How helpful would a CO2 monitor really be?

**Gill Envy** · 9th August 2006, 18:23

Sounds like a crazy question, i know.

But here is why i'm asking, when i was looking into buying a rebreather, i kept asking why there was not a CO2 monitor and got answeres mostly in the range of "dangerous levels of Co2 in the loop would account for such minute amounts of the overall gas mix that it would be very hard to detect before it reaches critical levels" and "the moisture content of the loop makes it very difficult to get an acurate reading even if one could be desined that was small enough to fit on a rebreather (currently they take up a lot of room)" and handle the high moisture environment.

then, as i started taking a more serious look at the vision electronics, someone (ok, a salesman), said, hey why do you want to detect CO2, by the time it's in the loop at detectable levels, it's too late... it's the scrubber duration you need to pay attention to...yada, yada...temp stick! At the time I bought the argument and it still makes sense to me. Now that there are rumors of CO2 monitors in rebreather future, i'm curious to know how helpful others feel that is likely to actually be?

***ScubaDadMiami*** · 9th August 2006, 20:21

From what I know, the CO2 monitor is more than rumor at this point. Someone I know has been diving the Titan to test it out. I haven't spoken to this person about it yet (though other people I know have witnessed the event), but I believe it is the working model with the CO2 monitor in it.

I can't see how having one could hurt. Some people are more tolerant to exposure than others. So, it would be great to know that hypercapnia was starting before blanking out or recognizing the symptoms (though it can come on before such recognition). Another tool is a good thing IMHO.

decoweenie · 9th August 2006, 20:57

The only way I think the CO2 could help is by showing the relative amount of CO2 in the loop over period of time.

For example, showing a steady rise of CO2 in the loop should trigger a warning to the diver that something is wrong when the rise exceeded a certain relative safe level and not stopping.

If the diver over-breaths the unit, the rise should be sharper than a canister getting close to break-thru over the last 30 minutes, for example.

So in my mind, I would look forward to using it as an trend indicator of a potential problem rather than an alarm that something has happened since I don't know if the diver could react in time to correct the problem (i.e. open loop, bail-out).

Think like a temperature gauge that you could monitor over time against a normal nominal value. If there is something wrong with your coolant system, the temperature gauge will show a steady climb before red light "Check Engine" comes on and the engine seizes up.

I am sure others will have different opinions about this issue/application...

Mdemon · 9th August 2006, 21:31

Given that people may have difficulty discerning between "I'm working hard" and "I'm having a hit", anything which helps them decide immediately is a good idea.

I also completely disagree with the fact that "it will be too late to do anything". Cobblers. The alternative is to wait until the symptoms are so bad that you either notice (and it's the brain being affected here boys and girls - the thing we're "noticing" with) or die. How much better to have a no-quibble stimulus like an alarm going off to trigger action? Is there anyone here that doesn't jump a mile when their handsets go "Beep!"?

I strongly suspect that most breakthrough, and even maybe some channeling, is not a "nothing/everything" event, but rather an increase over time. My reasoning is that even when the scrubber is being used up, I don't see the scrubber being used up evenly, so some of the slime will still be working. Come to think of it, I was breathing a unit (shallow) with no scrubber at all to test this last year, and it was still around 30 seconds before I had noticable symptoms. So any CO2 detectable (using DW's idea) is not a sign of instant disaster - disaster may just be imminent.

Here's a freebie for the masses:
Put a small temperature probe with alarm (about £12 GBP) in a slim metal basket with slime on the inhale side of the loop - how about under the Tpiece in the counterlung so we don't get a cocktail? Maybe next to the mouthpiece? Maybe just below the cells in the scrubber, but the difference in heat may be too small... Anyway, the alarm goes off when the temperature rises above the normal level of the loop - e.g. the slime touching the probe is reacting. You calibrate to your water temperatures and that's it.

Of course, if you made this into a disk, a bit thicker, and sat above the scrubber and with a spreader/oring of it's own, you would even have a short "reserve" of slime to cover bailing out, but I think the heat of the scrubber would be transfered to the unreacting slime.

Just a thought.

**Gill Envy** · 9th August 2006, 23:43

Quote: (Originally Posted by Mdemon)

Given that people may have difficulty discerning between "I'm working hard" and "I'm having a hit", anything which helps them decide immediately is a good idea...

I've never experienced a CO2 hit, and i've heard various perspectives on how fast it can come on. for those situations where it builds slowly enough to feel and reack to then i can certainly see how having some kind of meter/alarm would be good.

Quote: (Originally Posted by Mdemon)

Here's a freebie for the masses:
Put a small temperature probe with alarm (about £12 GBP) in a slim metal basket with slime on the inhale side of the loop - how about under the Tpiece in the counterlung so we don't get a cocktail? Maybe next to the mouthpiece? Maybe just below the cells in the scrubber, but the difference in heat may be too small... Anyway, the alarm goes off when the temperature rises above the normal level of the loop - e.g. the slime touching the probe is reacting. You calibrate to your water temperatures and that's it.

interesting thought, but still not an actual CO2 detector, more like an expanded version of the temp stick. It sounds like it could have merrit, but would still not satisy the folks that want an actual CO2 meter...which i believe is what is actually in the works.

E-man · 10th August 2006, 00:28

If you can get reliable co2 monitors in the loop you can have pre and post scrubber monitors, pre can calculate exactly how much Co2 is going into the scrubber and you can get an accurate prediction of scrubber life down to minutes, based on current work loads, and a post sensor as a safety precaution, co2 scrubbing is a chemical reaction and certain needs must be met for it to work properly...its good to know the gas your breathing is safe.

Genesis · 10th August 2006, 01:01

I can see two sides to this:

If you get some warning between too-high CO2 and mental incapacity, then it is of value. Definitely.

However, there is anecdotal evidence that it don't work that way in all (or even many) cases. Example - there were a few people killed in a CO2 fire extinguishing discharge accident a number of years ago. They were within ten feet of the door - and safety - when it went off. All evidence suggests that they fell almost literally where they stood, which implies that the blackout occurred essentially immediately. Unfortunately there was nobody near (but outside) who saw it and could thus effect a rescue, nor to report on exactly how fast they fell. (The discharge was not in response to an actual fire.)

Now granted, this was with a CO2 level VASTLY exceeding what you'd get from a breakthrough, but still - its sobering to think of in this way. What's the threshold for that sort of "bad result"? Do we know?

If the sensor serves much as many "idiot lights" do on some cars (e.g. "time to buy a new engine") then in truth you may as well leave the sensor out. Telling me that I've lost consciousness (as I do so) isn't very useful.

On the other hand, if you get a material warning - even if its 5 seconds worth - it could save lives. Most people can perform a bail/switch (especially with a BOV) in that amount of time, provided the warning is unambiguous (different tone or HUD light/sequence)

But if the sensor response is 30 seconds and you only get one breath (6 seconds at 10 resps/min) before blacking out, then the warning tells you that you just got killed - that'd be pretty un-funny.

What can be worse with a system that can work like that is the complacency that it can engender. If people believe they will be warned in time to bail, they may be inclined to push scrubber durations more than they do now.....

The temp sticks are nice BUT they can't necessarily detect channeling or sudden breakthrough. Exhaustion, yes - but that's only one of the potential problems......

***ScubaDadMiami*** · 10th August 2006, 02:18

Concerning how rapidly the CO2 rate climbs, my understanding is that it depends on the cause.

If due to breakthrough, the levels will rise rapidly as the scrubber material will not be working well enough to do much of anything. My understanding is that the material goes from working to not working without much of a phasing between the two.

With channeling, it is likely to rise quickly because gas will pass over the spaces that have exhausted scrubber material, in essence amounting to the same rapid rise as in the case of breakthrough. (Of course, actual channeling is probably only partial. So, the results might be moderated to some degree.)

If due to overbreathing but with fresh scrubber, the rate can rise temporarily but might not climb much beyond the accepted safe range, and likely will not continue to rise quickly unless the diver continues to overbreathe. The scrubber is still working but does not do enough to remove all of the CO2. Just slowing activity might allow the scrubber to work well enough to eliminate the CO2 back to an acceptable level (catching up in essence). (This does not mean I am advocating doing nothing else in this case--it is just an example of the rate of rise of CO2 level.) Also, the level of overbreathing could be such that CO2 levels rise more slowly.

In the end, some kind of indicator is better than none. The same rules (anything out of the ordinary: get off of the loop, take sanity breaths, go from there) still apply. So, this would just be another tool. That does not mean to follow it without applying what we already do.

Mixaddict · 10th August 2006, 03:44

I suspect that as smaller more compact CO2 monitors that are capable of operating in the mosit environment of a CCR loop become available and reliable, they will become standard issue on CCRs. Even if they are not fool proof, they would certainly be better than no warning. My Inspiration with Vision electronics has all sorts of bells and whistles on it now, but I don't rely on the alarms for 100% security. I have to also rely on how my body feels and use common sense to keep me alive. I suspect that CO2 monitors will eventually assist me in the same way - one of several tools to help me monitor the situation.

Mdemon · 10th August 2006, 06:26

Quote: (Originally Posted by Genesis)

However, there is anecdotal evidence that it don't work that way in all (or even many) cases. Example - there were a few people killed in a CO2 fire extinguishing discharge accident a number of years ago. They were within ten feet of the door - and safety - when it went off. All evidence suggests that they fell almost literally where they stood, which implies that the blackout occurred essentially immediately. Unfortunately there was nobody near (but outside) who saw it and could thus effect a rescue, nor to report on exactly how fast they fell. (The discharge was not in response to an actual fire.)

Now granted, this was with a CO2 level VASTLY exceeding what you'd get from a breakthrough, but still - its sobering to think of in this way. What's the threshold for that sort of "bad result"? Do we know?

I think there is more to it than that. Ever tried this? Drink half a large bottle of coke. Give it a gentle swirl to get some bubbles going then squeeze the bottle and inhale at the same time (not the coke!). That's pretty much neat CO2 and it's effects are almost instant. But!!!! We never get that, since we will always have O2 and N2 in the loop and the O2 being in fairly constant amounts. Remember my "non-scrubber" test above - a million miles from the 'coke' hit.

The problem we have is that all the reports we have from people taking CO2 hits have no idea of how long they have been breathing CO2 before they feel the effects. In fact, didn't someone post that "their mate" did an entire dive without o-ring and spreader bar!!! So here's the thing; others are reading this and extrapolating that the effects of CO2 come on too fast to make any monitor or alarm useful. I'd suggest that's wrong and that maybe, possibly, the noticable effects in some people may come on faster than some people react. However, there is no evidence I've read that shows CO2 levels going from 0 to lots instantly in a scrubber, in fact quite the opposite, but also there are no reports of how long it took people to notice these symptoms.

So, to my mind, anything which alerts the user before they know, or even as they know, they have a problem is a good thing.

9th August 2006, 18:23	#1 (permalink)
Gill Envy Shearwater Copis Diver Current Rebreather/s: Other CCR Other Rebreather/s: Evolution Other CCR Join Date: Nov 2005 Location: seattle Posts: 1,208	How helpful would a CO2 monitor really be? Sounds like a crazy question, i know. But here is why i'm asking, when i was looking into buying a rebreather, i kept asking why there was not a CO2 monitor and got answeres mostly in the range of "dangerous levels of Co2 in the loop would account for such minute amounts of the overall gas mix that it would be very hard to detect before it reaches critical levels" and "the moisture content of the loop makes it very difficult to get an acurate reading even if one could be desined that was small enough to fit on a rebreather (currently they take up a lot of room)" and handle the high moisture environment. then, as i started taking a more serious look at the vision electronics, someone (ok, a salesman), said, hey why do you want to detect CO2, by the time it's in the loop at detectable levels, it's too late... it's the scrubber duration you need to pay attention to...yada, yada...temp stick! At the time I bought the argument and it still makes sense to me. Now that there are rumors of CO2 monitors in rebreather future, i'm curious to know how helpful others feel that is likely to actually be? __________________ Gill Envy ...Because I wasn't born with gills! ><(°>><(°>><(°>><(°>><(°>><(°>><(°>><(°>
(Offline)

9th August 2006, 20:21	#2 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 1,887	Re: How helpful would a CO2 monitor really be? From what I know, the CO2 monitor is more than rumor at this point. Someone I know has been diving the Titan to test it out. I haven't spoken to this person about it yet (though other people I know have witnessed the event), but I believe it is the working model with the CO2 monitor in it. I can't see how having one could hurt. Some people are more tolerant to exposure than others. So, it would be great to know that hypercapnia was starting before blanking out or recognizing the symptoms (though it can come on before such recognition). Another tool is a good thing IMHO. __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
(Offline)

9th August 2006, 20:57	#3 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,509	Re: How helpful would a CO2 monitor really be? The only way I think the CO2 could help is by showing the relative amount of CO2 in the loop over period of time. For example, showing a steady rise of CO2 in the loop should trigger a warning to the diver that something is wrong when the rise exceeded a certain relative safe level and not stopping. If the diver over-breaths the unit, the rise should be sharper than a canister getting close to break-thru over the last 30 minutes, for example. So in my mind, I would look forward to using it as an trend indicator of a potential problem rather than an alarm that something has happened since I don't know if the diver could react in time to correct the problem (i.e. open loop, bail-out). Think like a temperature gauge that you could monitor over time against a normal nominal value. If there is something wrong with your coolant system, the temperature gauge will show a steady climb before red light "Check Engine" comes on and the engine seizes up. I am sure others will have different opinions about this issue/application... __________________ "...after a while you get bored offering advice to a bull that like to keep butting the fence with its head rather than walking through the open gate..." - Rebreather World PM
(Offline)

9th August 2006, 21:31	#4 (permalink)
Mdemon SiegeEngine II Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Inspiration Classic Home Build Join Date: Feb 2007 Location: SWUK Posts: 1,866	Re: How helpful would a CO2 monitor really be? Given that people may have difficulty discerning between "I'm working hard" and "I'm having a hit", anything which helps them decide immediately is a good idea. I also completely disagree with the fact that "it will be too late to do anything". Cobblers. The alternative is to wait until the symptoms are so bad that you either notice (and it's the brain being affected here boys and girls - the thing we're "noticing" with) or die. How much better to have a no-quibble stimulus like an alarm going off to trigger action? Is there anyone here that doesn't jump a mile when their handsets go "Beep!"? I strongly suspect that most breakthrough, and even maybe some channeling, is not a "nothing/everything" event, but rather an increase over time. My reasoning is that even when the scrubber is being used up, I don't see the scrubber being used up evenly, so some of the slime will still be working. Come to think of it, I was breathing a unit (shallow) with no scrubber at all to test this last year, and it was still around 30 seconds before I had noticable symptoms. So any CO2 detectable (using DW's idea) is not a sign of instant disaster - disaster may just be imminent. Here's a freebie for the masses: Put a small temperature probe with alarm (about £12 GBP) in a slim metal basket with slime on the inhale side of the loop - how about under the Tpiece in the counterlung so we don't get a cocktail? Maybe next to the mouthpiece? Maybe just below the cells in the scrubber, but the difference in heat may be too small... Anyway, the alarm goes off when the temperature rises above the normal level of the loop - e.g. the slime touching the probe is reacting. You calibrate to your water temperatures and that's it. Of course, if you made this into a disk, a bit thicker, and sat above the scrubber and with a spreader/oring of it's own, you would even have a short "reserve" of slime to cover bailing out, but I think the heat of the scrubber would be transfered to the unreacting slime. Just a thought. __________________ www.southwestmafia.com
(Offline)

9th August 2006, 23:43	#5 (permalink)
Gill Envy Shearwater Copis Diver Current Rebreather/s: Other CCR Other Rebreather/s: Evolution Other CCR Join Date: Nov 2005 Location: seattle Posts: 1,208	Re: How helpful would a CO2 monitor really be? Quote: (Originally Posted by Mdemon) Given that people may have difficulty discerning between "I'm working hard" and "I'm having a hit", anything which helps them decide immediately is a good idea... I've never experienced a CO2 hit, and i've heard various perspectives on how fast it can come on. for those situations where it builds slowly enough to feel and reack to then i can certainly see how having some kind of meter/alarm would be good. Quote: (Originally Posted by Mdemon) Here's a freebie for the masses: Put a small temperature probe with alarm (about £12 GBP) in a slim metal basket with slime on the inhale side of the loop - how about under the Tpiece in the counterlung so we don't get a cocktail? Maybe next to the mouthpiece? Maybe just below the cells in the scrubber, but the difference in heat may be too small... Anyway, the alarm goes off when the temperature rises above the normal level of the loop - e.g. the slime touching the probe is reacting. You calibrate to your water temperatures and that's it. interesting thought, but still not an actual CO2 detector, more like an expanded version of the temp stick. It sounds like it could have merrit, but would still not satisy the folks that want an actual CO2 meter...which i believe is what is actually in the works. __________________ Gill Envy ...Because I wasn't born with gills! ><(°>><(°>><(°>><(°>><(°>><(°>><(°>><(°>
(Offline)

10th August 2006, 00:28	#6 (permalink)
E-man On the loop! Current Rebreather/s: Inspiration Classic Optima Other Rebreather/s: Titan Join Date: Sep 2005 Location: Eastern Coast ;) Posts: 212	Re: How helpful would a CO2 monitor really be? If you can get reliable co2 monitors in the loop you can have pre and post scrubber monitors, pre can calculate exactly how much Co2 is going into the scrubber and you can get an accurate prediction of scrubber life down to minutes, based on current work loads, and a post sensor as a safety precaution, co2 scrubbing is a chemical reaction and certain needs must be met for it to work properly...its good to know the gas your breathing is safe.
(Offline)

10th August 2006, 01:01	#7 (permalink)
Genesis Bubbless Box of Death Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Oct 2005 Location: Sunny Florida Posts: 1,394	Re: How helpful would a CO2 monitor really be? I can see two sides to this: If you get some warning between too-high CO2 and mental incapacity, then it is of value. Definitely. However, there is anecdotal evidence that it don't work that way in all (or even many) cases. Example - there were a few people killed in a CO2 fire extinguishing discharge accident a number of years ago. They were within ten feet of the door - and safety - when it went off. All evidence suggests that they fell almost literally where they stood, which implies that the blackout occurred essentially immediately. Unfortunately there was nobody near (but outside) who saw it and could thus effect a rescue, nor to report on exactly how fast they fell. (The discharge was not in response to an actual fire.) Now granted, this was with a CO2 level VASTLY exceeding what you'd get from a breakthrough, but still - its sobering to think of in this way. What's the threshold for that sort of "bad result"? Do we know? If the sensor serves much as many "idiot lights" do on some cars (e.g. "time to buy a new engine") then in truth you may as well leave the sensor out. Telling me that I've lost consciousness (as I do so) isn't very useful. On the other hand, if you get a material warning - even if its 5 seconds worth - it could save lives. Most people can perform a bail/switch (especially with a BOV) in that amount of time, provided the warning is unambiguous (different tone or HUD light/sequence) But if the sensor response is 30 seconds and you only get one breath (6 seconds at 10 resps/min) before blacking out, then the warning tells you that you just got killed - that'd be pretty un-funny. What can be worse with a system that can work like that is the complacency that it can engender. If people believe they will be warned in time to bail, they may be inclined to push scrubber durations more than they do now..... The temp sticks are nice BUT they can't necessarily detect channeling or sudden breakthrough. Exhaustion, yes - but that's only one of the potential problems...... __________________ "A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American." http://www.denninger.net http://www.diversunion.org/liability.htm - Fix the Diving Cert racket
(Offline)

10th August 2006, 02:18	#8 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 1,887	Re: How helpful would a CO2 monitor really be? Concerning how rapidly the CO2 rate climbs, my understanding is that it depends on the cause. If due to breakthrough, the levels will rise rapidly as the scrubber material will not be working well enough to do much of anything. My understanding is that the material goes from working to not working without much of a phasing between the two. With channeling, it is likely to rise quickly because gas will pass over the spaces that have exhausted scrubber material, in essence amounting to the same rapid rise as in the case of breakthrough. (Of course, actual channeling is probably only partial. So, the results might be moderated to some degree.) If due to overbreathing but with fresh scrubber, the rate can rise temporarily but might not climb much beyond the accepted safe range, and likely will not continue to rise quickly unless the diver continues to overbreathe. The scrubber is still working but does not do enough to remove all of the CO2. Just slowing activity might allow the scrubber to work well enough to eliminate the CO2 back to an acceptable level (catching up in essence). (This does not mean I am advocating doing nothing else in this case--it is just an example of the rate of rise of CO2 level.) Also, the level of overbreathing could be such that CO2 levels rise more slowly. In the end, some kind of indicator is better than none. The same rules (anything out of the ordinary: get off of the loop, take sanity breaths, go from there) still apply. So, this would just be another tool. That does not mean to follow it without applying what we already do. __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com Last edited by ScubaDadMiami : 10th August 2006 at 04:06.
(Offline)

10th August 2006, 03:44	#9 (permalink)
Mixaddict Always Learning! Current Rebreather/s: Inspiration Vision Evolution Other CCR Dolphin Other Rebreather/s: Inspiration Classic Other CCR Dolphin Join Date: Jan 2006 Location: Draper, Utah USA Posts: 411	Re: How helpful would a CO2 monitor really be? I suspect that as smaller more compact CO2 monitors that are capable of operating in the mosit environment of a CCR loop become available and reliable, they will become standard issue on CCRs. Even if they are not fool proof, they would certainly be better than no warning. My Inspiration with Vision electronics has all sorts of bells and whistles on it now, but I don't rely on the alarms for 100% security. I have to also rely on how my body feels and use common sense to keep me alive. I suspect that CO2 monitors will eventually assist me in the same way - one of several tools to help me monitor the situation.
(Offline)

10th August 2006, 06:26	#10 (permalink)
Mdemon SiegeEngine II Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Inspiration Classic Home Build Join Date: Feb 2007 Location: SWUK Posts: 1,866	Re: How helpful would a CO2 monitor really be? Quote: (Originally Posted by Genesis) However, there is anecdotal evidence that it don't work that way in all (or even many) cases. Example - there were a few people killed in a CO2 fire extinguishing discharge accident a number of years ago. They were within ten feet of the door - and safety - when it went off. All evidence suggests that they fell almost literally where they stood, which implies that the blackout occurred essentially immediately. Unfortunately there was nobody near (but outside) who saw it and could thus effect a rescue, nor to report on exactly how fast they fell. (The discharge was not in response to an actual fire.) Now granted, this was with a CO2 level VASTLY exceeding what you'd get from a breakthrough, but still - its sobering to think of in this way. What's the threshold for that sort of "bad result"? Do we know? I think there is more to it than that. Ever tried this? Drink half a large bottle of coke. Give it a gentle swirl to get some bubbles going then squeeze the bottle and inhale at the same time (not the coke!). That's pretty much neat CO2 and it's effects are almost instant. But!!!! We never get that, since we will always have O2 and N2 in the loop and the O2 being in fairly constant amounts. Remember my "non-scrubber" test above - a million miles from the 'coke' hit. The problem we have is that all the reports we have from people taking CO2 hits have no idea of how long they have been breathing CO2 before they feel the effects. In fact, didn't someone post that "their mate" did an entire dive without o-ring and spreader bar!!! So here's the thing; others are reading this and extrapolating that the effects of CO2 come on too fast to make any monitor or alarm useful. I'd suggest that's wrong and that maybe, possibly, the noticable effects in some people may come on faster than some people react. However, there is no evidence I've read that shows CO2 levels going from 0 to lots instantly in a scrubber, in fact quite the opposite, but also there are no reports of how long it took people to notice these symptoms. So, to my mind, anything which alerts the user before they know, or even as they know, they have a problem is a good thing. __________________ www.southwestmafia.com
(Offline)

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode