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Emergency Lighting for Data Centers

IBM specialists have extensive experience in data center design and construction. Along with designing a robust electrical system, it’s important to design plans for emergency situations. The loss of electricity could be the result of a fire or a power cut leading to the failure of normal lighting. This may also lead to a blackout and pose a danger to data center occupants, either physically or just panic. Emergency lighting is normally required to operate fully automatically and illuminate at a sufficiently high level to enable all occupants to evacuate the premises safely.

Data center facilities are designed and built to meet the safety codes and international recommendations for the facilities. This article explores the best practices for the facilities' emergency lighting.

Self-contained emergency lights are recommended for data center facilities due to its great system integrity; each lighting fixture is independent of the other while complying with the fire resistivity directive such as BS EN 60598-2-22 for enclosures, in case of a fire. The lighting system contained inside (such as battery, the lamp, the control unit) should not be effected and should continue to function in an emergency situation.

In contrast, the ‘central battery source emergency lights’ have poor system integrity as they are susceptible to failure due to the failure of battery or wiring circuit resulting in failure of a large part of the system.

The self-contained emergency lighting system also provides flexibility to be extended with additional luminaires as it’s required. Installation is easier and inexpensive as additional power cables do not need to be run and standard wiring material can be used, as opposed to fire resistant cables required for central battery source. The failure of mains supply due to cable burn-through will automatically satisfy the requirement for a lighting fixture to be lit; moreover no special sub-circuit monitoring is required (Wiring practice for the 'Self Contained Emergency Lights' is explained in the subsequent section of this article).

In addition to the above, self-contained emergency lights require less maintenance as compared to the central battery source system.

Emergency Lighting Requirements

NFPA 101, Life Safety Code 2006, section 7.9, defines the requirements for emergency lighting. Emergency illumination (during operation) must be provided for a minimum of 1.5 hours in the event of failure of normal lighting. The emergency lighting must be arranged to provide initial illumination of not less than an average of one foot-candle and a minimum at any point of 0.1 foot-candle measured along the path of egress at floor level. These levels can decline to a minimum of 0.6 foot-candle average and 0.06 foot-candle at any one point at the end of emergency lighting time (1.5 hours). The maximum illumination at any one point can be no more than 40 times the minimum illumination at any one point to prevent excessively bright and dark spots (NFPA 101 2006

The emergency lighting system must be arranged to provide illumination automatically in the event of any interruption of normal lighting (NFPA 101 2006

Exit Sign Requirements

Every sign must have the word "Exit" in plainly readable letters not less than six inches high, with the principal stroke of the letter 0.75 inches wide (29 CFR 1910.37(b)(7)). (Please refer to NFPA 101 7.10 for further specifications). Where the direction of travel to the nearest exit is not immediately apparent, an exit sign or similar designation with an arrow indicating the direction to the exit is required (29 CFR 1910.37(b)(4)).

Wiring Installation for the Emergency Lighting w.r.t NEC codes

When installing self-contained emergency lights, it is a recommended practice to wire these on the same circuits as the general / normal lighting in the area, this ensures that the emergency lights will protect not just against a general power failure, but also against the failure of a lighting circuit. NEC (Article 700) refers to this practice and states that the branch circuit feeding the unit equipment must be the same as that serving normal lighting in the area and connected ahead of any local switches, and must be clearly identified at the distribution panel. The core logic behind this recommendation is that in the event of a fire, if the cabling used for the emergency luminaries has greater protection, there may be a chance of the normal lighting failing and the emergency lighting remaining in the normal mode i.e. inoperative. Hence it is recommended that self-contained emergency luminaries are wired in the same circuits as the general / normal lighting in the area.

Moreover, in large premises, it may be acceptable to connect the self-contained emergency lights to dedicated circuits from the same board as the general lighting. This arrangement would not protect against the failure of a 'lighting circuit', but it is presumed that sufficient light would be available from lamps on other circuits. Any failure of the 'supply' to the lighting board would of course bring the emergency lights on. NEC (Article 700) endorses this arrangement for areas with at least three normal lighting branch circuits and suggests that the emergency illumination unit equipment may be supplied by a separate branch circuit.

NEC (Article 700) states that wiring for legally required standby systems is permitted to occupy the same raceways, cables, boxes, and cabinets with other general wiring. This is because any failure of the supply to the common lighting board / cabinet or in the event of a fire damage to the normal lighting circuit this arrangement will bring the emergency lights on.

For more information

To learn more about how IBM can help on your journey to greater data center efficiency, contact your IBM representative or visit the following websites:

Syed Ahsan Baqi is an experienced engineering consultant.

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