Almost impossible, I only say "almost" because if I said it was impossible somebody would have a story of it happening to a brothers cousin's husband or something. Carry condition 1 and don't even worry about it. As long as your hammer hooks are in good shape (full cock and half cock) you will be fine. If you want you can even carry without a round in the chamber with the hammer back for a while to gain the comfort that it isn't going to release itself. Remember, in a PROPERLY maintained 1911 there are three things that need to happen before it will fire: thumb safety OFF, grip safety OFF, and trigger pulled. Impossible for all three things to happen in a properly maintained, and properly holstered 1911. Carry on my friend!
I mostly agree except for the carrying condition three as a learning experience. I think the condition of carry should be decided by the carrier, and consistent.
SOME 1911's will go off if dropped on the muzzle on a hard surface, whether cocked or not. Almost all NDs that happen that I know of are the result of booger finger in the trigger guard no matter what make of gun. They happen when the hand grips the frame, and the safety is off, and the finger touches the trigger when it is not supposed to. The three safeties mean and have absolutely no effect in stopping a ND. The brain is the most effective safety.
Most ND's are the result of brain farts. There are ways to minimize brain farts. Don't play with the gun while carrying. Don't play with the thumb safety while carrying. Don't touch the gun constantly as some people do. Don't keep your wallet, ID, credit card, phone, money anywhere near the same location as your firearm while carrying.
Remember Tex"I just ****ing shot myself" was carrying cocked and locked. I assume his grip safety was also working when he gripped his gun, took the thumb safety off, and pulled the trigger shooting himself in the leg. All clearly on video. It is a training video that ALL 1911 carriers should watch.
[video=youtube;paxk_LPmdMI]http://www.youtube.com/watch?v=paxk_LPmdMI[/video]
Carrying a unloaded gun is also a bad idea, because numerous gun ND happen with a supposed unloaded gun. If a person is going to carry condition 3 then is should be part of normal carry, not way of learning. The gun carrier should decide what is best, what they are comfortable with, and then carry that way only. All modes of carry are safe, until the carrier has a brain fart. Playing with less than the mode used is as dangerous as a loaded gun. I can hear it now at the ER, "But Doc, there wasn't a round in the chamber!"