ALL Colt 1991 1911's have the Series 80 firing pin safety pictured in red below.
The firearm cannot fire unless the trigger is pulled, the grip safety engaged to ALLOW the trigger to move, and the manual safety off.
Colt went through a HUGE liability case and this 'modification' to the design was the result.
Does the design take into account EVERY part being manipulated by an external force? The forces around the MRI magnet are not limited to triggers and external safety releases, they pull on ALL parts, making them move in ways that were probably not anticipated by Colt.