Data center metrics and standards guide
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IT professionals haven't generally known much about NFPA 75 and 76. That will have to change.
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In 2012 and 2013, the National Fire Protection Association (NFPA) revised NFPA standards 75 and 76, which cover data center fire suppression. Important new requirements for containment cooling structures apply to new builds and data center upgrades.
Understanding the terminology
Before addressing the standards changes, we need to first clarify definitions, and there are several new ones.
NFPA 75 and 76 work with NFPA 70, also known as the National Electrical Code. NEC covers the design and installation of everything electrical in every type of building.
Data centers struggle often with NEC Article 645, which specifies the infamous and dangerous Emergency Power Off (EPO) button. The same language is now used, often verbatim, in NFPA 75, NFPA 76 and NEC Article 645. Since these documents all reference each other, expect NEC's 2014 revision to reference the 2013 NFPA 75 revision. At that point, both the code and the standard will have the weight of law everywhere the newest NEC is adopted.
The NFPA codes and standards do not use the terms data center or computer room. Instead, they define information technology equipment in ITE rooms and ITE areas. Rather misleadingly, the codes refer to ITE as "equipment and systems ... normally found in offices or other business establishments and similar environments classified as ordinary locations that are used for creation and manipulation of data, voice, video and similar signals" (emphasis added). That doesn't sound like data centers, does it? But the technical requirements of NEC Article 645, NFPA 75 and NFPA 76 include dedicated cooling, a room accessible only to qualified personnel, and an EPO to instantly shut down all power and cooling.
The NFPA standards' titles also require interpretation. NFPA 75, "Standard for the Fire Protection of Information Technology Equipment -- 2013 Edition," addresses data centers and the areas around them. NFPA 76, "Standard for the Fire Protection of Telecommunications Facilities -- 2012 Edition," addresses common carrier entrance rooms, emergency services call centers and any other utility services that support or affect public communications.
Containment cooling and fire suppression
The most important change in NFPA 75 and 76 makes containment cooling designs more complex, but safer.
Containment cooling closes off data centers' hot and cool aisles to prevent supply and return air from mixing. It is one of the best, and heretofore easiest, ways to improve data center cooling and energy efficiency. Containment ranges from permanent overhead panels and end-of-row doors to simple hanging plastic curtains that are fire-retardant and antistatic.
Retrofitting existing data centers to containment cooling setups was easy even if sprinkler and inert gas heads were not installed in every aisle. Any containment panel or curtain that blocked water or gas discharge could use a fusible link that melted in the heat of a fire, dropping the obstruction. Heat-shrink panels were another option. But these links and panels need a fairly strong fire to melt, essentially the same heat strength it takes to trigger sprinkler heads.
While the heat builds, these containment structures can hide the fire and smoke. If a fire goes undetected, inert gas is not released, and pre-action pipes and sprinklers remain dormant. If the fire is detected, but the aisle is still isolated, the inert gas can't reach the fire.
A standard revision was in order. Fusible links and thermal mechanical removal are simply not permitted anymore in data centers with containment cooling.
NFPA 75 and 76 now require one of two things in these facilities:
- Design or re-design the fire protection (gas and/or sprinkler) to properly cover all areas at all times, including contained aisles.
- Include mechanisms with the containment panels, doors and/or curtains that will open or remove the containment barriers automatically when fire sensors detect smoke or heat. In other words, electrically couple the containment to the fire and smoke detection in a fail-safe manner. That also means the dropped panels or curtains can't impede egress.
So things aren't as easy as they were before. For new data centers, the first option is the best choice. Put fire protection that covers every aisle and area, contained or not.
For retrofitting existing data centers, the task gets a little more challenging and expensive. Re-piping and testing sprinklers and gas systems in working data centers is risky, time-consuming and costly. Electrically activated containment, the second option in the revised NFPA 75 standard, makes more sense here. The only problem is that most manufacturers still need to develop the product. Plan to pay a little more for it than for the old method of heat-shrinking or fusible links.
Don't forgo containment cooling because of the revisions to NFPA 75. If cost or physical changes prohibit full containment, go for partial containment. You can make a substantial difference in energy costs without interfering with fire protection, just by closing the ends of aisles.
A word of caution, however. Temperatures in contained hot aisles can exceed 120 degrees Fahrenheit, even hitting 150 degrees Fahrenheit if cooling fails. When selecting sprinkler heads and detectors, be sure that the temperature ratings support this environment. Also, smoke detector performance in high air movement conditions is still under research.
Another revision will make contained aisles and hot air collars (also called cabinet and air conditioner chimneys) easier to build, especially for nonmetal elements. Contained aisles and hot collars are not considered air plenums. Therefore, data centers do not have to use plenum-rated cable and patch cords or follow other plenum-specific code requirements. Materials used for any type of containment must now meet specified flame spread and smoke development indices' criteria.
About the author:
Robert McFarlane is a principal in charge of data center design at Shen Milsom & Wilke LLC, with more than 35 years of experience. An expert in data center power and cooling, he helped pioneer building cable design and is a corresponding member of ASHRAE Technical Committee 9.9. McFarlane also teaches at Marist College's Institute for Data Center Professionals.