I’ve seen three designs for purely mechanical flush door handles in production use:

• A handle with a central hinge where one side is pushed inward to make the other side stick out to be pulled. This design has been used on aircraft for many decades, and has also made its way to a few cars.
• A pull-up door handle with an additional flap in front of the access area. This was used on the Subaru XT/Alcyone/Vortex.
• A handle that pushes in to open, usually found on a portion of the door that’s more horizontal to the ground. Used on the C3 Corvette, among others.

The push-then-pull central hinge is probably not a great choice for the application because its operation will be less obvious to a rescuer trying to get the door open quickly. It’s still better than something that requires electronics.