Safety stops when monitoring SurGF

[justinthedeeps]

Not to blow up any heads, but it's just a math model and your "Surface GF" number on the computer knows nothing about your actual body state.

Ascend slowly, pause and enjoy the shallows before finishing the dive. Call it whatever you want.

If you fully believe in the GF theory, look at how much it spikes in the dive log when you go from ~5 or even ~3 meters to the surface. It's usually the highest spike in most people's dives.

The PADI style rigid safety stop is great for pausing ascents and regrouping divers so that the DM can SMB and make sure people surface together, so they don't get scattered or run over by boats. If they really cared about DCS it would be 6m/20ft & 3m/10ft safety stops, at least three minutes per.

Another problem with safety stops is when the insistence of doing them exposes you to highly increased other dangers, such as getting carried away in a current, delaying critical care to a distressed diver, or even delaying the ability to access oxygen on the surface etc.

 

[Fastmarc]

What happens when there's another diver with the same strategy?

Very little chance of that with my local diving. Everyone just heads up following their 3 min safety stop.

 

[L13]

If you fully believe in the GF theory, look at how much it spikes in the dive log when you go from ~5 or even ~3 meters to the surface. It's usually the highest spike in most people's dives.

All decompression theories (not just GF theory) show a spike from ~5 or ~3 meters to the surface. That is because the greatest proportional pressure change occurs as you approach the surface, and is part of why the shallowest stops are always longer than the deeper stops.

In an NDL dive, it will always be the highest spike.

 

[inquis]

I am not sure if the last stop was set to 10ft that it will not start counting

Last stop depth is for decompression dives and unrelated to when the NDL counter starts. I use a last deco stop of 10 ft on my Teric and get the NDL safety stop count starting at 20 ft.

 

[boulderjohn]

If you fully believe in the GF theory, look at how much it spikes in the dive log when you go from ~5 or even ~3 meters to the surface. It's usually the highest spike in most people's dives.

Just to expand on L13's reply...

That last ascent will always spike like that during the final ascent after a safety stop. It has nothing to do with using SurfGF. It also happens after your last deco stop on a decompression dive. SurfGF assumes that spike will occur and accounts for it. What is your point?

If they really cared about DCS it would be 6m/20ft & 3m/10ft safety stops, at least three minutes per.

Will you be providing the research indicating that this two level approach makes enough difference to make it worthwhile? No one disputes that longer safety stops are safer than short safety stops, but I am unaware of any research indicating that the approach you recommend provides any real difference between a standard safety stop of that length or even the shorter, standard 3-minute stop.

 

[NDonahue]

L

What happens when there's another diver with the same strategy?

Last diver to 30 bar wins!

 

[scubadada]

All decompression theories (not just GF theory) show a spike from ~5 or ~3 meters to the surface. That is because the greatest proportional pressure change occurs as you approach the surface, and is part of why the shallowest stops are always longer than the deeper stops.

In an NDL dive, it will always be the highest spike.

Good reason to make a slow final ascent from the safety or deco stop

In this example GF 21 when arriving at the safety stop, 18 at the end of the safety stop, 70 at the surface after a 1:10 final ascent. This is about what I expected from following SurfGF

 

[TheCatFish]

I've just recently configured my Perdix to display GF99 and SurGF in OC Tec. These are no-deco dives using the default 85/85 gradient factors. Typically when I hit 20', SurGF was around 60% and the display was showing "Clear" where it would if I was in OC Rec and did a 3-minute safety stop.

So the question: Under these circumstances, is a 3-minute pause really warranted at 20'?

SurGF is telling you that if you shot up you'd theoretically be at 60% of the M-line, or 25% shy of your 85% acceptable threshold.

Doesn't mean you want to skip your safety stop. Fast ascents still create stress on the body. Pausing between 3-6m provides an opportunity for your tissue:atmospheric differential to stabilize and reduces statistical chance of injury and fatigue.

Edit: Lowwall caught my shoddy subtraction. Thanks.

 

[lowwall]

SurGF is telling you that if you shot up you'd theoretically be at 60% of the M-line, or 15% shy of your 85% acceptable threshold.

85-60=?

More to the point, it's 40% short of the full M-value which is already adjusted away from the theoretical tissue saturation limits.

 

[justinthedeeps]

Just to expand on L13's reply...

That last ascent will always spike like that during the final ascent after a safety stop. It has nothing to do with using SurfGF. It also happens after your last deco stop on a decompression dive. SurfGF assumes that spike will occur and accounts for it. What is your point?

Will you be providing the research indicating that this two level approach makes enough difference to make it worthwhile? No one disputes that longer safety stops are safer than short safety stops, but I am unaware of any research indicating that the approach you recommend provides any real difference between a standard safety stop of that length or even the shorter, standard 3-minute stop.

The point, my friend, is that

1. the original poster should not be putting much numerical importance in their precise "Surface GF" number on a dive with no explicit deco stops, and should just stick to the basic idea of a shallow pause period in their ascent for safety, and/or a very slow ascent rate while surfacing.

2. nor should the original poster be confident that any completely arbitrary prescription of "X minutes at X metres/feet" during rec dives is proven to be specifically ideal for DCS avoidance

The "3 mins @ 5 metres/15 feet" thing is mostly an industry crowd control technique to train customers. Any number of minutes at any shallow depth is probably helpful, though not required for everyone, nor completely protective for those already prone to DCS that day.