With thanks to several members of Technical Committees of the National Fire Alarm Code for their contributions
Fire alarm systems, and the technology that supports them, have
broadened substantially from the earliest systems that were manually
activated notification systems. To cover the range of the latest
developments, it is best to consider the two primary functions of
today's fire alarm systems: detection and notification.
Video Smoke Detection
Software developments are making the use of video cameras for smoke
detection practical by analyzing digital images. This emerging
technology may be applied as very early detection of smoke in large open
spaces, as unobtrusive smoke detection in cultural buildings, and as a
means to provide video images of the protected space to responders.
Proposed revisions to NFPA 72, The National Fire Alarm Code,
would require such systems to be designed and installed using a
performance-based approach. Product standards for listing video
detection systems, including hardware and software, are being undertaken
by Underwriter's Laboratories.
The technologies of physically and chemically sensing the gas and
particulate signatures of materials under combustion, and the technology
of processing that information against known profiles representing real
fires, are being combined to provide fire detection that discriminates
between real fires and other sources of gases and particulates that do
not represent accidental fires.
Unlike "combination detectors" of past decades, which were part of a
horsepower race for faster detection, the new developments use the
combination of technologies to provide more reliable fire detection –
less prone to unwanted alarms yet no less effective to detect real
fires. Sources of aerosols that may have caused nondiscriminating smoke
detectors to alarm, such as steam, are not falsely identified as fire
because one or more components of the fire profile are missing.
These developments are establishing a new standard of performance for stability in automatic fire detection systems.
Joists, Beams, and Confined-Dimension Spaces
It has been recognized for many years that solid, deep beams on
ceilings retard the ceiling jets that carry heat and smoke to spot-type
detectors. The pockets formed by solid beams act as reservoirs,
retarding the ceiling jet from flowing along the ceiling. The
requirements found in NFPA 721 for locating detectors
on ceilings with solid joists, beams, and "waffle" pan-type construction
had originally been empirically developed and revised from time to
Research sponsored by the Fire Protection Research Foundation2
has shown that a companion to the reservoir effect is the effect to
increase the optical density, temperature rise, and gas velocities as a
beam pocket fills and the smoke collected spills into adjacent pockets.
For small beam pockets, "waffle" pan-type ceilings, and corridors with
ceiling beams, these results have justified proposed changes to NFPA 72 that
will permit smoke detector locations on the ceiling or bottoms of the
beams using the same spacing as for smooth ceilings, where the solid
joist or beams are less than 600 mm deep and spaced no more than 3.66 m
center to center.
Quantifying Detector Response for Modeling
Past practices related to calculations for predicting the activation of
heat and smoke detectors to flaming fires have been based on listed
"spacing" ratings for heat detectors and on empirical results from
full-scale fire tests which suggested a temperature rise correlation for
smoke detectors. As fire modeling has become more widely used for even
more purposes, corresponding development of improved performance
criteria and detector parameters for heat and smoke detectors is needed.
Work is currently underway at the Fire Protection Research Foundation
to assign RTI values to heat detectors and to refine quantification of
smoke detector performance for calculations, which may also justify
additions and revisions to related standards and models.
Fire Service Interface
Requirements and explanatory material for a Standard Fire Service Interface was introduced in the 2002 edition of NFPA 72 for
use by the fire service in responding to fires in buildings. NEMA has
responded by developing a NEMA Standard for the fire alarm system-based
interface as an applicable Product Standard.3 These
developments provide for improved notification to the first responders
upon arrival at the building, and open the opportunity for transmission
of standardized information to responders en route to the building.
Conceptually, the technology employed will permit touch-screen
inquiries to inform a fire commander of conditions at selected locations
in the building. Digital network technology would permit the interface
to be located at several points within a building or complex or at a
The information available is intended to enable the fire service response to be smarter and safer.
Visible Notification Appliance Applications
The majority of the hearing-impaired community has been well served by
several iterations of improvements in the standards and products used to
notify people of a fire threat using visible notification appliances –
strobe lights. Practices are in common use related to awakening sleeping
people and to alerting people who are awake.
Research presented by Dorothy Bruck at the 10th Fire Suppression
& Detection Research Application Symposium has shown that some
minority hearing-impaired populations may not yet benefit from the
practices which serve the majority. These populations include the very
young, very old, and even the majority when in certain environments such
as large, high-ceiling spaces – for example, discount retail stores.
Real-world testing has commenced to understand the related
characteristics of the very young and very old, which may be addressed
by notification technologies. The NFPA 72 Technical Committee on Notification Appliances is addressing the large-enclosure application.
New Horizons in Notification
New challenges are presented to society by the war on terror and by
structures with complex egress paths, where occupants are unfamiliar
with the way out, or in certain complex structures such as ships,
industrial buildings, and very large buildings. These challenges can be
addressed with two recent occupant-notification developments.
Mass notification systems are being planned or installed to provide
information and/or direction to large numbers of people simultaneously.
Such systems are intended to reach beyond a single building, potentially
to widely distributed buildings, even to some which may be in remote
locations. The challenges include flexibility, coverage, integrity,
security, availability, and effectiveness. It is clear that
voice-enabled fire alarm systems can form a part of a larger mass
Amendments to NFPA 72 proposed for the 2006 edition will
permit fire alarm systems to be a portion of a mass notification system
and will permit a mass notification message to override a fire alarm
The technologies to be applied will include digital network
interfaces, which will require greater contact with equipment that is
not a part of the listed fire alarm system. This challenge, to meet
society's larger need for broader information, will include the
necessity to permit system interconnections that have not been permitted
under traditional fire alarm system codes and standards.
Exit-Marking Directional Sounders
A new class of sounders has been developed that can audibly lead
occupants along a path of egress to safety from a threatened interior
space. Amendments to NFPA 72 proposed for the 2006 edition will
permit use of the newly developed exit-marking technology and provide
installation requirements and guidance.
Changes Affecting Alarm Transmission
Some of the alarm transmission options that supervising station systems
have relied upon are disappearing due to major changes taking place in
the telecommunications industry.
For supervising station and protected premises systems, continued
developments in the use of nonfire data networks and Internet-friendly
technologies must be pursued while continuing to assure society that the
level of integrity expected of code-conforming protective signaling
systems is maintained.
Ralph Transue is with Rolf Jensen & Associates, Inc.
NFPA 72, National Fire Alarm Code , National Fire Protection Association, Quincy, MA, 2002.
O'Connor, D., "Smoke Detector Performance for Level Ceilings with Deep
Beams and Deep Beam Pocket Configurations – An Analysis Using
Computational Fluid Dynamics" Fire Protection Research Foundation,
Quincy, MA (Draft Report).
SB 30, Fire Service Annunciator and Interface, National Electrical Manufacturer's Association, Rosslyn, VA, 2005.
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