The dangers of back-clipping the rope to a quickdraw are fairly well known (www.petzl.com), and most climbers soon learn to avoid situations where the rope can unclip itself during a fall. Equally distressing, but somewhat less known, is the sight of a quickdraw unclipping itself from a bolt hanger. Here are some situations that can cause this.

Change of direction When a quickdraw rotates to a new direction, the top of the hanger can pry open the carabiner gate and the quickdraw can detach itself completely from the bolt.
Catching the bolt The bolt itself can catch and open the gate of a carabiner. This can happen with wiregates or even with regular carabiners whose gates have edges that can catch the bolt.
Some of these situations have actually happened to me, but I didn't recognize what was going until I actually tried to make a quickdraw unclip itself from a hanger. Try this yourself with a hanger and a quickdraw. Bet it'll give you something to think about! Here's an excerpt from the "Biner Orientation for Sport Draws" thread in rec.climbing (search www.dejanews.com for the full thread). Chris Harmston writes: I have to dissagree with the recommendations of having the gates face the same way or the opposite way, every situation is different and may require different techniques. I recommend setting up draws with a selection of different length of runners with the biners oriented in the same direction and the opposite direction. I only recommend fixing the bottom biner. Here are my reasons in order of importance (based on likelyhood of failure in my opinion): Note, I think through these issues EVERY TIME I clip a piece of pro on every route. Learn to do this quickly. Assess every piece of pro every time. I do not believe that there is one technique that works in every situation. 1) Bottom biner must not be loaded over an edge or buldge. Use different length of draw if needed. If this is not possible then use a locking biner. Look for rotational effects. The buldge or edge may not be located directly below the bolt but could be off to the side. Make sure you think about how the draw will move when you fall from different places on the route above you. Often times a route will force you to climb both to the right and to the left of the piece below you. Remember this when clipping your pro. Try to assess where you might be most likely to fall from and set up your pro accordingly. 2) Top biner must not be loaded over an edge or buldge. On bolted sport routes this does occur fairly often. Use a locking biner for these situations, two biners, add a backup tie off, or better yet if you think you might fall on this bolt-BAIL. Then slap the first ascentionist repeatedly until they fix their fuckup. Often times you can simply rotate the biner with the gate opening downwards to reduce the likelyhood of the buldge opening the gate. In general I try to make sure that the gate faces away from the bolt head. It can interfere with the biner gate in some rare situations. Top biners are much less likely to unclip if they are not fixed to the quickdraw, therefore I do not fix the top biner to the draw. 3) Bottom biner must not be back clipped. Unclip and reclip the rope until it is clipped correctly. 4) Bottom biner gate must face away from the direction you are climbing towards. 5) Orientation of either biner is independent of where you are clipping from. They are dependent on where you are going and the variables above. Be able to clip with either hand with the biners facing either direction. Setting up your draws and clipping them in one direction just because you have poor technique is a bad excuse that could have harsh consequences given the right circumstances. Learn the pinch clip and the index clip and the palm clip and and and. Be proficient at any clip! There are times when this is not feasible. When climbing at your limit you may need to force a certain type of direction to make the clip easier. Be aware that this may not be the best situation when falling from above. 6) Carry 1 or two draws with locking biners on both ends for those situations where you can't avoid biner interaction with buldges or edges or when faced with a hard crux or runout where gear failure would be disastrous. These are my personal opinions from my own experiences in climbing not from testing that I have done. Chris Harmston (chrish@bdel.com). Quality Assurance Manager. Materials Engineer BS, ME. Black Diamond Equipment Ltd. 2084 East 3900 South, SLC, UT 84124 phone: 801-278-5552