A Summary Comparison of Fire Alarm System Requirements in the US and UK

Issue 61: A Summary Comparison of Fire Alarm System Requirements in the United States and United Kingdom

By James R. Lugar, P.E.

Introduction

Fire alarm systems are all designed and installed with the same basic objective in mind: detect a fire, effectively alert and provide information to occupants, and signal and provide information to first responders. Exactly how these goals are met depends on the specific conditions of each scenario – and the codes in the region of the world under consideration.

In the United States, NFPA 72¹ is a consensus based code and describes how to design, install, inspect, test, and maintain a fire alarm system, while the adopted building code identifies when and where fire alarm systems are required, and to what level. This article considers the 2010 edition of NFPA 72 and the 2012 edition of the International Building Code^® (IBC).²

In Europe, the Comité Européen de Normalisation (CEN) develops European standards known as ‘EN’ that are adopted as national standards in the 33 member countries. Each member country has a standards body that publishes the EN standards with modification in addition to standards for the specific nation, such as the British Standards Institution (BSI). This article considers the British Standard (BS) version of EN 54,³ Fire Detection and Alarm Systems and BS 5839,⁴ Fire Detection and Alarm Systems for Buildings, which provides specific guidance and recommendations for the design and installation of fire alarm systems.

Building Code Discussion

The model building codes that are generally applicable in North America and Europe differ in that North American codes tend to provide prescriptive solutions that favor active fire suppression while European codes tend to provide performance requirements that favor passive fire protection.

With respect to means of warning and escape, The Building Regulations for England and Wales states in part that, "The building shall be designed and constructed so that there are appropriate provisions for the early warning of fire.” BS 5839 provides recommendations and performance criteria for the design and installation of fire alarm systems to meet this objective while BS EN 54 provides the minimum requirements for fire alarm system performance and associated testing parameters.

In contrast, the Intent of the IBC includes a statement that, "The purpose of this code is to establish the minimum requirements to safeguard the public health, safety, and general welfare,” through a variety of factors including "safety to life from fire and other hazards attributed to the built environment”.

NFPA 72 provides the minimum requirements for the design and installation of a fire alarm system while referenced standards published by other standards-making bodies provides the minimum requirements for fire alarm system component performance and associated testing parameters.

Control and Indicating Equipment – Fire Alarm Control Unit

BS EN 54 Part 2 provides specific requirements for the function of fire alarm control and indicating equipment (CIE). These requirements are related to the operation of the CIE during alarm conditions, fault conditions, upon loss of power, and associated indications.

These requirements are similar to the fundamental requirements for fire alarm control units (FACU) prescribed in NFPA 72. The significant difference is that BS EN 54 Part 2 provides specific testing procedures for the CIE, while NFPA 72 defers the specific testing procedures for FACU to UL 864.⁵

Alarm Initiation and Detection Levels

BS 5839 Part 1 specifies three categories of detection system levels. These categories and their subcategories include:

Specific guidance exists for certain situations; however, the fire protection engineer is often responsible for selecting the appropriate level of protection based on the specific hazards and safety features of an individual project.

NFPA 72 defines levels of detector coverage as total (complete) coverage, partial or selective coverage, and nonrequired coverage. The fire protection engineer designs to these minimum requirements, but has flexibility to propose additional (nonrequired coverage) where warranted or required by a performance-based design to meet or exceed the minimum level of safety prescribed by the building code.

In both regions, the type of detection selected is generally left to the discretion of the fire protection engineer based on the specific hazard(s) of the protected spaces. The types and function of alarm initiating devices are also similar across each region. The primary difference is the emphasis on fire sprinkler protection in the North American codes while smoke detection is more prevalent in European fire alarm system installations. In addition, manual call points or break-glass stations per BS EN 54 Part 11 are provided in lieu of manual fire alarm boxes. Manual call points consist of a frangible cover that initiates an alarm condition when broken or removed.

Alarm Notification Appliances

Audible alarm signals in European countries may consist of bells, electronic sounders, or voice annunciation. Sounders can be utilized for phased evacuation, in which case they are designed to provide different alert and evacuation tones.

Voice messaging has become more prevalent in recent years, and is often recommended in facilities where the occupants are unfamiliar with the surroundings, in areas with high occupant loads, in fire engineered solutions, or in areas where the risk analysis determines that live messaging is appropriate.

Specific component requirements and performance criteria can be found in BS EN 54. Voice alarm control and indicating equipment per BS EN 54 Part 16 will often take the form of modular, rack-mounted components in lieu of equipment integral to the fire alarm control and indicating equipment.

BS 5839 recommends that a fire alarm system be sufficient to all persons intended. Sound pressure levels are generally recommended to be a minimum of 65 dBA and a maximum of 120 dBA. A reduction to 60 dBA is applicable in certain circumstances, and a sound differential of at least 5 dBA is only applicable in spaces with an ambient sound level greater than 60 dBA. Sleeping areas are recommended to have a sound pressure level of 75 dBA. The principles are similar to NFPA 72; however, NFPA 72 typically requires a 10 dBA difference, or 5 dBA above the maximum ambient noise, with a maximum sound pressure level of 110 dBA.

Sounders can be supplemented by visual alarm signals, especially in areas with high ambient noise levels. Visual alarm signals are not typically recommended to be installed on their own; however, they may be appropriate to alert staff for staff-assisted evacuations or to alert the hearing impaired.

Providing visual alarm devices in sleeping accommodations and sanitary accommodations satisfies a component of the disabled access and use requirements of The Building Regulations. Red beacons are the most common form of visual alarm devices. These beacons can be standalone units ,or more commonly, as an integral part of a sounder, and can be incandescent or xenon strobe type. BS 5839 recommends a minimum mounting height of 2.1 m (83 in.), but no maximum mounting height. Beacons have not historically had any minimum light output requirements; however, the latest version of BS EN 54 Part 23 has introduced greater light output requirements.

In contrast, occupant notification in the US includes minimum and maximum alarm audibility and visibility requirements to be met throughout a protected premise. Fire alarm systems utilizing emergency voice/alarm communications are additionally required to be intelligible, and standardized test methods are available to evaluate the intelligibility of a voice system.

NFPA 72 provides specific requirements for strobes to include spacing based on the strobe intensity measured in candelas (cd), and other prescriptive requirements such as mounting height and spacing such that all areas are provided with a minimum illumination at any point. Visible appliances must comply with the photometric requirements of UL 1971.⁶

1. NFPA 72, National Fire Alarm Code, National Fire Protection Association, Quincy, MA, 2010.
2. International Building Code, International Code Council, Washington, DC. 2012.
3. BS En 54, Fire Detection and Alarm Systems, British Standards Institute, London, 2011.
4. BS 5839, Fire Detection and Fire Alarm Systems for Buildings, British Standards Institute, London, 2011.
5. UL 864, Control Units and Accessories for Fire Alarm Systems, Underwriters Laboratories, Northbrook, IL, 2008.
6. UL 1971, Signaling Devices for the Hearing Impaired, Underwriters Laboratories, Northbrook, IL, 2002.

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