sprinklernotes
Clearance to Storage with In-Rack Sprinklers for Group A Plastics
You have asked the following questions: “I have a project with storage of
exposed, unexpanded Group A plastics in racks to a height of 20 ft with a
building height of 40 ft 7 in. Is Section 12.1.3.4.8 requiring an acceptable
clearance from storage to the ceiling with in-rack sprinklers or does it remove
the acceptable clearance requirement from storage to the ceiling if in-rack
sprinklers are installed? If I were to install in-rack sprinklers per Section
12.1.3.4.8 would I be able to use any of the rack configurations described in
Section 17.2.1.4? For example, I could use any of the rack options for 20 ft of
storage in a 25 ft building or 20 ft of storage in a 30 ft building? Also,
Figure 17.2.1.4(j) shows a line of sprinklers directly over the top level of
storage. Would this configuration require a solid barrier above the top of the
storage?” In response to your question, we have reviewed NFPA 13, 2013 edition
as the applicable standard. Our informal interpretation is the Section
12.1.3.4.8 negates the excessive clearance.
There are multiple sections that have to be referenced when you determine a
design criteria and when the acceptable clearance between the top of the
storage and ceiling is exceeded. The main section to review is Section 12.1.3,
which covers the requirements pertaining to storage height and building height.
Section 12.1.3.3 requires the design to be based off of the storage
configuration that routinely or periodically is found in the building requiring
the greatest water demand. The clearance from storage to ceiling requirements
are contained in Section 12.1.3.4. Then Section 12.1.3.4.2 states: “for spray
sprinkler criteria where the clearance to ceiling exceeds those identified in
this section, the requirements of 12.1.3.4.3 through 12.1.3.4.8 shall apply.”
Since the term “through” is used every applicable part of those sections have
to be adhered to. With the storage commodity being exposed, unexpanded Group A
plastics stored to a height of 20 ft. Section 17.2 contains the design
requirements. Thus Sections 12.1.3.4.5, 12.1.3.4.7, and
12.1.3.4.8 are applicable. Section 12.1.3.4.5 requires the protection criteria
to be determined by using a storage height that would result in clearance to
the ceiling of 10 ft. or install a supplemental row of in-rack sprinklers. For
example, use the design requirements for storage height of 31 ft for a building
height of 40 ft 7 in. even if the storage height is only 20 ft. An equally
acceptable approach is to install one level of supplemental, quick-response
in-rack sprinklers located directly below the top tier of storage at every flue
space intersection to be provided instead. Then Section 12.1.3.4.7 in
conjunction with the supplemental in-rack sprinklers dictates the ceiling
density to be based upon the given storage height as if the acceptable
clearance to the ceiling were met. In other words, the supplemental in-rack
sprinklers negates the excessive clearance. Next, Section 12.1.3.4.8 states if
the design criteria already requires in-rack sprinklers for a certain storage
configuration, provide those in-rack sprinklers as well as the supplemental
in-rack sprinklers required by Section 12.1.3.4.5. After reviewing Figure
17.2.1.4(j) it is believed the line of sprinklers shown above the top level of
storage is an error (effectively a typo) and those sprinklers are to be
installed directly below the top tier of storage. This is supported by the
configuration in the 2019 edition being shown without the sprinkler above the
top tier (Figures 25.9.3.3(g) and 25.9.3.3(i)).
