PADI dive table question

[cwodavids]

I have just finished my PADI Open Water course yesterday and I have a question that has annoyed me since reading the manual. I asked several of my instructors but they didn't know the answer either.

The manual and dive tables both state that "when planning a dive in cold water or conditions that might be strenous, plan the dive assuming it is 4m deeper than actual"

On my course I was cold but not shivering, however a girl on the same dive was shivering and was struggling with the cold. The theory of it makes perfect sense but what constitutes "cold"?

Does this mean on a "cold" dive I can only dive to 14m as I will be diving deeper than my certification (in the deco sense anyway).

Regards

Dave

 

[Pearldiver07]

Dave,

"Cold" is in the eyes of the beholder. Not only should you consider the water temperature, but your exposure protection, and length of the dive.

What does this mean, practically speaking? If you dive in 75 f (24 C), and you're in a 3mm suit, you may be cold. Or maybe not. But another diver may be. If you dive this same temperature water in a 7mm suit with hood and gloves you may not be cold at all.

And then, consider the length of the dive. The longer you dive (and more dives you do), your body core temperature will be dropping. This will cause latter dives in the same termperature to be "cold."

Bottom line is that there is no simple measurement to go by. You should also consider that your bodyfat level ("Bio-prene") will not only affect your perception of how cold the water is, but your circulatory effectiveness as well.

If you're in doubt, I'd add the 4m. As I'd always err on the side of caution.

 

[Booyakasha]

If a girl was struggling witht the cold, shouldn't the dive have been stopped by the instructor?

I guess it is all relative and you have to be there to make a decision but a valid question no?

B.

 

[muddiver]

Dive tables are based on imperical data and the original research by the U.S. Navy found that when a diver is cold or exerts a lot of energy, less notrogen is released during decompression than a warm, calm diver. Even a "No Decompression" dive is still a process of decompressing, the deco is just done during the ascent and during the safety stop. To compensate most U.S. dive tables follow the reccomendation to go to the next deeper depth on the table for dive planning and use the Residual Nitrogen Time letter designation for the depth deeper than the actual dive Maximum Depth.

 

[fnfalman]

Usually "Cold" is considered by various agencies to be under either 70-F or 60-F, I can't remember which.

 

[gearhound]

If you are cold or straining yourself, you are theoretically breathing harder and on gassing at a faster rate. When you plan your dives 10 feet deeper, your NDL is shortened, so you have a shorter dive or wind up at a higher pressure group. If you go for a repetitive dive, you will start it at a higher pressure group, which shortens your ANDL. So again, you get a more conservative dive.

 

[muddiver]

Usually "Cold" is considered by various agencies to be under either 70-F or 60-F, I can't remember which.

I belive that "cold" in reference to dive tables is weather the diver is chilled and possably shivering, not what the ambient temperature of the water is. Weather the water is cold based on the temperature of the water is totally subjective, because 60-F to you is warm to me.

 

[muddiver]

If you are cold or straining yourself, you are theoretically breathing harder and on gassing at a faster rate. When you plan your dives 10 feet deeper, your NDL is shortened, so you have a shorter dive or wind up at a higher pressure group. If you go for a repetitive dive, you will start it at a higher pressure group, which shortens your ANDL. So again, you get a more conservative dive.

Nope, on-gassing is based on pressure differential that will cause the profusion of gas into one's tissues. Your breathing rate will only effect the removal of CO2 from respiration and the length of time your gas supply will last.

 

[dbulmer]

cwo,

The planner in my tables state: When planning a dive in cold water or under conditions that may be strenuous plan the dive assuming the depth is 10feet deeper than usual (4m or so).
However, it also says!

Always be conservative and avoid using the maximum limits provided.

In practical terms UK waters are considered cold water so plan 4m deeper and remember the golden rule! If your bladder, feet and hands are cold get out of the water

I'll pass on the reasons for bladder control
If your feet are cold your brain will wonder why you are diving.

If your hands are cold you are starting to push it safety wise as you may not be able to operate your equipment efficiently nor assist your buddy if something goes t*its up.

In the winter most divers tend to dive shallower and reduce their exposure to the cold for the reasons others have already explained.

 

[DiveNav]

......Does this mean on a "cold" dive I can only dive to 14m as I will be diving deeper than my certification (in the deco sense anyway)....

~18m/60ft is the recommended max depth for OW divers, when you plan a cold dive use the table as if you were diving at 22m - but during the dive do not go deeper than ~18m/60ft.
In this way the table will make your dive shorter.

Getting cold underwater is NO fun.

Getting VERY cold underwater is dangerous.

Acute Hypothermia from cold water.... (Tc = Core Temperature)
Physical Events
1) Skin temperature decreases rapidly, Stabilizes at water level +2/3C, Vasoconstriction
2) Core temperature increases 0.2C, higher metabolic rate
3) Core temperature starts to decrease slowly, Then accelerates

Physiological Events
1) Hyperventilation: Initial 1-5 minutes
2) Shivering: Maximum at Tc = 35C
3) Metabolic output falls for Tc < 35C
Affects Stamina Muscular Rigidity for Tc < 30C
4) Loss of Consciousness: 28C < Tc < 30C
5) Death: 24C < Tc < 28C

Mental & Behavioral State
Normal: 37C
Cold Sensation: 36C, violent shivering (controllable); extrovert, tend to be noisy, complain about cold, alert
Quiet: 35C, shivering uncontrollable, loss of muscle strength, especially in periphery. still able to respond to signals and instructions
Introversion: 34C, lack of interest in events, lack of motivation - beginnings of confusion, disorientation;
Disorientation: 33C, attention drifting, decline in shivering activity, weak muscle strength
Semi-Conscious: 30C..33C
Unconscious: 30C
Cardiac Arrest: 25C


In our simulator we have implemented a thermal model of the diver. You can play with it and see what happens when you get too cold

Alberto (aka eDiver)