So why is it a bad idea to go back to do a safety stop if you blow it?

What's the technical reason for not going back down to finish a safety stop if you happen to blow it? Say you ascended way too fast from 130ft, or even greater, and blew through safety stops. Why is it a bad idea to immediately go back down and do more safety stops, assuming nothing is stopping you from being able to go back down and do them?

If you couldn't competently do them the first time, why try to drown yourself a second time?

If you have DCS in-water recompression has many hazards and if you don't have DCS there is no need to go back in the water. A better idea is: Don't skip safety stops from below 100 feet and don't shoot up like a polaris missile ever.

First off, while required by the PADI dive tables for certain circumstances, your safety stop is just that -- a safety stop. You are still diving a no-decompression profile if you are using standard recreational tables and therefore can theoretically safely ascend from such dives without doing the safety stop.

I'm not going to re-type the relevant sections of the Navy dive tables here, but there are procedures in place for non-recreational divers to re-enter the water if they miss a decompression stop. None of the recreational dive agencies advocate this practice for divers they train. If you read the in-water re-compression section you will quickly see that even for highly trained and well equipped diving professionals it is an unideal solution to potential DCS -- also look at all of the required equipment the Navy requires you to have on hand -- defn not standard gear on a recreational dive.

I recommend in addition to the US Navy dive tables you also pick up a copy of Mark Powell's Deco for Divers. Between those two sources you'll be able to glean the background information you want on why we don't teach this in recreational diving.

Michael

All good responses. I doubt it would hurt to go back to 15 feet. Count your lucky stars if no DCS symptoms. Do you use a pony for such depths? If so, use that at the safety stop if you miscalculate air.

Reasons (in no particular order):

• Theoretical risk of bubble-pumping should the diver not remain at safety stop depth "long enough."
• Safety stops are optional, so no harm done if it's missed.
• If you missed the safety stop due to poor buoyancy control, you might want to ask why that occurred. If you were under-weighted, that should be addressed prior to re-descending. Most inexperienced divers who surface after a missed safety stop are too flustered to address this possibility. If you were properly weighted, what makes you think you can hold a safety stop on the second try?
• Most inexperienced divers who unintentionally miss a safety stop have ascended faster than 30 ft/min. Accordingly, the greater risk is not DCS (since NDLs weren't exceeded, right?) but re-descending and having to manage symptoms of arterial gas embolism or other sequellae of lung-overexpansion underwater. If lung-overexpansion injury did occur, help is going to be more readily available at the surface.
• The diver might not be 100% certain that he/she has enough of a remaining gas supply to do an extended safety stop. Imagine the scenario of an uncontrolled, rapid ascent from great depth...followed by re-descending to safety stop depth...which culminates in a panicked, out-of-gas situation. Not good.

Safety stops are just there to slow you down, as to not get a lung over expansion injury.
If you missed it and your not coughing blood then you are ok.

Same reason you don't do "bounce" dives!!

Another good reason is that at least one person has died trying to pull off such a maneuver, i.e., re-descend to perform a missed safety stop (granted she initially missed the safety stop because she was OOA).

Incident: Mia Tegner (Scripps Institute of Oceanography research scientist) - diving fatality on the El Rey wreck in 2001
Here is a biographical sketch of the woman who lost her life.
Please read the ScubaBoard thread on this incident.
In particular, pay attention to Post #11 which is a rather detailed description of the incident.
Also, please read Dr. Deco's Post #18.

As Bubbletrouble said: if bubbles have begun to form, then re-descending will shrink them and allow them to pass through barriers in the body they otherwise couldn't breach. When you re-ascend a second time, they can re-grow where you definitely don't want them...

The same principle applies to multiple bounce dives, see-saw diving and those 'quick trips' back down to un-set the anchor etc...