I've wondered this myself.
Wouldn't the airflow about the fuselage "hold" the door closed? I've had a Seminole door open in flight and it is impossible to close in the air due to it not being a completely airtight vessel. So, since the CRJ is pressurized there would be nothing pushing the door open aside from the person opening the door. And I doubt that person is strong enough to overcome the outside pressure holding the door closed.
Maybe?
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