Rack ‘em up, NFPA 30 then and now
In 1992, I designed the fire protection systems for a Hazardous Materials Storage Building. The building had a separate area for storage of flammable liquids (Class IA, IB, and IC), and a separate area for storage of combustible liquids (Class II and III). Both areas would store containers with capacities greater than five gallons.
The warehouse was arranged with double row racks with a maximum storage height of 25 feet. Using the design criteria provided in Appendix D, Table D-4-6.2(c) of the 1990 edition of NFPA 30, the protection of the flammable liquids area consisted of a ceiling automatic wet pipe sprinkler system and in-rack sprinklers at each level. The ceiling system used high temperature sprinklers with a design density of 0.60 gpm per square foot over a design area of 3,000 square feet. In-rack sprinklers were located in the longitudinal flue space, staggered by level. In-rack sprinklers were K=5.6 and the design called for 24 sprinklers operating, six sprinklers on each of the four levels, with a minimum operating pressure of 30 psi. The required hose allowance was 1000 gpm.
The protection of the combustible liquids area consisted of ceiling automatic wet pipe sprinkler system and in-rack sprinklers at two levels. The ceiling system used high temperature sprinklers with design density of 0.25 gpm per square foot over a design area of 5,000 square feet. In-rack sprinklers were located in the longitudinal flue space, staggered by level. In-rack sprinklers were K=5.6 and the design called for 24 sprinklers operating, six sprinklers on each of the two levels, with a minimum operating pressure of 30 psi. The required hose allowance was 750 gpm.
The building had many other features of fire protection, including smoke and heat vents, but this column will focus on sprinkler criteria.
A more recent case history illustrates how much sprinkler system design criteria for the protection of flammable and combustible liquids has changed.
The building is located on the Navy Base in Yokosuka, Japan, and the area in question is operated by the Defense Logistics Agency (DLA). The project is being administered by the Air Force Civil Engineer Center (AFCEC). AMEC Environment and Infrastructure, Inc. is the design A-E. The general contractor for the project is Gilbane Federal (Tokyo office). The installing sprinkler contractor was Nippon Dry Chemical supported by Viking Sprinkler of Japan.
My role in this project as the quality control fire protection engineeris to ensure and assist the contractor to comply with the requirements of the contract documents.
This project involves upgrading the protection in a warehouse area used for rack storage of flammable and combustible liquids. The racks are double row type open racks which permitted storage of commodities on three levels to a maximum height of approximately 14 feet. The ceiling height is 21 feet.
Chapter 16 of NFPA 30 (2015) contains design criteria for fire protection systems, specifically, automatic sprinkler systems using water-only and low-expansion foam-water sprinkler systems.
Of note is paragraph 16.1.2, which states: “16.1.2* This chapter shall not apply to Class IA flammable liquids or to unstable flammable or combustible liquids.”
The reason as explained by the annex note to 16.1.2 is that no full scale testing has been conducted for these liquids, thus their exclusion.
Based on this the Class IA, liquids in our 1990 project could not be properly protected. To permit these systems designed to the older appendix criteria Annex paragraph A.16.1.1 offers some permission in stating: “Protected storage allowed under previous editions of this code can be continued if the class of liquids stored, the quantity of liquids stored, fire protection and building configuration remain unchanged.”
Of course for something to “remain unchanged” since 1993 is unlikely.
Now back to the present. To determine if a particular storage arrangement can be protected by NFPA 30 criteria and by what sprinkler design criteria, one needs to step through one of three flow charts, Figures 16.4.1(a), 16.4.1(b), or 16.4.1(c). Figure 16.4.1(a) is used for miscible and non-miscible liquids in metal containers.
Figure 16.4.1(b) is used for miscible and non-miscible liquids in non-metallic containers.
The actual protection criteria is contained in one of 12 tables, Tables 18.104.22.168 through 22.214.171.124. Tables 3 and 4 are for foam-water sprinkler systems, the remaining tables are for water-only sprinkler systems.
For the Yokosuka project, using Figure 16.4.1(c) the A-E established the design criteria will be based on Table 126.96.36.199. From this table, the protection measures for containers in cartons each with a capacity less than or equal to one gallon was selected. For this container style (cartoned) and capacity, the maximum storage height and ceiling heights are unlimited. The table directs one to specific sprinkler design criteria of paragraph 16.6.2, identified as “Fire Protection Design Scheme B”. The minimum aisle width is eight feet and the maximum rack depth is nine feet.
Fire Protection Design Scheme B requires horizontal barriers, constructed of minimum 3/8-inch plywood or 22-gauge sheet metal, be installed at each level of storage. For this project, three levels of horizontal barriers are needed. It is noted that the protection scheme requires all commodities to be stored below barriers, so the top level of the rack above the highest fire barrier cannot be used for storage.
In-rack sprinklers must be installed beneath each barrier. For double-row racks, in-rack sprinklers must be located along the longitudinal flue space at maximum five feet spacing and along the face at transverse flue spaces with maximum nine feet spacing (see NFPA 30 Figure 188.8.131.52(c)). In-rack sprinklers were hydraulically calculated based on eight in-rack sprinklers, four on each of two rows. The in-rack sprinkler K-factor is 8.0 and minimum flow per sprinkler is 57 gpm. The ceiling system is required to provide a minimum of 0.20 gpm per square foot over a minimum 3,000-square foot design area. The hose stream allowance is 500 gpm.
One challenge facing the contractor on this project was the construction of the horizontal barriers. The contract documents did not detail how the barriers were to be fabricated and installed. It was essentially a performance-based design. The drawings called for non-combustible horizontal fire barriers at all levels. Since non-combustible barriers were required the contractor needed to use stainless steel metal sheet to fabricate the barriers. The configuration for the double row racks did not permit a continuous flat sheet to be lain across the full depth of the rack. It was decided to put in a three-part system, a flat sheet to cover the shelving portion, located under the wire grid and the rack beams, and a preformed cup to sit in the longitudinal flue space (see Figure 1). . After being put into place, the flat sheets and preformed cup were screwed in.
The final barrier installation came out quite nice. Careful attention must be given to how horizontal barriers will actual fit into the rack system, especially if they are existing racks. Though NFPA 30 allows the use of 3/8 plywood sheet, I would think twice about using it. Plywood will be much cheaper, but I am guessing it will not stand up very well to the abuse that will be inflicted on it by fork lift operators.
The location of sprinklers in the rack is always a concern, as these same fork lift operators will be “trying” to avoid hitting the sprinklers. Sprinklers in the longitudinal space are relatively easy to protect. It is the face sprinklers that are more vulnerable to damage. Locating face sprinklers so rack uprights can offer protection without obstructing sprinkler spray requires careful attention.
Samuel S. Dannaway, P.E., FSFPE is a licensed fire protection engineer and mechanical engineer with bachelor’s and master’s degrees from the University of Maryland Department of Fire Protection Engineering. He is a past president and fellow of the Society of Fire Protection Engineers. He is vice president of Fire Protection Technology at Coffman Engineers Inc., a multi-discipline engineering firm with over 360 employees across eight offices. Dannaway can be reached at firstname.lastname@example.org.