March 29, 2019

Scuba diving tank is one of the most important scuba diving equipment. We all know from our open water course that the air inside our tank is the same air we breathe every day. It contains 78% nitrogen, 21% Oxygen and 1% carbon dioxide and small amounts of other gases.

We understand that nitrogen is a key contributing to decompression sickness. Therefore, can we reduce our risk of DCS by reducing the percentage of nitrogen in the air we breathe underwater?

To answer this question, British diver Henry Fleuss made what was possibly the first Nitrox dive using a rebreather in 1874. After more than a hundred years of study and research, many training agencies started to offer Nitrox course in the early 90s. In 1996, PADI announced full educational support for nitrox. Since then, Nitrox became a key component in recreational diving.

There are more Oxygen and less nitrogen in a Nitrox air mix. With less nitrogen, we can have longer no decompression limits, shorter surface intervals, a lower risk of decompression sickness.

However, divers, especially new divers are often confused by some features of Nitrox. Following, let’s have a look at some common misconceptions.


         1. I can dive longer with Nitrox.

We can have longer no decompression limits diving with Nitrox. But that does not necessarily mean a longer dive time. A decompression limit is a time that we can dive without suffering from decompression sickness. However, there is another factor in diving that restrict our dive time – remaining air in the tank.

Air consumption is a concept that we don’t talk a lot in recreational diving. To better understand it, you can think it as gas consumption while driving. Normally, we burn more gas while driving a pickup truck than a tiny car. Nonetheless, an experienced driver can drive a huge truck with small gas consumption.

Same idea applies to diving. Bigger guy tends to use more air but a very experienced big diver sometimes can have really low air consumption. In average, the air consumption of a new certify diver is about 15-20 L/Min (15 liters of air per minute) while the air consumption of an experienced diver is about 10-15 L/Min.

Using Nitrox can not make the dive longer with a high air consumption. For example, that most common aluminum air tank holds about 2,000 L of air in 200 bar / 3,000 PSI. For a diver with a 20L/min air consumption, the tank will be burn out in 33min in 20meters. But in fact, the no decompression limit in 20 meters is 45mins. In others words, this diver will run out of air before reaching the no decompression limit.

Therefore, even diving with Nitrox, this diver can only dive for maximum 30 minutes regardless of how much time before he reaches the no decompression limit. As a result, diving with nitrox does not offer a longer dive time for this diver.

2. It is safer to use Nitrox

Diving with Nitrox reduces the risk of decompression sickness. However, it is not quite true to say it is safer to dive with Nitrox than with air. That is because diving with Nitrox introduces another potential risk – oxygen toxicity.

We need oxygen to survive, but oxygen toxicity kicks in when the partial pressure of oxygen is too high. Underwater central nervous system (CNS) oxygen toxicity is dangerous. A typical symptom is a no-preceding-warning convulsion. This is extremely dangerous underwater. A diver will most likely spit the regulator out and drown underwater when it happens.

When oxygen partial pressure is over 1.4 bar/ATA, we reach the limit of CNS oxygen toxicity. Thus, with a higher percentage of oxygen in the air mix, the depth limit is shallower. If we are diving with 40% O2 Nitrox, the depth limit for oxygen toxicity is only 25 meters.

While diving with Nitrox reduces the risk of DCS, it increases the risk of CNS toxicity. As a result, it is not correct to say it is safer to dive with Nitrox. Before using a Nitrox tank, make sure you have the proper training and perform the proper predive safety check.

3. I can use the same gears in air and Nitrox

Oxygen is not flammable, but it is an essential part of burning. With a higher oxygen concentration and pressure, substances that would not burn in atmospheric air burn freely. While diving with Nitrox, there is potential risk of burning while performing predive check or filling a Nitrox tank.

To reduce such risks. Many training agencies and local governments implemented a 40% rule. That is, we need to use special equipment, especially tanks and regulators, while handling an air mix with an oxygen level higher than 40%. Otherwise, a fire might break out.

As a result, most of our recreational Nitrox certification are limit to a mixture of 40% oxygen and in most of the cases, the highest Oxygen level in a Nitrox tank is about 36%. However, if a diver is using a higher percentage of oxygen in decompression diving, all scuba gears shall be oxygen cleaned before use.

4. It is expensive to use Nitrox

After all the misconceptions, it is easy to find that if handled with extra care, the pros outweigh the cons in Nitrox diving. But does it mean with all these benefits, diving with Nitrox will be much more expensive than diving with normal air?

Unfortunately, it is correct for most cases. There are different ways to mix nitrox but all of them are much more complicated and requires more sophisticated equipment. As a result, it cost much more to fill a Nitrox tank than an air tank. Especially when diving in remote area such as isolated islands or on a liveaboard, divers pay much more when diving with Nitrox than with air.

Nonetheless, there are always exceptions. In Pro Dive International, Nitrox is FREE to use as long as divers are certified. You can enjoy the benefits of more bottom time, less surface interval and a lower risk of decompression sickness while diving in Cozumel, Conotes and with the amazing Bull Sharks.

Huh? Not yet Nitrox certified? Then do the Nitrox course with Pro Dive and enjoy the unique ultimate free Nitrox experience with us.