I need to determine the minimum design concentration (MDC) per NFPA 2001 – 2015 for a containerized large-scale lithium-ion battery energy storage system (ESS) using a halocarbon clean agent extinguishing system. Each container includes multiple lithium-ion battery racks operating around 1000VDC. My focus is on Section 5.4 - Design Concentration Requirements.
The battery vendor has provided the minimum extinguishing concentration (MEC) from a cup burner test of the electrolyte, and using a safety factor of 1.3 calculated the recommended MDC (per Section 126.96.36.199). However, this assumes that the battery electrolyte is a Class B Fire hazard - flammable liquid. The raw electrolyte may well enough be a flammable liquid, but when packaged into a cell, multiple cells assembled into a module, then multiple modules assembled into a rack energized at 1000VDC, the product is now a fuel in a different class: Class C Fires – energized electrical equipment.
OK, a Class C Fire designation for lithium-ion batteries seems obvious, but here is my problem: the battery vendors address safety with monitoring and control equipment in their Battery Management System (BMS), and rarely are responsible for any fire extinguishing equipment in their scope of supply. Battery vendors for the most part sell battery modules and racks listed to UL 1793 that are deemed to be “safe.” In some cases, ESS vendors do not install any fire suppression systems, e.g. Tesla. Without arguing the merits of fire suppression vs “let-it-burn” for thermal runaway, let’s assume fire suppression is a customer requirement (for reference the 2018 approved draft of International Fire Code requires fire suppression systems in Section 608 Stationary Storage Battery Systems). The worst of it is that the batteries I purchased last year are already outdated as battery vendors constantly release new and improved cells, leaving little incentive for them to invest time and money testing older versions.
So here I am with a Class C fuel hazard but only a Class B cup burner test of the electrolyte. NFPA 2001 Section 188.8.131.52 for Class C hazards specifies the MEC to be tested through a listing program, then multiplied by a factor of 1.35 to get the MDC. The battery vendor did test fire propagation between multiple modules and used a concentration of clean agent to successfully extinguish the fire, but that test is flawed in many ways: (1) it was not tested through a listing program, (2) the minimum concentration was not determined, and (3) only a few modules were used, not a fully energized 1000VDC rack. How should I proceed?
Below are my perceived options:
- Negotiate/pay battery vendor to send battery rack to a lab to determine MEC.
- Send one of my purchased racks to a lab to determine MEC, then replace damaged modules as needed before installation at site.
- Request exemption of NFPA 2001 from Authority Having Jurisdiction (AHJ) to use MDC from battery fire vendor propagation test
- Somehow argue to customer and AHJ that Class B fuel hazard is appropriate.