A repeat dive is a scuba‑diving term that designates a dive conducted after a preceding dive within a relatively short interval, typically on the same day or within 24 hours. Because inert gases—most commonly nitrogen—absorbed by the body during the first dive have not been fully eliminated, the residual nitrogen load must be taken into account when planning the subsequent dive. This influences the allowable bottom time, depth, and decompression requirements, and is reflected in dive‑table calculations or dive‑computer algorithms that adjust the diver’s “group” or “pressure‑group” status based on the prior exposure.
Key characteristics
- Residual nitrogen: The amount of nitrogen remaining in the diver’s tissues after the first dive determines the reduced no‑decompression limit for the repeat dive. Dive tables provide a “residual nitrogen time” (RNT) that is subtracted from the maximum allowable bottom time for the planned depth. Modern dive computers automatically incorporate this residual load into their tissue‑loading models.
- Time interval: The definition of a repeat dive varies among training agencies, but the most common criterion is a surface interval of less than 24 hours, or a surface‑interval time insufficient for complete off‑gassing of the prior exposure.
- Planning considerations: Repeat dives require careful surface‑interval planning to avoid excessive nitrogen accumulation that could lead to decompression sickness. Divers may also use “deep‑stop” or “repet‑up” profiles to manage residual load.
Related usage
In dive‑profile terminology, a “repeat dive” can also refer to a dive whose maximum depth exceeds that of an earlier dive performed on the same day, producing a reverse profile. Such a profile is characterized by a deeper segment later in the dive and may be associated with a “no decompression stop” if the residual nitrogen load is low enough. The concept appears in discussions of dive‑profile shapes and safety considerations for multi‑dive outings.
Safety implications
Because the residual nitrogen from the first dive reduces the safe exposure limits for subsequent dives, repeat diving increases the risk of decompression illness if the additional nitrogen load is not properly accounted for. Divers are advised to:
- Record the depth and duration of each dive.
- Observe recommended surface‑interval times.
- Use dive tables or a dive computer that incorporates repeat‑dive calculations.
- Remain within the adjusted no‑decompression limits or follow appropriate decompression stops.
References
- “Dive profile,” Wikipedia, which notes that a “reverse profile” can involve a “repetitive dive” deeper than the earlier dive.
- DiverTown, “What is a Repetitive Dive?” – describes repeat dives as those occurring after a previous dive within the same day and explains residual nitrogen considerations.
- Scuba‑Tutor, “Repetitive Dives” – discusses the impact of prior dives on dive‑table calculations and pressure‑group adjustments.