NFPA Journal - July/August 2018 - 40

In Compliance
personal protective equipment to
reduce the severity of injury should the
unexpected occur.
This is the story we need to consistently tell: the act of establishing an
electrically safe work condition is the
combination of a multitude of individual
tasks, a process that exposes employees to electrical hazards. It is not an
elimination control. All of the controls
mentioned apply to the individual tasks,
and only when those tasks are combined
do we reach the end goal of eliminating
employee exposure to electrical hazards.
However, not until these other controls
have been implemented is the pinnacle
of safety hierarchy achieved: elimination
of the hazard. Skip even one step and all
bets are off.
Derek Vigstol is an NFPA technical lead, Electrical
Tech Services. NFPA members and AHJs can use the
Technical Questions tab to post queries on NFPA 70
at nfpa.org/70next.

NFPA 72

Fire alarms, signaling, and
emergency communication

Using NFPA 72 to meet
the application challenges
of industrial
fire alarm systems
By Wayne Moore

lthough NFPA 72®,
National Fire Alarm and
Signaling Code, is not
meant to be a design
guide, the code nevertheless does contain certain application
information that can be valuable in
assisting fire alarm system designers in
meeting challenges presented by a variety of industrial occupancies.
In many instances, the conditions in
industrial occupancies can include an
array of challenges, including large open
spaces, high ceilings, varying ambient
noise conditions, hard surfaces, dusty
environments, and varying temperatures. For example, large open spaces
combined with high ceilings are the

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most challenging for almost any kind
of detection, and a fire must grow to
a "detectable size." The designer must
convey this information to the owner to
avoid any misunderstanding of the fire
alarm system's capabilities.

Having different
opinions of where a
control falls on the list,
however, can have
tragic consequences.
It is important to understand that there can
be multiple controls
employed in order
to reach the ultimate
goal of eliminating
the hazard.

There is a wealth of application
information available in both the
annexes of the code and in the code
handbook to help designers when
addressing these challenges. For example, when designing heat detection for
a large open space with 30-foot ceilings, designers can review section
17.6.3.5 and find the table that provides
information on reducing heat detector spacing based on ceiling height. As
the information in the annex states, the
tables are constructed to provide detector performance on higher ceilings,
up to 30 feet high, that is essentially
equivalent to what would exist with
detectors on ceilings 10 feet high.
In NFPA 72, Annex A recommends
that, in facilities with high ceilings,
spot-type smoke detectors are not
accessible for maintenance and testing. According to Annex A, a better
alternative would be to use projected
beam smoke detectors or, in some
applications, air sampling-type smoke
detectors. Designers are cautioned
that NFPA 72 does not possess all
the answers to the possible questions arising from applications in the
built environment, and the information provided in the annex are just

examples of what the technical committee thought would be most beneficial
for users of the code.
Possibly the most important part of
the design process occurs before any
design begins, when owners establish
their design goals. In many instances,
owners do not understand that it will
be almost always impossible to detect
a small fire in a large space with a high
ceiling. Early warning of small fires in
normal 10-foot ceiling spaces are difficult. Early warning of a small fire in a
large space with ceilings of 30 feet or
more is generally not possible.
The reason for this is stated in Annex
A, A.17.7.3.1: "A smoldering fire produces
little, if any, plume and no appreciable ceiling jet. Far more time elapses
between ignition and detection under
this circumstance." Alternatively, according to the annex, "A hot, energetic fire
produces large plume velocities and
temperatures and hot, fast ceiling jets.
This minimizes the time it takes for the
smoke to travel to the detector."
The system designer for industrial occupancy fire alarm systems
also needs to understand how difficult
these environments are with respect
to audibility and intelligibility of the
notification appliances. Industrial occupancies include numerous hard surfaces
that can reduce the intelligibility of
voice systems. Depending on the activity taking place in the building, such
as storage or manufacturing, there will
be high ambient noise levels that must
be overcome through design. The same
holds true for strobe notification appliances. There may be storage racks that
could interfere with wall-mounted
strobe appliances. In many cases, ceiling-mounted strobes will provide more
uniform coverage in a facility with
numerous storage racks.
An informed designer will know that
every building presents its own design
challenges that need to be addressed
using all the tools available, including
NFPA 72 requirements and sound fire
protection engineering principles.
Wayne D. Moore is vice president at Jensen
Hughes. NFPA members and AHJs can use the
Technical Questions tab to post queries on NFPA 72
at nfpa.org/72.
http://www.nfpa.org/70next http://www.nfpa.org/72
Table of Contents for the Digital Edition of NFPA Journal - July/August 2018
