How Long Can You Stay Underwater SCUBA Diving?
Candace Reno July 7th, 2023 Posted In: Articles Tags: SCUBA
How Long Can a Diver Stay Underwater?
How long can you stay underwater SCUBA diving? This is a very common question from anyone interested in SCUBA diving! The answer, of course, varies based on many factors. Let’s take a look at some of the main factors that affect time spent underwater while diving.
No Decompression Limits
The main factor that controls how long you can stay underwater SCUBA diving is no-decompression limits. When you breathe compressed air (21% oxygen; 79% nitrogen) you absorb both gases. Your body can utilize oxygen for metabolism. However, your body cannot do anything with the nitrogen absorbed, which if exceeded beyond a reasonable limit, can increase your risk of decompression sickness.
The recreational dive tables are what divers use to make sure they stay well within their limits. These tables were revised and edited from the old Navy dive tables. For each given depth while diving on air, there are maximum allowable bottom times that you must stay within to avoid going into decompression mode. The deeper you dive, the less time you have in the no-decompression limits.
Repetitive Dives
For multi-dive days, you will have less time on the second, third, fourth, etc. dives of the day than you did on the first. This is because your body still has nitrogen absorbed from every dive completed that day. Therefore, each sequential dive made, after a surface interval that lasts less than 6 hours, you will have less time to spend at the same depth. Most divers will do a couple dives in the morning with an hour in between those two dives and a longer lunch break for a couple hours before making any afternoon dives. This will maximize the amount of time you can stay underwater SCUBA diving on repetitive dives.
Typical dive schedules are the following:
- Dive 1- Deep: You will make your deepest dive of the day first. This will mean that this dive could be relatively short, like 30-40 minutes.
- Dive 2- After an hour surface interval, the second dive is usually shallower than the first and about the same time or about 5-10 minutes longer depending on depth.
- Dive 3- After a couple hours of surface interval, dive 3 is shallow, like 30-40 feet on a reef, but can be an hour long.
- Dive 4- After another hour surface interval, this dive is much like dive 3, shallow and about an hour.
I have done a fifth dive on a day and it is usually a night dive taking place several hours after the afternoon dive. Night dives are also usually shallow and can be an hour long on average.
Just because you have less time at the same depth on each repetitive dive, if you make shallower dives as the day progresses, then you can actually have more time underwater on a repetitive dive than on your first dive!
Enriched Air
You can increase your bottom time by diving with enriched air nitrox. This gas is also an added benefit on days you will make several dives. Enriched air decreases the amount of nitrogen in the SCUBA tank by increasing the amount of oxygen allowing you to stay underwater longer before risking decompression sickness. There are depth limits associated with nitrox gas due to the chance of oxygen toxicity. As always, to be safe SCUBA diving, you need to be certified in enriched air nitrox in order to be able to dive with it.
Depth
Based on physics, the deeper you SCUBA dive, the faster you will breathe through your air. As you descend underwater, the pressure and density increase while the volume decreases. This occurs every 33 feet (10 meters). This means that at 33 feet, you will breathe twice as much air from your tank than if you were at the surface. At 99 feet, this increases to four times as much air consumption compared to the surface. If you are concerned about your personal air consumption limits, you might consider planning shallower dives. The advanced open water and deep diver courses cover some of these factors and should be taken by those that wish to dive deeper than 60 feet.
Air Consumption
Lastly, another main contributor of how long you can stay underwater SCUBA diving is personal air consumption. The no-decompression limit to a dive to 35 feet is 205 minutes. At this depth, you will probably never get close to the no-decompression limit before you start to get low on air. Every SCUBA diver will have different rates of air consumption based on a few factors: physical fitness, buoyancy control, and experience. Females also tend to breathe less air than males. Sorry guys!
Furthermore, with deeper depths you usually wear SCUBA diving wetsuits for exposure protection which will affect your buoyancy and could lead to different air consumption rates. The best thing you can do is get more experience and become more comfortable in the water. Your air consumption will improve over time.
So, How Long Can You Stay Underwater SCUBA Diving?
Overall, no one can say for sure how long you can stay underwater SCUBA diving. Your personal factors and your dive profile will greatly affect your time spent underwater. So go get more experience and dive, dive, dive!
