Oxygen Analyzers

Many divers benefit from using nitrox when diving for extending bottom times or shorter decompression intervals. There is potentially a safety benefit for using nitrox, however this has not been demonstrated with statistical significance due to the relative number of divers who have experience decompression illness on nitrox compared with air.

Analyzing the oxygen content of gases is critical when using non-air breathing gases. Gas analysis is performed by each diver themselves at a good scuba shop fill station when the cylinders are filled, and again at the dive site on the day of the dive. For this reason, a portable oxygen analyzer should be part of a divers kit. Several types of analyzers and their advantages and disadvantages are discussed below.

All analyzers must be calibrated before they are used to analyze an unknown gas mixture. The measurement must be performed on a known reference gas, e.g. a cylinder of pure oxygen or regular air, and adjusted until the analyzer is in agreement. The analyzer can then be used again immediately on the test gas under identical ambient temperature and pressure conditions, and gas flow rate.

Types of oxygen analyzers

Analyzers are typically available as cheaper handheld units, or more expensive systems that can also measure other gases, e.g. helium content in trimix for very deep dives. Handheld units are sufficient for recreational nitrox diving provided that they are used according to the manufacturers instructions. The oxygen percentage is measured to one decimal place, e.g. 32.1 %, but rounded up to a whole number for use in dive tables, e.g. 33 %.

A handheld oxygen analyzer.

Other features that are available for more expensive systems are attachments for DIN/yoke valves, flow-rate limiters, inline pressure gauges, a hardwired power source and thermal sensors.

Dive shops will typically have a pressure gauge and flow rate limiter for ease of use, allowing the diver to verify the cylinder mixture and pressure in one operation. The flow rate limiter will provide a consistent flow rate from a high pressure source that can be tuned to the optimum rate for the analyzer, and so is consistent when measuring the known reference gas and the gas under test.

A hard power source removes the need to replace batteries. A thermal sensor can be used to measure the cylinder temperature to provide a more accurate reading, but are not commonly used in practice.

A multi-gas analyzer.

How oxygen analyzers work

The heart of the analyzer is a galvanic cell that acts as the detector.  The cell has an exposed membrane and a port to connect to the analyzer electronics. When oxygen in the surrounding gas contacts the membrane it reacts chemically producing an electric current and consuming the fuel in the cell. For this reason cells have a limited lifetime and are disposable.

Disposable galvanic cells for different analyzers

The more oxygen that is present in the gas, the more current is produced. The job of the analyzer is to measure the current and infer the percentage of oxygen that is present in the gas. It is therefore critical that the analyzer is calibrated with each use (or according to manufacturer instructions) so that this calculation remains accurate. Like all sensors, they are designed to work with sufficient accuracy under a range of conditions, like gas flow rate, ambient temperature, and with “normal” gases. Old cells will have the galvanic fuel consumed, and will not be able to produce as high a current, and so can only read up to a maximum oxygen partial pressure that degrades over time. A new cell might be able to read up to 2.0 atmospheres (ata), but fall over its lifetime.

At sea level a mixture of 100 % oxygen will produce a partial pressure close to 1.0 ata, and the degradation will not be noticeable for a few years with normal use and conditions. However, this is a concern for applications where hyperbaric oxygen is present, for example in a rebreather with 100 % oxygen at a depth of 20 feet where the oxygen partial pressure must read 1.6 ata. Hence oxygen sensors in handheld analyzers have a much longer useful lifetime than in rebreathers.

The oxygen sensor is a current source, but this is converted into a voltage in millivolts (mV). This reading is often available on an analyzer, and will also degrade as the sensor ages. The normal range is available from the manufacturer, e.g. 7–14 mV for air at sea level on a Teledyne R-17 sensor.

Best practices

  1. Keep new cells sealed in their plastic packaging until they are installed.
  2. Do not use new sensors immediately after unsealing, wait at least 30 minutes for the sensor to acclimate to the ambient pressure and temperature in case the packaging conditions are different.
  3. Only use oxygen sensor cells specific to the analyzer specifications.
  4. Label the install date on the sensor cell in permanent marker when it is removed from  its packaging.
  5. Discard sensor cells 3 years from the date of manufacture, or 1 year from the date of opening.
  6. Always calibrate the analyzer against a known gas source with the correct flow rate.
  7. Label analyzed cylinders appropriately immediately after being filled.
  8. Reanalyze (and calibrate!) cylinders again on the day that they are used to verify the mix.
  9. Store analyzers in a dry environment close to room temperature.
  10. Dispose of used batteries and sensors properly, away from water sources.

Further reading

NAUI Advanced Scuba Diver

 Class Structure

The class consists of one classroom session and six dives in open water.

All participants should be a minimum 15 years old and a NAUI Scuba Diver or equivalent. Divers should have recent experience in similar conditions to their training, and have all gear serviced in its normal maintenance period as specified by the manufacturer.


To participate in the NAUI Advanced Scuba Diver course, each diver must have access to scuba diving equipment, either rented or owned. Any equipment that is not rented must be approved for use by the Instructor, and be serviced within the past two years for buoyancy compensators (BCs) or regulators.

Special additional equipment that is needed is a cutting device, flashlight and cylinder light.

Gear considerations

Every piece of equipment that is taken diving should be make specially for diving. Repurposed general equipment is typically not waterproof, corrodes easily in marine environments, can be difficult to attach or to use underwater with thick gloves.

You should always label your dive gear with some identifying mark. It is likely that you will lose some piece of equipment at some point, and the chances of it being recovered and returned to you are much improved. Labelled gear makes it much easier to identify your own gear on a boat or gear wash tub.

All gear should be streamlined on the divers rig. Consider where it would be attached to the diver so that is does not dangle and impose an entanglement hazard or a risk to precious formations like stalactites or corals.

Pay attention to how well the devices can be attached to your gear, and how secure they are in sheath. You don’t want to lose a poorly attached piece of equipment in rough surf, and you need to be able to reach and deploy it on the surface or underwater in a trim or vertical position. The addition of full gear for an actual dive can greatly change the accessibility of gear when you add weight pockets, other devices or tighten straps down for diving. Would you still be able to reach your gear in an entanglement?

Most scuba BCs are constructed with 1″ or 2″ width webbing for the straps. It is helpful to know the construction of your BC. If in doubt, take your gear to the shop to try various configurations before you buy.

Carry spare batteries in your save-a-dive kit so that you are not affected by a failure before or between dives. Check all your gear in your pre-dive checks that it is present, deployable and working.

Cutting device

The cutting device is used to remove entanglements like kelp or fishing line, and for removing a diver’s buoyancy compensator straps or wetsuit in an emergency. Only one cutting device is required and should be in an accessible location. Typical locations on the waist strap or BC inflator hose. Many BCs have attachment points on the integrated weight pockets.

DeviceMounting PointAdvantagesDisadvantages
Dive KnifeWaist strap, inflator hose, computer wrist strap, inner calf.Can have a sharp or blunted tip to prevent accidental puncture of the BC, Mounting location should consider ease of sheathing underwater after deployment.
ScissorsWaist strap, inflator hose.Prevents accidental cuts and punctures, easy to safely remove a wetsuit from a victim, useful as a general tool.Bulky.
EZ CutWrist computer strap, waist strap, inflator hose.Easy to deploy and sheath, prevents accidental cutting, velcro system prevents loss, small and easy to carry multiple devices.Blades need to be occasionally replaced due to corrosion (comes with spare blades).



A safety knife with sheath.

A safety knife is small and streamlined, and easy to use underwater. The protected blades prevent accidents and velcro on the tab keeps is secure in the pouch. The pouch should fit most 2″ webbing.

Dive scissors with sheath.

Although bulky, scissors are easy and safe to use on land an underwater. They can be convenient for dive rescues when a diver needs to be removed from an exposure suit quickly or without aggravating a neck or spinal injury due to the bent blades.

A small dive knife with serrated edge, line cutter on spine and stubbed tip.

A titanium technical-style dive knife with velcro pouch.

Dive knives vary in size, can can have a straight or serrated edge, a notched line cutter, and a pointed or blunted tip. Small dive knives are usually sufficient. Technical-style knives are tyipcally thin and light for streamlining and reducing additional weight. Some knives are titanium so they do not corrode. The pouch should be tested to ensure the knife is well secured to prevent loss.

Dive lights

Most modern dive lights are LED due to their high intensities, long burn time and small size. Lights can be rated by number of Watts (amount of power consumed), lumens (total light output) or lux (density of light per square foot). They are not directly comparable without knowing a lot about the LED bulb(s) and the geometry of the output light beam. However, many manufacturers have settled on lumens.

Divers considering specialized forms of diving in the future, like cave or wreck, or decompression diving should consider equipment appropriate for technical diving. For example, a primary dive light for recreational diving that can be used as a backup light in technical diving.

Lights, more than other equipment, can be very bulky and hang precariously from a divers body when stowed. It is advantageous to have be hands free by using a hard goodman handle, or a short leash for securing the light to the body.

Considerations for a dive light should include sufficient burn time for the intended dives, e.g. 1–2 hours, and the type of beam. Flood lights are undesirable unless using as a video light to illuminate a scene because they can easily blind dive buddies. A narrow beam of 10–15 degrees is good for creating an intense spot for communication, with a wider spill area that is less intense.

A magnetic switch on lights prevents underwater flooding. Lights that use a twist action to turn the light on or off should be double o-ringed for additional flood protection. All lights should have a means to closely attach to the divers gear when not deployed.

Light options are discussed on the Technical Gear page.

Cylinder lights

Cylinder lights are used so that you can easily locate your buddy, especially if their primary light fails, or if they are partially obstructed. If it is possible different colors can designate teams or buddy pairs if multiple teams are in the water at the same time. Cylinder lights are often a requirement in dive tours when a guide is responsible for a large group of divers. Chemical lights are mounted around the neck of the cylinder or the BC cylinder band so they float above the diver or behind their head when in the water.

An LED cylinder light.

LED cylinder lights could be a fixed color, or have multiple colors that can be chosen at the start of the dive. Batteries typically last many dives before needing to be replaced.

A disposable chemical cylinder light.

Disposable chemical lights are single use, and work like typical glow sticks where a glass chamber is broken to activate the chemical compound. One use typically lasts multiple dives. For limited use they are the cheapest option, but contribute to plastic waste.


Technical Gear Chart

The following table shows gear required for NAUI Intro To Tech and NAUI Technical Decompression Diver, and shows gear available for rent at Pro Scuba Dive Center (PSDC).

NAUI Technical Decompression Diver is available for diver progression after NAU Intro To Tech. Gear requirements are shown below.

For detailed descriptions see the Technical Gear (Intro To Tech) post.

ItemIntro To TechTechnical Decompression DiverPSDC Rental
Double cylindersRequiredRequiredYes
Longhose regulatorsRequiredRequiredYes
Necklace regulatorsRequiredRequiredYes
Timer, depth gauge or computerRequiredRequired
Redundant computerRecommended
Cutting deviceRequiredRequired
Primary light on hard goodman handleRecommendedRequired
Backup lightsRecommended
Spool and DSMBRequiredRecommended
Primary reel and liftbagRequired
Secondary reel and liftbagRequired
Oxygen stage cylinder with labels gauge and regulatorRequired
Straight finsRequiredRequired

Technical Gear (NAUI Intro To Tech)



NAUI Technical Equipment Configuration (NTEC)

The minimum equipment requirements for NAUI classes are summarized in the NTEC Guide. These are broad requirements.

Course information is available in this Overview.

Specific equipment requirements for the Intro To Tech class are summarized in this Checklist. The post below provides more information for consideration.

More gear is required for NAUI Technical Decompression Diver. For a quick overview and comparison to NAUI Intro To Tech, see the Technical Gear Chart post.

It is not recommended to purchase diving gear until you have determined your needs in a class. Discuss any diving gear purchases with your instructor. Pro Scuba Dive Center offers technical dive gear for rental as part of a NAUI Tec dive class.

The following gear is available for rent:

  • Double cylinders
  • Backplate, wing and harness
  • Regulators (long hose, short hose, inflator, drysuit hose, gauges and attached swivel snaps)


First Stage Regulators

Required. Two high performance first stages (one for each cylinder in doubles). Scubapro Mk25 are common due to their excellent performance, build in swivel, and 5th low pressure (LP) outlet on the base, making hose routing easy. NTEC requires a DIN valves and regulators (not the more common yoke valves). DIN adapters should not be used because they introduce another failure point and increase the regulator profile.mk25evo-din


Scubapro Mk25 first stage regulator with 5th port.

Second Stage Regulators

Required. Two second stage regulators are also required, the primary high second stage on a 7’ rubber hose (long hose), and the secondary a 22” rubber hose (short hose) with bungee attached. Both regulators should be high performance regulators.
Miflex hoses are not recommended due to buoyancy differences and tangling on the long hose.s600-2013


S600 second stage regulator.



G260 second stage regulator.





A700 second stage.


A bungee necklace to secure the secondary short-hose second stage.



Required. Solid metal (not plastic). Steel is recommended for a single cylinder. For doubles aluminium or steel are fine depending on ballast requirements. Check with your instructor if you are unsure how to weight yourself for doubles. The backplate must accommodate a continuous webbing.

A optional storage pack can be added to store a lift-bag.



An aluminium backplate.




A steel backplate with cover.


Required. NAUI recommends 55 lb lift capacity for doubles, but the smallest possible is best. A smaller 40 lb might be sufficient depending on ballast requirements. Proper sizing will be covered in class. No bungee on the wing. Wing can be horseshoe or doughnut shaped, but doughnut wings have the advantage of being able to easily shift an air bubble from side to side (or to the dump valves) in a slightly head down position. As a rough guide a 40 lb wing might be sufficient for double 80 ft3 or double 100 ft3 cylinders, but a larger 60 lb wing might be required for double 120 ft3 or 130 ft3 cylinders.

Contact your instructor to help appropriately size the wing. It is not recommended to purchase a wing until ballast requirements are known.

The inflator hose should be approximately 22″.


60 lb doughnut wing


60 lb horseshoe wing with illegal bungee.


Thermal protection

Required. A drysuit is required for steel doubles due to the negative buoyancy characteristics of the cylinders. Extended dive times also increase thermal exposure with long dive times. Divers should train in the same exposure suit used in open water. An advantage of trilaminate drysuits vs crushed neoprene drysuits is that they allow for lots of undergarments, and do not perceptibly change volume with depth. Care should be taken to find fins that fit the boots. Additional storage in two thigh pockets are a major advantage.


A trilaminate drysuit with kevlar kneepads and cargo pockets.


LP hoses

The following hose lengths are should be used as a guide for a person of average height, approximately 5′ 10″.

  • 7′ hose for primary second stage regulator (“long hose”). Shorter people might be more comfortable with a 6′ hose.
  • 22” inflator hose for wing inflator
  • 30” drysuit inflator
  • 24″ SPG hose

Pressure gauge

The SPG must be made of metal (not plastic) and attached to a short rubber hose (about 24”). The SPG will be tied with a swivel snap.


Required. Solid stiff fins are recommended to perform technical finning techniques. Fins with a broad side are recommended in order to back-kick. No split fins. Spring heel-straps are highly recommended.


Scubapro Jet fin


Required. A low-volume mask is recommended. A neoprene slap-strap is recommended to make donning and doffing easier. No snorkel is to be attached, but a folding snorkel can be work in a drysuit cargo pocket if desired. A spare mask carried in the drysuit pocket is recommended.


Required. A few double-ended bolt snaps and swivels are required to secure gear. Snaps must be made from marine grade stainless or brass. I recommend marine grade stainless because the springs are typically more corrosion resistant and easier to operate. Double-ender bolt-snaps are usually 3.5″ or 4″ long, I recommend 3.5″. The smallest 3″ swivel snaps can be hard to operate with thick gloves, 3.5″ swivel snaps are common in cold water. The largest 4+” swivel snaps are usually used to secure a stage or decompression cylinder. Butterfly snaps are forbidden due to being able to be accidentally clipped and entangling the diver.

At least two double ender snaps:

  • Finger spool
  • At least one spare
  • Liftbag (not required for Intro To Tech)

At least three swivel snaps:

  • Long hose
  • Pressure Gauge
  • One per light (minimum of one light)


Double ender bolt snap, and 3 sizes of swivel bolt snaps.

butterfly snap

Forbidden butterfly snaps.


Recommended. Wrist mounted on the right. It is preferable able to read seconds (not just minutes). Most Scubapro  computers can do this in gauge mode, or cycling through the alternative display. The solid strap is typically replaced with bungee. A bottom timer and depth gauge can be used in place of a computer. Either a bottom timer and depth gauge, or a computer, is required.


Wrist mounted dive computer.


Required. Wrist mounted on the left. Technical divers will typically remove the strap and secure the compass with bungee through the mount holes to prevent the strap from becoming loose with depth compression on the exposure suit. Console compasses can typically be converted to wrist-mounted with a different housing or adaptor.fs1wrist_compass_left

Wrist mounted compass.


Required. At a minimum each diver will have one 100 ft spool and 3 ft yellow DSMB.

At the NAUI Decompression Diver level and above two surface marker devices are required. At least one much be a reel and lift-bag, the other can be another lift bag, or a spool and delayed surface marker buoy (DSMB). A liftbag is used for redundant buoyancy in case of wing rupture.

Some dive teams will designate a color for inflation device, typically yellow is the “normal” color and orange or red is the “emergency” color.



A reel and liftbag.



A spool and DSMB.



Required. Back-gas cylinders can be steel or aluminium, all deco and stage bottles may be aluminium only. Some doubles divers prefer alumimium cylinders or low-pressure steel cylinders because the additional cylinder volume can assist diver trim, and the reduced weight can relieve strain on the divers body, however a minimum amount of ballast will be needed in cold water diving, and will likely need to be added to aluminium cylinders anyway.


Double steel cylinders with bands and 300 bar manifold.


Required. One light is required. Is is strongly recommended that the primary light is attached to a hard goodman handle, even if it does not have a power cord and canister battery. Two lights or more light are recommended (one primary light and at least one backup light). Even when not diving in an overhead environment, lights are useful as a communication tool.

The primary light should be either attached to a hard goodman handle (preferred), or a long handheld light with a swivel snap secured to the base. Pistol-grip lights are too bulky and not streamlined.

Backup lights (optional) should be a long handheld light with a swivel snap attached to the base.

best-divers-goodman-handleA hard goodman handle.

Canister lights (not required) are used as a primary light for higher intensity light and longer burn times. Canister lights are recommended for longer duration dives and overhead environments.  If available in class techniques will be taught to avoid entanglement with the light cord. A cord length of 35 inches is recommended as a nominal length, but should be comfortable on the diver. The canister light is attached to the right hip and the cord should reach the left hand with the left arm outstretched.

Canister light

A LED canister light with goodman handle.

A narrow beam angle (approx 10 degrees) is recommended to produce a spot beam for communication. This is important in overhead environments.


Handheld light.

A handheld light is appropriate for the NAUI Intro To Tech course. In more advanced diving where a canister light is required a narrow handheld light can be attached to the harness as a backup. The light should have a hole for a lanyard or other attachment that can be used to attach a swivel bolt snap.

Cutting device

Required. At least line line cutting device is required. A cutting is typically worn on the left waistband or inflator hose. A cutting device can be a knife, surgical scissors or a safety knife.


A low profile titanium dive knife with waist pouch.

Portable table

Recommended. Having a strong, collapsible, portable table is useful for gearing up in training or shore diving. Relatively cheap tables are available from hardware stores, such as the Husky X-Workhorse Workbench.

husky x workhorse openhusky x workhorse closed

A foldable dive table.