Undoubtedly, the most critical component in any mission-critical data center isn’t the capacity of data servers or the types of UPS batteries; it’s the life-safety measures. Smoke, not the flame itself, is the greatest threat to safe evacuation and survival during a fire event, so fire-suppression systems, means of egress, fire containment and fire-alarm systems are by far the most important ways to decrease the chance of injury or loss of life from a burning building.
But building codes may require additional life-safety instruments, or the building’s owner or operator may add them to increase safety. The following is a brief overview of such measures.
Automatic fire-suppression systems come in four basic types: water-based wet, water-based dry, non-water-based wet and non-water-based dry. A water-based “wet” system is the ordinary pressurized water system run through iron pipes (referred to as “black iron”); it usually operates on its own dedicated water supply line, separate from the building’s domestic water line. A water-based “dry” system, used in unheated locations such as warehouses, parking garages, attics and crawl spaces, is a water-based wet system except its black-iron pipes are primarily kept empty to avoid freezing. These pipes become pressurized on activation. Since water-based systems (wet and dry) are effective and usually less expensive than other systems, they’re often used but seldom considered the best option for computer rooms, because they can damage the expensive servers and their irreplaceable data.
Non-water-based systems come in wet chemical and dry chemical. The “wet” chemical systems (foams and gels) primarily serve in commercial kitchen hoods to suppress grease, oil and electrical fires; and since the wet foam and gels can damage printed documents, fabric and computer files, they’re seldom used in other parts of the building. Some “dry” chemical systems, however, are designed to intentionally leave a sticky residue (to help douse embers), which is good for some situations but certainly not for data servers. Other dry chemical systems are designed to leave no lasting residue, and they’re promoted as using “clean agents.” A clean agent is defined by the National Fire Protection Agency (NFPA) as an “electrically non-conducting, volatile, or gaseous fire extinguishant that does not leave a residue upon evaporation”—so many prefer it for fire suppression in server rooms.
Means of Egress
Means of egress are paths to safely escape a burning building. They’re most often protected by fire-rated enclosures (such as fire-rated walls, fire-rated stairs and fire-rated floor/ceiling assemblies), and they provide observable guidance along the way using backlit exit signs, flashing strobes and emergency lighting. They lead out of the building to an open-air public space that meets the legal definition of a public right-of-way.
The means of egress in a data center is more complicated than in other buildings, however. The large floor plate of a typical data center requires special consideration owing to its long corridors (often 500–800' long) and its egress stairs, which will need their own exit corridor when located near the servers (instead of residing at both ends of a main corridor, like in a typical office building or hotel). In addition, the data center’s long corridors need alternate exits because large floor plates easily exceed the building code’s “common path of travel” and “dead-end” distance limits.
In a word, fire containment is preventing the spread of fire and smoke throughout a building by employing fire-rated barriers at major locations. Such barriers include fire-rated doors, fire-rated floor/ceiling assemblies, fire-rated opening protectives (fire-alarm-released window shutters and overhead doors) and fire-rated walls (employed at most stair walls, most corridor walls, many interior tenant-separation walls, some exterior walls and any interior wall that separates two buildings). Maintaining a fire barrier’s integrity by fire-rating any penetrations is also critical (e.g., by sealing around electrical conduits, electrical trays and plumbing pipes or by providing automatically released fire-rated dampers on mechanical ducts and registers). Also critical is forming a smoke barrier by employing smoke seals (providing gaskets around interior fire-rated door and window frames, drop seals at interior fire-rated doors, and drywall-to-drywall tape or smoke-sealant spray/caulk at wall-to-ceiling connections).
Fire containment in data centers is also more complicated than other building types owing to the desire to phase its interior fit-out construction. Since most data centers must be online as quickly as possible, the building is often constructed in phases: the first sections receive their own building permit and construction schedule, then they’re turned over to operations before or during the construction of subsequent phases. These early phases need special consideration during the design process to provide a complete standalone means-of-egress system. Additionally, since data centers typically use rated drywall that connects to the exposed underside of the floor or roof (such as concrete flooring or metal roof decking), fire- and smoke-sealing the wall-to-ceiling joints need special attention.
Data centers are also different from other building types in that their equipment (specifically, their server racks and cable trays) may occasionally undergo relocation, potentially breaching the fire-containment barriers. On one site visit to an operational data center, I came across rectangular cutouts through several rated walls (with the openings all being aligned with each other) where, evidently, a server’s electric-cable tray had once penetrated the walls then was later removed. But the openings were left rather than being closed in with rated construction. On the flipside, during other site visits I’ve found penetrations into rated walls (particularly for cable trays or single security wires) that don’t appear to conform to the requirements of any tested fire-rated penetration system.
Fire-alarm systems generally contain bells or horns (as well as strobe lights) that are connected to fire and smoke sensors, and often they must be connected to the local fire department. These alarm systems—which usually require bells or horns throughout the building and strobe lights in nearly all accessible areas for those who are hearing impaired—are meant to prompt an evacuation and then help guide the evacuating occupants along the safe means of egress. Data centers, with their sophisticated management systems, have a special need to ensure that their life-safety alarms never connect to other alarm systems, such as security and energy management.
But in addition to the standard life-safety methods described above, the building code or local jurisdiction may also require other life-safety instruments, or the building’s owner or operator may employ them to increase safety. The following are a few examples.
- An ADA fire-rated safety zone (with two-way communication), called an area of refuge, provides a haven for persons who have a physical handicap and are unable to evacuate quickly, enabling them to remain in a more protected environment while phoning and waiting for help.
- You-are-here evacuation floor plans along main egress paths, particularly near egress stairs, allowing occupants to review and understand the building-evacuation paths during normal work hours and well before an emergency event occurs.
- Wall-ratings stenciled high on rated walls to help avoid inadvertent fire-rating breaches during daily maintenance of the physical plant, later during a renovation’s construction or when building out new interior phases.
- Warning labels on specific room doors to signify which ones (e.g., a server room) are protected by a chemical fire-suppression system, thereby encouraging personnel to evacuate these rooms and not consider them a fire safety zone.
A final measure is periodic inspections. During construction, and particularly before punch-walk demonstrations before sign-off on a building’s (or phase’s) upcoming use and occupancy permit, the project’s general contractor should conduct a pre-inspection review of everything that affects life safety. At a minimum, it should do the following:
- Ensure availability of safe paths through any phase’s temporarily stored construction materials and out to a public right-of-way (during one site visit I actually saw an exterior egress door intentionally covered with plywood sheets to prevent its use for a few days, and yet the exit sign above the door was still lit).
- Verify that the backlit exit signs are installed and visible along all egress paths (including in a large server rooms).
- Pre-mark small but visible designations on all emergency lights (I have found that many manufacturers neglect to provide such an indication).
- Make sure all lights in an area or zone can be turned off to test the uninterrupted emergency lighting.
- Enable testing of interior smoke-rated overhead doors to ensure their automatic drop-down release is functional (often being as simple as flipping the switch to disengage its fusible link).
- Confirm that smoke seals are in place at all fire-rated doors.
- Confirm that smoke seals (drywall tape as well as sprayed or caulked smoke sealant) and firestopping penetrations are in place at fire-rated walls.
- Confirm that the standard orange-colored plastic covers on sprinkler heads and smoke sensors (factory installed and maintained during most of construction for damage and dust control) have been removed—I’ve found they’re hard to see in the cold aisles of a computer room, since they’re surrounded by layers of ducts, pipes, cable trays and wiring rows.
- Verify that the fire-rating designations on doors and door frames aren’t painted over (it’s tough to scrape off the paint or even find the signs if painted over, especially when the door is equipped with an alarm that only allows it to be open for 15 seconds at a time).
- Verify that any wood installed in a noncombustible designated building (such as for temporary walls, electric- or phone-service plywood backers, and rooftop mechanical platforms) has noncombustible labels present and visible (in my experience, painted-over labels and use of standard, combustible plywood sheets on wood studs occurs too often).
Employing the above life-safety precautions and procedures during design and construction, as well as afterward, will decrease the spread of fire and smoke and increase the survival rate in any burning data center, thereby protecting its most valuable asset: its occupants.
Image courtesy of DVA Architects
About the Author
Dean Ventola, RA, NCARB, LEED AP BD+C, is the Director of Construction Administration at DVA Architects in Gaithersburg, MD, a nationally prominent mission-critical data center architect.