I started replacing old bolts for rock climbing a couple of years ago with the Alaska Mountaineering Club, when I was living in Anchorage. Fixe Stainless Steel Wedge bolts, 3/8 by 3 1/2 are the way to go.
http://www.fixehardware.com/shop/bolts/fixe-ss-3/8-x-3-1/2-wedge-bolt/ Pair those bolts with a stainless steel hanger. With the bolt and hanger, it comes out to something like $8 a bolt, expensive, but $16 can build a safe anchor that you are staking your life on.
I'm seen a lot of people rappelling on sketchy bolts into caves. Usually people justify this by saying something like "rappelling is only a static force" or "i've rappelled on worse." We all know that these are just excuses, and one day someone is going to get into trouble because of it. Accidents in North American Mountaineering will show plenty of examples of a single bolt pulling out when someone is rappelling or being lowered (a "static" force).
Using a blow tube remove dust from the hole, and the appropriate size drill bit is also essential. Hell, you're even supposed to place them with a torque wrench to acheive full strengh (all climbing bolts with have a "torque to" rating). Remember, that KN rating is on a perfectly placed bolt. Also, if you don't blow the dust out after drilling it becomes lodged in the threads severely decreasing the bolt's strength.
Hardware store bolts and concrete fastners are generally more brittle and will sheer before they bend under pressure. None of those were developed or rated for climbing and are suspect at best.
http://www.safeclimbing.org/education/dangerbolts.htmIf were are placing bolts, lets take in the interest of the caving community and our personal safety. Two bolts are minimum for a safe rappel. If you place anything that you don't remove, other people will certainly rappel on it after you. In the interest of cave conservation, we should really be placing as few bolts as possible anyway.
If we are setting bolts why not do it right the first time? By making good multi point anchors and using stainless steel wedge bolts, we can rappel and climb on them for the next 50 to 100 years.
Hopefully that doesn't sound to much like a rant, but this is a subject I have been a little fired up on lately. Last weekend I was going through the Odyssey cave when we encountered a suspect bolt. We came through the Illiad entrance, and at the second drop past the nozzle (i think its the 5th drop from the Illiad entrance) we came to a single bolt rappel. It looks like it was originally placed as a rebelay, and both drops were done with a single rope. It was solid and stainless steel, but not set as well as it could be, showing about 1/16th of the bolt itself visible from behind the hanger (when looked at from the bottom). This means it was not set totally horizontally to the wall, thus decreasing its strength. Even if it had been perfect, it was still only one bolt, and there is no telling how long it was.
Anyway, I stopped there, while the rest of our group continued on. Even as a rebelay it wasn't safe, and had it failed on ascension, it would have created a dynamic force in which an ascender would have severed the rope.
http://vimeo.com/24521052 They say a tensioned rope can be cut with a plastic butter knife.
I wanted to bottom that cave, and now I'm intent on adding another bolt in this spot. We all rappel and climb on stuff like that all of the time while know it either isn't safe/ or could be safer. I would like to get some folks together and start replacing some of the aging bolts in TAG. Is anyone doing something like this already? Is there an NSS grant for something like this? The American Safe Climbing Association does this sort of thing for rock climbs. Anyone interested, or know how I could find some funding for this project?
Any thoughts welcome, Cave safe,
_ Brandon