Sport and timing
Diving Time Limits: Safe Bottom Time, Safety Stops and Freediving Rules
· 6 min read
In short
- In diving, time is about safety rather than speed: the no-decompression limit indicates how long a diver can remain at a given depth without mandatory decompression stops.
- A typical recreational limit is about 20 minutes at a depth of 30 metres; at 40 metres, the usual maximum depth specified by recreational training systems, it is only about 8 to 10 minutes.
- Most organizations recommend a 3-minute safety stop at 5 metres.
- Before flying after diving, the recommended wait is at least 12 hours after a single no-decompression dive and 18 hours after multiple dives or multiple days of diving.
In most sports, time determines who is faster. In diving, it helps determine who returns safely. Time limits in this sport protect health.
No-Decompression Limits and Depth
When scuba diving, nitrogen dissolves in the body under pressure. The deeper and longer the dive, the more nitrogen accumulates. The no-decompression limit is the maximum time at a given depth after which it is still possible to ascend directly to the surface without mandatory decompression stops. As a rough guide, the limit is about 20 minutes at 30 metres. At 40 metres, the usual maximum depth specified by recreational training systems, it is only about 8 to 10 minutes. Values vary according to the tables, computer and dive profile used.
The Safety Stop
Most organizations recommend a 3-minute safety stop at 5 metres at the end of a dive, giving the body additional time to release nitrogen. It is not mandatory, but it is a common standard.
After Diving: Waiting Before Flying
Divers Alert Network recommends waiting at least 12 hours before flying after a single no-decompression dive, 18 hours after multiple dives in one day or several days of diving, and even longer, often 24 hours or more, after dives that required decompression stops. These are recommendations, not laws.
Freediving: 15 Seconds After Surfacing
In competitive freediving, time is a rule that determines the result. Under AIDA rules, a competitor has 15 seconds after surfacing to remove equipment from the face, make the OK sign and say that they are okay. Failure to complete these actions in the required order and within the time limit results in disqualification. The rule exists for safety reasons because loss of consciousness can occur shortly after surfacing.
What Diving Has in Common with Racing
If you organize an outdoor event, you know that time limits are a safety measure, not bureaucracy. We explain how they are set and monitored in running and triathlon in Time Limits at Events. Timekeeping Standards shows how timing accuracy and standards differ among sports.
A Note on Sources
This article is neither a diving guide nor a substitute for a course. The figures are approximate, and divers must follow the tables and computers prescribed by their organization and instructor.
Frequently asked questions
What is a no-decompression limit in diving?
It is the maximum time a diver can spend at a given depth without needing mandatory decompression stops during the ascent. The greater the depth, the shorter the limit; at 30 metres, for example, it is about 20 minutes.
How long should you wait before flying after diving?
DAN recommends waiting at least 12 hours after a single no-decompression dive and 18 hours after multiple dives in one day or several days of diving. An even longer interval, often 24 hours or more, is recommended after dives involving decompression stops.
What rule applies after surfacing in competitive freediving?
Under AIDA rules, a competitor has 15 seconds after surfacing to remove equipment from the face, make the OK sign and say that they are okay. Failure to complete these actions in the required order and within the time limit results in disqualification.
Why is time measured in diving?
To prevent decompression sickness. Time and depth determine how much nitrogen accumulates in the body, which is why dive computers continuously monitor both.