Emergency power for fire, life safety systems

Know the requirements for the design of an emergency or standby power systems.

By Randolph W. Tucker, PE, and Shaun Grimm, PE, ccrd partners September 20, 2011

For many years there were no accepted standards for the design of emergency and standby power systems, even though these systems have been in use since World War II. Recognizing this need, NFPA formed the Technical Committee on Emergency Power Supplies in 1976. Although the committee developed a report proposing adoption of NFPA 110: Standard for Emergency and Standby Power Systems, it wasn’t until the 1984 NFPA Fall Meeting that the document was adopted as a standard and became the 1985 edition.

Today emergency and standby systems are used to provide backup power for building systems to provide assurance that life safety systems and critical equipment can maintain their operation during a power outage. The use of these systems almost comes as second nature when designing large, complex facilities. Yet, how well do you know the specific requirements for these systems? Questions we must consider include:

  • When is emergency and standby power required?
  • What are the requirements for the design of an emergency and standby power system?
  • What building fire safety systems need to be provided with emergency and standby power?

What is it?

In general terms, as defined in NFPA 70: National Electrical Code (NEC), there are three types of emergency and standby power: emergency power, legally required standby power, and optional standby power. Emergency power is required by codes for systems whose operations are essential for safety to human life. Legally required standby power is required by codes for illumination and power equipment that is not categorized as requiring emergency power, but whose failure could create hazards or hamper rescue or firefighting operations. Optional standby power is not required by code and provides equipment whose failure will not impact life safety.

When is it required?

The basic requirements for where the provision of an emergency and standby power is necessary come from the building and fire codes. Whether the local jurisdiction follows NFPA 5000: Building Construction and Safety Code, NFPA 1: Fire Code, NFPA 101: Life Safety Code, the International Building Code (IBC), or the International Fire Code (IFC), the requirements are reasonably consistent. Each of these codes broadly defines the fire, life safety, and critical operations power systems (COPS) that require emergency and standby power systems. While the building codes primarily deal with requirements for new or remodeled buildings, the requirements of the fire codes and NFPA 101 may also apply to existing buildings, as such there may be retroactive emergency and standby power issues to be addressed under these documents.

Specific requirements for emergency and standby power will vary based on building occupancy type, facility use, and critical function. With these parameters, the need for emergency or standby power is determined and described in either a building or fire code. For example, the 2009 IBC requires emergency power for:

  • Emergency voice/alarm communications systems in Group A assembly occupancies
  • Exit signs
  • Means of egress illumination
  • Fire alarms and exhaust ventilation in HPM facilities
  • Power operated doors in detention facilities.
  • Some of the places where the IBC requires standby power include:
  • Smoke control systems
  • Emergency voice/alarm systems in large covered mall buildings
  • Accessible means of egress elevators and platform lifts
  • Horizontal sliding doors used for egress
  • Membrane structure auxiliary inflation systems
  • Mechanical vestibule and stair shaft ventilation systems and fire detection systems for smokeproof enclosures.

While the 2009 edition of the IBC and NFPA 5000 have similar requirements for emergency and standby power (such as high-rise buildings and healthcare facilities) there are some requirements that differ slightly. Some of these differences include:

  • NFPA 5000 identifies elevators in towers that are used as a second means of egress, in such buildings, the elevator equipment, communications, machine room cooling, and controller cooling all must be provided with normal and standby power
  • Also in NFPA 5000, in buildings more than 120 ft in height, a first responders use elevator must be provided that is served by standby power.

NFPA 101 and NFPA 99

NFPA 101 and NFPA 99 are two principal documents widely used in the design of healthcare facilities. While NFPA 101 covers all classifications of building occupancy use, NFPA 99 specifically addresses healthcare facilities.

The 2009 edition of NFPA 101 presents basic requirements for emergency lighting in Section 7.9. Emergency power systems for emergency lighting are to comply with the 2005 edition of NFPA 110. Stored electrical energy systems are required to comply with the 2005 edition of NFPA 111: Standard on Stored Electrical Energy Emergency and Standby Power Systems. Each of the occupancy chapters identifies whether emergency lighting is required in that occupancy.

High-rise building requirements in NFPA 101 are presented in Section 11.8. Among the requirements are the need for the installation of automatic suppression, fire detection, alarm, and communications systems. To provide assurance that these systems will be available in a fire emergency, emergency and standby power are required. The system is to be in accordance with NFPA 110 to serve the electric fire pumps, emergency command center equipment and lighting, elevators, mechanical equipment for smokeproof enclosures, and mechanical equipment serving the smoke control systems.

While emergency and standby power requirements are found in several other occupancy use areas, the healthcare occupancies have the most detailed requirements. NFPA 101 provides the overall requirements where fire detection, alarm, and suppression systems are required, where emergency lighting is required, and other basic fire and life safety needs. However, when it gets to the details of what specific systems need to be served by what level of power reliability, NFPA 99 takes the lead.

The 2009 edition of NFPA 99 identifies three classifications of essential electrical equipment categories based on the level of criticality of the systems served:

  • Life safety branch
  • Critical branch
  • Equipment system.

The life safety branch is defined as:

A subsystem of the emergency system consisting of feeders and branch circuits, meeting the requirements of Article 700, of NFPA 70 and intended to provide adequate power needs to ensure safety to patients and personnel, and that is automatically connected to alternate power sources during interruption of the normal power source.

The life safety branch of the emergency system provides the emergency power for:

  • Illumination of the means of egress
  • Lighting of the exit and directional signage
  • Fire detection and alarm system
  • Non-flammable medical gas system and vacuum systems alarms
  • Hospital emergency communication systems
  • Task lighting, battery charger, and selected receptacles in generator set location
  • Elevator control, communication, and lighting
  • Automatic operating egress doors
  • Auxiliary fire alarm system functions.

The critical branch is defined as:

A subsystem of the emergency system consisting of feeders and branch circuits supplying energy to task illumination, special power circuits, and selected receptacles serving areas and functions related to patient care and that are connected to alternate power sources by one or more transfer switches during interruption of normal power source.

The critical branch may be divided into multiple branches. The critical branch is dedicated for use in powering specific circuits related to patient care and includes the following:

  • Task illumination, selected receptacles, and fixed equipment in critical care areas using anesthetizing gas
  • Isolated power systems in special environments
  • Task illumination and selected receptacles in patient care, medication preparation, pharmacy dispensing, and nurses stations
  • Task illumination and receptacles in specialized patient care areas
  • Nurse call systems
  • Bone, blood, and tissue banks
  • Other selected illumination and receptacles.

In order to be able to meet the time requirements of these two essential equipment categories, it is typically necessary to have some combination of stored power and generator power solution.

The equipment system is defined as:

A system of circuits and equipment arranged for delayed, automatic, or manual connection to the alternate power source and that serves primarily 3-phase power equipment.

The equipment system is allowed to serve the following delayed-automatic or manual connection to the alternate power source:

  • Heating equipment serving various treatment spaces
  • Patient rooms under specific conditions
  • Certain elevators
  • HVAC systems for select areas
  • Hyperbaric and hypobaric facilities
  • Autoclaving equipment
  • Controls for the above listed equipment
  • Other selected equipment.

Fire codes

While the fire codes are companion documents to the building codes, remember that the fire codes are an occupancy and use enforcement document, not a construction enforcement document per se. As such, it is unusual to find requirements in a fire code that would require a new system to be installed in an existing building under a fire code. The typical requirements of a fire code will be to maintain the systems in the building that were required under the version of the code followed when the building was first built. Exceptions to this distinction would include:

  • Substantial changes made in building construction, occupancy, or use after the adoption of the code
  • Existing buildings, structures or operations that were not legally in existence prior to adoption of the code
  • Specific hazardous conditions when specifically addressed by the code
  • Existing facilities that have been identified as constituting a distinct hazard to life or property.

With this basic differentiation, the following are some of the primary fire code implications for emergency and standby power.

Since the primary focus of both NFPA 1 and the IFC is on assuring that fire protection and life safety equipment is properly maintained, it should come as no surprise that both documents require building owners to keep up to date records on inspection and maintenance of their emergency and standby power.

In Section 604 of the 2009 IFC, requirements for emergency power systems are delineated. The section is consistent with the requirements of Section 2702 of the IBC and requires compliance with the 2005 NFPA 110 or the 2005 NFPA 111 where emergency and standby power systems are to be installed. The required locations and systems include emergency voice and alarm communications systems for assembly occupancies, smoke control systems, exit signs, means of egress illumination, accessible means of egress elevators, horizontal sliding doors, membrane structures, semiconductor manufacturing facilities, and several other facilities. It further requires stationary emergency and standby power systems to be in compliance with the 2004 edition of UL 2200: Standard for Stationary Engine Generator Assemblies.

In the 2009 NFPA 1, Section 11.7.3 covers emergency and standby power requirements. Section requires compliance with the 2005 NFPA 110 for stationary generators while Section 11.7.4 requires compliance with the 2001 NFPA 111 for stored electrical energy and standby power systems. Emergency lighting requirements are in Section 14.13. This section refers to NFPA 101 for specific facilities requirements.

Design requirements

Once the building code establishes the need for an emergency and standby power system, their design requirements are found in installation standards, such as the 2008 NEC. Article 700 of NFPA 70 establishes the ground rules for emergency system’s components, equipment and their installation. The article addresses basic requirements for these systems, defines circuit wiring, sources of power, and emergency system circuits. In accordance with Section 700.12, the emergency lighting and emergency power must be available within 10 seconds of a failure of the normal building power supply. This can be accomplished by:

  • A storage battery that can maintain the load for a minimum of 1.5 hours without a voltage drop below 87.5% of normal
  • Generator set that automatically starts on failure of normal service that has an automatic transfer switch for all required circuits (if the generator requires greater than 10 seconds to develop power, an auxiliary power supply must be provided until the generator can pick up the load)
  • A UPS that meets the requirements of one of the two means described above
  • Separate service (where approved by the authority having jurisdiction)
  • Fuel cell with a rating and capacity to supply and maintain the total load for not less than two hours of full demand operation.

Similarly, Article 701 of the 2008 NEC covers installation requirements for legally required standby systems. Article 702 of the NEC covers these requirements for optional standby systems.

Emergency and standby power systems have different requirements for the time required to transfer the load. Emergency and legally required standby systems must have automatic transfer switches. As previously noted, emergency system loads must be transferred within 10 seconds after the failure of the primary power supply. Legally required standby system loads must be transferred within 60 seconds after the failure of the primary power supply. Optional standby systems are not required, so there is no maximum transfer time. In addition, an optional standby system is permitted to have a manual transfer switch.

Emergency systems also have requirements for separation from nonemergency circuits. This requirement is intended to prevent simultaneous impairment of the normal and emergency systems. Legally required and optional standby systems can be mingled with wiring for other power systems.

NFPA 110 provides the following definitions:

  • Emergency Power Supply (EPS) – The source of electric power of the required capacity and quality for an emergency power supply system (EPSS).
  • Emergency Power Supply System – A complete functioning EPS system coupled to a system of conductors, disconnecting means and overcurrent protective devices, transfer switches, and all control, supervisory, and support devices up to and including the load terminals of the transfer equipment needed for the system to operate as a safe and reliable source of electric power.

NFPA 111 provides the following additional definitions:

  • Stored Emergency Power Supply System – A system consisting of a UPS, or a motor generator, powered by a stored electrical energy source, together with a transfer switch designed to monitor preferred and alternate load power source and provide desired switching of the load, and all necessary control equipment to make the system functional.
  • UPS – A system consisting of a stored energy source, designed to continuously provide a clean, conditioned sinusoidal wave of power under normal conditions and for a finite period of time upon loss of the primary power source.

In NFPA 110, emergency power supply systems (EPSS) are assigned a class by minimum time (in hours) the EPSS is designed to operate at its rated load without being refueled or recharged. In addition to the class, they are further identified by type that defines the maximum time in seconds the EPSS will permit the load terminals of the transfer switch to be without acceptable power.

In NFPA 111, stored emergency power supply systems (SEPSS) are rated by type, class, category, and level. The type defines the maximum time in seconds the SEPSS will permit the load terminals of the transfer switch to be without acceptable power. The class determines minimum time, in hours, the SEPSS is designed to operate at its rated load without being refueled or recharged. There are two categories; Category A is devices that receive their energy from the normal supply and Category B is all other devices not in Category A and not specifically excluded elsewhere in the standard. There are two SEPSS levels. Level 1 is where failure of the SEPSS to operate could result in injury or loss of human life. Level 2 are where failure of the SEPPS is not as critical to human life and safety.


In the 2008 edition of NFPA 70 a new Article 708: Critical Operations Power Systems was added to the mix of emergency and standby power. COPS raises the bar for the reliability of power systems well above previous versions of NFPA 70.

The article provides for the protection of vital infrastructure facilities that, if destroyed, would disrupt public health, safety, or national security. The intended application would be for facilities such as communications centers, air traffic control centers, hazardous materials handling, financial data processing, transportation centers, and other at-risk structures. Potential exposures to these facilities would include natural disasters, such as hurricanes and tornados, and manmade disasters such as terrorist acts.

Reason for COPS

For many years the NEC has addressed the need for emergency power in buildings to assist in getting people safely out of buildings. The focus on emergency power in assembly and healthcare facilities in particular has enhanced the safety for high occupancy facilities and in the facilities where the occupants may have limited ability to be moved.

Over the past 20 years we have witnessed many disasters including devastating wind storms, hurricanes, and floods, many of which have caused loss of power to many of the key emergency management operations. Such emergency management facilities need to be operational in order to appropriately respond to these incidents. Other recent events that have raised concern over reliability, operation, and approach to building emergency and standby systems include the Sept. 11, 2001 attacks, threats of biological terrorist attacks, and threats of attacks on our infrastructure.

COPS have been developed to provide guidance on the design of power systems for facilities or parts of facilities that require continuous operation for the reasons of public safety, emergency management, national security, or business continuity. These facilities may include:

  • Air traffic control centers
  • Chemical, petrochemical, and hazardous material (including biohazard) handling facilities
  • Communications centers, telephone exchanges, cellular tower sites
  • 911 call centers
  • Central station service facilities (fire and security system monitoring)
  • Financial, banking, business data processing facilities
  • Hospitals and associated support facilities
  • Police, fire, civil defense facilities including power for radio repeater operations
  • Emergency evacuation centers
  • Transportation infrastructure –airports, rail stations, seaports
  • Municipal infrastructure –water and sewer treatment facilities
  • Fuel supply pumping stations (i.e. natural gas distribution and delivery infrastructure
  • Offices and facilities deemed critical to continuity of government
  • Radio and television stations.

Similar to the approach taken to Articles 700 and 701, the determination on where COPS is required is from the authority having jurisdiction (AHJ) in the form of emergency management directors, fire officials, police officials, building officials, Federal Emergency Management Agency, and others.

In accordance with Section 708.4, a risk assessment must be conducted for COPS to:

  • Identify hazards (naturally occurring and human caused)
  • Determine the likelihood of their occurrence
  • Assess the vulnerability of the power system to those hazards
  • Evaluate the need for physical security
  • Develop a mitigation strategy.

The system is required to be commissioned and periodically tested.

A facility with a COPS is required to have a documented plan that considers emergency operations, and response, recovery, and continuity of operations.

As our world continues to change, the applications for emergency and standby power should be expected to continue to play a key role in providing reliable power for our most critical needs. The more we come to rely on consistent delivery of power to run our world, the more we will need to rely on emergency and standby power.

Tucker is associate principal of fire and life safety with ccrd partners in the Houston office. His experience includes development of fire safety master plans, egress analysis, equivalency studies, smoke control systems design and testing, evaluation of fire resistance of structural assemblies, detection/alarm and suppression systems design, and negotiations with public officials. Grimm is associate principal and project manager with ccrd partners in the Phoenix office. He is the lead electrical engineer, and leads the electrical design of different projects including hospitals, institutional facilities, and office buildings.