A valve system for ensuring well closure upon exposure to a predetermined condition even where a well access line is disposed through the valve. This system may be configured with a supplemental power supply capable of effectuating a cutting closure of the valve. Thus, any obstructing well access line such as coiled tubing may be cut during closure to ensure sealing off of the well, even if the cutting mechanism is separated from its traditional power supply by shear or parting of a portion of the landing string. Once more, the supplemental power sufficient for a cutting closure is only provided in the event of a predetermined condition such as the emergence of a potentially hazardous tubular separation.