safety stops, deco stops....

[vicmac]

Hi, sorry for my ignorance here, I tried to find out myself but just got confused. Please can someone clarify for me the difference between deco stops and safety stops, and when they are used. Cheers!

 

[ScubaSteve]

A safety stop is a stop recommended to increase the safety margin on a dive. All things being equal, this safety stop can "safely" be omitted from the dive profile.

A deco stop get applied to a diver once they have passed their NDL's. A deco stop is not a stop you want to skip unless it is really hitting the fan around you. Failing to fulfill a deco obligation can carry heavy consequences (these may vary depending on what the obligation is and what lead up to the obligation).

Decompression diving should not be considered by anybody that does not have the experience or the training.

 

[Blackwood]

An easy way to delineate them:

A "deco stop" is an output from the decompression algorithm, a "safety stop" is not.

 

[ajduplessis]

Deco stops are compulsory and performed after completing decompression dives (performed by technical divers). Safety stop are recommended stops and done for 3 minutes at 5 meters (recreational divers). If you are unclear on the function of the safety stop, please consult your OW training manual.

 

[Peter Guy]

vicmac -- in very simple terms, a "safety stop" is an "advisory" decompression stop ("advisory" in that the statistics show there is very little, or no, increase in the risk of decompression illness for not doing it) while a "deco stop" is a "mandatory" decompression stop ("mandatory" in that the statistics show there is an increased, perhaps significantly increased, risk of decompression illness for not doing it).

What I have real trouble wrapping my mind around are the "mandatory safety stops" from DSAT's Recreational Dive Planner -- if "mandatory" doesn't that mean they are "deco stops" and if NOT "mandatory" then aren't they merely "advisory?" In fact, "all dives are decompression dives" and you will be off-gassing the N2 you absorb, either in the water or on the surface or some combination thereof.

 

[tfsails]

As you are probably aware, recreational diving is set up so that divers don't have to do deco stops. Just about everybody recommends a "safety stop" at 15 ft for 3-5 minutes.

In my personal opinion, every dive is a deco dive. If you're breathing pressurized gas at any ambient pressure greater than sea level atmospheric pressure, you're getting a larger dose of nitrogen than you do on the surface, and it is being absorbed by your body. Therefore, when you come up, that excess nitrogen comes out of the tissues and into the bloodstream to the lungs, where it's excreted. You may not need to make a deco stop according to the depth and time spent at that depth in order to avoid DCS, but the body is still offgassing excess nitrogen all the same. Therefore, in my humble opinion, the body is decompressing.

That said, a "deco stop" is a mandatory stop for a period of time to allow the body to get rid of excess nitrogen while there is still enough ambient pressure to keep some of the excess nitrogen dissolved in the bloodstream. The plan is to get rid of most of the nitrogen before surfacing, and without any bubbles in the bloodstream (DCS). There may be multiple deco stops on a particular dive, and some stops may be done on gases with very high concentrations of oxygen in order to limit nitrogen intake and to aid nitrogen off-gassing. This is getting into the technical diving field which requires specialized training in order to keep the diver from killing himself. Should one inadvertently get into a situation that requires a deco stop, his computer will calculate how deep and for how long he/she should stop.

On the other hand, we have the "safety stop". This is really nothing more than an added safety step to prevent DCS by stopping at 15-20 feet for 3-5 minutes to allow off-gassing just as mentioned above. It is really a deco stop. Some agencies are now recommending safety stops at 1/2 the maximum depth of the dive for a couple of minutes as an additional safety stop.

When I'm diving a reef on a shore dive, such as Bonaire, I like to take my pretty little time ascending and doing about a 20-minute "safety stop" at about 15 feet exploring what's on the sandy bottom above the reef. Much better than hanging on a line!!

 

[vicmac]

Thanks everyone, this is how I thought, and I always do my safety stops, just wanted to make sure.

 

[vjanelle]

If you stay within their NDLs, don't exceed the recommended ascent rates, you'll be doing all the decompression you need according to DSAT. It gets horribly more complicated from there, so you'll might want to read deco for divers by Mark Powell.

Their mandatory stops are suggested if you come within certain parameters as defined on their charts. Things like coming close to certain time limits, exceeding the limits, temperature, etc.

The reality of it is, if you don't exceed 60'/min and stay within the time limits the chart say, you won't need to do additional stops along the way. The key here is to not exceed 60'/min (and really, keep it to 30'/min IMHO). Doing a 20-10' stop for 3-5 minutes is recommended and really not a hard thing to do, since it gives you a chance to offgas some nitrogen while keeping the pressure gradient the nitrogen in you lower than it would be above the surface.

IANADRD (I am not a decompression researcher or diver) Decompression stops are when you've exceeded the "m-value" of a compartment as determined by your chosen decompression algorithm, and you need to stop at a ceiling for a certain amount of time to allow the nitrogen in your tissues to reach equilibrium with the new depth. Going past this ceiling could cause excessive super-saturation and may cause bubbles to form that your lungs can't filter out, or are too large for your system to handle and cause your immune system to attack. Stopping at certain depths and combining mixes that contain less nitrogen will facilitate a safe ascent.

This is why padi recommends you stay within 60' of the DSAT NDL charts, it's too easy to misplan your gas usage or exceed NDLs at depths below it.

 

[Crush]

...a "safety stop" is an "advisory" decompression stop ("advisory" in that the statistics show there is very little, or no, increase in the risk of decompression illness for not doing it)...

Were you speaking (typing) figuratively here, or is the above statement literally true? :shocked2:

 

[NC Wreck Diver]

As you are probably aware, recreational diving is set up so that divers don't have to do deco stops. Just about everybody recommends a "safety stop" at 15 ft for 3-5 minutes.

In my personal opinion, every dive is a deco dive. If you're breathing pressurized gas at any ambient pressure greater than sea level atmospheric pressure, you're getting a larger dose of nitrogen than you do on the surface, and it is being absorbed by your body. Therefore, when you come up, that excess nitrogen comes out of the tissues and into the bloodstream to the lungs, where it's excreted. You may not need to make a deco stop according to the depth and time spent at that depth in order to avoid DCS, but the body is still offgassing excess nitrogen all the same. Therefore, in my humble opinion, the body is decompressing.

That said, a "deco stop" is a mandatory stop for a period of time to allow the body to get rid of excess nitrogen while there is still enough ambient pressure to keep some of the excess nitrogen dissolved in the bloodstream. The plan is to get rid of most of the nitrogen before surfacing, and without any bubbles in the bloodstream (DCS). There may be multiple deco stops on a particular dive, and some stops may be done on gases with very high concentrations of oxygen in order to limit nitrogen intake and to aid nitrogen off-gassing. This is getting into the technical diving field which requires specialized training in order to keep the diver from killing himself. Should one inadvertently get into a situation that requires a deco stop, his computer will calculate how deep and for how long he/she should stop.

On the other hand, we have the "safety stop". This is really nothing more than an added safety step to prevent DCS by stopping at 15-20 feet for 3-5 minutes to allow off-gassing just as mentioned above. It is really a deco stop. Some agencies are now recommending safety stops at 1/2 the maximum depth of the dive for a couple of minutes as an additional safety stop.

When I'm diving a reef on a shore dive, such as Bonaire, I like to take my pretty little time ascending and doing about a 20-minute "safety stop" at about 15 feet exploring what's on the sandy bottom above the reef. Much better than hanging on a line!!

Hey Vicmac:

Listen to this advice from tfsails, and everybody who posted on your question. Remember, ASCENT is decompression. So, stick to your 60'/minute up to 60' depth, and 30'/minute for the balance of the dive (remembering your safety stop at 15 feet for 3-5 minutes) before surfacing.

As you heard, the 'deco stop' is an obligation to make stops since you have gone past NDL's, and the 'safety stop' is a factor of safety to help offgass fast tissues (they load quick and offgass quick).