PADI Open Water Diver

According to Boyle’s Law, holding your breath during ascent causes the trapped air in the lungs to expand as surrounding water pressure decreases, leading to lung overexpansion injuries. Decompression sickness relates to dissolved nitrogen bubbles forming in tissues, not expanding lung air, while narcosis and oxygen toxicity are related to depth and gas toxicity.

If a dive computer fails, you must end the dive by safely ascending and completing a safety stop, as you can no longer accurately track your personal nitrogen absorption. Sharing a computer is dangerous because it does not track your specific depth profile, and estimating time increases the risk of decompression sickness.

Saltwater is denser than freshwater, which increases the upward buoyant force on your body and equipment according to Archimedes’ principle. Therefore, you must add weight to achieve neutral buoyancy; otherwise, you would be positively buoyant and struggle to descend.

Since your buddy is close and aware of your presence, using their alternate air source is the safest and most reliable method to resolve an out-of-air emergency. A CESA is reserved for when a buddy is too far away, dropping weights risks a dangerous rapid ascent, and traditional buddy breathing is an outdated, higher-risk skill.

Starting a dive by swimming into the current ensures you have the most energy and air when the work is hardest, allowing the current to assist you on the return trip when you are fatigued. Swimming with the current initially could leave you exhausted and dangerously low on air when trying to fight your way back.

If you experience pain during descent, your ear is not equalizing, so you must ascend slightly to reduce the ambient pressure and try again gently. Forcing the equalization or continuing to descend can cause a ruptured eardrum, while a rapid ascent poses its own risks like lung overexpansion.

Fully inflating the BCD provides positive buoyancy, ensuring you stay safely afloat without treading water, while keeping the mask and breathing apparatus in place protects your airway from choppy waves. Deflating the BCD or removing your airway protection significantly increases the risk of water inhalation and drowning.

Repetitive dives have shorter no-decompression limits because your body retains residual nitrogen from the first dive, which must be accounted for in the second dive’s profile. You do not start with a ‘clean slate’ until you have off-gassed completely, which takes many hours, not just 30 minutes.

The best practice for marine life interaction is passive observation while maintaining good buoyancy to avoid damaging the fragile reef ecosystem or provoking the animal. Touching coral damages it, and reaching toward or feeding marine life can alter their natural behavior or result in defensive bites.

Decompression Sickness (DCS) is caused by nitrogen gas coming out of solution and forming bubbles in the tissues and bloodstream due to exceeding no-decompression limits or ascending too rapidly. Breath-holding causes lung overexpansion (Arterial Gas Embolism), while contaminated air causes toxicity, neither of which are DCS.

A free-flowing regulator provides a continuous stream of air that you can ‘sip’ by holding the mouthpiece loosely outside your lips, allowing you to breathe while excess air escapes as you ascend. Sealing your lips can cause lung barotrauma from the high pressure, and turning off your air creates an unnecessary out-of-air emergency.

For multiple dives or multiple days of diving, the recommended minimum pre-flight surface interval is 18 hours to allow sufficient time for residual nitrogen to off-gas. A 12-hour wait is only for a single dive, and commercial aircraft cabins are pressurized to an altitude that can still trigger DCS if you fly too soon.

At 20 meters, the ambient pressure is 3 atmospheres absolute (ata), meaning each breath requires three times as many air molecules to fill the lungs to the same volume. Therefore, the diver’s air consumption rate is three times faster, reducing the time the air lasts to one-third of the surface time (10 / 3 = 3.33 minutes).

The standard recreational scuba procedure for buddy separation is to search the immediate area for no more than one minute, and if they are not found, begin a normal ascent to the surface. This ensures both divers follow the same protocol and reunite safely at the surface, rather than getting further lost underwater.

Proper weighting is confirmed when you float at eye level with an empty BCD while holding a normal breath, and then begin to slowly descend upon exhaling. If you float higher, you are underweighted; if you sink while holding your breath, you are overweighted, which can lead to poor trim and excessive air consumption.

Nitrogen narcosis causes an intoxicating effect at depths typically below 30 meters, leading to impaired judgment and bizarre behavior. The immediate and effective treatment is to ascend to a shallower depth, where the reduced partial pressure of nitrogen will quickly reverse the symptoms without lingering effects.

Because water is much denser than air, it conducts heat away from the human body about 20 times faster, meaning prolonged exposure to water cooler than body temperature will gradually drain core heat. Without thermal protection, divers can become chilled and eventually hypothermic, even in tropical environments.

The ‘rule of halves’ is a common recreational practice for out-and-back dives, meaning you use half your air supply (100 bar out of 200) for the outbound leg and half for the return, ensuring you arrive back with a safe reserve. Waiting until 50 bar to turn around would leave you without enough air to complete the return swim safely.

Divers must monitor their air supply frequently to maintain situational awareness and ensure they have ample air to complete the dive, safety stop, and surface with a reserve. Waiting to check the SPG until resistance is felt means the tank is nearly empty, which is a critical emergency.

Crossing the arms and rubbing the shoulders is the standard scuba hand signal for ‘I am cold.’ Because a cold diver is at risk for hypothermia, impaired judgment, and an increased risk of DCS, the correct response is to safely end the dive.