5min or 3min Safety Stop ?

Why do we (here in Australia) have a 5 minute safety stop as opposed to the
3 minutes that other countries have ?

bc

"Hi-Soft" <nospam@spam.com> wrote in message
news:9bCVj.153$IK1.28@news-server.bigpond.net.au...
>
> Why do we (here in Australia) have a 5 minute safety stop as opposed to
> the 3 minutes that other countries have ?

When I first started diving it used to be 2-3min at 3ms for dives over 10
ms. I believe the change to 5m on the SS stop was that it was an easier
depth to maintain don't know why the time was changed maybe to compensate
for the slightly extra depth although a lot of the articles you can read
suggest 3-5 minutes. Maybe the 5min came around because boat and tour
operators where being on the conservative side. PADI I believe recommends 15
foot and a 3min+. I always do 5 at 5 except if it is a shore with a gradual
slope up to the egress point.

Hi-Soft wrote:

>
> Why do we (here in Australia) have a 5 minute safety stop as opposed
> to the 3 minutes that other countries have ?

The short answer is, "if 3 minutes is good the 5 minutes is better."

The longer answer is:

1) A 3 minute stop probably is "good enough" provided that you
actually hold a depth of 5-6 metres and don't get above 4.5
metres at any time on the stop

2) A lot of beginners that I have observed really don't hold
their depth on the stop very well

3) the more time that you spend at around 5 metres at the end
of a dive (particularly deeper dives) the better. At 5 metres
you are still under 1.5 BAR absolute pressure but there
should be a good pressure gradient between the nitrogen in
your blood and the nitrogen in your lungs. Also, from memory,
all of the decompression research agrees that a differential
of no more than 1.5:1 won't cause bubbles -- staying at 5
metres gives you time to off-gas and move towards that 1.5:1
ratio. (And, of course, when you are at 1.5 bar absolute the
pressure in your lungs can be up to 2.25 and still be safe.)

4) If it wouldn't annoy the charter boat operators, (and doing
this definitely would annoy them) the ideal situation would
be to ascend to hit 5 metres with about 60-70 bar and then
sit at 5 metres until you get down to about 10-15 bar. This
could mean a 5-10 minute stop or longer.

5) another technique that you might want to consider is ascending
to 10 metres and stopping there for a minute, then moving on to
5 metres for 5 minutes. The point of the 10 metre stop is
2-fold. First, it is a chance to off-gas a little bit and
reduce the gradient before you get to 5 metres. And second
it gives you a "set-point" to get your ascent under control
before moving the final bit to 5 metres.

The bottom line on all of this is that even if you are doing
"no decompression" diving, you are still decompressing on your
ascent. What makes "no-decompression" diving ND diving is that
there aren't any required decompression *stops*. The design of
the ND dive tables is such that the partial pressure of nitrogen
should never exceed the point where dangerous bubbles would form
if you ascended directly to the surface at a rate less than 18
metres per minute -- I'd actually recommend a rate of 9 metres
per minute. A faster ascent increases the chances of bubble
formation -- just like when you pop the cork on a champagne
bottle and suddenly reduce the pressure. If you carefully extract
the cork, the pressure is released a little bit slower and you
are less likely tho have champagne all over the bench top.

Again on the point of letting the pressure reduce slowly, the
greatest percentage change in pressure occurs in the final
10 metres of the ascent when you go from 2 bar to 1 bar.
Slowing the ascent rate in the final 10 metres is a really
good idea. Taking 2 or 3 minutes to ascend from the safety stop
is an excellent idea.

There's been some ongoing research about "silent bubbles" that
suggests that some bubble formation may occur in dives that are
made within the limits of the tables. (Deco and no-deco) But
people are not affected by the bubbles since they are small enough
that they don't block the blood flow anywhere. Safety stops
are likely to reduce the size and number of these bubbles.

Another point to consider with the charter operators is that
their business is based on divers going out and having fun,
not getting hurt and comming back to do it again. They are
going to promote the safest possible options since that's
in the long term best interest of their business.

The final point is that you can get bent diving within the
limits of the tables. All it takes is going close to the limits
and possibly an extra risk factor or two -- and you've
earned yourself a trip to the Alfred. (Our local hospital
with a re-compression chamber) So if a 3 minute stop is good,
then a 5 minute stop is better.

-Don

"Don Gingrich" <aussie.import2@gmail.com> wrote in message
news:q6ednUOQM7xAE7rVnZ2dnUVZ_rjinZ2d@posted.inter node...
> Hi-Soft wrote:
>
>>
>> Why do we (here in Australia) have a 5 minute safety stop as opposed
>> to the 3 minutes that other countries have ?
>
> The short answer is, "if 3 minutes is good the 5 minutes is better."
>
> The longer answer is:
>
> 1) A 3 minute stop probably is "good enough" provided that you
> actually hold a depth of 5-6 metres and don't get above 4.5
> metres at any time on the stop
>
> 2) A lot of beginners that I have observed really don't hold
> their depth on the stop very well
>
> 3) the more time that you spend at around 5 metres at the end
> of a dive (particularly deeper dives) the better. At 5 metres
> you are still under 1.5 BAR absolute pressure but there
> should be a good pressure gradient between the nitrogen in
> your blood and the nitrogen in your lungs. Also, from memory,
> all of the decompression research agrees that a differential
> of no more than 1.5:1 won't cause bubbles -- staying at 5
> metres gives you time to off-gas and move towards that 1.5:1
> ratio. (And, of course, when you are at 1.5 bar absolute the
> pressure in your lungs can be up to 2.25 and still be safe.)
>
> 4) If it wouldn't annoy the charter boat operators, (and doing
> this definitely would annoy them) the ideal situation would
> be to ascend to hit 5 metres with about 60-70 bar and then
> sit at 5 metres until you get down to about 10-15 bar. This
> could mean a 5-10 minute stop or longer.
>
> 5) another technique that you might want to consider is ascending
> to 10 metres and stopping there for a minute, then moving on to
> 5 metres for 5 minutes. The point of the 10 metre stop is
> 2-fold. First, it is a chance to off-gas a little bit and
> reduce the gradient before you get to 5 metres. And second
> it gives you a "set-point" to get your ascent under control
> before moving the final bit to 5 metres.
>
> The bottom line on all of this is that even if you are doing
> "no decompression" diving, you are still decompressing on your
> ascent. What makes "no-decompression" diving ND diving is that
> there aren't any required decompression *stops*. The design of
> the ND dive tables is such that the partial pressure of nitrogen
> should never exceed the point where dangerous bubbles would form
> if you ascended directly to the surface at a rate less than 18
> metres per minute -- I'd actually recommend a rate of 9 metres
> per minute. A faster ascent increases the chances of bubble
> formation -- just like when you pop the cork on a champagne
> bottle and suddenly reduce the pressure. If you carefully extract
> the cork, the pressure is released a little bit slower and you
> are less likely tho have champagne all over the bench top.
>
> Again on the point of letting the pressure reduce slowly, the
> greatest percentage change in pressure occurs in the final
> 10 metres of the ascent when you go from 2 bar to 1 bar.
> Slowing the ascent rate in the final 10 metres is a really
> good idea. Taking 2 or 3 minutes to ascend from the safety stop
> is an excellent idea.
>
> There's been some ongoing research about "silent bubbles" that
> suggests that some bubble formation may occur in dives that are
> made within the limits of the tables. (Deco and no-deco) But
> people are not affected by the bubbles since they are small enough
> that they don't block the blood flow anywhere. Safety stops
> are likely to reduce the size and number of these bubbles.

My understanding of micro bubbles was there is a long term health dangers
like osteoporosis and such. Probably more likely with proffessional divers
or recreational divers who are in the water heaps.

>
> Another point to consider with the charter operators is that
> their business is based on divers going out and having fun,
> not getting hurt and comming back to do it again. They are
> going to promote the safest possible options since that's
> in the long term best interest of their business.

and in some States like Queensland there are very stringent regulations/
laws on what dive operators must do.

>
> The final point is that you can get bent diving within the
> limits of the tables. All it takes is going close to the limits
> and possibly an extra risk factor or two -- and you've
> earned yourself a trip to the Alfred. (Our local hospital
> with a re-compression chamber) So if a 3 minute stop is good,
> then a 5 minute stop is better.

A point that a lot of people don't realise. If the computer says it is safe
to dive this profile than it MUST be safe is the attitude alot of the time.

O.K. that all makes sense..so thanks..

on a slightly different note...If I do a sure dive (Portsea Pier) is all
that erelevant...seeing that it's only a max depth of around 5 meters(
correct me if I'm wrong )..? My dive tables tell me it's a ND limit of about
4.5 hours at that shallow...

Also, what about if I surface a few times during this dive..? I plan on
doing a pier dive with a few buddies, just to get our new gear / weight all
sorted...

bc



cheers,
Hi-Soft
"dechucka" <dechucka@vomithotmail.com> wrote in message
news:482793d5$0$22120$5a62ac22@per-qv1-newsreader-01.iinet.net.au...
>
> "Don Gingrich" <aussie.import2@gmail.com> wrote in message
> news:q6ednUOQM7xAE7rVnZ2dnUVZ_rjinZ2d@posted.inter node...
>> Hi-Soft wrote:
>>
>>>
>>> Why do we (here in Australia) have a 5 minute safety stop as opposed
>>> to the 3 minutes that other countries have ?
>>
>> The short answer is, "if 3 minutes is good the 5 minutes is better."
>>
>> The longer answer is:
>>
>> 1) A 3 minute stop probably is "good enough" provided that you
>> actually hold a depth of 5-6 metres and don't get above 4.5
>> metres at any time on the stop
>>
>> 2) A lot of beginners that I have observed really don't hold
>> their depth on the stop very well
>>
>> 3) the more time that you spend at around 5 metres at the end
>> of a dive (particularly deeper dives) the better. At 5 metres
>> you are still under 1.5 BAR absolute pressure but there
>> should be a good pressure gradient between the nitrogen in
>> your blood and the nitrogen in your lungs. Also, from memory,
>> all of the decompression research agrees that a differential
>> of no more than 1.5:1 won't cause bubbles -- staying at 5
>> metres gives you time to off-gas and move towards that 1.5:1
>> ratio. (And, of course, when you are at 1.5 bar absolute the
>> pressure in your lungs can be up to 2.25 and still be safe.)
>>
>> 4) If it wouldn't annoy the charter boat operators, (and doing
>> this definitely would annoy them) the ideal situation would
>> be to ascend to hit 5 metres with about 60-70 bar and then
>> sit at 5 metres until you get down to about 10-15 bar. This
>> could mean a 5-10 minute stop or longer.
>>
>> 5) another technique that you might want to consider is ascending
>> to 10 metres and stopping there for a minute, then moving on to
>> 5 metres for 5 minutes. The point of the 10 metre stop is
>> 2-fold. First, it is a chance to off-gas a little bit and
>> reduce the gradient before you get to 5 metres. And second
>> it gives you a "set-point" to get your ascent under control
>> before moving the final bit to 5 metres.
>>
>> The bottom line on all of this is that even if you are doing
>> "no decompression" diving, you are still decompressing on your
>> ascent. What makes "no-decompression" diving ND diving is that
>> there aren't any required decompression *stops*. The design of
>> the ND dive tables is such that the partial pressure of nitrogen
>> should never exceed the point where dangerous bubbles would form
>> if you ascended directly to the surface at a rate less than 18
>> metres per minute -- I'd actually recommend a rate of 9 metres
>> per minute. A faster ascent increases the chances of bubble
>> formation -- just like when you pop the cork on a champagne
>> bottle and suddenly reduce the pressure. If you carefully extract
>> the cork, the pressure is released a little bit slower and you
>> are less likely tho have champagne all over the bench top.
>>
>> Again on the point of letting the pressure reduce slowly, the
>> greatest percentage change in pressure occurs in the final
>> 10 metres of the ascent when you go from 2 bar to 1 bar.
>> Slowing the ascent rate in the final 10 metres is a really
>> good idea. Taking 2 or 3 minutes to ascend from the safety stop
>> is an excellent idea.
>>
>> There's been some ongoing research about "silent bubbles" that
>> suggests that some bubble formation may occur in dives that are
>> made within the limits of the tables. (Deco and no-deco) But
>> people are not affected by the bubbles since they are small enough
>> that they don't block the blood flow anywhere. Safety stops
>> are likely to reduce the size and number of these bubbles.
>
> My understanding of micro bubbles was there is a long term health dangers
> like osteoporosis and such. Probably more likely with proffessional divers
> or recreational divers who are in the water heaps.
>
>>
>> Another point to consider with the charter operators is that
>> their business is based on divers going out and having fun,
>> not getting hurt and comming back to do it again. They are
>> going to promote the safest possible options since that's
>> in the long term best interest of their business.
>
> and in some States like Queensland there are very stringent regulations/
> laws on what dive operators must do.
>
>>
>> The final point is that you can get bent diving within the
>> limits of the tables. All it takes is going close to the limits
>> and possibly an extra risk factor or two -- and you've
>> earned yourself a trip to the Alfred. (Our local hospital
>> with a re-compression chamber) So if a 3 minute stop is good,
>> then a 5 minute stop is better.
>
> A point that a lot of people don't realise. If the computer says it is
> safe to dive this profile than it MUST be safe is the attitude alot of the
> time.
>

"Hi-Soft" <bjcanham-nospam-@hotmail.com> wrote in message
news:4827ccc3$0$22173$5a62ac22@per-qv1-newsreader-01.iinet.net.au...
>
>
> O.K. that all makes sense..so thanks..
>
> on a slightly different note...If I do a sure dive (Portsea Pier) is all
> that erelevant...seeing that it's only a max depth of around 5 meters(
> correct me if I'm wrong )..? My dive tables tell me it's a ND limit of
> about 4.5 hours at that shallow...
>
> Also, what about if I surface a few times during this dive..? I plan on
> doing a pier dive with a few buddies, just to get our new gear / weight
> all sorted...
>
> bc

Probably not from a deco point of view and if you are exiting to the beach a
nice slow swim up the incline will be enough. Remember diving to only a
depth of 5m you are diving in the area of greatest pressure difference so
being aware of the dangers of barotrauma is a good idea esp if you plan to
surface during the dive.

Hi-Soft wrote:

>
>
> O.K. that all makes sense..so thanks..

No worries, glad to assist. And if aus.sport.scuba can avoid
some of the acrimony I see in rec.scuba, the it's all to the good.

>
> on a slightly different note...If I do a sure dive (Portsea Pier) is
> all that erelevant...seeing that it's only a max depth of around 5
> meters( correct me if I'm wrong )..? My dive tables tell me it's a
> ND limit of about 4.5 hours at that shallow...
>
> Also, what about if I surface a few times during this dive..? I
> plan on
> doing a pier dive with a few buddies, just to get our new gear /
> weight all sorted...

My suggestion, take it for what it's worth is to get under the pier
with a nearly empty cylinder, and empty your BCD. Then start removing
weight in small increments until you can fin pivot with no gas in
your BCD. That, IMHO, is as near to ideal weight as you are likely
to get.
>
generally speaking, from a DCI point of view it's not likely to be a
problem. Just make sure that you take it easy ascending. I have heard
of (admittedly extremely rare) cases of DCI from really shallow
dives. Possibly due to a rapid ascent or two starting some bubbles
that grew. (Mind you, this is partially my system administrator
"never say never" side comming out.) On the other hand, a couple of
hours under the pier with a short surface interval followed by a
dive to 30 metres in Portsea hole could put you into a world of
hurt pretty quickly. So, yes it is shallow, but it still demands a
degree of respect.

-Don

Thanks again Don ( and all ), for your invaluable advice ;)



cheers,
Hi-Soft
"Don Gingrich" <aussie.import2@gmail.com> wrote in message
news:jJSdne7SFq0QvLXVnZ2dnUVZ_qDinZ2d@posted.inter node...
> Hi-Soft wrote:
>
>>
>>
>> O.K. that all makes sense..so thanks..
>
> No worries, glad to assist. And if aus.sport.scuba can avoid
> some of the acrimony I see in rec.scuba, the it's all to the good.
>
>>
>> on a slightly different note...If I do a sure dive (Portsea Pier) is
>> all that erelevant...seeing that it's only a max depth of around 5
>> meters( correct me if I'm wrong )..? My dive tables tell me it's a
>> ND limit of about 4.5 hours at that shallow...
>>
>> Also, what about if I surface a few times during this dive..? I
>> plan on
>> doing a pier dive with a few buddies, just to get our new gear /
>> weight all sorted...
>
> My suggestion, take it for what it's worth is to get under the pier
> with a nearly empty cylinder, and empty your BCD. Then start removing
> weight in small increments until you can fin pivot with no gas in
> your BCD. That, IMHO, is as near to ideal weight as you are likely
> to get.
>>
> generally speaking, from a DCI point of view it's not likely to be a
> problem. Just make sure that you take it easy ascending. I have heard
> of (admittedly extremely rare) cases of DCI from really shallow
> dives. Possibly due to a rapid ascent or two starting some bubbles
> that grew. (Mind you, this is partially my system administrator
> "never say never" side comming out.) On the other hand, a couple of
> hours under the pier with a short surface interval followed by a
> dive to 30 metres in Portsea hole could put you into a world of
> hurt pretty quickly. So, yes it is shallow, but it still demands a
> degree of respect.
>
> -Don
>