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.

By Brian Rener, PE, and Josh McConnell, NICET, SET, M+W U.S. Inc. November 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. 

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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

The 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).

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.

Emergency 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.

Life safety loads: Fire detection and alarm systems

NFPA 72: National Fire Alarm and Signaling Code, contains requirements for emergency power to fire alarm and detection systems. NFPA 72 specifies the need for two independent power supplies with adequate capacity to serve the connected loads.

The primary source may be either a commercial utility source or an engine generator. The secondary source maybe either a storage battery or an engine generator.

A dedicated branch circuit for the primary power supply must be provided. It is not acceptable for the fire detection/alarm system to share power with any other load. The branch circuit connections must be mechanically protected against physical damage, have suitable overcurrent protection capable of interrupting the maximum short-circuit current they may be subjected to, and be clearly marked as a “FIRE ALARM CIRCUIT.”

Typical operating voltage for fire detection and alarm systems in the United States is 120 Vac supplied to the primary side of the system power supply, which is then rectified and stepped down to 24 Vdc (system operating voltage). The most typical configuration for the primary power is a dedicated branch circuit fed from a commercial utility source.

The most typical configuration of the secondary power supply is battery backup, usually two 12 Vdc batteries connected in series. The battery amp/hour rating (size) is calculated by the system designer based on the maximum load conditions of the system and the time period the system will need to receive the secondary power upon loss of the system primary power. NFPA 72 also requires that the battery calculations include a 20% safety margin added to the calculated amp-hour rating.

The intent of providing secondary power to the fire detection/alarm system is to allow the system to operate in a “standby” or normal mode for a period of time (typically 24 hours) in a scenario where the primary power has been entirely or partially lost, and also to provide sufficient operating power to the system at the end of this supervisory period to perform evacuation functions (alarm mode) for a sufficient period of time (typically 5 minutes) to allow occupants of the protected premise to evacuate safely. 

Therefore, the battery calculation method is as follows:

Required standby time (hours) x total system standby current (amps) = Required standby capacity (amp/hours) + required alarm time (hours) x required alarm current (amps) x 120% (20% safety factor) = adjusted battery capacity (amp/hours)

NFPA 72 also requires that the secondary power supply shall automatically provide power to the protected premises’ fire detection/alarm system within 10 seconds whenever the primary power supply fails to provide the minimum voltage required for proper operation.

Further, any required signals shall not be lost, interrupted, or delayed by more than 10 seconds as a result of the primary power failure.

It is important to understand that there are several types of protective signaling systems that are also addressed in NFPA 72 that may have differing requirements related to secondary power supply capacity. Table 1 summarizes some of these systems and the associated capacity requirements for secondary power.

Life safety loads: Fire pumps

The major electrical power requirements for fire pumps are found in NEC Article 695. The intent of the requirements is to provide uninterrupted power to the fire pump and to protect all power equipment and wiring from fire. Other major requirements for the installation of fire pumps are found in NFPA 20.

The following four items are major electrical power requirements for fire pumps per NEC 695:

  1. Electric motor-driven fire pumps shall have a “reliable” source of power. Typically the “reliable” power source is an electrical utility service connection. The service connection is located to minimize damage from a fire. Many times the power connection is found remotely located from the building or major fire load area. An electrical tap used for the fire pump power connection can be located ahead of the service disconnecting means when installed in accordance with NEC 230. Alternate feeders can also supply power to the fire pump if those feeders are supplied from separate utility service connections.
  2. Circuits that supply electric motor-driven fire pumps shall be supervised from inadvertent disconnection. One can minimize the opportunity for disconnection by directly connecting the supply conductors to the power source of the listed fire pump controller, or listed combination fire pump controller/power transfer switch. The disconnecting means is typically supervised by a central monitoring station so that the operation of the disconnect is reported to a constantly attended location. A local supervisory alarm signal may also be installed to alert local service personnel.
  3. All power supplies shall be located and arranged to protect damage against fire from within the premises and exposing hazards, and multiple power sources shall be arranged so that a fire at one source does not cause an interruption at the other source. Physical location(s) of fire pump power sources in relation to the specific fire hazards at those location(s) must be carefully considered during the electrical power design phase of a project to accommodate the requirements of Article 695.
  4. Power circuits and wiring methods shall comply with the requirements of Article 695. The power conductors feeding the fire pump must be physically protected from the fire hazard, structural failure, or operational accident. This is typically accomplished by physically routing the conductors outside of the building, encasing the conductors/raceways in a minimum of 2 in. of concrete, or installing them in a minimum 2-hour fire-rated assembly.

Life safety loads: Special facilities

Specific requirements for emergency power and life safety loads will vary based on building occupancy type, facility use, and critical function. Various codes such as the International Building Code (IBC), NFPA 5000: Building Construction and Safety Code, NFPA 99: Health Care Facilities Code, and others will have specific requirements. Facilities with special requirements include hospitals, high-rises, large places of assembly, and hospitals.

One interesting example of a special building type is semiconductor manufacturing facilities (H4/H5 occupancies). Continuous gas detection and emergency alarm systems are commonly used in these facilities. In this type of facility, emergency power is provided following NFPA 110 requirements for both continuous gas detection and emergency alarm systems.

Lastly, recent versions of the NEC have added Article 708: Critical Operations Power Systems (COPS). These are systems, operations, or facilities designated by local, state, or federal government as “mission critical”; examples can include police or fire stations or other facilities for reasons of public safety, national security, or business continuity. This new section (introduced in 2008) has some notable requirements for things like commissioning, which has long been practiced in data centers and other previously unclassified mission critical facilities.

Brian Rener is electrical engineering discipline platform leader and quality assurance manager at M+W U.S. He has more than 20 years of experience in management and engineering for new and existing facilities, and is a member of the Consulting-Specifying Engineer editorial advisory board. Josh McConnell is the life safety systems discipline platform leader at M+W U.S. He has 27 years of experience in engineering and construction of life safety systems.