Why aren’t scrubber monitors (aka TempStick) standard on all rebreathers?

[Wibble]

Two dive shops then.

The others are suppliers that don’t allow walk ins, i.e. not dive shops.

I get mine from Custom Divers who are a wholesaler that will collections by appointment only during office hours. For once it’s massively cheaper than you pay, about $100/keg with discounts for five kegs or a pallet.


The point is that you’re not going to be able to pop down to the Local Dive Store and find kegs of lime hiding behind the snorkels.

 

[Tracy]

Two dive shops then.

The others are suppliers that don’t allow walk ins, i.e. not dive shops.

I get mine from Custom Divers who are a wholesaler that will collections by appointment only during office hours. For once it’s massively cheaper than you pay, about $100/keg with discounts for five kegs or a pallet.


The point is that you’re not going to be able to pop down to the Local Dive Store and find kegs of lime hiding behind the snorkels.

That is weird that all of these places in the UK sell and train on rebreathers, but wouldn't have sorb for them.
Again, with a 10 second search using only only two different rebreathers for keywords.

 

[SavageSeaCow]

If you say so. Anyplace with tanks and a booster to support O2 and dil/BO fills seems to have sorb available nowadays. Sure there's the occasional OC only recreational facility - but a temp stick doesn't solve much since they can't support CCR sorb nor the needed fills either.

If you have the luxury of always having sorb available at your diving destinations and the time to always go and repack you’re scrubber when your three or four hours are up, then a temp stick might not be for you. Many people dive rebreathers in places that aren’t particularly easily suited for normal supply chains, or in situations where breaking down a unit and repacking a scrubber isn’t practical. I’ve found that sorb can be limited and must be used judiciously when you’re off the beaten path. The rms provides reliable data about usage that allows you to confidently and safely make better use of what is potentially a scarce resource. There are still lots of “anyplaces” where this bit of kit comes in handy.

 

[Geo7]

Temp sticks work: The performance of 'temperature stick' carbon dioxide absorbent monitors in diving rebreathers - PubMed

And hypercapnia made up 60% of all incidents in a study of military divers: Descriptive epidemiology of 153 diving injuries with rebreathers among French military divers from 1979 to 2009 - PubMed

However, I am not convinced that exceeded scrubber duration was the cause in all these hypercapnia cases (think of failed flapper valves, overbreathing, etc.), so the temp stick addresses only one issue (duration/capacity).

My dilemma is this: If your scrubber is rated for 3 hours and the temp stick on a given dive deviates a little and allows for e.g. 3.5 hours, I guess you'll trust the temp stick. But if the temp stick goes way beyond, say 4 or 5 hours, at what point do you draw the line and distrust the stick?

And does that mean in practice one will follow a rating based on averaged previous experiences? For example if one's temp stick usually indicates e.g. 4 hours or so, then you'd use that rating instead of the 3 hour manufacturer rating? But when we'd be back to using a rating, just from own data.

So it's an extra source of info and you still use your brain to determine the duration. Personally, I am ok with simplifying that decision-making process and using the conservative manufacturers rating. However if the temp stick can warn about a wrongly packed scrubber, a missing o-ring (or missing scrubber), that adds safety (if reliable).

 

[GiraffeMarineSalvage]

At point do you draw the line and distrust the stick?

And given my (limited) understanding of CO2 breakthrough dynamics from training/scubaboard/research articles, hopefully pretty conservatively considering what reserve is built in at the end of the dive for a high-workload situation? "Time" reading a book clearing deco is a such a dramatically different level of CO2 production (and respiratory rate which makes it even hard on the remaining sorb capacity..) than a hard surface swim towing a buddy after they had a medical emergency... Granted in relation to a surface swim that's probably a bad example because I would likely switch to a snorkel on a long surface swim regardless of gas supplies and sorb capacity so a better example is probably cutting free of a fishing net or other entanglement with the dive knife "you've been meaning to sharpen")

 

[Wibble]

That is weird that all of these places in the UK sell and train on rebreathers, but wouldn't have sorb for them.
Again, with a 10 second search using only only two different rebreathers for keywords.

View attachment 760469 View attachment 760470

Of that lot, only Divemaster Scuba stocks Sofnolime and possibly Dive Manchester (if they're the same as DiveLife).

ALL of the others are NOT shops. They're either a registered office (frequently a home address), a "micro dealer" or an instructor. None of which will sell Sofnolime.

Maybe it's a quirk of the UK for all these micro businesses.

One other that stocks Sofnolime is Scapa Scuba in Stromness, Orkney, Scotland. None of the dozens of "Shops" with physical and internet presence (aside from Divemaster & Dive Life) stock it.

 

[stuartv]

I think it’s kinda funny that a number of people here knocking the value of rMS are also (I believe) regularly diving their units to scrubber durations that exceed the manufacturer’s spec.

I can understand not assigning any value to a gauge that tells you remaining scrubber time if you always stuck to the manufacturer’s spec. That is akin to driving a car where you never, ever drove more than 100 miles without stopping to fill the fuel tank back to the top. Sure, if you do that, you don’t need a fuel gauge. Plan your drive. Drive your plan. Never run out of gasoline.

But, exceeding the spec AND saying a “sorb gauge” has no value just seems silly. I assume you don’t use an SPG either? I mean, why would you need one? You planned your dive. You know your RMV in all the different conditions you’ll be diving in (just like you know your CO2 production, right?). Your plan includes a suitable safety margin. So, why would you compromise your rig with all those extra O-rings and HP hose that could blow out, just for a gauge you don’t need?

Maybe you have an SPG because they’re cheap and pretty reliable. But, if it died just before a dive, you’d just take it off and dive without it, right? It doesn’t tell you anything more valuable than what rMS tells you, right? They both tell you how much longer you’ll have breathable gas…

 

[Geo7]

Great post, that logic is sound, i.e. if you exceed the manufacturer's rating, take advantage of the temp stick.

One difference to the SPG though might potentially be that it shows actual gas content and it is very reliable. I only did few dives with a temp stick long time ago, so I am not too familiar and have to ask: is the temp stick as reliable as an SPG and as directly linked to air supply? If it is, then I can see why people use it as a car fuel gauge, and then, yes, I'd want one!

Perhaps the people you refer to above simply aren't familiar enough with temp sticks. I know I am not, but don't discount them either.

Great thread, looking forward to more info. Some anecdotes perhaps?

 

[Wibble]

@stuartv — good analogy with the car fuel gauge

 

[Geo7]

Maybe you have an SPG because they’re cheap and pretty reliable. But, if it died just before a dive, you’d just take it off and dive without it, right?

Yup, been there done that...