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Inspiration Advocacy

A rebuttal of George Irvine's "Buddy Inspiration or Expiration?" article.

GI3's rather infamous, and now somewhat dated, article on the Inspiration comes up in the group every so often and gets knocked back again. The following was collated by Dominic Humphries from various comments posted to one of threads spawned by the article.

Georges's comments are labelled in blue, the group's responses in black. While the rebuttal information was collated from various sources, alot of it originated with Vic Watson.

Comments from the thread...

There is a small metal screw inside the oxygen sensor compartment, it is located directly across from sensor number two. Condensation often forms on this metal screw and will allow droplets to fall onto the oxygen sensors. This will happen particularly if the diver moves from side to side as in dumping gas from a drysuit or if they invert from horizontal for any reason.

This is the fixing point for the battery box. Condensation can form on this screw under high-humidity conditions (such as the end of a dive). But droplets only go anywhere near the sensors if you tip a damp unit on its back. This is why users are very cautious about how the unit is handled post-dive; it can sit upright, or it can be laid on its front without hazard.

Condensation is inherently found within this area and will form on the oxygen sensors even without this metal catalyst.

This just doesn't happen with the proper cells in place. Using cheap replacements may pose some risk, so don't use cheap replacements. The recommended cells have a hydrophobic membrane on the face and a conformal coat on the board. They are not affected by moisture.

The O2 sensors are located on the inhalation side of the breathing loop, so you have warm gas that just went through the scrubbing process meeting with cooler gas that you will inhale thus the condensation forming on the cell faces. This condensation causes discrepancies/inaccuracies within the cell readings and they begin to VOTE trying to figure out which one is more than .2 bar out of line with the other. Cell warnings will manifest within this period of time and the diver will begin to get audible and visual alarms ...task loading increases.

The voting system is not about "which one is more than .2 bar out of line with the other". A quick read through the manual will tell you this.

The unit alarms if it senses a PO2 over 1.6, which is a good thing. Problem with this is that many of the divers will run 100% oxygen at 20 ft, which is a PO2 of 1.6, if they drop below the 20 ft they get an alarm, fair enough.

Anyone decompressing on O2 mode at 6m will find it incredibly difficult to achieve 100% FO2. They will also do the same as OC divers on pure O2, and make sure they don't go below 6m/20ft.

Weight must be placed on the top of the rebreather in order to balance the trim.

Weight must be placed on ANY diving system for correct trim.

If divers put to much gas in the counter lungs the upper body is lifted and trim is then off center.

Putting too much gas in the counter lungs can cause problems, in the same way that too much gas in a BCD or drysuit can. So don't put too much gas in.

Many divers use the Inspiration to extend their times in open ocean, this in itself may pose problems. If the decompression gained by the increased bottom times is met with undesirable conditions such as rough seas it is not so easy to adjust buoyancy as with breathing open circuit.

This is why rebreather courses drum into you the concept "You are a novice again" and insist you build up your experience slowly. By the time you take a CCR into rough seas, you should be capable of dealing with them.

Many of the buoyancy characteristics involved with rebreathers require a longer learning curve and must be anticipated, if the diver is not up to par they are much less forgiving than OC. If the constant PO2 is increased or decreased too quickly due to unforeseen circumstances the diver could quickly become hypoxic/hyperoxic.

This is just wrong. It's like someone worrying about technical diving because manifolded twinsets can inject pure argon into your breathing system.

Mouthpiece does not have OC bailout built into it, bailout is a time of increased stress so it is pertinent the transition should be smooth without chance for a mistake.

The reasons for me coming off-loop are because it's flooded (with the attendant risk of caustic cocktail) or because I've chucked into it. In either case, the mouthpiece is not viable, so I don't *want* it to be part of my OC bailout.

The CCR mouthpiece has to be effectively closed before the transition to OC bailout is performed or it will flood the breathing loop making the diver negatively buoyant.

This is common to all rebreathers, even the RB80, and is a basic skill.

If the O-ring on top of the cartridge lid is dirty or not aligned properly CO2 will take the path of least resistance and bypass the carbon dioxide scrubber therefore breathed back into the loop. Hypercapnia begins and the diver is faced with another problem to solve.

This is why the pre-dive checks include making sure the O-ring IS clean.

As the diver descends they must equalize the counter lungs, if this procedure is not adhered to and they begin an uncontrolled descent the lungs collapse and the diver is not able to breath, an automatic diluent add is an aftermarket product which does combat this. But since we are talking factory here the diver is faced with equalizing counter lungs, ears, sinuses, mask drysuit, BCD, monitoring PO2 on handsets, buddy position, light and depth in the water column. It has been mentioned before that this is "a busy time".

Out of the list "lungs, ears, sinuses, mask drysuit, BCD" counterlungs are the only thing there an open circuit diver doesn't also have to worry about. And rebreather divers don't usually use a BCD, so it's a straightforward exchange of one bag of gas for another.

Inspiration does not have SS backplate and utilizes many plastic fastex clips, which some view as failure points. There are seven quick releases on the soft harness including the crotch strap and handset clips. The clips that hold the yellow casing lid on the unit break frequently so spares are required as well.

Frequent clip breakage is not a complaint voiced by any of the people who actually dive the unit.

Often difficult to transport with Sofnolime, if you do not have an MSDS on your person you will be declined, even if you do have the Material Safety Data Sheet on hand and the handler does not feel comfortable with the issue they will not let the scrubber material on the plane. Most Inspiration divers seek out `Inspiration friendly dive Centers` so they are able to obtain the wide array of parts required to service and maintain.

Divers seek out Inspiration-friendly centres so that they can hire cylinders and buy lime on site, rather than having to pay for extra baggage allowance.

The oxygen sensors are proprietary to the Inspiration, which limits the diversity on this product. Many of the CCR's will allow various types of sensors to be used but not so the case with Inspiration's and it is strongly voiced by Martin Parker.

The R22-BUDs are the only cells to have gone through the testing process, so they're the only cells approved by APD. Many divers use equivalents, but this leaves their units effectively untested, so it's on their own heads. The reason other CCRs allow various sensors is that *none* of them have undergone the level of testing that the Inspiration has - in effect, they're all at the "untested" stage.

Patrick Duffy with Oxycheq in the US sells similar sensors and says there is absolutely no difference between the Teledyne's he sells and the Inspiration sensors.

There probably isn't - a number of people run the R22-Ds with no problems. However, "probably" is all we can say - the R22-Ds have not been formally tested in the Inspiration, so they're not recommended. Where's the problem with that?

Scrubber canister is small (2.45 Kg of 8-12 mesh, 797 diving grade sofnolime) and does not facilitate the use many of the mixed gas Inspiration divers put it through. At depth CO2 breakthrough is rapid even with a resting diver, if breathing resistance is elevated the scrubber is near void. With increased CO2 build up the diver is of course exposing oneself to further malady. Diving high helium concentrations assist with this problem as it is less dense than air, easier to breath therefore less CO2 buildup and the scrubber should last longer but it is playing on the edge. High PPN2 should be ultimately avoided.

The scrubber will last three hours. The problems he lists above will only arise if you try to push the scrubber beyond its rated life. So don't push it.

If counter lungs are not situated adequately they will float above the divers shoulders and increase breathing resistance.

So situate them correctly. It involves pulling one piece of webbing each side as you kit up.

The LP hoses which feed the diluent and the oxygen inlets on the counter lungs use a different end than the BCD inflator.

This is correct. The reason is explained further down in the same paragraph:

The reason the end is different on the BCD inflator is to supply a greater amount of gas to the Auto Air regulator used as a bailout/inflation device.

This Auto Air is prone to free flow situations and can dump the diluent gas if not tended to quick enough.

Service the device at reasonable intervals and it's bomb-proof. Fail to service it, and it behaves like any other unserviced regulator. And with this particular regulator, the manufacturer not only supplies parts to anyone who asks, they supply the service manual as well (FOC last time I asked for one).

Most Inspirations divers discard this Auto Air early into their CCR career.

No they don't.

If both handsets shut off in the water the diver is faced with a series of questions in order to `reboot` the system. One of the questions ask if you would like to calibrate `yes or no` if the diver is stressed and chooses `yes` they will effectively be adding 100% oxygen into the breathing loop no matter what depth they are at in the water column.

So don't shut off both handsets in the water. In the extremely unlikely event that you do, the only questions you have to answer are "Dive now?" (to which you answer "yes", of course) and (on earlier units) "Calibrate?" (to which you answer "no"). Current units won't even ask the second question.

If the battery is low it will not supply enough EMF for the oxygen solenoid to open the valve and add life sustaining gas.

EMF is Electromotive Force - more or less synonymous with "voltage". He's wrong actually - it's current that drives a solenoid. But that's by the by - you get plenty of warning of this sort of thing happening (about a week unless you're in very cold water, in which case just a couple of days), and you've got a spare battery in the other handset to take over when it's too low. And if that one's flat as well, you've get enough life in the handset to switch to manual mode, where the solenoid isn't needed at all.

The control handsets are secured to the canister via rubber hose, the wiring is run through this conduit down to the electronic handsets that are monitoring the dynamics of the oxygen sensors. These rubber conduits enter into the scrubber/O2 sensor compartment where it is humid and if not perfectly sealed will allow condensation to migrate into the hose and wreak havoc with the electronics in the handsets.

No it won't. I'll close with a quote from earlier in his document - "I will waste all of your time with this one"