Hypoxia Experiment

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In 1997, members of the U.S. Deep Caving Team were preparing for a ground breaking project at Wakulla Springs. We had shiny new Cis-Lunar Mk5P rebreathers but little formal instruction. We were all test pilots in those days. tWe decided that we wanted to know what hypoxia felt like. Would we be able to detect it in time to bailout? Would we be incapacitated even after bailing out? Were our heads better than the audible and visual alarms that were supposed to protect us?

We set up a simple experiment in a classroom in Hudson, Florida. With an oxygen kit in hand, we intentionally cut off the oxygen supply to the rebreather and let the diver choose when to bail out. What we learned was that you should never try to repeat this experiment. In the face of hypoxia, you may not be able to revive the stricken diver.

We hope you learn that you should follow good protocols to prepare your rebreather including a proper pre-dive checklist. Prevention is the best action you can take. In the event that you experience an odd feeling on a rebreather, immediately bailout to open circuit gas or flush the counterlungs with breathable diluent. With fresh diluent* or open circuit gas you have bought time to figure out how to handle your emergency.

*Please note that CO2 emergencies can ONLY be solved with open circuit bailout. Diluent flushes do not solve CO2 emergencies.

Original footage supplied by Andrew Poole.

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Shearwater Petrel Calibration Tip

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Calibration Errors on a Shearwater Petrel

Q. I’m trying to calibrate my unit. The HUD shows 1.0 with green and yellow rows of lights. I have fully flushed with oxygen. The handset reads .97, .98 and 1.00 already. The millivolts on the first screen look right and are in range. What is it failing calibration? Looking at the failure screen the millivolts are off the charts, each reading over 200? What’s going on?

A. Check your System Settings. Ensure the Calibration O2 is the correct value. After a battery failure, numerous parameters in your computer such as “units” reset. Your cal gas might be registered at 0, rather than .98. Check that value. Once you reset it, the calibration will likely pass.

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More Tips for Traveling with Rebreathers

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Mask, fins, rebreather and you are ready to go, right? There are many small items that you might not think about that can ruin a trip in their absence.


Inquire about the local power supply. As an example, Mexico has the same current as the US, but many wall outlets do not have grounding plugs. You will need to purchase “cheaters” that convert your three-prong plugs to two-prong. Power strips are worth their weight in gold since wall outlets may be few and far between. In Europe, recessed wall plugs may not fit the fancy converter you bought at the airport. Those converters also often lack a hole for the grounding plug, making them impossible to use without the “cheaters” mentioned above. Many chargers are already rated for 120 and 240v power supplies. Do not waste converters on these devices as they are not needed.


Disinfectant may be challenging to take to your destination. Steramine tablets are very convenient for travel since they are dry and will not spill in luggage or take up precious weight allowance. If you have forgotten to pack Steramine, Betadine is relatively easy to find in foreign pharmacies (though a few people are allergic to Betadine). Dilute it in a tub to soak your breathing loop. If you are camping on an expedition, use one of your shipping cases as a bath. If you cannot find Betadine, Listerine will get your through a trip with reasonable cleanliness, but it does not kill all bacteria. Use proper disinfectants as soon as available.


You can never give enough credit to duct tape. It can repair an awful lot of damage in a difficult situation. I always carry some on trips, but rather than taking a heavy roll, I just wind a few yards around a business card for a small supply. A product called “Rescue Tape” is also fantastic. It is made of clear silicone self-binding tape. It does not have a sticky backing, but instead, bonds to itself in mere moments. It is extremely useful.


Clear plastic Ziplock bags allow you to neatly separate and pack gear so that it does not get lost during inspections. If you simply roll your DSV in your pajamas, the screener is likely to pick up the garment and send the sensitive device crashing to the floor in pieces. Slide delicate items into dive boots and fin pockets. Tape them in place or put them in a Ziplock bags if necessary.


Always make a photocopy of your critical personal identification like your passport and carry it separately in case of loss. Consulates can easily assist if you have back-up documents. Also hand-carry documentation about your rebreather and MSDS sheets for sorb or any other questionable items. Be prepared to share this information with screeners.


Place a friendly letter in your rebreather case that describes the device. Indicate on your letter that all parts are “safe for airline transport on passenger aircraft.” Invite the TSA screeners to contact you via cell phone and even offer up your seat assignment if they need it. Leave a photo of yourself wearing your CCR with a big smile in the case. It helps them to quickly understand what they are looking and let’s them know you are trying to be safe and compliant.

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Travel by Boat of Car with Your CCR

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When using a car and boat, your dive destination may be a lot closer to home, but there are still a few special tips to consider.

  • Bring extra bungee cords for boat travel. Many boats are specifically constructed for single tank divers. The benches may be awkward for a rebreather diver. Bring your own method of securing the rebreather to the bench or the floor.
  • Consider the orientation of your rebreather scrubber. If your rebreather is lying on its back, vibrating on a moving boat or in a car for hours, will your particular canister design be subjected to drastic settling? Some canister designs are equipped with springs that help to resolve settling issues, but if the orientation of the rebreather in relation to the settling forces is incorrect, you could get some channeling of material.
  • Fully assemble and check your rebreather before leaving the dock. You don’t want to be packing sorb on a bouncing boat and also don’t want to capture diesel fumes within the breathing loop.
  • Beware of extreme heat. If you gear is sitting sealed in a hot car for a long period of time, you can damage the oxygen sensors.
  • Beware of extreme cold. If your packed rebreather sits in a freezing car overnight, the moisture in the sorb can freeze causing damage to the canister and dusting in the material itself.
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Test Your Knowledge – PO2 Drop

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Question: You are swimming along the deck of your favorite wreck. For some reason your PO2 is dropping, causing frequent oxygen injections to catch up to your stepping. You keep dumping gas. What’s going on?

Answer: It is possible that you have a leak in your ADV that is causing small amounts of gas to sneak into the counterlung. If your rebreather has a manual diluent injection button, that could also be leaking. Failures always require you to abort the dive, but you can diagnose the problem on the dive boat by removing and replacing the diluent connections to the counterlung or ADV if your rebreather will allow. If fixing those connections does not help, then you may be in need of service on your diluent first stage.

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Full Face Masks and Rebreathers

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DSCN4492I recently published this short news item in the “In The Loop” newsletter I wrote for Hollis. It examines their efforts to build full face masks for rebreathers.

At the international RF3.0 (Rebreather Forum 3.0) event in 2012, delegates unanimously agreed that further study off FFMs was warranted by the industry. As a result, Hollis launched a challenging investigation and design process, while training agencies PADI and TDI decided to begin curriculum development for programs to train CCR users in the safe use of FFMs.

Full face masks (FFMs) are specialized enhancements that should only be used by  experienced CCR divers after completion of advanced training. Filmmakers sometimes use FFMs to capture clean vocals when shooting underwater and commercial divers use them for routine communications. FFMs may provide the benefit of airway protection in the event that a diver loses consciousness, but most people choose to use them for easy and enjoyable communication with their dive partner. Before you jump in to a FFM, it is wise to look at the design and training factors that engineers and educational designers are currently considering.


  • Easy vocal communications within the dive team
  • Ability to record audio for films
  • Warmth and environmental protection
  • Potential to save an unconscious diver


  • Challenges of fit
  • Unique procedures for clearing
  • May use significant gas volume to clear
  • Special adapters needed to connect to different rebreathers
  • Range of motion and peripheral vision limitations
  • Potential for carbon dioxide dead space
  • Developing procedures for dealing with failures
  • Designing procedures and devices for redundancy

Stay tuned! We’ll see what the industry has in store for divers that are interested in talking underwater!

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Rebreather Workshop in Dallas – January 24

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Rebreather Fundamentals Workshop – Saturday January 24 from 8am – noon_JEH3825l

at Our World Underwater – Dallas

Classroom session: $75

Tickets available online at:


(space is limited)

Enjoy a half-day academic session with CCR expert Jill Heinerth. Using fascinating stories and a multimedia presentation, Jill will cover all the essentials of rebreather diving.

If you are looking to purchase a rebreather, this is an opportunity to learn how to be a wise consumer and make the choice that is right for you.

If you already own a rebreather and want a review of academics, new trends and the future of CCR diving, then this seminar will offer an opportunity to gather new information.

If you want to prevent yourself from joining the ranks of 20 or so people who perish each year on rebreathers, this workshop will inform you about accident analysis and prevention.

If you want a half day in a small group with an expert who will carefully answer your questions and help you find solutions, then this is your best opportunity to spend time with Jill.

If you want to see how rebreathers are being used in exciting expeditions around the world, this full-day road show will entertain and motivate you to participate in CCR diving.

The workshop is non-denominational… all training agencies and all manufacturers are welcome. All levels of divers are welcome from recreational through technical divers.


Rebreather operations and procedures

Basics, types, operation and essential care

Selecting a rebreather: comparing apples and oranges

Selecting an instructor

Understanding CE testing

Myths and misconceptions about rebreather diving

Carbon dioxide: dangerous and ignored

Reducing oxygen issues

Planning for the future: deep mixed-gas operations

Accident analysis and prevention: beating the complacency trap

Traveling with rebreathers: tips and warnings

Lots of time for questions!

Bailout Bottle Trim for Rebreathers

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A Lesson from Sidemount Divers


Sidemount diving has taken the diving community by storm. The popularity of this style of carrying tanks has grown tenfold in the last few years. Now rebreather divers are taking a lesson from sidemount divers to help them streamline their bailout bottles. Standard stage rigging generally hangs bailout tanks nearly perpendicular to the diver’ s body. This is neither streamlined nor conservation-minded. It is far more effective to mount your tanks in a way that aligns them with your body. There are numerous ways to achieve this, but here are two simple solutions:

1. Use your SMS 75 or SMS100 sidemount harness on your rebreather.

SideBungeeKnot9054l2. Make your own simple sidemount bungees: – Take a length of heavy bungee cord (approximately 18 inches) and place a knot in one end. – Thread the bungee cord through a hole in the backplate of your rebreather. Use a hole on the edge of the plate, halfway down or roughly below your scapula. The knot should be on the back side of the plate so it does not press into your shoulder or back.

3. Loop the free end of the bungee through the ring of a small bolt snap or other type of clip and secure it to the clip with two zip ties.

4. Clip to the lowest shoulder D-ring on your harness.

5. Place a butterfly D-ring on your crotch strap or use a butt plate (as shown in the photo) for the lower tank attachment point.

6. Mount the lower bailout bottle clip on the tank roughly 180° opposite from the tank valve hand wheel.SideBungee9055l

7. Use the bungee to snug the tank close to the body by looping it over the tank valve so the tank tucks into your armpit region.

8. Move the knot to shorten or lengthen the bungee and adjust for size.

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Interview with Nick Hollis

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JillRPOVJoe Cocozza, DIVER Magazine and PodDiver Radio Host interviews Nick Hollis about the Explorer rebreather.

Click here for full interview.


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$1500 Training Credit for PRISM2 Buyers

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Dive Rite In Scuba is offering an exciting promotion this month. They are offering a $1500 training credit for buyers of a PRISM2 rebreather and $1000 for training when buying an Explorer. If you want to jump in on this really terrific deal call the shop at 815-267-8400 or email  Mike@diverightinscuba.com.




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