The rules, if not using radar, is described in PANS-ATM 5.7.
The one we use is the departure may take off in a direction which is different by at least 45 degrees from the reciprocal of the direction of approach of the arriving aircraf before the arriving aircraft passes a fix, which in our case is located 5 NM from the threshold.
Rest are for us either not relevant, are downright stupid, or simply not usable.