1
20 NAUI Nitrox Diver
Comparision of Dive Plans Using Air and EAN36
Diver 1: Air Diver 2: EAN36
NAUI Dive Tables NAUI RGBM Tables NAUI Dive Tables NAUI RGBM Tables
First Dive First Dive
RGBM Tables, he has a maximum dive time of 55
minutes for the second dive.
Diver two, using EAN36 and NAUI EAN36 Dive
Tables, finishes the first dive with a Letter Group of F.
One hour later, she begins the second dive as an “E
diver.” She has an adjusted maximum dive time of 60
minutes for her 16-meter (53-foot) dive. If using the
NAUI RGBM EAN36 Tables, she would have a
maximum dive time of 115 minutes!
On the second dive, the diver using enriched air
nitrox has a 55-minute advantage over the diver using air
if using the NAUI Dive Tables or a 60-minute advantage
if using the NAUI RGBM Tables.
Another benefit of nitrox is the possibility of a
shorter required surface interval (Figure 1-9). In the
example above, the nitrox diver has 60 minutes available
dive time after a one-hour surface interval if using the
NAUI Dive Tables. If the air diver using the same tables
wanted to have a dive time of 30 minutes, he would have
to attain a Letter Group of C before beginning the second
dive. To move from “H” to “C” requires a surface interval
time of at least 4 hours 22 minutes! The NAUI RGBM
Tables are based on a one-hour surface interval, so those
numbers do not change.
Technical divers will breathe a highly oxygen-rich
nitrox mixture during their shallower decompression
stops or long exposures in the shallow zones in order to
more efficiently eliminate nitrogen from their bodies.
Another very common use of nitrox in diving is
simply as a safety margin. Divers who choose to dive
conservatively will often breathe nitrox but continue to
use air dive tables or an air computer. Over a series of
dives, they will absorb significantly less nitrogen than
their tables or computers indicate, effectively lowering
their risk of decompression sickness.
Finally, there may be truth in the claim of divers
that they are less physically tired after a series of dives
on enriched air nitrox. With less nitrogen in their bodies
than they would have had diving on air, the divers may
indeed feel less fatigue at the end of their diving day or
diving trip.
COMMON MISCONCEPTIONS
ABOUT NITROX
As was said earlier, many misunderstandings developed
about nitrox as it began to be known (but not well
understood) in the recreational diving industry. Before
you move on to the next topic in this course, you should
be aware of some of the persistent myths about nitrox
and be able to sift the fact from the fiction.
Myth 1: “Nitrox is for technical diving.”
Although technical divers use oxygen-enriched air when
appropriate, such as during in-water decompression
stops, the use of nitrox does not make a dive “technical.”
Technical dives are planned decompression dives, deep
dives where both nitrogen and oxygen in the breathing
gas may be diluted with helium (trimix), dives in which
24 meters (80 feet)
Dive Time: 30 minutes
Ending Group H
24 meters (80 feet)
Dive Time: 30 minutes
24 meters (80 feet)
Dive Time: 30 minutes
Ending Group F
24 meters (80 feet)
Dive Time: 30 minutes
One hour surface interval One hour surface interval
Entering Group: G — Entering Group: E —
Second Dive Second Dive
16 meters (53 feet)
Max. Dive Time:
10 minutes
16 meters (53 feet)
Max. Dive Time:
55 minutes
16 meters (53 feet)
Max. Dive Time:
60 minutes
16 meters (53 feet)
Max. Dive Time:
115 minutes
Figure 1-8 A comparison of dive plans showing the dive time advantage using nitrox–the diver breathing EAN36
has significantly greater no-decompression time than the air diver.