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Simply stated, Enriched Air NITROX is similar to normal breathing air with the important difference that NITROX has a greater percentage of oxygen than air.  The additional oxygen reduces the amount of nitrogen a diver breaths giving longer bottom times and an increased margin of safety.

As a NITROX diver you join the elite group of mixed gas divers who are interested in safety and increased bottom times!  NITROX divers require a NITROX certification.  You can get a NITROX certification by taking the SSI NITROX Specialty Course from Chesapeake Bay Diving Center.  You will learn the benefits of using NITROX and how to plan your dives using NITROX in the range of 22% to 40%.  Note that NITROX divers are required to show proof of NITROX certification when getting NITROX fills.

NITROX gives longer bottom times and larger margins of safety - for example:

Using the SSI Combined Air/NITROX tables, a first dive to 63 feet using air gives 40 minutes of bottom time.  But that same dive on 32% NITROX gives 70 minutes of bottom time.  So if we stayed down for 35 minutes on air, we would be only 5 minutes away from the No-Decompression Time Limit.  But, on 32%, we could stay down another 10 minutes say, and still be 25 minutes away from the No-Decompression time limit.  Again, longer bottom times and more safety.

Do you have a dive computer that is NITROX ready?  Then bring it to class and our instructors will assist you with configuring your dive computer for your NITROX dives.  Don't have a NITROX-compatible dive computer?  Then let us show you our line the state-of-the-art dive computers that are 100% NITROX compatible. 

Do you own a dive computer but are not confident that you really understand how to use it?  Take our SSI Computer Specialty class!  See our schedule of NITROX and Computer classes.
NITROX Frequently Asked Questions
  1. What is NITROX?
  2. Why would I want to dive with it?
  3. What is a NITROX Certification?
  4. Does it smell or taste different that regular SCUBA air?
  5. What happens when I pick up my NITROX fills?
  6. Can I use NITROX with my current regulator?
  7. Why does my cylinder need to be O2 Cleaned?
  8. Can I still get an air fill in my NITROX cylinder?
  9. How do you make NITROX?
  10. Does it cost more?
1.  Simply stated Enriched Air NITROX (EAN) is any percentage of of a Nitrogen/Oxygen mix that contains more oxygen that air.  A standard NITROX mix is EAN 32.  EAN 32 means that the gas mix in your cylinder would be 32% oxygen and about 68% nitrogen.  Air is 21% oxygen and about 79% nitrogen.  
  2.  NITROX offers longer bottom times and increased levels of safety when used properly.  For example, according to the US Navy Doppler tables, Your No-Decompression time limit on a dive to 75 feet is 30 minutes.  EAN 32 allows 50 minutes at 75 feet.  That is a 60% increase in available no-decompression bottom time.  So if you carry enough gas to make the EAN 32 dive to 75 feet for 35 minutes, you have increased your bottom time and still had 15 minutes left as a margin of safety.  You haven't pushed your bottom time close to the no-decompression time limit!  Absorbing less nitrogen is better!  Note that some dive instructors use EAN 36 or EAN 40 when teaching open water class to minimize their nitrogen exposure over a long day of diving with several groups of students.  
 
  3.  NITROX divers must be certified to use NITROX as there are some risks that the NITROX diver must understand.  NITROX certification primarily focuses on learning to plan dives with NITROX mixtures ranging from EAN 22 to EAN 40.  Proper dive planning is very important to minimize risk.  
 
  4.  Both oxygen and nitrogen are odorless and tasteless gasses.  You cannot tell the difference between regular breathing air, EAN 32 or 100% oxygen.  This is one of the biggest risks to diving NITROX since you cannot tell what percentage of oxygen or nitrogen you are breathing.  NITROX certification includes learning how to operate a simple oxygen analyzer to measure the percent of oxygen in your cylinder.  The MEASURED oxygen percentage is used to plan and execute your dive plan.  
  5.  A NITROX diver must show proof of certification.  At CBDC, NITROX divers will be asked for their NITROX cert card when bring their cylinders to the shop for a fill.  With the diver's permission, we make a photocopy of the divers NITROX card for our NITROX log book, just in case the diver forgot the card another time.  The diver measures the oxygen content of their mixture with the analyzer provided by the shop, or witnesses the analysis made by one of CBDCs certified NITROX blenders.  The serial number and O2 percentage for each cylinder is then entered into the CBDC NITROX log book and is signed off by the diver.  This sign-off shows that the diver has analyzed or witnessed the analysis of their NITROX mix.  
6.  SCUBA regulators fall into several categories of NITROX use, all based on the manufacturers specifications and warranties.  Some older regulators cannot be used with NITROX at all, or else the manufacturer's warranty is void.  Some of these older regulators can be upgraded for NITROX use by O2 cleaning the regulator and replacing all of the rubber o-rings and seals with NITROX compatible o-rings and lubricants.  Most newer regulators are certified by the manufacturer for use with NITROX up to EAN40.  Regulators for use with NITROX mixtures above 40% are designed to be compatible with 100 percent oxygen.  If you have questions about your gear, consult the manufacturer for guidance. 
7.  O2 cleaning prepares a SCUBA cylinder,  valve and o-rings for use with NITROX.  Cleaning is necessary because, depending upon the filling method, your cylinder may be exposed to high pressure oxygen at concentrations greater than 40% and typically up to 100% during a NITROX fill.  O2 cleaning removes hydrocarbon particles that may be in the valve or cylinder left there from regular SCUBA air compressors that deliver Standard SCUBA Air. Standard SCUBA air is perfectly good for breathing but is not compatible with increased levels of high pressure oxygen. The air compressors used at CBDC have special hydrocarbon filters and deliver what is called "Oxygen Compatible" breathing air.  O2 cleaning is described on the Equipment Service page.
8.  You can still get air fills in your NITROX cylinders provided that the air is Oxygen Compatible grade air.  O2 compatible air is similar to SCUBA grade air with the important exception that there are far fewer hydrocarbon particles allowed in the air.  Hydrocarbon particles can spontaneously combust when exposed to the conditions possible in a cylinder during a NITROX fill.  This is obviously bad for two reasons.  One reason is that if a fire starts, the NITROX blender risks severe injury.  It is possible also for a hydrocarbon particle to combust but not continue to burn.  This event would not be detected by the blender and could introduce carbon monoxide into the mix.  CO is an odorless, tasteless gas that is poisonous on the surface and even more so under the water.

9.  NITROX fills are made in one of several ways.  The most popular method is partial pressure blending (PPB).  During PPB, USP (medical grade) 100% oxygen is first pumped into the cylinder, the amount based on the percentage of NITROX desired.  O2 is pumped in at a very slow rate to prevent fires (50 psi per minute or less).  Once the O2 is in, then the cylinder is topped with O2 compatible air at 50 psi per minute or less until the O2 is diluted, then no faster than about 300 psi per minute.  The advantage of this method is that any NITROX mix can be made.  Note that you have to be certified in Advanced NITROX to get fills in the EAN41 to EAN 99 range.

Some live-aboard boats and remote diving locations use a membrane system where air is first pumped at low pressure (500 psi) through a special membrane system and nitrogen is filtered out.  Output from the membrane can be up set for up to EAN40.  The EAN is typically pumped through another compressor to boost the pressure up to SCUBA cylinder pressure of 3000 psi.

Continuous blending injects 100% oxygen directly into the compressor's intake air stream where it is first mixed then sent into the compressor at the desired EAN.  This method increases the maintenance on the compressor and typically is not advised by compressor manufactures and can void compressor warranty. 

In some cases, high volume shops will "bank" a large amount of a standard NITROX mix to speed the filling of individual cylinders.  This is sometimes referred to, for example, as EAN 32 "on-tap".  This method has a large initial cost due to the amount of storage required and that additional booster pumps must be used to fill SCUBA cylinders to the proper working pressure, i.e. 3000 psi, as the bank pressure drops.  An O2 compatible Haskle Pump can cost up to $10 grand!
10.  NITROX fills are typically almost three times the cost of an air fill due to the increased labor and equipment required to make NITROX fills.  By joining the Chesapeake Bay Barracudas chapter of the Club Aquarius, you can receive three free NITROX fills!