Safety Stop in Scuba: Why 3 Minutes at 5 m and When It Matters

What does a safety stop do, and what is the evidence?

It gives your fastest tissues a few minutes to release nitrogen before the last part of the ascent, where the relative pressure change is largest: PADI points out that the biggest pressure difference is between 10 m (33 ft) and the surface. Most of the evidence comes from bubble counts made with Doppler ultrasound after the dive, not from counts of decompression sickness, which is rare. DAN puts it at 1-4 cases per 10,000 recreational dives. Our dive computer and decompression guides cover the no-stop limits that come before the stop.

Some of the first field data came from Andrew Pilmanis in the 1970s. After dives to 30 m (100 fsw) for 25 minutes, divers who stopped for 2 minutes at 3 m, or for 1 minute at 6 m and 4 minutes at 3 m, had venous bubble counts 4-6 times lower than divers who came straight up. Neuman, Hall and Linaweaver reported similar findings. Later, Donna Uguccioni's Doppler study, supervised by Richard Vann, found less bubbling in divers who made safety stops, and DAN credits it with introducing the optional safety stop for dives inside the no-decompression limits.

The clearest modern numbers come from Bennett and colleagues in 2007. Volunteers dived to 25 m (82 ft) for 25 minutes, with repeat dives of 20 minutes, ascended at 10 m/min and were scored with Doppler afterwards; a lower score means fewer bubbles. In the results below, a 5-minute stop at 6 m cut the score by about a fifth compared with no stop, and doubling it to 10 minutes helped a little more. The big drop came from adding 2.5 minutes at 15 m. That is the deep stop question, and the Navy data covered further down complicate it.

Why 3 minutes at 5 m?

Because it is a workable convention, not a measured optimum. An American Academy of Underwater Sciences ascent workshop, summarised by Bruce Wienke in 1992, suggested discretionary stops of 2-4 minutes in the 3-6 m (10-20 ft) zone. PADI settled on 3 minutes or longer at 5 m, and the German VDST uses 3 minutes at 5 m with the DECO 2000 table.

The depth is a compromise between off-gassing and control. Wienke noted that a stop near 4.5 m (15 ft) is easier to hold than one at 3 m (10 ft) in surge and surface chop, and 5 m leaves room to drift a metre either way without leaving the zone.

The exact minutes matter less than the habit. In Bennett's data, once a deep stop was included, shortening the 6 m stop to anything in the 1-5 minute range made no significant difference to bubbles. The authors still advised keeping 3-5 minutes, partly because a slow finish also lowers the risk of lung overexpansion injury.

Some computers lengthen the stop after harder dives. Shearwater's Adapt setting uses 3 minutes but switches to 5 if you went deeper than 30 m (100 ft) or your NDL dropped below 5 minutes, and DAN notes that other computers extend stops in the same situations.

Safety stop recommendations by agency and computer

They agree on a stop of a few minutes somewhere in the 3-6 m band and differ on the details. The table below uses each source's own figures.

CMAS's 2025 ascent rate fact sheet gives no stop time but sets the pace around it: 10 m/min from the bottom, then about 6 m/min between stops and from the last stop to the surface. For divers trained on the DECO 2000 table there is one more detail. Its decompression stops are at 3 m, and on a deco dive the VDST places its 3-minute safety stop at that last stop, not at 5 m.

When is a safety stop optional and when is it required?

A safety stop is optional by definition; a decompression stop is not. Shearwater's manual shows the switch: while the NDL is above zero the computer suggests a safety stop, and once it reaches zero the stop becomes mandatory decompression with a depth and time you must hold. Only after those stops clear does the safety stop count down.

Skipping it is sometimes the better decision. BSAC lists running low on gas, and sea conditions that make accurate depth control difficult, as reasons to omit the stop and ascend directly. A stop spent bobbing between 2 and 8 m is not the stop the Doppler studies measured.

Some systems make the safety stop itself compulsory in certain cases:

• The PADI Recreational Dive Planner requires one after any dive deeper than 30 m (100 ft) and after any dive that comes within 3 pressure groups of the no-decompression limit.
• Suunto computers turn the recommended 3-minute stop into a mandatory one if you exceeded the ascent rate during the dive, and add time after repeated violations.
• Shearwater never enforces it. There is no lockout or penalty for skipping a safety stop.

Deep stops: what the 2011 NEDU study found

It found that moving stop time deeper increased decompression sickness on air dives. The US Navy Experimental Diving Unit compared two schedules for an air dive to 170 fsw (52 m) for 30 minutes, both with 174 minutes of total stop time. The shallow schedule's first stop was at 40 fsw (12 m); the deep schedule started at 70 fsw (21 m). The trial was stopped at the interim analysis with 11 DCS cases in 198 deep-stop dives against 3 in 192 shallow-stop dives (p = 0.030). One deep-stop case was later excluded, and the difference stayed significant (p = 0.047).

The authors' explanation was that slower gas washout, or continued uptake, in slower tissues during the deep stops outweighed the benefit of less bubble growth. Their conclusion: controlling bubbles in fast compartments with deep stops is unwarranted for air decompression dives.

NEDU tested decompression dives, and Bennett's 25 m results came from adding a deep stop on top of the usual stop time. Schellart and colleagues ran the NEDU-style swap on a recreational profile instead: on a 20 m, 40-minute dive, 3 of the 7 minutes at 4 m were moved to 10 m. The deep-stop version produced significantly more bubbles.

CMAS's 2025 fact sheet on deep stops says that for air dives it is best to disable the deep stop function on your computer, while it still recommends short deep stops for helium dives. Check your own settings. The Suunto EON Core can add a deep stop halfway up from your maximum depth on dives deeper than 20 m (66 ft), while the Shearwater Perdix 2 adds none.

How to hold a safety stop at 5 m

Start with weighting, because the stop is where both overweighting and underweighting show. DAN's test: with no air in the BC and 500 psi (about 35 bar) in an aluminium cylinder, you should hover at 5 m (15 ft) without effort. Aluminium cylinders become more buoyant as they empty, so the check belongs at the end of the dive, not the start.

• Arrive slowly. Keep to 10 m/min or slower on the way up; the VDST recommends no more than 5 m/min above 10 m.
• Use a fixed reference. An anchor or mooring line, a wall or the reef slope makes depth changes visible. In open water, check your computer every few breaths.
• Hold depth with your breathing. Make small BC adjustments early, then keep your breathing even. Big breaths and repeated bursts of air cause the up-and-down drift.
• Stay inside the counting window. Suunto counts the stop between 2.4 and 6 m, and Shearwater pauses its timer outside 2.4-8.3 m.
• Leave slowly. BSAC wants at least a minute from 6 m to the surface, and after dives near the limit the VDST recommends no more than 1 m/min above 5 m.

Safety stops in current and surge, with a DSMB

In current you either hold a line or drift, and drifting needs a delayed surface marker buoy (DSMB). DAN describes it as a way to mark your position below the surface and alert boat traffic, and to help surface support find you. It can be sent up from depth, so the boat can follow you through the whole stop.

Never clip the reel or spool to yourself. DAN warns that if it jams, the buoy's lift can pull you into a rapid ascent, and recommends a cutting tool within reach whenever you deploy. In one DAN case, the broken release on a self-inflating DSMB caught a diver's glove at 13 m and pulled them up at a peak of 72 m/min before they tore free.

In surge, use the deeper part of the window. Wienke's point about 4.5 m being easier to hold than 3 m applies here, and stopping at 5 m rather than 3 m still keeps you inside the counting window of both Suunto and Shearwater computers.

Low on gas: shorten or skip the safety stop?

Shorten or skip it. BSAC names low gas as a reason to omit the safety stop, and Shearwater applies no penalty for skipping one. A decompression stop is different: DAN's advice is that divers should avoid interrupting a mandatory decompression by any means.

The gas involved is small, which is why running short at the stop is a planning error. Our gas planner uses gas = SAC × time × (depth ÷ 10 + 1). A diver with a SAC of 20 L/min needs 20 × 3 × 1.5 = 90 L for 3 minutes at 5 m. That is 7.5 bar from a 12 L cylinder, shown as 10 bar after rounding up to the next 5 bar. A 5-minute stop needs 150 L, or 15 bar.

Sharing air changes the picture. Two divers on one 12 L cylinder, each breathing a stressed 40 L/min, need 360 L (30 bar) for the same 3-minute stop. The planner's rock-bottom figure already includes 3 minutes at 5 m for two divers, so if you start the ascent at rock bottom the stop is covered. Measure your own breathing rate with the SAC calculator.