The Importance of Monitoring Combination FIRE/SMOKE Dampers
The National Fire Protection Association, NFPA 75 Standard for the Fire Protection of Information Technology Equipment requires all Data Center air ducts and air transfer openings that pass through the fire rated construction be provided with fire and smoke dampers. A combination fire/smoke damper installed at the fire rated assembly meets this requirement for ducts serving the Data Center. Ducts passing through the Data Center but only serving other rooms are only required to have a fire damper. The intent of NFPA 75 is to limit the spread of fire and restrict the movement of smoke to other areas of the building outside the Data Center. Air-cooled Data Center’s with externally located air handling units are at risk of losing air conditioning if a fire/smoke damper should fail and subsequently close when it should otherwise be open under normal, non-emergency conditions. Monitoring the damper position is very important since your cooling depends on these dampers being open when the cooling equipment is located outside of the Data Center.
The fire damper portion automatically closes when the integral fusible heat link fuses under a fire condition in the duct. Heat links in most dampers today are bimetallic links that automatically reset themselves when cooled below their trip setting, usually 165°F. A damper actuator controls the smoke damper function, upon receiving a signal from the fire alarm system. A pneumatic or electric actuator operates the smoke damper
and it is common to use a powered open arrangement with a spring return mechanism that closes the damper upon release of the power source to the actuator. The fire alarm system receives detection from local or area smoke detectors, then responds in signaling the appropriate dampers within the smoke isolation zone to close, usually through a zone relay that simply drops out a set of contacts thus disconnecting the power circuit used to hold the damper open. NFPA 75 also requires smoke damper operation through the Data Center disconnecting means, usually referred to as the emergency power off or EPO system. Additionally, if an early response fire suppression system is used, such as a clean agent system, activation of that system will also be interlocked to shut down the dampers as required to properly seal the room for the fire suppression discharge. A failure of an actuator or a loose connection that interrupts the power source which holds the damper open, will result in both a nuisance closure of the damper and potentially blocking the air flow to the data center.
For this reason, a position switch should be specified and used for monitoring a closed position. The switch can provide a binary input to the Building Automation System (BAS) and initiate an alarm whenever a damper is in the closed position. The criticality of this alarm would be considered high to initiate a fast response by the facilities technicians. After ascertaining a false alarm damper closure, the damper can be manually re-opened to restore cooling airflow to the Data Center while the problem can be fixed.