Integration: Power and fire/life safety systems

Integrating power and life safety systems requires an understanding of the sources of power and the life safety system load requirements.

11/13/2013


Learning objectives

  1. Learn which codes and standards pertain to power system integration.
  2. Understand the codes and standards that pertain to life safety.
  3. Determine which power sources are correct for life safety applications. 

Figure 1: The new Massachusetts Green High Performance Computing Center was developed on a brownfield site in Holyoke, Mass. Courtesy: M+W

High-performance data center achieves LEED Platinum

Designed by M+W Group, the Massachusetts Green High Performance Computing Center is the first university research data center to have achieved U.S. Green Building Council LEED Platinum certification. The 90,300-sq-ft facility located in Holyoke, Mass., is operated by a consortium of Massachusetts’s most research-intensive universities. See Figures 1 and 2.


 

The integration of power and life safety systems requires an understanding of both the sources of power and the specific requirements of the life safety loads. It also requires a team approach of various types of consulting engineers including electrical, life safety, mechanical, and fire protection.

It becomes confusing when the terms “emergency life safety power” or “standby power” are used incorrectly or interchangeably to refer to either the power sources or the load. The following codes have very specific definitions for these sources and loads:

These codes break things down into two types or levels of systems: one is emergency/life safety and the other is standby.

Emergency systems are covered under NEC Article 700, which classifies these systems as “those systems legally required and classified as emergency by municipal, state, federal or other codes, or by any governmental agency having jurisdiction.” The NEC further states that “these systems ... automatically supply illumination, power or both … essential for safety to human life.”

In practical terms this normally includes providing power to egress lighting, fire detection and alarms, fire pumps, selected elevators, public safety communications, smoke or toxic exhaust systems, or any system where loss of power would cause serious endangerment to life or health within 10 seconds of normal power loss. Under NFPA 110, these are referred to as Level 1 systems. NFPA 101 Level 2 systems would be equivalent to the NEC Article 701 for legally required standby systems.

The NEC also contains requirements for legally required standby systems in Article 701. Code-required standby systems may include communications, selected ventilation or smoke removal systems, lighting, or certain types of industrial processes that may create hazards or hamper firefighting operations if power was not available. The code-required standby systems must be available within 60 seconds and may be routed in the same raceway as normal power systems.

Having clearly separated emergency/life safety from standby loads, let’s look at the most common emergency power systems and associated life safety loads.

Emergency power sources

Figure 2: A computer-based model of the Massachusetts Green High Performance Computing Center shows the top level high-performance computing space with overhead utilities. Courtesy: M+WThe term “emergency generator” is often used mistakenly as a description of any type of engine generator used to provide power in a facility. However, not all generator types will meet NEC or NFPA requirements to power life safety loads. First, the emergency power from a generator is required to be available within 10 seconds or less. Second, the source of fuel to a generator must be reliable; this typically eliminates natural gas generators from consideration unless on-site liquefied petroleum (LP) storage is provided. Traditionally, this has meant a diesel engine generator set.

NFPA 110 has additional requirements for emergency generators:

  • A certified 0.8 power factor, full load factory test. Test report must be furnished to owner for proof and kept on record by manufacturer for 5 years.
    • Requires certified NFPA 110 generator controller which includes all pre-alarms and a 16-light annunciator.
    • Requires a certified NFPA 110 battery charger that has the following alarms: low voltage, high voltage, and common fault.
    • A four-hour full load test is required to be completed annually.

Beyond traditional diesel engine generators, newer forms of power sources including motor generator flywheels, and fuel cells may be considered by local authorities having jurisdiction (AHJ) as emergency power sources.

Batteries, including inverters and uninterruptible power supply (UPS) systems, may also be used as an emergency power source for buildings of a limited type and size, and for certain systems like egress lighting and fire detection and alarm systems.

This standard also includes two other power source terms:

Class: Refers to the time, in hours, for the energy source to provide power. For example, Class 2 means 2 hours of power at full load (see Table 1).

Table 1: This shows the secondary power supply requirements for typical life safety systems. Requirements are based on the 2010 edition of NFPA 72: National Fire Alarm and Signaling Code. Courtesy: M+W

Type: Refers to the maximum time for the emergency power source to be unavailable or restored. Type is commonly referred to by seconds; for example, Class 10 would be a power source that is online in 10 seconds or less (see Table 1).

Two final points on emergency power sources should be kept in mind. First, in most electrical system sizing, demand or diversity is applied to the electrical loads. However, for life safety loads the entire load must be fully applied, without demand factors. This also includes the starting currents of motors on emergency systems. This is particularly important with loads like fire pumps.

Secondly under NEC, emergency circuit wiring must be routed separately from legally required or optional standby circuits. An example of emergency power distribution is shown in Figure 3.

After examining the types of emergency power sources available, the engineer should focus on the specific types of life safety loads. The most common ones encountered in buildings include egress lighting, fire alarm systems, and fire pumps.

Power distribution requirements

Under NEC, emergency circuit wiring must be routed separately from legally required or optional standby circuits (see Figure 3). However, legally required standby circuiting may be combined with optional and other loads.

Emergency generator power distribution systems must also have fire protection when installed in buildings with occupancies of 1000 or more people, or in certain types of buildings that are taller than 75 ft. This fire protection shall be accomplished by installing the distribution in spaces protected by sprinklers, or by providing a 2-hour rated enclosure for the circuit wiring. The fire protection requirements also apply to the physical feeder circuit equipment itself (panels, transfer switches, etc.), which must be in 2-hour rated rooms, or rooms with fire protection.

Figure 3: Emergency circuit wiring must be routed separately from legally required or optional standby circuits. Courtesy: M+WEmergency and legally required standby generator power distribution systems also are required under the NEC to be selectively coordinated. This will require a protective device coordination study, looking at fault levels, and overcurrent devices to ensure that faults are isolated by opening the protective device nearest the fault, allowing the rest of the system to function. Optional standby systems are not required to be selectively coordinated. Another notable protection requirement is that emergency and legally required standby power systems do not have to include ground fault protection, but rather must have ground fault alarms.

Life safety loads: Lighting

While the NEC designates that lighting is an emergency load, NFPA 101 covers specific requirements for that lighting. The requirements are focused on paths of egress and exiting from certain types of buildings and structures. When required in these buildings, this includes designated stairs, aisles, corridors, ramps, escalators, and passageways leading to an exit.

The source of emergency power (NFPA 110 Level 1) must come on line with 10 seconds after loss of primary power (NFPA 110 Type 10) and must provide power for a minimum of 1.5 hours (NFPA 110 Class 1.5).

Various power sources may be considered for typical buildings including a central UPS or inverter system, localized internal battery packs, or diesel generators. However, in certain types of buildings such as high-rises or high-occupancy buildings, the larger loads and a requirement for a fire pump and/or one or more elevators will require a diesel generator.

The illumination levels for egress lighting are very specific. Lighting should be provided to achieve an initial level of not less than an average of 1 foot-candle (fc). The level is permitted to decline to not less than 0.6 fc at the end of the 1.5 hours. In addition a maximum-to-minimum illumination uniformity ratio of 40:1 shall not be exceeded.

NFPA 101 requires regular testing of emergency lighting systems every 30 days.


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