At least once a month someone asks me whether it’s ok to use a deadbolt with a thumbturn on a door that is required to be accessible. It took some digging to get a definitive answer, because the accessibility standards don’t specify a certain dimension that would be acceptable for the thumbturn. The ADA guidelines and ICC/ANSI A117.1 both state that hardware has to be operable without tight grasping, pinching, or twisting of the wrist, but that still leaves a lot up to interpretation.
In my opinion, there are thumbturns that can be operated by someone with a disability, as long as the hardware is installed correctly (incorrect installation can cause binding and make the thumbturn difficult to turn). I requested a staff opinion from the ICC, and I was told that if you can operate the thumbturn with the side of your palm, without grasping it with your fingers, it would be considered accessible. Many thumbturns are now designed so that they pivot from the end rather than the center, requiring less leverage to operate.
Here are some thumbturns that are likely to be accessible if installed correctly:
Here are some thumbturns which may not be accessible (test operation with the side of palm):
