimming Ascent. Swim slowly upward while exhaling the whole time. This skill is taught and practiced only with an instructor, on a secured vertical line, so the instructor can stop the ascent if needed.

Flying and Getting Help

After a single no decompression dive, DAN recommends waiting at least 12 hours before flying. Airplane cabins have lower pressure than the ground, like being 6,000 to 8,000 feet up a mountain.

After several dives a day or several days of diving, DAN recommends waiting at least 18 hours before flying. More dives mean more stored nitrogen, so it needs more time to leave. Dives that required decompression stops call for substantially longer than 18 hours.

If you have possible DCS symptoms before a flight, seek medical advice and avoid flying. Flying lowers the pressure around you and can make DCS worse.

In a life-threatening dive emergency, contact local emergency medical services first, then the Divers Alert Network emergency hotline at +1 919 684 9111. DAN is staffed 24 hours a day for dive injury advice.

Regulator and Air

A scuba regulator reduces tank pressure in steps. The first stage attaches to the tank valve and reduces high cylinder pressure to intermediate pressure. The second stage delivers air when you inhale.

The second stage has a demand valve. Inhaling drops pressure and opens the valve, so air comes when you demand it.

The alternate air source, often called an octopus, is a spare second stage. It lets a buddy breathe from your tank in an air emergency.

A submersible pressure gauge, or SPG, displays how much air remains in the tank. It can be a separate gauge or built into an air-integrated dive computer.

A standard recreational scuba cylinder contains compressed air, not pure oxygen. Pure oxygen becomes toxic at depth, so it is not used for standard sport diving. Enriched air nitrox for recreational diving has 22 to 40 percent oxygen.

An aluminum 80 scuba tank filled to 3000 psi holds about 80 cubic feet of air. Its inside volume is only about 11 liters. The 80 is the cubic feet of air squeezed in.

Buoyancy and Weighting

A buoyancy control device, or BCD, helps you control buoyancy. Add air to rise, vent air to sink, and make small adjustments to hover. It also holds your tank.

Small buoyancy adjustments are often made with breath control. Breathing in makes you a little more buoyant and breathing out makes you sink a little. Use breathing for fine control and the BCD for bigger changes, but never hold your breath. Add or release air from your BCD in small amounts and give each change time to work.

Do a weight check with an empty BCD and a normal breath. Properly weighted, you should float at eye level, and you should start to sink slowly when you breathe out.

Exposure Gear and Fins

In cooler water, a thicker wetsuit mostly provides more thermal insulation. Common wetsuit thicknesses are 3 mm for warm water, 5 mm for temperate water, and 7 mm for cold water. A wetsuit lets in a thin layer of water that your body warms, and the suit material insulates you from the cooler water.

Open heel fins are designed to be worn with dive boots. Boots help in cold water and protect your feet on shore or a boat deck. Full foot fins slip on like a shoe and are popular for warm water boat diving.

Mask and Fin Skills

To clear water from a scuba mask, press the top of the mask with your fingers, look up, and exhale through your nose. The air pushes the water out. If water remains, exhale again.

To stop mask fog, use a commercial defog or dilute a few drops of baby shampoo in water. Coat the lens, swish, and rinse. Many divers use spit the same way.

The first fin kick most new scuba divers learn is the flutter kick. Move each leg back and forth one at a time. Avoid a bicycle kick that bends the knees a lot, because it wastes energy.

Hand Signals

The OK signal is a circle made by touching thumb and index finger, with the other three fingers pointing up. It asks 'Are you OK?' and also answers it.

Underwater, a thumb up means ascend, not OK. A thumb down means descend.

To signal out of air, move a flat hand side to side across your throat. To signal low on air, hold a clenched fist against your chest.

To tell your buddy something is wrong, hold a flat hand out and rock it side to side like a seesaw, then point to the problem. If your ears will not equalize, give this signal and point to your ear so your buddy waits.

Surface and Current Safety

The recreational diver down flag is red with a white diagonal stripe. It warns boats that divers are below. Some places require it by law, so learn local rules.

If caught in a strong current during a drift dive, do not fight it. Relax, go with the flow, and stay close to your buddy. A delayed surface marker buoy can signal the boat from underwater.

Marine Life Safety

Do not touch coral. Even a light brush with hands, fins or gear can damage delicate coral animals, and some corals sting or are sharp enough to cut skin.

If you see a lionfish, do not touch it. Lionfish spines are venomous and can be very painful.

Avoid touching jellyfish. Stinging cells in the tentacles fire when you touch them. If stung, rinse with vinegar or ocean water and see a doctor if pain grows or breathing is hard. Never rub sand on the sting or scrape it.

Do the stingray shuffle on shore entries. Shuffle your feet to send vibrations that scare buried stingrays away, so you do not step on one and get stung.

Before You Dive

Before scuba training, answer the Diver Medical Participant Questionnaire about your lungs, heart, ears, surgery and medicines. Certain yes answers mean a physician must evaluate you before diving. If you answer no to all 10 questions, no medical evaluation is required.

To reduce seasickness before a dive, take motion sickness medicine before boarding if needed, but read the label and ask a doctor because many cause drowsiness. A wider boat is usually more stable.