Executive Summary - Fire Protection Guidance for Warehouse Storage of Cartoned Li-ion Batteries

 

Executive Summary - Fire Protection Guidance for Warehouse Storage of Cartoned Li-ion Batteries

By Tom Long and Andrew Blum
Exponent, Inc

 

This article summarizes fire tests conducted to determine fire protection guidance for warehouse storage of cartoned Li-ion batteries. For full report see reference 1.

The main methodology for this project consisted of a two-pronged approach to analyze the fire hazard of Li-ion batteries in cartons: (1) a comparison of free burn flammability characteristics of a large-format polymer pouch Li-ion battery to FM Global standard commodities and previously tested small-format Li-ion batteries in a rack storage array2,3 and (2) a large-scale fire test to assess the performance of ceiling-level sprinkler protection on cartoned large-format polymer pouch Li-ion batteries. The goal of the experimental approach was to maximize the application of the successful large-scale fire test result.

Additional tasks of this project involved (3) assessing the impact of internal ignition within a pallet load of batteries versus the external ignition typically used in large-scale fire testing, and (4) assessing the effectiveness of sprinkler water at suppressing a fire at a later stage of battery involvement than could be achieved in the large-scale test. These tasks reinforce the sprinkler protection guidance resulting from the successful large-scale fire test. All data, test descriptions, data analysis and figures in this report were provided by FM Global. Exponent has relied on the FM Global testing report titled “Development of Protection Recommendations for Li-ion Battery Bulk Storage: Sprinklered Fire Test” as a basis for this report4.

This project was conducted in partnership with the Property Insurance Research Group and in collaboration with the Fire Protection Research Foundation. The previous two phases of the project included a use and hazard assessment report5 (Phase I) and a series of reduced-commodity fire tests comparing the flammability characteristics of common Li-ion batteries/products to FM Global standard commodities (Phase II)2,3. These tests showed that bulk storage of small-format (2.6 Ah) Li-ion batteries exhibit similar fire growth, leading to first sprinkler operation as other more common cartoned commodities. Further, it was determined that the time required for involvement of the Li-ion batteries in a fully developed fire is approximately five minutes. These conclusions provided the basis for sprinkler protection recommendations for small-format Li-ion batteries in bulk storage, with the goal of suppressing the fire before the anticipated time of involvement of Li-ion batteries.

The Li-ion batteries available for this project were 20 amp hour (Ah), 3.3 volt (V), polymer pouch batteries with lithium iron phosphate (LiFePO4) chemistry. The battery dimensions were approximately 6.0×9.0×0.3 inches, and the state-of-charge (SOC) was nominally 50%. Packaging consisted of corrugated containerboard cartons that housed 20 batteries separated by 10 levels of plastic dividers. This packaging and battery layout was consistent with the previously tested small-format Li-ion polymer batteries2,3.

The free burn flammability characteristics of the 20 Ah Li-ion polymer pouch battery were tested and compared to those of FM Global’s standard commodities and small-format Li-ion batteries from Phase II2,3. The test, referred to as a “reduced-commodity” test, was used to estimate the fire hazard present at the time of first sprinkler operation in a sprinklered warehouse fire scenario. Measurements focused on the fire development of each commodity and the time of battery involvement for the Li-ion batteries during a free-burn rack storage fire test. The key findings reported by FM Global from these tests when compared to the previous reduced-commodity tests included:

  • The cartoned 20 Ah large-format battery used in the present study represented a higher hazard than the previously tested 2.6 Ah small-format cylindrical and polymer pouch batteries.
  • Product packaging (corrugated board containers and plastic dividers) was identified as a key factor driving the hazard in Li-ion batteries in storage. While the corrugated board cartons were shown to dominate the initial fire growth, the plastic content within the cartons was shown to be a driving factor in the overall commodity hazard.
  • Cartoned batteries containing significant quantities of plastics exhibited a similar rapid increase in the released energy due to involvement of the plastic early in the fire development.
  • Cartoned batteries containing minimal plastics (such as the small-format cylindrical and polymer Li-ion batteries tested in Phase 2) exhibited a slower increase in energy release and a delay in the battery involvement due to heating of the batteries. In this case, the plastic dividers represented a lesser combustible load than the heavy plastic dividers used for the 20 Ah polymer pouch battery.

The performance of ceiling-level automatic fire sprinkler protection was assessed with a large-scale sprinklered fire test. The test evaluated the above-mentioned battery type and SOC stored in cartons in a three-tier, high-rack storage array at 15 ft. in height and a ceiling height of 40 ft. Protection was provided by quick-response, pendent sprinklers, having a 165ºF rated link with a K-factor of 22.4 gpm/psi1/2. The key findings reported by FM Global from this large-scale test included:

  • Storage up to 15 ft. under ceiling heights up to 40 ft. can be adequately protected by a fire sprinkler system comprised of pendent sprinklers having a K-factor of 22.4 gpm/psi1/2, a nominal 165ºF temperature rating and RTI of 50 ft1/2S1/2, installed on 10 ft.×10 ft. spacing at an operating pressure of 35 psig.
  • Protection guidance established from the large-scale fire test can be reasonably applied to small-format (such as 2.6 Ah cylindrical and polymer pouch) Li-ion batteries previously tested for this project.

Two additional tasks were performed to reinforce the sprinkler protection guidance mentioned above. The first evaluation assessed the likelihood and impact of ignition resulting from thermal runaway of one or more batteries within a carton. The second analyzed the effectiveness of sprinkler water at suppressing a fire at a later stage of battery involvement than was achieved in the large-scale test. The key findings reported by FM Global from these additional analyses/tests included:

  • For all small- and large-format Li-ion batteries used in this project, the development of a rack-storage fire leading to sprinkler operation should be similar for both an ignition scenario where the fire initiates inside or outside of the carton.
  • The sprinkler system used in the large-scale fire test was sufficient to protect against a fire where the Li-ion batteries were contributing more to the overall fire severity than occurred in the large-scale test.

 

References

[1] R. Thomas Long and Andrew Blum, “Lithium Ion Batteries Hazard and Use Assessment - Phase III,” Final Report, November 2016.
[2] B. Ditch and J. de Vries, “Flammability Characterization of Lithium-ion Batteries in Bulk Storage,” FM Global Technical Report, March 2013.
[3] R. Thomas Long Jr., R. T. Long Jr., J. Sutula and M. Kahn, “Li-ion Batteries Hazard and Use Assessment Phase IIB: Flammability Characterization of Li-ion Batteries for Storage Protection,” Report prepared for the Fire Protection Research Foundation, 2013.
[4] B. Ditch, “Development of Protection Recommendations for Li-ion Battery Bulk Storage: Sprinklered Fire Test,” FM Global, September 2016.
[5] C. Mikolajczak, M. Kahn, K. White and R. Long, “Lithium-Ion Batteries Hazard and Use Assessment,” Report prepared for the Fire Protection Research Foundation, June 2011.