Do I need an explosion proof damper actuator if the medium
in the duct is explosive but the actuator is mounted on
the damper shaft out of the airflow?
Yes, you do require an Ex actuator. There are various points
on the duct (flange connections, temp/pressure sensor duct
probes etc.) where some leakage from the duct may occur. If
this happens, an Ex area zone 1, 2, 21 or 22 will be outside
the duct. There is the potential for explosion and only
if all equipment outside the duct is Ex safety can be guaranteed.
The same applies to sensors, switching contacts, monitors,
valve actuators etc.