Fundamentals of Nitrox

Question 1

Can a diver dive deeper on a Nitrox gas mix?

Answer 1

Contrary to what many people believe, Nitrox is not a deep-diving gas mixture. In fact the higher the blend of Oxygen the sallower the diver must stay.

Question 2

In the SCUBA diving community Nitrox refers to any SCUBA diving gas mixture composed of what?

Answer 2

In the SCUBA diving community Nitrox refers to any SCUBA diving gas mixture composed of nitrogen less than 78% and oxygen greater than 22% and less than 40%. The trace gases are ignored.

Question 3

What are the benefits of diving on a Nitrox gas blend?

Answer 3

The benefits are; NITROX generally provides less sub-clinical decompression stress to your body when associated with diving. If you dive with a NITROX gas and follow the AIR diving table/computer no decompression limits (NDL), the amount of Nitrogen accumulation within the body will be less and therefore less stressful to the body.

Question 4

What does Nitrox extend when diving?

Answer 4

NITROX will extend your allowable no decompression limits or bottom time. It does this simply by reducing the amount of Nitrogen gas you are exposed to under pressure.

Question 5

What other names can Nitrox be known as?

Answer 5

NITROX is known by many names: Enriched Air Nitrox, Oxygen Enriched Air, NITROX, EANx or Safe Air.

Question 6

What are the two most popular blends of Nitrox?

Answer 6

The two most popular blends are EANx32 and EANx36, developed by NOAA for scientific diving, and also named Nitrox I and Nitrox II, respectively.

Question 7

What is the percentage of oxygen and nitrogen in Nitrox32?

Answer 7

If you see “NITROX32” or “NITROX36”, the number is referring to the percentage of oxygen content in the gas mixture and in turn the diving cylinder you are using.

So “NITROX32” or “EANx32” or “Oxygen Enriched Air 32” contains 68% nitrogen and 32% oxygen.

Question 8

What is very important to check before each dive when diving on Nitrox?

Answer 8

It is very important that you check the gas mixture in your cylinder before each dive, because you need to know what mixture you have for calculating your dive times and to find out the maximum depth you can dive.

Question 9

What happens to oxygen as the pressure increases at depth?

Answer 9

Oxygen is toxic at depth for us humans! The increased pressure at depth will increase the partial pressure of oxygen (PpO2) and this increased pressure can become toxic.

Question 10

What two limits do you need to stay within when diving on Nitrox?

Answer 10

With NITROX diving we have to stay within two limits, the NDL limit, which as a diver you already know about and the other is the oxygen toxicity limits.

Question 11

How long has Nitrox been being used for?

Answer 11

NITROX gas mixture is nothing new and has been in use under differing names since before the Second World War.

Question 12

Nitrox reduces the nitrogen absorbed into our bodies. What risks does Nitrox remove?

Answer 12

Nitrox does not remove the risk of decompression sickness. Nitrox does not remove the risk of pressure related injuries. Nitrox does not reduce Nitrogen Narcosis

Question 13

Why may a Nitrox diver stay longer for at a given depth?

Answer 13

With Nitrox the oxygen fraction or percentage is increased and the Nitrogen is reduced. The actual Nitrogen loading would be equivalent to a shallower depth. We call this adjusted Equivalent Air Depth (EAD) and this is the reason why a NITROX diver may stay longer for a given depth.

Question 14

A high oxygen partial pressure exposes the diver to a greater risk of what?

Answer 14

A high oxygen partial pressure exposes the diver to a greater risk of central nervous system (CNS) oxygen toxicity.

Question 15

What may oxygen toxicity cause?

Answer 15

Oxygen toxicity may cause convulsions, whilst these are not in themselves harmful underwater these will lead to drowning.

Question 16

What procedure should you follow if the a person convulses underwater?

Answer 16

When a person convulses underwater there is little that can reasonably be done to assist other than stand by and bring them to the surface. The exact procedures whether to take them directly to the surface or wait until the convulsions have stopped are still debatable.

Question 17

What is the partial pressure of oxygen at sea level?

Answer 17

So the partial pressure of oxygen at sea level is 0.21. And written as PpO2 = .21

Question 18

What is the maximum partial pressure of oxygen agreed by the recreational diving community?

Answer 18

The recreational diving community has agreed that the maximum partial pressure of oxygen limit is 1.6 bar and the recommended limit is 1.4 bar.

Question 19

Does the percentage of oxygen in a gas change the deeper the diver descends?

Answer 19

The percentage of oxygen in the gas is fixed, say
32% Nitrox, the deeper the diver descends the higher the absolute pressure and the proportional partial pressure of oxygen will be when the diver is exposed to the gas during breathing.

Question 20

What is the Maximum Operating Depth (MOD) limit based on PpO2?

Answer 20

The MOD or maximum
operating depth (based on a limit of 1.6PpO2)

Question 21

What is the Target Operating Depth (TOD) limit based on PpO2?

Answer 21

The TOD or Target Operating Depth (based on a limit of 1.4PpO2)

Question 22

When does Pulmonary Oxygen Toxicity occur?

Answer 22

This type of toxicity occurs when you are exposed to partial pressures of between 0.5 - 1.6 bar for a long period of time.

Question 23

What are the symptoms of Pulmonary Oxygen Toxicity?

Answer 23

Symptoms are burning in the chest and an irritating cough. When continuing the exposure, effects get worse.

Question 24

What is Hypoxia?

Answer 24

Hyperoxia is a form of Oxygen Toxicity when the oxygen partial pressure exceeds 1.6 (Recreational Diving Limit) and/or when you are exposed underwater to elevated partial pressures of oxygen over an extended time.

Question 25

What are the symptoms of Central Nervous System (CNS) toxicity?

Answer 25

CNS oxygen toxicity can be sudden, without warning or following Vision disturbances (blurriness), Ears (ringing sound), Nausea, Twitching, Irritability, Dizziness, and Convulsions. However, evidence indicates that most convulsions are not preceded by any warning symptoms at all.