Safety Stop

What a safety stop is

A safety stop is an optional pause on a no-decompression dive, made before the final ascent to the surface. It is called a safety stop, rather than a decompression stop, because the dive didn't require one. It's an extra margin, and training agencies recommend making one at the end of every dive.

The usual stop is 3 minutes at about 5 m (15 ft), though anywhere from about 3 to 6 m (10 to 20 ft) is generally accepted. Some divers and computers extend it to 5 minutes after deeper dives or when diving near their limits.

Why it helps

During a dive your body absorbs nitrogen. On the way up it releases it, as explained in decompression sickness. The stop gives faster tissues time to release some of their nitrogen while you are still under some pressure, which is thought to reduce the chance of bubbles forming. Studies using ultrasound have found fewer bubbles in divers who make safety stops.

There's a practical benefit too. A stop breaks the ascent into two slow, controlled parts. It gives you time to check your neutral buoyancy, look out for boats and get ready to surface. And it's in the shallowest water, where gas expands fastest, as described in Boyle's law, that a careful ascent counts most.

Ascent rates

Ascending slowly is as important as the stop itself. Many training agencies and computers now recommend no faster than about 9 to 10 m (30 to 33 ft) per minute, especially in the last stretch, and many computers sound an alarm above that. Older guidance allowed up to 18 m (60 ft) per minute. As a rough check, don't rise faster than your smallest bubbles. After the stop, take a full minute or more for the last 5 m to the surface.

How to hold a stop

• Use a reference if you can: an anchor line, a descent line or a reef slope.
• Make sure you are weighted for a near-empty tank, especially with an aluminium tank, which floats as it empties (see scuba tanks).
• Vent your BCD during the ascent so you arrive at the stop under control.
• Use your breathing to fine-tune your depth.
• In open water or a current, many divers deploy a surface marker buoy before or during the stop so boats know where they are, as in drift diving.

When to skip it

The safety stop is recommended, not required, on a no-decompression dive. In an emergency, such as a buddy who is out of air or a serious injury, getting to the surface may matter more. Ascend as slowly as safely possible in that case. If you overstay a no-decompression limit, the stops your computer shows are no longer optional and must be completed.

Frequently asked questions