Printable View
When one rope is loaded and the other not, the unloaded rope is fatter and can prevent the Shunt from grabbing the (smaller diameter under tension) loaded rope. Essentially creating the mismatched diameter situation (middle panel in the diagram)Quote:
Originally Posted by Brian in SLC
I work in a confined space rescue teams and so I always keep safety backup along with me because any time there can be emergency immediate rescue confined space is important.
I've used backups for big free hanging raps if i'm the first one down and/or a bottom belay isn't available. which i agree with several comments about that fireman belay needs to be alert or its kind of useless. and my thoughts on autoblocks and other self belays is that the need comes up only once in awhile. the first time i did pinecreek back as a mere beginner i used my VT on top but that's pretty much the last time i used a safety backup, i can think of 2 other times since then on bigger raps that i'd never done before but have since gone back and new what the rap was like so it was all good.
If you want to put one on then feel free to add that safety, but know what you are doing with it. I'd hate to hear of anyone that's said they never use em and they aren't necessary had fallen off a rap and injured themselves....that would be terribly ironic...
After the recent Subway accident I thought it might be a good time to bump this thread. From reports out so far it appears an autoblock was when the snowball started rolling.....
From what I understand either his autoblock locked off and he didn't know how to escape from it... or... his autoblock got sucked into his rappel devise and caused a clusterf**k he didn't know how to escape from.
But...then...he cut off the harness to free himself? And, the leg loop trapped his leg/ankle?
Yikes.
I can't imagine a properly positioned autoblock would have been a dealio. But, the cord or knot or something got stuck in his belay device and caused him to grind to a stop? Unable to get free, he cut himself loose? Not an unreasonable solution I suppose. "It" happens that his foot got trapped? Ugh.
He apparently took a "how to" type class where he learned this autoblock thing? Who teaches that around Zion? And, how is it taught? Ie, do they put the rappel device out away from the harness on a tether, or, is it close off the belay loop with the autoblock off the leg loop?
Kinda wonder the gritty details of what happened. If his rappel device sucked up the autoblock and that's what jammed his progress?
Scary stuff. Being stuck upside down with your foot trapped in a leg loop from the harness, and, your harness on the rope due to being stuck on a knot...all five feet or so from ground level but free hanging? Yikes. Crappy scenario to try to recover from. If you were super tired, and, lacked a bit of strength, I wonder if most folks could aid themselves in that situation? Especially sans any equipment. Knife taped to a stick and cut yourself free?
I think good to split off from the accident thread to discuss...
But your rope is hanging next to you and scured above you.... so even if you lacked strength you should be able to construct some type of prusik system to right yourself.... that is if you even know about prusik systems.Quote:
Originally Posted by Brian in SLC
One thought... I always teach people to climb and rappel with their packs on (or at least attached). And my reasoning is when things go bad you will have your gear with you. A prusik systems does no good if it was in your pack that you tossed to the bottom of the rappel.
If it were attached to your harness...then, a Prusik would be WAY out of reach.Quote:
Originally Posted by Iceaxe
Even so, difficult at best upside down with all your weight on your ankle. Not like you can step in a foot loop!
Ok, you get a Prusik on the rope, now what? You could even add another. Then what? Not many folks could correct this orientation solo. Yes, you're welcome to try this at home. Please report results.
No I have to agree with you Brian, I think once you're hanging from your ankle you're pretty screwed. One important factor we are missing though is there a partner to help you out. Let's also not forget that the helper can be above or below him. Although not sure if a 60 year old can walk up that slippery log but is feasible. She walked down it without slipping sounds like.
I do think with a cleverly made loop in the rope, snug it on the stronger arm up past the elbow, and a pull from above, this could be sorted out. Or at worst case scenario a stick with the knife attached would make quick work or the bind. Again though an elderly person falling headfirst is very dangerous. Really depends on how it looked on the scene.
By the time the guy was hanging upside the snowball had been rolling for a while and was moving pretty fast... part of the issue was not dealing correctly with the first problem and then creating a second bigger problem.
It takes some real work to go from a stuck rappel device to hanging up side down by one foot.
Sent using Tapatalk
I think his wife rappelled down first...
My bet is this situation played out for awhile. He was stuck. Probably fiddled a fair bit before coming to a solution. They were tired and gettin' more so. Day had been a long one for them. He decided a course of action with more than likely bad results, unseen ahead of time, there but for the grace, in the heat of battle...hard to be too critical IMHO. Yeah, screwed up. Tried to correct, didn't work. So, hanging there, probably feeling fairly worked and who knows what else, I can totally understand him telling the wife, "go for help". No risk for her in trying to get above him, etc. Sad, but, a pretty sober and reasonable choice. Maybe he didn't know how much the clock was ticking.
She'll never forgive herself for not being faster, or, getting lost. I've known folks in that situation, and, don't know how they got on with life, really.
Accident. Preventable? Sure. Tragic.
I can answer this: ZAC. Took a one day first timer class from them several years ago. Jonathan Z. took us out himself. Gave us autoblocks to attach to our leg loops and taught us to use them on every rap. This was in Water canyon. Next day we bought cord and made our own and used them in Keyhole and Pine Creek. Had never rapped ever until that day and thought it was required.Quote:
Originally Posted by Brian in SLC
Maybe they don't teach this any longer. I was ok using one but my friends never liked the block. One actually got his stuck coming off a 130ft drop and had to cut it off halfway down. Pretty scary to be hanging there playing with a knife.
Since that time we have done many more canyons and usually don't use a block. But in cases like the last rap in PC, I usually go down first to belay people from the bottom, and I usually use an autoblock on that rap. I don't really like it but the lack of any backup on that rap freaks me out. One mistake and it is all over. But having said that we always rap on double 9's so it's probably not as dangerous as I am thinking? I am not sure - what can you do if your break hand cramps up on a big free hanging rap like that?
Add more friction. Technique varies based on what device you are using
I'd suggest just switching hands....Quote:
Originally Posted by Renard
Also... if I had someone that was uneasy on something like the last rap in Pine Creek and was not able to provide a fireman's belay I would use my pull cord and set up a top belay. YMMV
I don't know if it was ZAC but "someone" still teaches this for sure. We took a noob along on one of our trips who took a one day class, and she insisted on using it also. By the end of the trip though we had convinced her of the dangers of it and got her to abandon it. But at first she was utterly convinced she would die without it. Hard to argue when someone is scared, so we just let her use it, but once she understood the fireman's belay it made more sense. I think the reason they do this is because there is only one guide on most of these trips yeah? So the pro is at the top and you can't rely on a noob to belay correctly.Quote:
Originally Posted by Renard
I did see two separate guided groups in Water canyon though, not ZAC the other guys down the street that also do bike tours, can't recall the name. But both guys in that group just belayed them from the top. Looked very legit and competent to me. No bad habits were taught.
I remember a dust-up a few years back where Rich took Darren (of ATS/WCCM fame) to task for teaching the use of autoblocks in flowing water situations. Rich said by doing so it was only a matter of time before someone dies in a waterfall due to a stuck autoblock. There is a reason they don't use them outside of the US. And Rich was right.
No guide/teaching service should be teaching autoblocks in flowing water. And those that teach autoblocks on dry rappels must drill into their student's heads that they are not to be used in flowing water. Anything less is dangerous and possibly negligent.
I hate autoblocks. They cause more trouble than they are worth. It is better, I think, to teach proper rappelling technique. If someone can't safely and competently rappel, perhaps they need more training and practice before entering a canyon. Or they should have a belay - from the top.
I say this because I don't like fireman belays much either. In theory they are nice, I know of a few folks who claim they saved them, and on occasion I do ask for one, but I do so merely for the psychological boost they provide to the rappeller. The fact is, in practice they are pretty bad, for two reasons.
First, nobody knows how to do them. I would say 95% of fireman belays I have seen in canyons - even by very experienced canyoneers - are done wrong. If you are standing at the bottom, holding the rope by your side or waist, you are doing it wrong. But that's how everyone does them. If you have a bunch of slack in the rope, or if you are looking around and not at the rappeller, you are doing it wrong.
To do it correctly you need to be very cognizant of the amount of slack out. You need to watch the rappeller for the entire length of the rappel. And you should be holding the rope above your head, because pulling the slack out is much easier when you pull vertically. Yes, your arms will get tired. Don't rest them by your side, unless your rappeller is ok with you giving a marginal fireman's belay.
The other reason is that it is simply difficult to stop someone who loses control of a rappel, it is a lot harder than you think. There is the delay when they lose control and your brain registers it. There is the time to remove the slack from the system. And in those delays the rappeller can generate a lot of speed/force. Add in canyoneer's propensity to use skinny ropes or rigging incorrectly for friction, and the problem gets worse.
I also find that someone providing a good belay somewhat impedes my ability to safely rappel. A good analogy is climbing, you are on lead, desperate to clip your gear, but your belayer is slow offering slack... usually things end ok, but not a comfortable situation, and it could lead to disaster.
Cavers did an interesting test on the fireman's. The methodology isn't perfect. Results show that they can save your butt, but they aren't a 100%. Or maybe even 50%.
http://www.caves.org/section/vertica.../bottblay.html
I would love to set up a practice rigging that is safe for the belayer, but also an element of surprise, where you don't know at what point the "rappeller" loses control. I suspect many people would not be able to catch the rappeller, but I need to test that hypothesis.
If you really need a safety backup, a top belay should be used. Or just lower the person if you don't have enough rope for a top belay.
M
Personally I'm a big fan of the fireman's belay. Simple to teach and simple to execute. It's one of the first things I teach noobs.... but like anything else, there is a wrong way and a right way to do it.
Anyhoo..... here is a short video of my 14 year old daughter saving a canyoneer's ass using a fireman's belay.
http://www.youtube.com/watch?v=zFTunPbjjxU
I will say that was probably Sierra's first real test under fire in a canyon and I was extremely proud that she preformed at such a high level.
:cool2:
No offense to you or your daughter Shane, but I'm not convinced. I do concede that it is hard to tell from the video, but what I see is someone falling and not letting go of their break hand, and then stopping almost instantly, which means they most likely caught themselves, with your daughter pulling on the rope acting as a backup. The reason I say that is after the person falls over the edge, they stop falling just when Sierra is beginning to pull on the rope. When the person stops falling you can see that there is still significant slack in the system below the rappeller. In other words, the person is already stopped before the fireman's belay is fully executed. It's also hard to tell from the video what your daughter's hand position was in before the fall occurred. When we finally see her hands in the video, they are at her waist. Of course this is after she is already pulling on the rope, so they could've started above her head out of video frame.Quote:
Originally Posted by Iceaxe
If the person was in a truly uncontrolled fall (e.g., knocked out with no hand on the break line), I am willing to bet this video would've had a very different outcome.
But as I said, it is hard to tell what is going on from the video.
I think it would be very eye opening for canyoneers to set up a test like the one in the caver article. I think many people will be surprised at how unreliable a fireman's belay is.
A fireman's is better than nothing. I think a top belay, or even better, good/safe/competent rappelling skills offer a much better safety margin.
But as you say, YMMV.
M
Bogus info. Not applicable in canyoneering. We never do 800 foot raps or very rarely. We almost always position ourselves in a place where we can see the rapeller and know when they are in trouble, and we also have help pulling from the rappee to assist them in stopping, not dead weight doing nothing. If the person on bottom can't stop the rapper, then the friction was set wrong and that is where the fault lies, period.Quote:
Originally Posted by mdd
Your info about doing a firemans belay properly though is spot on, pay attention, hands up, etc. Good stuff. But I think done properly it's completely safe and standard.
Top belay is just as sketchy using the mitigating factors you just mentioned. Especially since it's always pretty hard to look over the edge and see them actually fall. You just get a surprise yank on your device. Have your hands in the wrong spot feeding out line and you are just as screwed IMO. If instead you are looking up and see it happen, you can prepare for it.
Both methods are safe IMO though, but I reject your idea that top belay is more safe. At least I think that is what you are saying. Good post! :2thumbs:
Most our raps arent even over 300 feet. So the person would have already fallen the entire distance of the rap before this reaction time even occurred.Quote:
TEST # # BARS MASS
(lbs.)HEIGHT
(Ft.)BELAY 1 5 175 115 CATCH 2 4 175 115 FAILURE 3 4 175 230 FAILURE 4 4 175 300 FAILURE 5 4 175 225 FAILURE 6 4 150 200 FAILURE 7 4 150 400 FAILURE 8 5 175 395 FAILURE 9 5 225 240 FAILURE 10 5 200 240 CATCH
Look at the link again. The rope was tied to an 800 bridge, but control was lost at between 115 and 400 feet, with most of the tests having control lost at 240 feet or less, all within the realm of canyoneering.Quote:
Originally Posted by Deathcricket
Granted the extra rope above the fall point does factor in, but I'd bet it isn't much.
I saw a video of a canyoner who slipped and fell, letting go of their break hand in the process, before free falling. How would this canyoner assist in stopping with your fireman's belay? Do you assume that anyone in need of a catch while falling on rappel is cognizant and oriented enough to aid in their stopping?Quote:
Originally Posted by Deathcricket
You've obviously never belayed a second up from an anchor in a multi-pitch trad climb and caught a fall, or belayed a leader who falls when out of site (over a lip or something). I've gotten the "surprise yank on my device" many, many, many times, and with climbers the fall forces are generally greater than a rappeller being belayed from above, meaning the "yank" is stronger. I've also had many times where I've belayed a second from above, and they fell, out of my sight, and I barely registered that something happened. It's no big deal at all, if it was you'd hear about seconds falling to their deaths all of the time... but you don't, why not? What you are describing is belaying a rappeller from above using incorrect technique. Of course it won't work then, any more than a fireman's won't work with incorrect technique. My point is that it is a lot more difficult to catch a true out of control fall with a fireman's than with a top belay, and that people underestimate how hard it is to catch a fall with a fireman's to the point where it provides a very false sense of security.Quote:
Originally Posted by Deathcricket
The only way for sure is to set up the caver's scenario and try it yourself. I would love to be proven wrong since fireman's are so "easy", and I hope a canyoneer takes the test to prove me wrong (in a controlled environment, of course).
M
I've used both prusik and autoblocks numerous times in various situations and like them. The secret is to have the know-how and common sense when and how to use them.
I'll back the fireman's belay! I took "whale" over average weight noob down Rock Canyon early this year. He slipped near the top of the big rap and with very little ease i stopped him dead in his tracks, he got his feet back under him and he continued down the rappel. I try to always use a fireman's when possible, competent canyoneer or not.
Got a link? I searched and searched for a failed firemans belay on video but I've yet to see one or even heard of one existing. If it failed and someone splatted it would be on video, trust me. The only one I could find was a dude let completely go of the rope with no belay at all. And again, I'm saying they are both safe methods. I think your assumption that a correct top belay is more safe than a correct bottom belay doesn't hold water with me. Plus a bottom belay is way faster and infinitely more efficient for groups, plus you dont need an extra rope. I've caught hundreds of noobs falling and you don't have to end up pulling any harder on the line than they were. Using 2 hands and my body weight, I can stop anyone pretty damn quick.Quote:
Originally Posted by mdd
You're introducing variables like you cant see the person, the person gains speed, completely let's go of the rope, falls 100 feet before starting a brake, etc, To try and prove a bottom belay is dangerous, yet use a correctly performed top belay experience to support your premise and discount any variables? What planet you from dude? :lol8:Quote:
You've obviously never belayed a second up from an anchor in a multi-pitch trad climb and caught a fall, or belayed a leader who falls when out of site (over a lip or something). I've gotten the "surprise yank on my device" many, many, many times, and with climbers the fall forces are generally greater than a rappeller being belayed from above, meaning the "yank" is stronger. I've also had many times where I've belayed a second from above, and they fell, out of my sight, and I barely registered that something happened. It's no big deal at all, if it was you'd hear about seconds falling to their deaths all of the time... but you don't, why not? What you are describing is belaying a rappeller from above using incorrect technique. Of course it won't work then, any more than a fireman's won't work with incorrect technique. My point is that it is a lot more difficult to catch a true out of control fall with a fireman's than with a top belay, and that people underestimate how hard it is to catch a fall with a fireman's to the point where it provides a very false sense of security.
I have caught people with a fireman's belay. I am 300lbs, he was about 190. He was on a ~45ft waterfall rappel using an ATC. He slipped and used his break hand to prevent smashing into the wall. When performing a fireman's I always keep my hands up high on the rope. I pulled back using all my weight/arm strength. He ended up falling about 3-4 ft and hit his head against the wall (That is why we always wear Helmets). The Fireman's belay completely worked the way it should. The rappeler was fine except for a bruised ego that he let go of his life line.
I can.Quote:
Originally Posted by Brian in SLC
I've done a rappel off a log at this location in the past, and it features the exciting "Rodeo Start". Nudge off the ledge and fall onto the rappel, swinging wildly underneath the log.
A beginner doing this? I can see turning upside down, grabbing at things... very definitely the kind of upside-downess that puts the leg-loop-attached autobloc into the rappel device. He may even have been unable to get back up into an upright position.
Yeah, falling 15 feet to the deck was not a good option, but it may have been the best available. Unfortunately it did not work.
Tom
I'm with Mike on the top belay v the fireman's. I much prefer to belay from the top (or sling shot, from the bottom). Top belay requires me to do something the entire time forcing me to pay attention. Fireman's is reactive.
Another reason is I don't like to be right below someone who might dislodge something. You can't really be on top of a fireman's and out of the way at the same time.
Different styles I suppose. And, I do appreciate the fireman's for less experienced friends on rappel, too. If I don't trust that they can rappel, I just prefer to be above and have them on belay.
I've practised fireman's a bunch. Actually did it last weekend climbing whilst stopping quickly on rappel to grab some tat from around a tree to the side of the rappel anchor. Had my partner at the anchor be my brake hand for a second. Works slick when it works!
I said, "properly positioned". Seems like most folks using an autoblock effectively have it so it doesn't come any where near the rappel device...Quote:
Originally Posted by ratagonia
I've seen "properly positioned" autoblocks grab onto the rope and stop someone. No biggie. Easy fix.
Folks that are taught the leg loop method with an autoblock too near a rappel device not pitched out from their belay loop on the harness? Not good. If you can rotate your hip and get that autoblock anywhere near the rap device, you've really defeated the purpose of using one in the first place. It'll either fail to grab the rope, or, jam. Neither situation a good option in the heat of battle.
Proper rappel technique and experience trumps all this back up stuff.
EVERYONE in Springdale teaches a one-day beginner course. There are now at least four options, Zion Adventure Co, Zion Rock, Zion Mountain School and Red Desert Adventures.Quote:
Originally Posted by Deathcricket
When I (and most of the we, including Zion Adventure, and most probably the rest of the above) teach a one-day or half-day class, we make careful evaluations about the student's natural abilities and their rate of learning. We (in this case ZAC) stress teaching a simple system and practicing it a lot. The system I teach depends on the students, but generally I would pick one way of rigging a rope and one way of setting oneself up on rappel, and sticking with that. If this couple were my students, I probably would have set them up on a double-rope rappel with a Pirana and an autobloc.
It is a matter of judgment about when to move past the autobloc. In most of my classes for people that I think will continue canyoneering, I make a point that the autobloc is a crutch that they need to understand and grow past quickly. However, most of the classes I teach are three-day classes, where I make a point of getting people past the "autobloc phase" during the class. In a one-day class, it is much harder to get past that point, or even to get to the point where the idea of no-auto-bloc can be introduced.
We also emphasize the Fireman's belay as being a better overall backup system than the autobloc.
For many people, a canyoneering class is extremely stressful, and they only remember some of the material presented. Thus, we like to have many repetitions of the simple system, and not confuse things by introducing conflicting or complementary ideas.
I have had several couples (as it turns out) fail the one-day basic class. At the end of the class, the question is what canyons can they do on their own. On two occasions, I have told couples that they would not be up for doing the Subway (but yes for Keyhole); although mostly that is because 240-lb non-hikers would not be able to do The Subway in July. On both occasions, they knew it, and were grateful for the confirmation (rather than pissed off), and were happy with the experience of the day, and reveled in the knowledge that canyoneering would not be their sport.
Tom
No argument from me that a top belay is much better then a fireman's all things being equal.Quote:
Originally Posted by Brian in SLC
My reason for liking a fireman belays is they are simple, fast, anyone can do them with a few minutes practice and my family uses them as a back-up. Realistically we are not going to top belay the entire group of experienced canyoneers because of time constraints. But there is really no reason not to set a fireman's belay in most cases as it requires almost zero effort or additional time.
x2 We always fireman belay if possible. I've stopped 2-3 people completely out of control and another handful who were losing it. Way more practical and quick than a top belay. Top belay is more full proof, true, but generally people who need the fireman belay are trying in some way to stop themselves and the added force of the fireman belay is enough. I've never encountered a situation where it wasn't enough. I once had a girl completely let go of the rope on her way down the 300 footer in engelstead. She was about 150-200 feet up and I pulled hard to stop her and then lower her slowly. When she got to the bottom I asked her what happened and she said "I got tired and knew you would take care of me" :facepalm1::facepalm1::facepalm1: That totally gave me the chills :cold: I never took her again.. but the fireman belay worked.Quote:
Originally Posted by Iceaxe
x3! on the fireman's belay.Quote:
Originally Posted by Iceaxe
All you strong advocates of the top belay: I'll believe it when I see someone do it. I don't. EVER. Except certain guides.Quote:
Originally Posted by Brian in SLC
Tom
Maybe you just need to get out more, Tom...Quote:
Originally Posted by ratagonia
Attachment 59281
Attachment 59282
I do it all the time...
North Wash season coming soon ...Quote:
Originally Posted by Brian in SLC
T
North Wash? Heck, I'd gladly accept a top belay from you for some of them down climbs....!
Skinny, narrow slots are frightening to me.... A man has to know his limitations.
I use a belay from top all the time (practice and for real). On long lowers the belayer better understand "rope weight" vs "belayed mass" particularly when visual contact becomes an issue. Large bellys can easily be introduced into the belay line as the belayer thinks the rope weight is actually the weight of the person being belayed. Back tension is critical to prevent "a belly" or slack into the belay line. We did a pick-off on Angels Landing last summer. Using 2 -1300' ropes and a 300' rope tied to the ends of each, an operation of shared load for both main and belay was done. Without radio comm. a large belly could have easily been introduced into either main or belay. Finally it took 2 of us to use hand-over tension on the belay to prevent a belly. Same thing could happen whilst belaying from the top of lets say Heaps? Unless the belayer shares the mass of the rappeler. a large belly could easily develope in the belay line and if the rappeler lost control lets say 50' above the ground, by the time the top belay could accept the total mass, with stretch I bet the rappeler will have decked?Quote:
Originally Posted by ratagonia
Yeah, Bo, keep an eye on them large bellys...
For me, and "my people" (the folks I feel responsible for), the most critical time is just gettin' going on rappel. Once they start down and they're fairly smooth, then, I try to give them enough slack that they don't feel the belay. Near the bottom, when the rope weight changes, I let the "belly" disappear and want to feel them a bit more, or, if I can see them, then see that there's a bit of tension in the line. Usually try to get a verbal from them that they're doing ok too.
But, you're right, near the bottom, when the friction is lower due to less rope weight, it'd be easy to blow it. At 100 feet, even with only 3% elongation, you wouldn't need much "belly" to have someone hit the ground fairly hard if they lost control of the rappel near the ground.
Good thoughts!
When the primary (or only) concern is helping people make that transition over the edge, try giving them a short 2:1 belay. Requires a length of rope that is twice the distance from the anchor to the spot over the edge where you want the belay to end. I typically figure out that distance, then connect the rope with a clove hitch to a carabiner on the anchor. Pass a loop of rope through a carabiner on the rappeller's harness, then back through a second carabiner on the anchor. If the rappeller is heavy or you are simply concerned about your ability to arrest, use a munter hitch on the second carabiner.Quote:
Originally Posted by Brian in SLC
Once the rappeller reaches the belay-end spot, the tail of the rope will come out of your second carabiner. The belayer should control where the tail drops -- don't let it hit the rappeller, drag loose rock over the edge, etc. The advantage of this system is that the rappeller does not have to stop to disconnect the belay rope. Also no need to pull up a long belay rope and it is quick to rig on the next rappeller.
Needless to say, it is not a system that will work in all situations. Depends on the anchor location, etc. When it is deemed prudent to provide belay all the way to the ground, choose another belay method.
Attachment 59447
Quote:
Originally Posted by Brian in SLC
I have successfully stopped someone with a Fireman's and yet not been directly below. When there is a risk of rocks being dislodged from above, I have moved off vertical, out to the side, and still been able to effectively employ the Fireman. The rappeller often gets pulled off vertical, but the effect is still the same.
Kerry
Personal preference, I just much prefer a single rope rap to the double rope unless its just such a short rap as to make setting up a beaner block(or releasable figure 8) just time consuming. The times I have done Heaps, I like to single with an autoblock on that looong freehang.....unless the rope is wet and sandy. Game changer!
I consider using an auto block or prusik system for belay to be extremely unnecessary and potentially dangerous. I often use the phrase, it is so safe, it creates more problems than it solves. A competent belayer should be able to tie off their descender in an emergency and should never let go of the break hand.
The reason I feel this way is because of stories I've been told regarding accidents related to auto blocks and a first hand experience. I've heard of people getting their auto blocks jammed in their belay devices and getting stuck mid rappel. Also correct me if I'm wrong, but didn't that old man in subway die because he couldn't untension his autoblock in the waterfall?
I also think autoblocks are like training wheels that teach bad form and develop a dangerous reliance to the device. Once when I met a Canyoneer who was using one, I suggested he don't use it because it tends to create more problems. He unfortunately listened to me and on his next rappel, slipped, let go of his break hand and fell 30 feet. Fortunately he was not hurt. Because he relied on the autoblock, he never built the muscle memory to grip his break hand no matter what.
People use it as a crutch and become comfortable letting go of their break hand with an autoblock when this practice should never be done.
So this is why I do not recommend using an autoblock unless there is a special circumstance that deems it appropriate.
I also agree with other posters that a fireman belay is a great alternative.