Decompression Stop

The physics of gas absorption dictates the need for decompression stops. When you descend, the increased ambient pressure causes inert gases from your breathing air (primarily nitrogen) to dissolve into your body's tissues. The deeper and longer you stay, the more nitrogen your body absorbs. As you ascend, the ambient pressure decreases, and these dissolved gases begin to come out of solution. If the ascent is too fast, the gases can form bubbles within your tissues or bloodstream, leading to decompression sickness.

Decompression stops provide a controlled pause at shallower depths, where the pressure is lower than at depth but still higher than at the surface. This allows the dissolved nitrogen to off-gas gradually from your tissues into your bloodstream, where it is then transported to your lungs and exhaled, without forming harmful bubbles. It's a critical safety mechanism that allows your body to re-equilibrate with the changing pressure.

There are several categories of decompression stops, each with a distinct purpose. A 'safety stop' is a precautionary measure, typically for 3 minutes at 5 metres (15 feet), recommended even during no-decompression dives. It's not strictly mandatory by dive tables but is highly advised to add an extra margin of safety for nitrogen off-gassing and to help avoid micro-bubbles.

Conversely, 'mandatory decompression stops' are non-negotiable. These are calculated by your dive computer or dive tables when you exceed no-decompression limits. Skipping or shortening these stops significantly increases your risk of DCS. Technical diving often involves 'planned decompression' with multiple, deeper, and longer stops, sometimes utilising different gas mixtures like enriched air nitrox or trimix for more efficient decompression.

Liveaboard trips, with their emphasis on multiple daily dives over several days, require particular attention to decompression. While most recreational liveaboards stick strictly to no-decompression profiles, the cumulative nitrogen load from repetitive dives can bring you closer to no-decompression limits than single dives might. Your dive computer is your best friend here, constantly calculating your nitrogen saturation and alerting you to any potential decompression obligations.

Even if you plan no-decompression dives, always incorporate a safety stop. It's a standard practice on all reputable liveaboards and adds a vital layer of protection. For liveaboards catering to technical divers, planned decompression stops are an integral part of the dive profile, supported by dedicated gas management and surface support. Always discuss the liveaboard's policy on decompression diving if you plan to exceed recreational limits.

Myth: If your computer shows a 'deco stop', you must have done something wrong. Fact: Not necessarily. While recreational divers aim to stay within no-decompression limits, factors like repetitive dives, slight overstays, or even highly conservative computer algorithms can occasionally lead to short, shallow decompression obligations. It's crucial to follow your computer's instructions if a deco stop becomes mandatory, rather than ignoring it.

Myth: Safety stops are the same as decompression stops. Fact: While both involve pausing during ascent, a safety stop is a *precautionary* measure typically done for 3 minutes at 5 metres (15 feet) and is not strictly mandatory by dive tables. A *mandatory decompression stop* is required when you've exceeded no-decompression limits and is essential to prevent decompression sickness.

Myth: You can 'cheat' a decompression stop by ascending slowly instead of pausing. Fact: While slow ascents are always good practice, a continuous slow ascent cannot replace a dedicated decompression stop at a specific depth. Decompression models are depth-specific, and the pressure gradient at a constant depth allows for more efficient off-gassing than a continuous, albeit slow, ascent.