C H A P T E R  5

Safety and Security

Safety and security issues relate to both the hardware and the operators working in the room. Design considerations should take the safety of those exposed to the environment into account in the design. In most cases, the goals for the electronic equipment are in keeping with the human safety goals. A balance must be achieved.


5.1 Fire Prevention in a Computer Room

A fire within the data center can have catastrophic effects on the operations of the room. The destructive force of a large-scale fire can damage electronic equipment, and the building structure, beyond repair. The contamination from a smoldering fire can also have very damaging effects on the hardware, and can carry heavy costs in cosmetic repairs. Even if the actual fire is avoided, discharge of the fire suppression medium can have a damaging impact on hardware. Whether measured in their threat to human safety, damage to computer equipment or loss of business due to systems disruption, the costs of a fire can be staggering.

Numerous steps can be taken to avoid the risk of fire in the computer room environment. Compliance with NFPA 75 will greatly increase the fire safety in the data center. The following precautions should be taken into consideration in the design and maintenance of the computer room and support areas.


5.2 Physical Structure

The first line of fire defense and containment is dependent upon the actual building structure. The various rooms of the data center must be isolated by fire-walls that extend from the concrete subfloor deck to the structural ceiling. Appropriately controlled firebreaks must also be present. NFPA 75 states:

2-1.3: The computer room shall be separated from other occupancies within the building by fire-resistant rated walls, floor, and ceiling constructed of noncombustible or limited combustible materials. The fire resistant rating shall be commensurate with the exposure, but not less than one hour.

2-1.4: The fire-rated enclosures of the computer room and/or storage rooms shall extend from the structural floor to the structural floor above, or the roof.

The HVAC system should be dedicated exclusively to the data center controlled areas. If this is not, however, the case, appropriately rated fire dampers must be placed in all common ducts or plenums.


5.3 Fire Detection and Suppression

The most common sources of fires in data centers are the electrical system or the hardware. Breakdowns in insulation and the resultant short circuiting can lead to intense heat that can melt materials or cause a fire. Computer room fires are often small or smoldering, with little effect on the temperatures in the room. Because the smoke itself can impact the computer hardware, it is necessary to employ a detection system that is sensitive to smoke and other products of combustion rather than temperature. The specific detection and extinguishing system is dependent on the specific design and exposures of the individual data center area. NFPA 75 states:

5-2: Automatic detection equipment shall be installed to provide early warning of fire. The equipment used shall a be listed smoke detection type. Each installation shall be engineered for the specific area to be protected, giving due consideration to air currents and patterns within the space and shall be installed and maintained in accordance with NFPA 72E, Standard on Automatic Fire Detectors.

2-4.3a: An automatic detection and extinguishing system shall be installed in the space below the raised floor.

A passive suppression system reacts to detected hazards with no manual intervention. The most common forms of passive suppression are sprinkler systems or chemical suppression systems. Sprinkler systems can be flooded (wet pipe) or pre-action (dry pipe). A flooded system incorporates pipes that are full at all times, allowing the system to discharge immediately upon threat detection. A pre-action system will flood the sprinkler pipes upon an initial detection, but will have a delay before actual discharge. Chemical total flooding systems work by suffocating the fire within the controlled zone. The suppression chemical most often found in data centers is Halon 1301. Halon is being eliminated in favor of the more environmentally friendly FM200 or various forms of water suppression. Carbon dioxide suppression systems are also used, but can be a concern due to operator safety issues in the instance of a discharge. These can be used independently, or in combination depending on the exposures in the room, local ordinances and insurance requirements.

The ideal system would incorporate both a gas system and a pre-action water sprinkler system in the ambient space. The gas suppression systems are friendlier to the hardware in the event of a discharge. Water sprinklers often cause catastrophic and irreparable damage to the hardware, whereas the hardware in a room subjected to a gas discharge can often be brought back on-line soon after the room is purged. Gas systems are, however, "one-shot" designs. If the fire is not put out in the initial discharge, there is no second chance. The gas system cannot be reused until it is recharged or connected to a back-up source. Water systems can continue to address the fire until it has been brought under control. While this is more likely to damage the hardware, it is also a more secure means of protecting the building structure. Water suppression systems are often preferred or mandated by building owners or insurance companies. Water systems are also highly recommended in areas containing a high level of combustible materials use or storage. The decision of what means of fire suppression to utilize must incorporate numerous factors including the mission and criticality of the data center operations.

Halon 1301 fire suppression gas is no longer in production, as of January 1994, and may be subject to punative tariffs under certain circumstances. Alternate gasses, such as FM-200, are available. FM-200 requires a slightly higher gas concentration than Halon 1301 (7% versus 5%), but is similar in effectiveness and has none of the environmental side-effects that led to the banning of Halon 1301.

Manual means of fire suppression system discharge should also be installed. These should take the form of manual pull stations at strategic points in the room. In areas where gas suppression systems are used, there is normally also a means of manual abort for the suppression system. In designs where it is necessary to hold the abort button to maintain the delay in discharge, it is essential that a means of communication is available within reach.

Portable fire extinguishers should also be placed strategically throughout the room. These should be unobstructed, and should be clearly marked. Labels should be visible above the tall computer equipment from across the room. Appropriate tile lifters should be located at each extinguisher station to allow access to the subfloor void for inspection, or to address a fire.


5.4 Water Detection and Leak Precautions

Water detection is important for a number of reasons. Leaks in the subfloor can cause serious threats to both personnel and hardware. Leaks are indicative of inappropriate functioning or conditions of the building infrastructure. They are normally caused by problems with the air conditioners or support piping, and early detection of leaks can help identify problems with the air conditioners. Less frequently, leaks are caused by infiltration of water from outside the room perimeter. Standing water in the subfloor can be extremely dangerous. Shorts where the water enters electrical connections can interfere with systems up-time, and can pose a shock hazard to personnel working in the subfloor. Standing water in the subfloor has also been known to breed biological material that can be recirculated through the room by the air conditioning. This can cause a health hazard to operators, and can even impact hardware in extreme instances. Problems such as efflorescence, the release of trapped mineral salts from masonry, can also be caused or aggravated by water leaks.

Monitoring, barriers and drains can all be used to address the detection and containment of liquids in the data center. At the very least, spot liquid detectors should be placed in the vicinity of air conditioners or water sources within the room. A more comprehensive system would employ a network of sensing cables. Drains, troughs and dams can all help contain leaks in the subfloor void. These should be used to isolate potential problem areas, such as the air conditioners or piping from the electrical and data lines in the subfloor.


5.5 Personnel Safety

Manual controls for the various support systems in the data center should be located conveniently in the room. Ideally, fire, leak detection, HVAC, power and abort or silence controls and an independent phone line should all be grouped by the appropriate doors. All controls should be clearly labeled, and concise operating instructions should be available at each station.


5.6 Operator Health Considerations

The most important safety precautions that can be taken in a data center are to limit the number of personnel in the sensitive areas to the absolute minimum, and ensure that all personnel are fully trained to respond to emergency situations.

In order to maintain the appropriate control over in-room psychrometric conditions necessitated by the hardware, the air in a computer room is primarily recirculating. Only a minimum amount of make-up air from outside the computer room must be introduced for ventilation and positive pressurization purposes. It may actually be necessary to introduce air in excess of the minimum ventilation requirement per workstation in order to maintain a positive pressure differential in the controlled areas. Ventilation for the human occupants of the data center should be assessed and adjusted as changes in room design or procedure dictate. In addition, gaseous contaminants can pose a threat to both hardware and human occupants. Contaminant problems can be accentuated by the recirculating air-flow patterns of the room.