You’ve finished your dive and signal your buddy that it’s time to surface. You start up slowly, but with more than 30 years of dive experience and hundreds of logged dives, you long ago stopped timing your ascent to the surface — which you learned should be 60 feet per minute.
Well, that was the ascent rate if you got certified before 1996. That’s the year gas cost $1.22 a gallon, Cal Ripken Jr. broke Lou Gehrig’s record for consecutive games played in Major League Baseball, Cuba Gooding Jr. famously said, “Show me the money” in Jerry Maguire, and the U.S. Navy adopted the 30-foot-per-minute ascent rate for scuba divers. Navy studies found that a slower rate resulted in fewer cases of DCS. Training agencies, including PADI, followed suit.
“Diving along a reef at one depth, coming back at a shallower depth, and then spending time in the shallowest depth range is a great target,” says Dr. Neal Pollock, research director at Divers Alert Network. “The controlled ascent rate and staged ascent facilitate gas elimination through the lungs, which can reduce the likelihood of bubble formation.”
Avoiding “bubble formation” is the reason your instructor hammered home the 30-feet-per-minute rule. Decompression injuries occur when your tissues are saturated with nitrogen as you ascend too quickly. The idea behind off-gassing at a slow rate is to give nitrogen bubbles the chance to leave your body before they turn into a problem.
Understanding Bubble Formation
You don’t have to be a whiz in physics or physiology to understand what happens to bubbles of nitrogen in your body as you ascend. As you swim up, the nitrogen gas that your body has absorbed expands, but it’s safely eliminated when you exhale.
If you ascend too quickly, however, your body can’t eliminate all of the expanding nitrogen, and the excess nitrogen forms bubbles in your tissues and blood. These bubbles are elastic (like half-filled water balloons) and can change shapes. After a bubble stuffs itself into a capillary, it may eventually squeeze past an obstruction. But dangerous blockages are possible when nitrogen molecules form into large bubbles.
When your circulatory system fails to get the nitrogen bubbles in your bloodstream into your lungs, the bubbles can jam tiny capillaries, causing blood flow to slow down and nitrogen to back up into your tissues. Bubbles then grow in the tissues and joints. This is what leads to decompression sickness.
Once bubbles get to your lungs, they are filtered out of your blood and dumped into alveoli, the thousands of tiny balloonlike sacs in your lungs. If you don’t drain your alveoli by exhaling, these sacs can burst, similar to how bubbles of soap pop. The air has to go somewhere, and that somewhere is your blood vessels. This can lead to an arterial-gas embolism; those bubbles can spell serious trouble if they travel to your heart or brain.
Decompression sickness and arterial-gas embolism are the most serious consequences of a rushed ascent, but there are other issues as well. Kell Levendorf, casualty investigator for Dive and Marine Consultants International, says that when he’s teaching students about the consequences of fast ascents, “I make it a point to tell them never to attempt a Valsalva during ascent, as it will overpressurize the airspace that’s already filling with expanding air, leading to possible ear barotrauma.”
Pretty scary stuff, but it’s nearly 100 percent avoidable if you follow the rules of a safe ascent.
Tip No. 1: Vent Your BC
It’s important to get in the habit of venting all the air out of your BC or drysuit before you begin the ascent and risk the possibility of an express trip to the surface.
The air in your BC is growing, just like the nitrogen bubbles in your body. The problem is that many of us tend to react to “getting light” underwater rather than to anticipate it. You know the feeling — you’re exploring the reef and you feel yourself drifting higher in the water column. You dump air from your BC, establish your buoyancy, and go on with your dive.
But when you’re swimming up and start getting light, your ascent can get away from you. So before you head up, vent all the air from your BC. “Learn to use the different exhaust valves your BC has,” says Karl Shreeves, PADI’s technical development executive. “Most models have a ‘quick dump’ by pulling down the inflator/deflator hose, as well as exhausts on the low part of the bladder. Use these so you can vent your BC regardless of your orientation in the water — it’s more convenient, but it also reduces an accidental runaway ascent because you don’t have to turn vertical to vent.”
If you typically add a lot of air to your BC when you’re at depth, try taking off a pound or two of weight. “Overweighting is a problem because divers have to put additional air in their BCs, which means they need to vent more gas more often to keep buoyancy under control,” says Shreeves.
Tip No. 2: Slow Your Roll
A slow ascent is like taking your foot off your car’s gas pedal as you travel through a construction zone — the slower rate is safer, and allows your body to flush out and exhale dissolved nitrogen before it forms bubbles.
“Even within the maximum rate your computer allows, it’s easier to control your ascent by going slowly,” Shreeves says. “The slower you go, the more time you have to adjust expanding gas. Tec CCR divers really understand this because they have three gas volumes they have to control: drysuit, rebreather loop and BC.”
Tip No. 3: Make Your Safety Stop
It’s pretty simple: The nitrogen you breathe out at 15 feet significantly reduces your risk of forming a bubble.
“The first tip is to make the safety stop in the first place,” says Shreeves. “Not only does it help make your profile more conservative, but having a target stop depth at 15 feet helps you keep your ascent under control. At the stop, you should be neutrally buoyant, and three minutes gives you plenty of time to get that dialed in before you finish your ascent.”
DAN’s Pollock takes it one step further: “Extra shallow stop time is the least ‘expensive’ and most effective way to reduce effective decompression stress. If a three-minute stop is good, five minutes is better.”
Tip No. 4: Take Care in the Last Few Feet
With the surface so close, does it really matter if you take the last few feet too quickly? Yes, it can. Remember, during the last 15 feet, bubbles grow fastest.
This is where it’s helpful to have a routine, and to follow it each time you dive. “Make sure your computer is clear and it’s OK for you to ascend,” says Divetech’s Jo Mikutowicz. “Check one final time that there is no air in your BC. Have a good look above to make sure there are no divers, boats or a low dock, and then slowly kick toward the surface. Look up the entire way, with one hand over your head in case there is something above you cannot see — it’s better that your hand hits it before your head does.”
Keep your throat open all the way up — inhaling is as safe as exhaling, but do one or the other constantly. The 30-feet-per-minute rule still applies, so if you’re at 15 feet when you start, it should take 30 seconds to surface. For a more in-depth look at making a safe ascent in the last few feet, read How to Make a Safe Ascent after Your Safety Stop.
One final tip, adds Jeanne White, director of education for Jack’s Diving Locker in Hawaii, “is to keep your regulator in your mouth after you’ve surfaced, and keep it in until you have inflated your BC and have a chance to see what conditions are like.”
Tip No. 5: Be Conservative
Take it slowly as you climb up the boat ladder or exit the water at the shore, and don’t strain yourself. Rest, hydrate and stay warm. Extend your surface interval, especially after long, deep and repetitive dives. In other words, take advantage of this time to relax so you’re ready to make the next dive.