While they were recently completing their Advanced Open Water Course on the Zenobia wreck two divers raised the question of how important safety stops really are after completing dives. Along with good ascent control and correct ascent rates, safety stops are a fundamental and most important part of safe diving procedures at the end of a dive.
During every dive a diver is taking on levels of Nitrogen that are being absorbed into tissues as a result of what depths you dive to and how long the dives are. The deeper we dive and the longer the dives are the more Nitrogen we absorb. There are limits to how much we can absorb during dives and this is monitored by every diver through dive computers or planning with dive tables.
If we stay well within these limits then the possibility of Decompression Sickness is almost zero. However once the dive is finished there is another important step in ensuring the completion of a safe dive. Unfortunately a lot of divers underestimate the importance of this especially after deep and long dives. This is the process of ascending in a safe, controlled manner and completing good safety stops.
As we ascend and the pressure on our bodies is reduced the Nitrogen starts to be released from our tissues. If this is done at a safe rate then it is released safely. High levels of Nitrogen and with an ascent being too fast is where the release of Nitrogen is too quick and where it can cause DCS.
Padi say that an ascent rate should be no more than 18 metres per minute, this is an absolute maximum and is in fact very fast in our opinion. A lot of dive computers give a maximum ascent rate of half this rate at 9 metres per minute. As is always you should slowly ascend from every dive and the slower the better. Good buoyancy control and technique are also very important in completing a good ascent.
Always ensure you have plenty of air left to complete a proper ascent. Ascend much slower than 9 metres per minute. With dives of 15 metres or deeper we always do a 1 minute safety stop at 9 metres to completely slow down the ascent and stop the continual pressure change. Stop at 5 metres for a good safety stop and not at 7 or 3 metres ! A safety stop at a depth of 5 metres is seen as the optimum depth for releasing Nitrogen before we finish the ascent to the surface. Once the 3 minute safety stop is completed and you have enough air left then why not do a longer stop ?
Especially on deep dives like the Zenobia we do slightly longer stops and then dive from the ascent line back to the exit ladders underwater getting slowly shallower and enjoying a great view below. All this time we are still releasing safe levels of Nitrogen with a nice shallow profile back to the surface.
So as divers we should never forget the importance of safe ascents and good safety stops after each and every dive.