Such apparent redundancy may, however, be ineffective because of capacity limitations or critical equipment items that are not connected to backup systems. Scenarios of this nature may arise, for example, during system expansion when additional loads are connected to the power systems. Sometimes UPS systems have been found to lack the best bypass provisions for restoring power promptly in the event of failure and to facilitate maintenance. Fire and Explosion Scenarios A data center often has characteristics that present a fire hazard. Typically, numerous pieces of computer equipment are situated on raised floors.
Ordinary combustibles are generally limited to stacks of paper or boxes.
Underneath the raised floor, there is often extensive cabling, with PVC insulation representing more mass than vacant space. Fixed fire protection may include a Halon 1301 system tripped by cross-zoned smoke detection, with no protection provided under the raised floor. Mobile fire protection may be limited to hand-held fire extinguishers, with the principal agent being carbon dioxide. The extensive cabling, particularly that below the raised floors, enhances the fire risk. A fire in such a data center, particularly under the raised floor, could result in significant downtime - in excess of a week or more.