Case study: Clean agent system design at a data center
A project involving total-flooding clean agent protection of a mission critical data center illustrates the clean agent selection and system design process.
In this total-flooding clean agent protection of a mission critical data center example, the engineer’s role was to design clean agent fire protection systems for a partial renovation of the 8th floor of a government-owned historic building in Washington, D.C. The project involved the downsizing of an existing data center from approximately 6,600 sq ft to 2,700 sq ft.
At the time of design, the existing data center was already protected by a halon fire suppression system and supplemented by a pre-action sprinkler system. The engineer had primary responsibility for preparing construction bid documents for a halon-replacement fire suppression system in the consolidated data center and its supporting uninterruptible power supply (UPS) room, jointly referred to as CDC. The system was designed in accordance with the building and fire codes enforced at the time of project award, as adopted by the building owner’s agency, including NFPA 101: Life Safety Code, 2012 edition, and NFPA 2001: Standard on Clean Agent Fire Extinguishing Systems, 2012 edition.
After considering many potential U.S. Environmental Protection Agency (EPA) Significant New Alternatives Policy (SNAP)-approved clean agent systems, research efforts were focused on FK-5-1-12, HFC-227ea, and HFC-125 agents. See Table 2 for further information regarding environmental features, toxicity characteristics, and minimum extinguishing concentrations of these agents, all of which can be found in the Society of Fire Protection Engineers Handbook of Fire Protection Engineering, fifth edition.
The most influential factor guiding clean agent selection was the potential to reuse the existing halon system piping, which would significantly reduce construction costs. This qualification immediately eliminated HFC-125 as an option, as at the time, HFC-125 was generally unavailable at the pressures required to reuse the existing piping. The other major, owner-
determined factor in the decision was the environmental impact of the agent. The ozone-depletion potential of both FK-5-1-12 and HFC-227ea is zero. However, HFC-227ea has a global warming potential around 3,000 times that of FK-5-1-12 and an atmospheric lifetime of more than 2,000 times that of FK-5-1-12. While HFC-227ea was slightly less expensive than FK-5-1-12, the environmental benefits and the lack of severe regulatory restrictions on the use of FK-5-1-12 at the time made it more favorable. For these reasons, FK-5-1-12 fire protection fluid was chosen.
- The design parameters associated with the clean agent suppression system installation included:
- The presence of a solid ceiling meant that only the CDC and its associated raised-subfloor area needed to be protected with the FK-5-1-12 system.
- To reuse the existing halon piping system, the pipe had to be Schedule 40 pipe with 300-psi-rated fittings; drawings of record provided to the engineer indicated that the existing piping met these requirements. The halon nozzles on the existing piping needed to be replaced with appropriate FK-5-1-12 nozzles, per the manufacturer’s specifications.
- The only new clean agent piping required was for connecting the existing halon system cylinder storage room to two rooms included in the CDC that were not previously protected by the halon system.
- A separate releasing panel was provided for the clean agent system, located in the northeast corner of the CDC near the main entrance to the space.
- Tanks for the clean agent were installed both in the existing halon cylinder storage room and in the UPS room, as halocarbon agents are required by code to flood the area within 10 seconds of discharge and the location of the tanks is critical to meeting this requirement. It was recommended that the owner erect a ramp in the current cylinder storage room to ease the installation and exchange of FK-5-1-12 tanks.
- Reserve banks of agent equal in quantity to the primary agent supply were connected to manifolds in the discharge systems in both the data center and UPS room to allow for manual switching to the reserve bank after discharge. The reserve supply ensured seamless continuity of data center operations following a discharge event while the discharged tanks are being replaced.
- Manual clean agent discharge switches were provided at all exits from within the CDC. Each manual discharge switch was outfitted with a protective polycarbonate cover that, when lifted to gain access to the switch, sounds a warning horn intended to deter unnecessary system activation.
- Constant-pressure abort switches, or dead-man switches, were provided at all exits from within the CDC.
- Electronically actuated dual-purpose smoke and fire dampers and their associated relays were installed in all supply and return house HVAC air ducts entering the CDC. Each relay was located within 36 in. of the damper it serves, per NFPA 72: National Fire Alarm and Signaling Code requirements. The dampers were connected to the FK-5-1-12 releasing panel and programmed to close immediately prior to agent release.
- Control of the existing supplemental cooling unit (a computer room air conditioning unit, or CRAC unit) in the area of the CDC was connected to the FK-5-1-12 releasing panel and was programmed such that the CRAC unit would shut down immediately before agent release. This was necessary to prevent the high-velocity CRAC-unit airflow from adversely affecting agent release and distribution.
- The owner took full responsibility to ensure that all walls that make up the boundaries of the CDC, both above and below the raised floor, were properly sealed. All architectural work was performed and inspected internally by the owner, and pressure tests were performed to the satisfaction of the engineer.
The design parameters associated with the fire-detection and alarm system installed with the clean agent suppression system were:
- Complete photoelectric smoke detection via individual smoke detectors was provided throughout the data center and UPS room, including the subfloor area. The photoelectric smoke detectors are monitored by the FK-5-1-12 releasing panel. They were chosen due to their ability to function accurately and reliably in the high-air-velocity environment found above and below the raised floor in the data center.
- The clean agent releasing panel was programmed to transmit alarm, supervisory, and trouble signals to the main fire alarm control panel in the building.
- Discharge and predischarge audible/video alarm devices were installed within and at the exterior of both the data center and the UPS room.
- Activation of the first smoke detector in the system results in a predischarge condition at the clean agent releasing panel, as well as activation of the building fire alarm notification devices, at the request of the owner. A second smoke detector activation will be required to initiate the clean agent system discharge sequence.
- Standard building fire alarm notification devices were provided inside both the data center and the UPS room.
Proper interconnection between the clean agent system and fire alarm-initiating devices, as well as the building fire alarm system, is key to having a reliable and effective system. NFPA 2001 provides guidance for the design and installation of detection, actuation, alarm, and control systems in Chapter 4.
In addition to system installation, proper disposal of the removed halon tanks was a primary concern of the building owner. As governed by the EPA, halon can be disposed of by selling it to critical users, donating it to the Department of Defense (DOD) Ozone Depleting Substances Reserve Bank, returning it to the original distributor for resale, or sending it to a halon recycler. The owner wanted to return the removed halon tanks to the government. As a result, all tanks removed from the data center were handed over to the DOD Reserve Bank in Richmond, Va.
M. Lee Draper III is a registered fire protection engineer with Koffel Associates.
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