1. Operable with one hand does not necessarily mean "operable in a single movement with one hand".
If a door is allowed by Ch. 10 "means of egress" to have more than one operation/motion to make it open - - then with a deadbolt, one action unlocks it, and it stays unlocked. The second motion is on the door handle itself.
2. That leaves the question of the action itself is accessible:
- Tight grasping is not allowed, but loose grasping is theoretically allowed.
- Keyholes are allowed because the key is not technically part of the
door hardware, and so no one know how big or easy the key is to use.
As to your question, see also:
https://idighardware.com/2010/08/accessible-thumbturns/
"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. I have also heard of code officials using the tip of a pencil to test the accessible operation of a thumbturn.
Many thumbturns are now designed so that they pivot from the end rather than the center, requiring less leverage to operate. "
For a more official guideline, see:
https://www.access-board.gov/guidel...andards/chapter-4-entrances,-doors,-and-gates
Latches and locks with small parts that must be manipulated can be difficult to use and will not comply if pinching is necessary. However, keys and access cards that are not part of the lockset are not required to comply (but those that do not require pinching or turning provide better access). Hardware that does not require simultaneous actions are better, but some types, such as handles with thumb latches are acceptable.
Recommendations:
- Specify hardware that is usable with a closed fist of loose grip
- Bars, pulls, and similar hardware should provide sufficient knuckle clearance (1½” minimum) to facilitate gripping
- Avoid hardware that requires hand or finger dexterity, fine motor movement, or simultaneous actions.