A valve which allows an item of plant or equipment to be isolated automatically from a safe location without the necessity for manual intervention. The inability to quickly isolate hazardous substances inventory in the event of a major accident was an issue in theAssociated Octel Company major accident (1st and 2nd February 1994). For new installations ROSOVs should normally be fitted unless there are good technical reasons why they are not appropriate. For existing installations, the decision needs to be based on ALARP/cost benefit analysis