Limits: what they are, why they are important and how to establish them

[The Chairman]

You may not realize this, but diving is all about limits. Those tables or PDC (Personal Dive Computer) on your wrist? They actually define some of your limits. Your gas, your gear, the dive op (or not) are also limits, but you may not realize it. In reality, a lot of accidents are caused by divers exceeding limitations without even realizing it. No one wants to get hurt, so lets discuss limits for a bit.

By definition, a limit is a boundary. It actually comes from the Latin that means the edge or path between feilds. Some limits are hard and inviolate. Other limits are soft or voluntary. Still, other limits are hard to define but they are still there, like it or not. They're still there and you need to figure them out and then respect them. It's your fun and safety on the line.

Every dive plan begins with three limits: Depth, Time and Gas. These should be established without question before every dive, and you should have strategies that enable you to keep or honor these limits. Don't go too deep, don't stay too long and please don't run out of air. Easy, right? Maybe. Let's explore it.

Depth: This is both a hard and a soft boundary. You're told not to exceed 60ft when you first get certified, but what if you do 61ft? How about 70ft, 90ft or deeper? There are no Scuba police out there to stop you. Moreover, 80ft in Cozumel may be easiier than 61ft in a quarry. You, and you alone are responsible for how deep you go on any particular dive, and that brings us to some other limits. These are limits like training, gear, conditions, your buddy and your mindset. Whatever, you need to establish that before you splash and be sure you don't change the plan at depth.

Time: Going hand and hand with depth, together they keep you from getting bent. But what about accidental or casual deco? Are you really ready for it? Most divers plan for everything to go well, but deco necessitates that you plan for things to go sideways. Don't know how things can go sideways? Perhaps you're not able to really plan deco responsibly. Again, training, gear, conditions, your buddy and your mindset affect these limits. Yes, it bothers me to see divers pushing this limit needlessly. Don't take it so casually.

Gas: In my estimation, this is the most misunderstood part of the three. Being on the boat with 500 psi is not a cogent plan for your gas. How do you do that? What's the rule of halves? How about the rule of thirds? If you don't know, then you're just hoping to get it right and hope is never a good plan. If you're diving recreationally then you probably should at least learn how to properly "halve" your air responsibly. Remember, you're not just planning for everything to go right: you're planning for when things go sideways with a buffer. Let's work this backward. I have found that you should start your ascent with a 100psi/10ft of depth but with a 600 psi minimum. This should give you enough air for you and a stressed out buddy to surface with maybe even a safety stop thrown in. So, take your planned depth, calculate your ascent pressure, subtract it from your start pressure and then divide the remainder in half. That's how much gas you get to use. Subtract it from your starting pressure (again) and you now have your turn pressure.

Here's a dive to 80ft with an AL80 @3,000psi

80x10= 800psi ascent pressure.
(3000-800)/2= 1100psi usable gas
3000-1100= 1900psi is now your turn pressure

So, there's the first three, and probably most important, limits to your diving. Don't forget the others, as they're pretty important too. Let's start a list and feel free to add to them.

• Training. Make a New years resolution to not exceed your training. Instead, get the training you need, then do the dives.
• Experience. Harder to come by as there are no shortcuts, but don't substitute oodles of training for experience. Knowledge is great, but its application takes time. Too much knowledge, too fast can be confusing and cause you to miss obvious solutions. It's all about muscle memory and the systematic addition of skills, not how fast you can get deep.
• Judgement. That's really the combination of the first two items on this list. I've heard people say that this comes from making bad decisions, and I think that's a lot of bull. Like experience, there's no shortcut to having good judgment. It's a matter of hours underwater making right decisions. Ever call a dive? Why not? OK, maybe you're just starting out and haven't had the need to do so. Just learn not to force your diving. You should feel free to be able to call a dive at any time, for any reason with no questions asked.
• Gear. When I was in high school, there was a Chevy commercial that posited that you shouldn't try to haul two ton of fertilizer with a one-ton truck. Do you have the right gear to do the dive? I'll call a dive before I splash without a cutting device, a finger spool and a sausage. If I'm diving deep or solo, I want a stage or pony of the appropriate size. Don't have it? Don't do the dive. Am I being overly cautious? I don't think that's possible.
• Conditions. How are the waves? How are you getting in and OUT of the water? Especially OUT??? Are there currents and can you swim against them?
• Your Buddy. Just as important as your own limitations are those of your buddy. Always use the lower limits.
• Attitude. Obviously, this is the most important limit of them all. Without a great and cautious attitude, the other limits won't mean much.

So, what are your limits? Do you know them? Do you care? Hopefully, this will give a pause to think about them and what they really mean to you. Why? Because a diver's got to know their own limitations. Think about it. Think about it before you exceed a limit by not thinking about it. Safe diving is no accident.

 

[flyboy08]

I called my first dive in over 500 dives on my recent trip to CZM...during the first dive of the vacation, I was suffering from mild vertigo during the dive...I reluctantly called the second dive but felt it was the right thing to do and watched my wife and daughter go off on their own for the first time evahhh without me:-(

I was fine by the next day and dove without issue the remainder of the week!


Good post Mr. Chairman!

 

[1000RR]

Awesome post!!

 

[Akimbo]

Divers also have to be aware of all the reasons behind their limits and they are a moving target. The main factor being what they learn -- through formal training, experience, self reflection, and conversations with other divers. The target also moves in both directions due to age, injury, and life factors that influence individual risk tolerance; having a child for example.

The most important part of all is to constantly expand and explore the logic supporting your limits so you see them as "it is stupid to exceed them" rather than "limitations on what you feel like doing".

 

[The Chairman]

The most important part of all is to constantly expand and explore the logic supporting your limits so you see them as "it is stupid to exceed them" rather than "limitations on what you feel like doing".

Amen, bro... amen!

 

[Edward3c]

I’d like to add

Location. When diving a new location, like on holiday, remember to adjust in stages. For example, 25m in UK waters is a lot darker that 25m in the tropics. I’ve know divers whom have exceed their depth because their were unconsciously using the ambient light level as a depth indicator.

Feel free to modify.

 

[Akimbo]

Location. When diving a new location, like on holiday, remember to adjust in stages...

I concur. We see that a lot in Monterey (California). Divers from all over the country, including Southern California, think conditions are much more benign than they usually are. Temperature, visibility, sea states, different critters, kelp, wind, and fog can conspire to ruin your dive or MUCH worse.

 

[1000RR]

@The Chairman (and others), being new to this we (my daughter and I) are learning tons all the time. In part to the reading I do on SB.

Question for you/others: where does experience begin to substitute for formal training in some form or fashion and how do you know? As an example, I see folks on SB that have tons and tons of dives, have an OW certification only, and do deep(er) dives all the time. I suspect they feel quite comfortable at the increased depths (past their formal training of 60') and I suspect they have (or feel they have) plenty of experience to enable their comfort and knowledge to dive that deep.

My daughter and I are just beginning this new adventure (diving). Our typical reef dives we go on are 60'. I have had her sit down at the dining table with me and do detailed dive planning calcs (calc'ing air usage based on RMVs for the dive, an issue, a return, a safety stop, etc.) mainly so she understands these things are not arbitrary and she understands the concept. Our dives have been drift dives for the most part so we haven't had a "return pressure" as much as we just have a "ascent pressure" where we end the dive and just go up. We have used return pressure to a slight degree when doing shark tooth diving in the Gulf, but the waters are very shallow and you really aren't venturing too far from the boat, we just made our returns early but basically kept searching for teeth... just changed our heading to return towards the boat. I think we'll do a wreck dive or more anchored dives this Spring so we'll get an opportunity to employ more planning relative to turn/return pressures etc.

For us, we don't plan (or have business) on doing deep (to me that means 90' plus) dives any time soon (due to lack of experience and training IMO). That said, if we were presented with the question of diving to 70' (or not), I don't think I would hesitate. I feel comfortable with both of us diving to there - is that bad? Now... if presented with diving to 80' by a DM, I would respond with - we have only dived to "X" feet (whatever that is... it's "60" right now) and would only dive to that depth if you (DM) are ok with us sticking with you on the dive and you are ok keeping an eye (buddy-style) on us - is that bad? Admittedly, we are new to this, and hence ignorant to plenty of things relative to diving. So we don't know what we don't know. And that's where more training and experience comes in. But right now, the above would be my approach - again, is that bad? Speak freely, I take no pride in this matter and don't have an ego to hurt... I'm ignorant to plenty of things diving.

 

[The Chairman]

Location. When diving a new location, like on holiday, remember to adjust in stages. For example, 25m in UK waters is a lot darker that 25m in the tropics. I’ve know divers whom have exceed their depth because their were unconsciously using the ambient light level as a depth indicator.

I see that more as "Conditions". There are days when your apparent depth seems different even at the same location. I've been on derepmet visibility dives in the Keys, where a day before I had virtually unlimited visibility. But, let's not lose sight of what you're pointing out: depth is absolute, but how deep you feel you are is not. This affects two things. Your DAC (Depth Air Consumption) will increase regardless how "easy" the depth feels, and your ability to resolve problems (narcosis) will decrease regardless in the same manner. "Feelings" are not reliable.

FWIW, derepmet visibility is when the only thing you can see, is the backward "tempered" on your facemask.

 

[Akimbo]

Question for you/others: where does experience begin to substitute for formal training in some form or fashion and how do you know?

It doesn't substitute, experience augments. In a short time you will appreciate how experience, self-reflection, and conversation with dive buddies and on Scubaboard will help you target formal training you want. It will also increase what you get out of formal training.

“The more I learn, the more I realize how much I don't know.”
--- Albert Einstein​