I always put a socket in the "chimney" that covers the duct had couple of calls from customers recently where repairs were needed under warranty and the manfacturers would not attend unless the cooker hood was plugged in as their engineers are not qualified to disconnect from spur units and removing a plug from a socket was their safe isolation procedure before working on the unit
If it isn't a ducted out cooker hood then the only other type I know is the one that has the filters in the hood to catch all the grease and moisture, I've never known of one that's designed to throw all the crap back into the room.
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