sprinklernotes
Obstructions and ESFR Sprinkler Spacing
You asked the following question: “We occasionally encounter rouge structural
members (drag strut beams) at the roof that can disrupt the spacing of ESFR
sprinklers. NFPA 13 Section 8.12.2.3 requires the minimum spacing of ESFR
sprinklers be 64 sq. ft. and Section 8.12.2.4 requires the minimum spacing be 8
ft. In some cases, we are required to relocate sprinklers in the entire
building to accommodate these obstructions to a sensible spacing pattern. FM
Global Data Sheet 2.0 Section 2.2.3.2, Table 17 has similar requirements, but
has an exception that says when sprinklers are located in every bay, the
sprinkler spacing requirements of Table 17 do not necessarily apply to
sprinklers in adjacent bays. Is there any discussion by the NFPA 13 committee
about exceptions to the spacing rules when sprinklers are located in every bay?
The 2019 edition of NFPA 13 does not seem to provide any new resources on this
issue. We realize that compressing spacing may result in more sprinklers
operating, but FM does not seem to have any caveats attached to their exception
that would suggest this is a concern.?” In response to your question, we have
reviewed 2016 edition as the applicable standard. Our informal interpretation
is NFPA 13 has no exceptions based on sprinklers being in adjacent storage bays.
As you indicated, the minimum separation between ESFR sprinkler is 8 ft. There
are no allowances (as applicable to spray sprinklers in Section 8.6.3.4.2)
whereby baffles can be used when the minimum separation cannot be achieved.
This approach applies only to spray sprinklers since it is only discussed in
Section 8.6. This is also confirmed by Sections 8.4.6.3.2 and 8.12.3.4 that
remind us that a minimum separation of 8 ft. is required even when separated by
solid structural members. The amazing thing about the FM allowance to treat the
beam at the edge of the bay like a wall, is that past fire tests have shown
that solid members (focused on draft stops or curtains) have an immensely
negative impact on the system performance (activation patterns). That’s why
section 12.1.1.3 states: Draft curtains shall not be used within ESFR sprinkler
systems.
Draft curtains can be used to separate an ESFR sprinkler system from an
adjacent sprinkler system with standard-response sprinklers, but there must be
nothing allowed directly beneath them (see Section 8.4.6.4 requirements for a
clear aisle beneath any draft curtains). If you have a clear aisle beneath the
beams of 4 ft., you have a solid basis for submitting an equivalency to the AHJ
to treat them as a wall even if you are not separating an ESFR sprinkler system
from an adjacent sprinkler system with standard-response sprinklers. The
purpose of the draft curtain separating two systems with a clear aisle width
and draft curtain is to eliminate the potential for a fire starting under or
near the draft curtain, operating sprinklers on both sides, as stated in the
NFPA 13 Handbook commentary. This purpose could be used as the basis for the
equivalency.
