I carry concealed whenever I legally can, and it's mostly a 1911 in condition 1 carried IWB in a Milt Sparks Versa Max 2 holster. I've never had the safety come off.
First, I make sure that any 1911 I might carry has a very positive "on-safe."
Second, the holsters I use are leather and have a sweat shield between my body and the gun. The sweat shield has become slightly scored by the safety in the engaged position, and that also helps.
"It is long been a principle of ours that one is no more armed because he has possession of a firearm than he is a musician because he owns a piano. There is no point in having a gun if you are not capable of using it skillfully." -- Jeff Cooper