Two divers critical - Hawaii

[chris kippax]

Can someone please answer a question, I have never dived a RB and have only ever seen two in my life.
When you kit up and get into position to splash how many times would you here the solenoid fire? Would it always fire or sometimes not? What about as you splash and get ready to begin your descent? would it fire then? Is this something an experienced RB diver listens for?

 

[Dusty123]

So not all rebreathers have solenoids. The solenoid firing doesn’t indicate the o2 is on ( although if you can hear it firing alot it might indicate your o2 isnt on). Some models you might not be able to hear it fire. Typically it doesnt fire when you splash and descend at least mine wont often as youll be set to your low setpoint when you splash and descend to your target depth, wreck diving anyway. Po2 tends to stay the same or increase a bit as you go down (depending on a lot of factors). Rule number one is always know your po2.

 

[Dusty123]

whoops double post

 

[rjack321]

Can someone please answer a question, I have never dived a RB and have only ever seen two in my life.
When you kit up and get into position to splash how many times would you here the solenoid fire? Would it always fire or sometimes not? What about as you splash and get ready to begin your descent? would it fire then? Is this something an experienced RB diver listens for?

You are trained to "prebreath" the unit and watch the O2 come up automatically (on an eCCR at least) from the solenoid as well at manually actuate the O2 add valve. Then watch for the unit to respond (both ways)

I generally can't hear my solenoid during prebreathe since my hood is thick. In fact my hood is so thick I rarely can understand someone talking. Its hit or miss if I can hear the solenoid in the water. Sound does travel better in the water so its in theory louder at my ear drum. Some solenoids are louder than others and many hoods are thinner than mine. Some boats are also far noisier environments than others. So hearing the solenoid is not something which is a requirement or even can be a requirement. Its an intermittent affirmation that the unit is trying to inject O2 - but the O2 has to be turned on for it to even work at all.

 

[Dan]

If the O2 valve is closed, solenoid firing does nothing.

 

[John the Pom]

You are trained to "prebreath" the unit and watch the O2 come up automatically (on an eCCR at least) from the solenoid as well at manually actuate the O2 add valve. Then watch for the unit to respond (both ways)

I generally can't hear my solenoid during prebreathe since my hood is thick. In fact my hood is so thick I rarely can understand someone talking. Its hit or miss if I can hear the solenoid in the water. Sound does travel better in the water so its in theory louder at my ear drum. Some solenoids are louder than others and many hoods are thinner than mine. Some boats are also far noisier environments than others. So hearing the solenoid is not something which is a requirement or even can be a requirement. Its an intermittent affirmation that the unit is trying to inject O2 - but the O2 has to be turned on for it to even work at all.

On O/C you are trained to take a few deep breaths from your reg while watching the SPG before entering the water, to indicate that your air is turned on sufficiently. Is this the CCR equivalent? It sounds like (literally) a life-saving drill.

 

[Jack Hammer]

So not all rebreathers have solenoids. The solenoid firing doesn’t indicate the o2 is on ( although if you can hear it firing alot it might indicate your o2 isnt on). Some models you might not be able to hear it fire. Typically it doesnt fire when you splash and descend at least mine wont often as youll be set to your low setpoint when you splash and descend to your target depth, wreck diving anyway. Po2 tends to stay the same or increase a bit as you go down (depending on a lot of factors). Rule number one is always know your po2.

I rarely hear my solenoid fire, others I know hear it more than I do. ALWAYS know your PO2.

 

[fsardone]

On O/C you are trained to take a few deep breaths from your reg while watching the SPG before entering the water, to indicate that your air is turned on sufficiently. Is this the CCR equivalent? It sounds like (literally) a life-saving drill.

It pretty much is.
Some believe prebreathe is to check that the scrubber is working or to preheat the scrubber. A study was published that shows that this is not true.
The pre breath is to show in a safe environment (dry and easily rescued) that life support equipment really is supporting life.
Then, if you have a scrubber temp, it might even help identify a missing scrubber. Hypercapnia symptoms are late appearing when in high ppO2 environment.

Cheers

 

[rjack321]

On O/C you are trained to take a few deep breaths from your reg while watching the SPG before entering the water, to indicate that your air is turned on sufficiently. Is this the CCR equivalent? It sounds like (literally) a life-saving drill.

Well you can't always do this. On a hypoxic trimix dive you are going to either get lightheaded or pass out doing this on the surface.
The prebreathe is the CCR equivalent of testing all your life support gear for functionality immediately before splashing however.

 

[sunnyboy]

it really depends on the unit. On my unit (Prism Topaz) I perform a pre-dive check at the dive site, where I run through positive, then negative loop pressure test. After that I fill the loop with O2 (to 100%) and then turn the system on. The solenoid clicks twice to indicate it's working, then does not fire again until I get in the water and breath the system down to the shallow PO2, which is 0.7.

Once below 17ft, the pre-set PO2 takes over and the solenoid will fire whenever the loop PO2 needs O2 as determined by loop PO2 and the head electronics.

I can hear my solenoid fire when I'm diving, even in my thick (10mm) hood. I actually anticipate it and it becomes one of the tools I use to evaluate how the rebreather is functioning during the dive (in addition to the HUD, the secondary display and generally listening for gurgles or bubbles or anything else 'out of the ordinary').