IDC Dive Theory & Safety Standards 2 — Questions and Answers
Question 1: What is the maximum recreational scuba diving depth limit according to PADI standards?
- 30 meters / 100 feet
- 40 meters / 130 feet (Correct answer)
- 50 meters / 165 feet
- 18 meters / 60 feet
Correct answer: 40 meters / 130 feet
PADI sets the recreational scuba diving depth limit at 40 meters (130 feet). Dives beyond this depth require technical diving training and equipment.
PADI's recreational diving depth limit is 40 meters (130 feet). This limit exists because at greater depths, nitrogen narcosis becomes more pronounced, decompression obligations increase significantly, and the risk of oxygen toxicity rises. Dives beyond 40 m require specialized technical diving certifications such as TecRec courses. Instructors must clearly communicate this limit to students and reinforce it during all confined and open water dives.
Question 2: Does PADI's Recreational Dive Planner (RDP) specify a minimum surface interval between dives?
- No minimum surface interval is specified by the RDP (Correct answer)
- At least 10 minutes must always elapse
- At least 1 hour must always elapse
- At least 30 minutes must always elapse
Correct answer: No minimum surface interval is specified by the RDP
The RDP does not specify a minimum surface interval. Divers must complete the required surface interval to reduce their pressure group before the next dive.
The PADI Recreational Dive Planner (RDP) does not mandate a fixed minimum surface interval between dives. Instead, divers use the table to calculate their residual nitrogen and determine the minimum surface interval needed to safely conduct their planned repetitive dive. Many instructors recommend a practical minimum of 1 hour between dives to allow off-gassing and avoid fatigue. The key principle is that the surface interval must be sufficient to reduce the pressure group so the planned repetitive dive remains within no-decompression limits.
Question 3: What does the term 'pressure group' refer to in recreational dive planning?
- The ambient pressure at depth
- A letter designation indicating residual nitrogen in the body (Correct answer)
- The group of divers in a dive party
- The pressure reading on a submersible pressure gauge
Correct answer: A letter designation indicating residual nitrogen in the body
A pressure group is a letter designation (A through Z) used with the RDP to track residual nitrogen levels in a diver's body between repetitive dives.
In recreational dive planning using the PADI RDP or eRDPml, a pressure group is a letter designation ranging from A to Z that represents the amount of residual nitrogen remaining in a diver's tissues after a dive. After completing a dive, divers locate their ending pressure group on the table. During a surface interval, nitrogen is eliminated, and divers find their new beginning pressure group for the next repetitive dive. This system allows divers to safely plan repetitive dives while staying within no-decompression limits.
Question 4: Which factor does NOT directly affect a diver's nitrogen absorption rate?
- Depth of the dive
- Duration of the dive
- Water temperature at the surface (Correct answer)
- Exercise level during the dive
Correct answer: Water temperature at the surface
Surface water temperature does not directly affect nitrogen absorption. The primary factors are depth (partial pressure of nitrogen) and time at depth.
According to Henry's Law, the amount of gas dissolved in a liquid is proportional to the partial pressure of that gas. For scuba divers, nitrogen absorption is primarily determined by the partial pressure of nitrogen (which increases with depth) and the duration of exposure at that depth. Water temperature at the surface does not meaningfully affect nitrogen loading. However, cold water at depth may affect circulation and nitrogen distribution in tissues. Exercise level and body composition can also influence absorption, but surface temperature is not a direct factor.
Question 5: What is oxygen toxicity and at what partial pressure of oxygen does it become a concern for recreational divers?
- Nitrogen build-up; above 1.4 bar
- Excess oxygen causing convulsions; above 1.4 bar PO2 (Correct answer)
- CO2 poisoning; above 1.6 bar
- Hypoxia from low oxygen; below 0.16 bar
Correct answer: Excess oxygen causing convulsions; above 1.4 bar PO2
Oxygen toxicity occurs when the partial pressure of oxygen (PO2) exceeds safe limits, potentially causing convulsions. Recreational diving limits PO2 to 1.4 bar maximum.
Oxygen toxicity is a condition caused by breathing oxygen at elevated partial pressures. Central nervous system (CNS) oxygen toxicity can cause convulsions underwater, which is life-threatening for a scuba diver. PADI limits the maximum PO2 for recreational diving to 1.4 bar (with 1.6 bar as an absolute maximum in technical diving). This is why air dives are limited to 40 meters — at that depth, the PO2 of air (21% oxygen) reaches approximately 0.84 bar, well within safe limits. Enriched air nitrox divers must calculate their maximum operating depth based on their mix's oxygen percentage.
Question 6: What is the proper first aid response if a diver surfaces with signs of decompression sickness (DCS)?
- Send the diver on another dive immediately to recompress
- Have the diver breathe pure oxygen and seek emergency medical care (Correct answer)
- Give the diver aspirin and have them rest for 24 hours
- Submerge the diver to 10 meters for 30 minutes
Correct answer: Have the diver breathe pure oxygen and seek emergency medical care
DCS treatment requires the diver to breathe 100% oxygen and receive emergency medical care, including transport to a hyperbaric chamber if needed.
Decompression sickness occurs when dissolved nitrogen forms bubbles in the body's tissues and blood. Proper first aid includes having the diver lie down, administering 100% oxygen via a non-rebreather mask, keeping the diver hydrated if conscious, and activating emergency medical services. The diver should be transported to the nearest hyperbaric treatment facility. In-water recompression is NOT recommended as standard practice due to the risk of drowning or worsening the diver's condition. PADI instructors must know DAN (Divers Alert Network) contact numbers and emergency protocols.
IDC Dive Theory & Safety Standards 2
What is the maximum recreational scuba diving depth limit according to PADI standards?