NFPA Journal - Spring 2021 - 45

write in the new FPRF report, the
requirements in the current edition of
NFPA 13 " are considered conservative
and have created difficulties in practical application. "
To address concerns over the perceived limitations imposed by NFPA
13, the FPRF proposed an ambitious
research project to study the impact of
various obstructions on the effectiveness of ESFR sprinklers. The project,
which began in 2014, contained multiple phases, including a literature
review, a research planning and development phase, and an extensive testing
phase that included nine full-scale
tests conducted at Underwriters Laboratories' large-scale fire test facility in
Northbrook, Illinois.
The project defined a testing scope
that researchers determined would be
the most useful for the broadest range
of warehouse storage occupancies.
According to the report, survey results
of NFPA 13 users worldwide indicated
that open web steel joists are the most
commonly used structural roof system,
and that bridging members, which
provide lateral support for maintaining
stability under vertical loads, are the
most problematic obstruction for ESFR
sprinklers. The survey also found that
the depths of the steel joists most commonly used range from 22 inches to 36
inches. The top chord of an open web
steel truss is typically located above the
sprinkler pattern discharge and does
not present as much of a concern as
the bottom chord, which resembles an
unattached flat horizontal obstruction
that is 4.5-5.5 inches wide.
Pendent-style ESFR sprinklers were
selected for the tests, since they are
more popular than upright ESFR sprinklers. K-17 sprinklers were selected-the
k-factor refers to the size of the sprinkler
orifice, which determines how much
water can be emitted-for the tests, and
the rationale was that the results of the
K-17 tests could be applied to the larger
K-22 and K-25 sprinklers, which are also
used in ESFR sprinkler systems. Tests
were also conducted using the slightly
smaller K-14 sprinkler.
A testing method known as actual
delivered density, or ADD-a tool
commonly used for sprinkler listings

and approvals-was used to evaluate
specific aspects of ESFR sprinklers and
how they are affected by obstructions.
Using the ADD testing apparatus, a
fire source simulated a rack storage
fire, and collection pans were used to
collect water into cylinders below the
apparatus. Sprinklers could be positioned directly over, centered between,
or offset from the centerline of the
fire source. The vertical position of
the sprinkler relative to the top of the
ADD apparatus replicated the distance
from the top of the storage array to
the ceiling sprinkler location. Once
the fire reached a steady-state burning
condition,
NFPA.ORG/
the pump
ESFR_RESEARCH
controlling
Read the FPRF report
water flow
on obstructions and
ESFR sprinklers.
to the open
sprinkler
Read more on the
was activated
development of the
2022 edition of NFPA
to produce
13, Standard for the
Installation of Sprinkler the desired
Systems.
sprinkler
Watch a webinar on the discharge
Research Foundation
pressure.
project on obstructions Data was
and ESFR sprinklers.
collected
and recorded for each collection pan,
and averages were calculated based
on areas of interest and the associated
obstruction. Sixty-five ADD tests were
conducted as part of this research.
While ADD testing does not account
for every variable, the methodology
identified trends such as how various
k-factors, as well as horizontal and
vertical offsets of the ESFR sprinklers,
impact the amount of water that can
reach the fire. These factors were
then used to select nine full-scale test
scenarios for K-17 sprinklers, which
analyzed joist obstructions with various
depths and distances to the sprinkler
deflector, as well as bridging members
and flat obstructions.
The full-scale tests yielded four key
takeaways cited in the report:
» The obstruction created by an open
web steel truss 22-36 inches deep,
located a minimum of 6 inches horizontally from an ESFR sprinkler
(K-14 or K-17), will not significantly
decrease sprinkler performance.

»T
 he obstruction created by a bridging member or other obstruction
1.5 inches square or less, located a
minimum of 12 inches directly below
an ESFR sprinkler (K-14 or K-17), will
not significantly decrease sprinkler
performance. This also applies to a
bridging member attached to open
web steel truss.
»T
 he obstruction created by a flat or
round obstruction less than or equal
to 12 inches wide, located a minimum of 6 inches horizontally from
an ESFR sprinkler (K-14 or K-17), will
not significantly decrease sprinkler
performance.
»T
 he obstruction created by a flat or
round obstruction less than or equal
to 24 inches wide, located a minimum of 12 inches horizontally from
an ESFR sprinkler (K-14 or K-17), will
not significantly decrease sprinkler
performance.
These findings could influence the
provisions of NFPA 13 related to ESFR
sprinkler installations, which in turn
could have a game-changing impact on
stakeholders throughout the industry.
While the NFPA 13 Technical Committee hasn't officially completed the
revision cycle for the 2022 edition
of the standard, if these findings
are applied to NFPA 13 they would
improve some of the installation
restrictions and allow ESFR sprinklers
to be located closer to obstructions.
Such changes would reduce the challenges designers currently face by
maintaining appropriate sprinkler
spacing while offering new approaches
to common obstructions. One of the
authors of the FPRF report recently
gave a virtual presentation on the
findings to the NFPA 13 Technical
Committee, and committee members
indicated that they agreed with the
research.
To follow the progress of the
upcoming edition of NFPA 13, visit
nfpa.org/13next.
JACQUELINE R. WILMOT is a research
project manager with the Fire Protection
Research Foundation.

N F PA . O R G / J O U R N A L * NFPA JOURNAL

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NFPA Journal - Spring 2021

Table of Contents for the Digital Edition of NFPA Journal - Spring 2021
