At the end of every dive you should make a safety stop.
According to a study done by researchers at the Divers Alert Network (DAN), a major finding when comparing various decompression models revealed that a deep safety stop, together with a shallow stop, yielded the lowest bubble grades (fewest silent bubbles). In fact, the optimal method for reducing post-dive bubble production (and therefore reducing the risk of DCS) was the combination of 1) an ascent rate of 10 m per minute with a deep stop at about half the depth of the dive for 2.5 minutes and a stop at 5 m for three to five minutes. The report concludes, “The introduction of a deep stop during decompression ascent appears to significantly decrease Doppler recorded bubbles and predicted gas tensions in the fast ‘tissues’ that may relate to actual gas exchange within the spinal cord. The authors conclude that such a deep stop may therefore significantly reduce the incidence of spinal cord-related decompression sickness.”
(DANAP Scuba Skills- A Safe Habit: Safety Stops as Standard Procedure)
But being close to the surface makes buoyancy a challenge, and without the right technique, you might find yourself ascending unintentionally. Here are some guidelines to making safety stops easy.
In recent years, new research into “two-phase” or bubble theories of decompression, including the Reduced Gradient Bubble Model (RGBM), has led divers, particularly those in the technical community, to incorporate an additional safety stop, known as a “deep stop,” into their dives. This means they routinely perform more than one safety stop before ascending to the surface, especially when diving at deeper depths and/or when doing repetitive, multiday dives.
Make a SLOW ASCENT to half your deepest depth, keep an eye on your computer to ensure you ascend no faster than 10 metres per minute.
Remember to vent expanding air from your BC as you go, and always send up a surface marker if you’re ascending away from your boat.
Once at the deep stop depth, adopt the diving position and keep your dive computer at chest level.
If you are holding onto the anchor line attached to the boat, grasp the line loosely with one hand, with your arm outstretched, to prevent the line from pulling you up and down.
Stay at this depth for a minimum of one minute- Always time your safety stop. Every diver should time their own safety stop — don’t rely on another diver.
When the minute is over ascend up to 10m for another minute, ascending slowly at 10 m per minute.
After one minute ascend to five metres and stay there for three minutes.
Divers sometimes think, once the safety stop is over, they can fin to the boat as fast as they want.
But the final five metres are the most dangerous part of the water column for lung overexpansion injuries.
Ascend the final five metres at the same, slow ten metres-per-minute rate.
When completing double dives on the Adelaide, I recommend a deep stop at 22m or Deck 02 for one minute.
This is easily achieved whilst swimming along the deck, to the base of the mast.
Then ascend to the top of the mast for another one minute deep stop at 12 m.
Then ascend to the bubble at 5 metres for three minutes.
Then slowly ascend to the surface.
Total stop time of five minutes, not including ascent time.
Quite easily achieved with a minimum fifty bar of air.