On the other hand, NFPA 13 indicates all the additional sprinklers will be added to the ceiling demand. Standard sprinklers are based on the theory of controlling the fire and are fairly tolerant systems. The ESFR sprinkler design approach is based on obtaining suppression in the first stages of a developing fire. It is a far more sensitive system and the flow from an additional unaccounted sprinkler could cause it to fail. A deluge system utilizes open sprinklers.
Open sprinklers are sprinklers that have had their heat sensing elements removed.
Before the 1996 edition of NFPA 13 this was not clearly addressed since it only stated that these heads were permitted. This will require that open sprinklers, in a deluge system installed under an unobstructed type of construction, will have a maximum deflector distance of 12 inches. This requirement only applies to the installation of deluge systems for structures and not to water spray systems installed per NFPA 15. We all know that all sprinkler devices must be listed, except those specifically identified by NFPA 13. One of the requirements of its listing is that the device be installed in accordance with the manufacturer's installation instructions.