Before you start scuba diving, one of the key things you must learn is the effects of compressed air on your body. As a diving instructor, I have taught over 400 students and can share all you need to know about decompression diving and what it really means.
So, how deep can you dive without decompression stops? A diver at 10 meters can spend 219 minutes there without needing to do a decompression stop. In contrast, a diver at 40 meters has only 9 minutes before needing to complete mandatory decompression stops for a safe ascent.
Decompression diving means a diver has on-gassed more nitrogen and needs to complete mandatory decompression stops before surfacing. The necessity to complete decompression stops depends on two factors, depth and time underwater.
This might sound like diving jargon, however, if you keep reading, I will share what exactly a decompression stop is, why depth affects your maximum bottom time and what you can do if you overstay your no-stop limit. Whether you are a new diver or simply looking to refresh your skills, this is all vital information to ensure you have a safe dive.
What is Decompression Diving
Whenever you scuba dive and breathe compressed air, nitrogen enters your bloodstream and tissues. The longer you dive, the more nitrogen is absorbed by your body. When you ascend at a safe rate of 18 meters per minute, this nitrogen will slowly off-gas.
Your no-stop limit signals the maximum amount of time you can spend at a specific depth and surface with no (decompression) stops. If you have surpassed your no-stop time, or your no-decompression diving limit, a slow ascent does not grant enough time for the nitrogen to naturally leave your system.
What is a Decompression Stop and Why You Need it
Decompression stops are a series of stops that divers undertake during an ascent to allow nitrogen to move out of the tissues and safely exit the body. Between each stop, the diver continues to move closer to the surface.
For example, decompression stops can include a first stop at 12 meters, then 9 meters, then 6 meters, and finally 3 meters. Overall, it’s a way of sufficiently slowing down your ascent to avoid nitrogen associated issues.
What is the Difference Between a Safety and a Decompression Stop
In all recreational diving, the depth is limited to 40 meters, and maximum bottom times are well within no-stop limits. However, even in non-decompression diving, certifying agencies recommend that divers perform a safety stop. This is typically a 3-5-minute stop at the depth of 5-6 meters to allow for additional off-gassing time.
How Deep Can You Dive Without a Decompression stop
The amount of nitrogen entering your bloodstream will depend on the precise time and depth of your dive. Therefore, you will need a dive computer, recording your dive, ready to signal your ‘no-stop’ time.
Scuba Diving tables, which were based on Navy Dive tables, show the maximum amounts of time you can spend at any given depth before needing a decompression stop.
- At 12m you can spend a maximum of 147 minutes.
- At 18m the maximum dive time is 56 minutes.
- At 30m a no-decompression dive would be 20 minutes long.
- At 40m no-stop diving limit allows 9 minutes.
Here is a table with more complete data:
10 m / 32.81 ft
12 m / 39.37 ft
14 m / 45.93 ft
16 m / 52.49 ft
18 m / 59.06 ft
20 m / 65.62 ft
22 m / 72.18 ft
25 m / 82.02 ft
30 m / 98.43 ft
35 m / 114.83 ft
40 m / 131.23 ft
42 m / 137.80 ft
The deeper you go, the shorter your maximum dive time at that depth can be. This is because as pressure increases, you will consume a larger quantity of air and subsequently nitrogen. The air you breathe underwater is pressurized regular air that contains 21% oxygen, 78% nitrogen and a remainder of argon, carbon dioxide and other various gases.
Emergency Stops - What to Do if You Overstay Your No-Stop Diving Limit
If you overstay the limit, follow your dive computer’s safety stop instructions.
If you exceed the no-decompression limit by no more than 5 minutes, you should make an 8-minute (or the maximum time your air allows) emergency decompression stop at 5 meters (16.40 feet). After this, you should wait a minimum of 6 hours before performing another dive.
If you overstay by more than 5 minutes, make a 15-minute (again, if you still have enough air supply) emergency decompression at 5 meters (16.40 feet) and remain out of the water for a minimum of 24 hours before your next dive.
Why Does Depth Affect Your No-Decompression Time
The deeper you go, the more pressure you experience and therefore the greater the amount of air you breathe. Did you know that every ten meters add an additional atmospheric pressure? Interestingly, the pressure difference from the surface (at 1 atmosphere) to 10 m underwater (2 atm) is the same as the surface all the way to space (0 atm)!
If you have been in a plane, you would have experienced your ears popping due to changing pressure. In terms of diving, this means that at 20 meters underwater you will empty your tank 3 times as fast and absorb 3 times as much nitrogen as on the surface. The deeper you go, the faster you absorb nitrogen, and the quicker you reach your no-decompression limit.
Which Depth Should You Dive To
You now know the importance of diving within recreational limits of both depth and time. However, what do varying depths allow you to see underwater? What are the benefits of diving at various depths?
10-15 meters underwater
Do you want to wonder at the beauty of coral gardens or feel as if you are in the biggest fish tank in the world? Then shallow diving is perfect for you. All this and more can be seen in the first 10-15 meters underwater.
The most spectacular reefs with astounding corals depend on sunlight and, therefore, will be found closer to the surface. The colour red disappears within the first 10 meters, and the other colours follow close behind.
15-20 meters underwater
Once you descend a little further, you will find it easier to dive, since the relative pressure differences will be smaller, and it will be easier to control your buoyancy.
Your buoyancy is dependent on your personal floatability and the amount of air in your BCD (buoyancy control device) and tank. Most first level certifying agencies will certify beginner divers up to 18 m or 20 m of depth. This includes the PADI Open Water course and SSI Open Water Diver.
20-30 meters underwater
Since you are at a greater depth, there is less light and colour here. However, these depths which you can reach by doing your Advanced Open Water unlock a mysterious underwater world.
Many shipwrecks are scuttled at this depth, and paired with your Advanced certification, you can explore history. This depth also has an array of impressive gorgonian fans, with an increased likelihood of seeing (harmless, don’t you worry) sharks, big predatory fish and impressive underwater structures.
Be careful! At increased depth, you can experience nitrogen narcosis, which feels like mild inebriation.
30-40 metres underwater
This depth is reserved for deep diving trained divers. This is because at this depth you are dealing with lowered light, a fast consumption of air and minimal bottom time.
Divers must remain alert, checking on their no-stop diving limits, remaining air and recommended safety stops. Once again, big depths often mean spectacular shipwrecks and impressive fish.
What to Consider Before Diving
If you are interested in swimming with deep-dwelling critters or visiting an impressive sunken ship, then you might want to consider a few of the following points.
Your level of certification
It is a good idea to complete an Advanced Open Water course to give you additional skills in navigation, buoyancy and increase your confidence. In PADI, this is a 5-dive course in addition to the 4 open water dives for the Open Water Diver certification. You can take the theory portion online.
If you are interested in physiology, dive theory and becoming a safe diver, the Rescue course is the most challenging, yet satisfying to complete.
The equipment you have
If you are yet to purchase any equipment, the first step you should take is to invest in a high quality, well-fitting mask. This will transform your experience.
On top of all the standard equipment, once you become an avid diver, you might want to consider some accessories to improve your dives.
Since light disappears as you descend, it is a good idea to bring a torch to help illuminate your view and enjoy the scenery.
A compass will help you find your way around underwater and a slate can ease your communication with your body.
Your diving experience
In diving, it is vital that you feel confident in your skills. If you are unsure, entrust yourself to a dive professional such as a divemaster or instructor. Especially when traveling to a new destination, having a local guide can vastly improve your dive since they know all the best spots.
If you haven’t dived for over 6 months, you might want to consider a refresher to go over the basic skills.
Your fitness level
Diving is known as the laziest sport in the world, since the aim of the game is to be as calm and slow-moving as possible. It is, however, vital to stay in good shape to minimize any risks to your health. This includes regular exercise and ensuring you are adequately hydrated before a dive.
If you have had any recent surgery, heart or breathing conditions, make sure to consult a dive doctor before attempting to dive again.
How Deep Can You Dive Without Getting the Bends
The bends are a colloquial term for decompression sickness, which occurs when nitrogen dissolved in the blood and tissues forms bubbles as pressure decreases.
Recreational diving is considered no-stop diving, so up until 40 meters you can safely ascend to the surface during any part of your dive at a rate of 18 meters per minute. It is, however, advisable to complete a safety stop at the depth of 5 meters for 3 minutes to allow additional time for nitrogen to off-gas.
If the pressure difference is too sudden, nitrogen can form bubbles in your blood and block oxygen from reaching vital organs. You can dive to any depth without getting the bends if you ensure to include decompression stops to allow for the nitrogen to safely exit your body, and also enough air to complete the stops.
What Are the Common Signs of Decompression Sickness
If you happen to ascend a little too fast or not complete your safety stops, you may experience decompression sickness.
All dive boats are on high alert for any of the following signs and symptoms, however, it is important to be able to identify them yourself to seek immediate medical attention. If you are unsure, speak up as decompression sickness can lead to serious health issues without immediate medical intervention.
The possible signs and symptoms include:
- Joint pain
- Weakness in arms and legs
- Skin rash
- Loss of motor control
- Paralysis on one side of the body
Decompression sickness is treated by placing the diver in a recompression chamber and decreasing the pressure gradually, simulating decompression stops to allow slow off-gassing of nitrogen.