In a recent Green Cubes webinar, we were asked, “What is the best fire suppression system for lithium-ion batteries?” We are asked this question often by all sorts of customers, whether it be for our lithium-ion material handling, large stationary, or our swappable cart power systems.
Safety is very important to us and our customers, and we want to ensure that everyone is prepared in the case of an unlikely lithium-ion fire. Fires in lithium-ion batteries are often a result of a process called thermal runaway. Thermal runaway is when one hot cell can light the next cell on fire just by getting it hot enough. This is a cascading type of failure where one cell may ignite, and then heat up the cells nearby, and then they ignite, and so on and so forth. This is the primary way fire propagates through lithium-ion batteries. Many battery systems have preventative measures built in to slow down the thermal exchange from cell to cell. This may slow the fire, but it usually doesn’t stop the fire.
The National Fire Protection Association is in charge of constructing U.S.-based best practice documents for building and commissioning of structures to prevent and reduce the risk of fires. There are codes and standards that cover construction, electrical, HVAC and plumbing systems. All NFPA codes are available at NFPA.org, and printed copies are available for purchase. All architects, contractors, engineers and tradesmen must reference these standards as they perform their duties.
Experts spend years researching and creating the NFPA codes. NFPA code 855 was released in 2020 and covers the Installation of Stationary Energy Storage Systems. A 2023 update will cover lithium-ion batteries.
In NFPA 855, Annex C is all about Firefighting Considerations. Here we find that “the NFPA’s Fire Protection Research Foundation and third-party engineering groups have shown that fires involving lithium-ion cells must be cooled to terminate the thermal runaway process.” “Firefighting foams and dry chemicals are not considered to be effective for these chemistries because they lack the ability to cool sufficiently and can conduct electricity.” It’s also noted that Carbon Dioxide and inert gas (such as Halon SF6) are also ineffective at cooling the batteries and cells.
How do we maintain the safety in data centers, hospitals, warehouses, and any other building with lithium batteries inside? What is the best fire suppression system? The simple answer is water, and lots of it, enough to go swimming, and then some! This will cool the cells and stop the thermal runaway process. Water is the agent of choice due to its abundance (in many areas), superior cooling capacity, and ease of transport to the seat of the fire. Water can come from a built-in fire suppression system, or a firefighting hose. In some unique systems where fire poses little to no risk to the surrounding uninvolved equipment the NFPA mentions that a “defensive posture” is to be considered, and the fire left to burn itself out. This is often a good strategy for outdoor cabinet locations that are far from people and other equipment since having water on site might not be possible.
As a further safeguard, the NFPA also limits the amount of energy stored and the density of these batteries to help prevent fire propagation. Section 9.4.1 states that each “rack” of batteries cannot exceed 50kWh and must be spaced at 3-foot intervals. This is to help prevent fire from spreading rack to rack in the case of an event. It also allows for enough room to get fire fighting equipment into the area to douse the fire with lots of water. Finally, most sites are limited to no more than 600kWh of batteries, or 30 of the max “racks” from above. As all NFPA rules, the AHJ (Authority Having Jurisdiction) has the final say on any installation and may require additional safety measures to be in place, such as local fire department training, annual walk throughs, etc.
