Fire protection engineering challenges in storage

Fire protection engineering challenges in storage

Contributors: William E. Koffel, P.E., FSFPE; Kerry Bell, P.E., FSFPE; and Phil Friday, P.E., FSFPE

Presentations

The Society of Fire Protection Engineers conducted the SFPE Forum on Fire Protection Engineering Challenges in Storage in September 2022.  The Forum consisted of interactive presentations discussing some of the challenges facing the fire protection community and recent research and solutions with respect to storage facilities.  While not in direct response to recent fire events, over the past 18 months there have been a number of significant fires in storage facilities around the world.  The purpose of this article is to provide an overview of some of the presentations and a summary of the full-scale fire test and laboratory tour that was made available to the participants.  For those interested, the SFPE is considering a second programme in early 2023. Additional information will be available at www.sfpe.org when a second programme is confirmed.

The programme began with a session on automatic storage by Wes Baker, FM Global. Wes discussed how storage within warehouses has been changing over the past decade to allow for material handling of products via the use of robots, while at the same time creating storage arrangements that minimise wasted space. A description of some of the automatic storage systems being used in warehouse environments, what the fire hazards are for these types of systems, full-scale fire testing that has been conducted on them, and the recommendations now offered in F.M. Global Property Loss Prevention Data Sheet 8-34, Automatic Storage and Retrieval Systems, for these types of storage systems. John Frank, AXA XL Risk Consulting discussed several large warehouse fires in the context of expectation gaps between various stakeholders and how these gaps contributed to major losses. Specific topics included final extinguishment of complex arrangements such as automatic storage and retrieval systems and multi-tier mezzanines, as well as smoke removal and impairment management. Sean DeCrane, UL Solutions, discussed a UL Solutions and AutoStore project that evaluated the potential fire service response to a sprinkler-controlled fire within an AutoStore system. Prior to the project, recommendations included the installation of remote master streams with the dismantling of the system to permit access to confirm or complete extinguishment. Due to the extensive damage and business interruption that would be experienced and the risk of injury to the responding firefighters with this particular approach, AutoStore was interested in an alternative approach. U.L. brought in five fire service operation subject matter experts to assist in the development of a bin removal methodology and a scaled fire scenario and response where firefighters from various departments deployed and implemented this removal strategy.

Other challenges discussed included the protection of multi-row racks by Tracey Bellamy, CFPS, Telgian Engineering and Consulting. Tracey discussed the provisions of NFPA 13, 2022 Edition that addressed rack depths greater than 20 ft without internal flue spaces, the impact on the fire sprinkler system design, along with the relevant test data utilized to support the change. John LeBlanc, FM Global, and Christina Francis, P.E. FSFPE, Tesla, looked at the changing commodities that are showing up in general purpose warehouses. Many of these products are hard to identify, and the hazard is not always apparent. The two primary commodities that were examined were cosmetics and consumer products that represent an ignitable (flammable and/or combustible) liquid hazard and lithium-ion batteries (cell storage through modules for cars) that can represent an ignition hazard up to a lithium-ion battery fire hazard. Dr. Noah Rider, Fire Risk Alliance, presented the research that has occurred regarding sloped ceilings in storage occupancies. The conclusions from the extensive Fire Protection Research Foundation work were presented along with advances in tools that can assist in assessing the performance of systems. Similarly, Garner Polenske, WJE, summarized the scientific basis of the new obstruction requirements for ESFR sprinklers found in both NFPA 13, 2022 Edition and F.M. Global Data Sheet 2-0. A new obstruction analysis tool was also be demonstrated through the evaluation of real-world obstruction scenarios.

The programme did not focus solely on water-based fire suppression systems. Robert Accosta, Jr, discussed the integration of storage technology, evolution of product design, and desire to store at greater densities/heights that continue to present challenges in the design of life safety and fire alarm systems for storage facilities, warehouses and distribution centres. The presentation identified common challenges encountered during the design, construction and operation of these facilities as well as propose a holistic approach to addressing these challenges. Although many codes do not require fire alarm systems in storage occupancies, the presentation encouraged design professionals to consider a variety of fire safety goals and how fire alarm systems can help address the challenges that were discussed on first day. The programme ended with a “back to reality” presentation by John Denhardt, P.E., FSFPE. John noted that the design criteria for storage has and will continue to evolve as more testing is completed. Addressing commodity classifications that do not fit into the examples provided in the annex of NFPA 13 can be a complex issue. Often, the design criteria specified for a project are not applicable to the actual building being built. The design team needs to coordinate the design criteria with the building design before a sprinkler contractor has been selected to avoid issues during the construction phase.

Fire Test and Laboratory Tour

In conjunction with the SFPE Forum on Fire Protection Engineering Challenges in Storage, UL Solutions invited participants to observe a large-scale fire test and tour of some of the other fire protection testing areas near Chicago at their Northbrook, IL, USA, corporate headquarters campus.

UL Solutions’ 45,000 ft2 (4,180 m2) large-scale fire test facility is designed to allow the simulation of a wide range of fires that may occur in large warehouses.

Figure 1. Exterior Images of UL Solutions Large Scale Fire Test Facility

The design of this large-scale test facility had the following objectives:

  • To provide the ability to evaluate the performance of automatic fire sprinklers intended to protect storage-type fire risks using large-scale fire test scenarios;
  • To enable the assessment of fire risks associated with different storage practices and burning commodities; and
  • To provide the ability to evaluate the performance of a variety of products and systems in a large-scale scenario including energy storage equipment.

One of the unique features of this facility is a 100-ft.-by-100-ft. (30.5 m by 30.5 m) movable ceiling installed within a 14,400 ft2 (1,338 m2) test cell that can be adjusted from heights of 6 ft. (1.8 m) up to 48 ft. (14.6 m) from the floor. The 10,000 ft2 (930 m2) ceiling is much greater in area than the design area for sprinkler system protection. The adjustable height ceiling also has special features that allow for flexibility in establishing design criteria relative to sprinkler test spacing and location. Combustion air is drawn in naturally from roof intake ducts located symmetrically around the square-shaped test cell.

To adequately supply the sprinkler system with water, the facility features a 200,000-gallon (760,000 L) water supply reservoir with a variable speed pumping system capable of providing flows in excess of 6000 gpm (22,700 lpm) and pressures in excess of 175 psig (12 bar) depending upon the flow condition.

In a separate test cell, a 25-ft. (7.6 m) diameter calorimeter having a 10-megawatt (MW) capacity is available to measure the rate of heat release and assess the fire suppression characteristics of burning commodities. For some products and storage configurations, this test cell can be used as a tool to characterize the fire risk.

The SFPE forum participants were permitted to walk the floor of the primary test cell and get a close-up view of the fire test arrangement (Figure 2 below). Participants were able to observe the large-scale test live from the observation room on the 2nd floor of the facility (Figure 3 below).

Figure 2. UL Solutions staff providing an overview of the test prior to the start of the test.

Figure 3. Participants observing the test from the observation room within the test facility.

Figure 4 – Standard cartoned Group A unexpanded plastic commodity with a portion of the exterior carton removed to illustrate the storage arrangement of polystyrene cups (left). Reinforced plastic pallet used in the test (right).

The test arrangement was an open double-row rack storage arrangement as described in NFPA 13, Standard for the Installation of Sprinkler Systems1. The main test array was a nominal 32 ft. (9.8 m) long and 25-ft. (7.6 m) high. Single row target arrays having the same storage height were installed with 4 ft. (1.2 m) aisles on both sides of the double-row rack main test array. The target arrays were installed to determine if the sprinkler system was capable of controlling or suppressing the fire in a manner that would prevent it from travelling to the outside perimeter of these single row arrays.

A standardised cartoned, unexpanded plastic commodity was stored on reinforced polypropylene pallets which is a rack storage arrangement permitted in NFPA 13 for the installed sprinkler system. The standard, cartoned test commodity comprised of single wall corrugated cardboard cartons measuring a nominal 21 by 21 by 20.5 in. high (530 by 530 by 520 mm) containing 125 crystalline polystyrene cups in separate compartments within the carton. Single wall corrugated cardboard sheets were used to separate the five layers of cups and interlocking single wall corrugated cardboard vertical dividers were used to separate the 25 cups in each layer. Eight of the cartons were arranged in a 2 x 2 x 2 array with the open end of the cups facing down and placed on a nominal 40 by 48 by 6 in. high (1016 by 1220 by 152 mm) four-way reinforced polypropylene pallet. Figure 4 below shows the test commodity and reinforced plastic pallet.

Reliable Automatic Sprinkler Co., Inc. collaborated with UL Solutions for the large-scale fire test, which was intended to evaluate NFPA 13 protection criteria related to plastic commodities stored on plastic pallets. The sprinkler system consisted of Reliable’s Model P25 nominal K-25.2 gpm/(psi)1/2 (360 L/min/(bar)1/2) pendent ESFR sprinklers spaced 10 ft by 10 ft (3 m by 3 m) apart with a 212oF (100oF) temperature rating as described in NFPA 13. The sprinkler deflectors were located 18 in. (47.5 cm) below the ceiling and 3 ft. (0.9 m) above the top of storage with the sprinklers arranged to discharge water at a nominal pressure of 15 psig (1 bar). During the test, three (3) sprinklers operated and suppressed the fire in a manner that the fire did not travel to the end of the main test array or involve the commodity stored in the target arrays.

Figure 5. Reliable Model P25 ESFR Sprinkler (top left), Fire immediately before sprinkler activation (top right, Fire immediately after sprinkler activation (middle), and UL Solutions thermal images and data during the test.

The large-scale test conducted at UL Solutions and witnessed by participants of the September 2022 SFPE Forum on Fire Protection Engineering Challenges in Storage was intended to be more than just a demonstration. It was intended to provide valuable data for the fire protection community, and it did just that.

References

1. “Standard for the Installation of Sprinkler Systems”, NFPA 13, National Fire Protection Association, Quincy, MA, 2022 Edition.



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