sprinklernotes
Calculating ESFR Sprinklers Located Below Obstructions
You asked the following question: “Is it required to calculate up to fourteen
(14) ESFR sprinklers when ESFR sprinklers are added below a continuous
obstructions?”
In response to your question(s) below, we have reviewed NFPA 13, Standard for
the Installation of Sprinkler Systems, 2019 edition and have answered each
question individually.
Our informal interpretation is only twelve (12) ESFR sprinklers are required to
be calculated.
27.4.4.4 ESFR Sprinkler Method. For ESFR sprinklers, the design area shall
consist of the most hydraulically demanding area of 12 sprinklers, consisting
of four sprinklers on each of three branch lines, unless other specific numbers
of design sprinklers are required in other sections of this standard.
The 2010 edition of NFPA 13 previously required an additional two ESFR
sprinklers to be calculated under the obstruction in section 22.4.4.6.4.1;
however, ESFR design criteria is based on FM Global testing data. During the
revision cycle for the 2013 edition of NFPA 13, FM informed the committee that
they do not include the additional two sprinklers in their fire test and the
committee removed the requirement from the standard. ESFR systems have only
required a twelve-sprinkler calculation since the 2013 edition. This
requirement was also removed from corresponding sections 14.4.4, 15.4.4,
16.3.3.6, 16.2.3.5, 17.3.3.5, and 17.2.3.4. It should be noted the FM pass/fail
criteria for storage sprinklers allows 6 sprinklers to activate. The 12
sprinkler calculation is an added safety factor.
