4.21 Single and Double Interlock Pre-Action Systems

Reference: NFPA 13 2002, Section 7.3.2, The Nineteenth edition of the NFPA Fire Protection Handbook, and Manufacturers Recommendations.

Double interlock pre-action systems are acceptable for protection of deep-freeze facilities where accidental valve operation may result in freezing of the pipe in a matter of minutes. When pre-action systems are proposed for protection of a specific room or hazard (i.e., computer equipment rooms, server rooms, communication equipment rooms, etc.) in buildings requiring a wet pipe sprinkler system, only a single interlock pre-action system will be approved for use in these buildings. The Fire Department considers the use of a double interlock pre-action system for the above reference hazards as inappropriate. An unacceptable delay may occur in the release of water from the sprinklers.

NOTE:
Flow cycling systems employing normally closed fire detection devices to activate the flow cycle valve shall not cause the building fire alarm system to activate an alarm condition when a single open or single ground fault condition occurs. Such occurrences shall activate a trouble condition.