by Ahmed Ibrahim
With the market for electric vehicles projected to grow from 2.5 million units in 2020 to 31.1 million units in 2030, concerns about public safety related to their lithium-ion batteries have also increased. The problem arises when a short circuit occurs in these batteries. The heat from the short circuit makes the battery’s internal temperature rise to the point where a chemical reaction can start and spread to the adjacent cells, known as a “thermal runaway,” which is difficult to stop.
Battery fires also release toxic gases that can threaten first responders and building occupants. These fires are difficult to extinguish and even frequently reignite. Tesla itself warns that a battery fire can require up to 3,000 gallons of water for full suppression, which can take up to 24 hours. It has even been proposed to let the battery burn while protecting adjacent areas from further exposure. When multiple vehicles are housed in enclosed spaces like parking garages, the likelihood of this risk increases significantly due to the multiplication of the fire load.
Throughout the past century, sprinkler systems have been a reliable and effective fire protection feature. While many states mandate sprinkler installation, the National Fire Protection Association’s (NFPA) code, known as NFPA-13, is the U.S. standard that has been continually updated and provides the design criteria for the required sprinkler flow to extinguish or control fires. However, until the most recent edition of NFPA-13, published in 2022, there had been no design criteria for sprinkler flow that would be required to extinguish fires caused by electrical vehicles inside of facilities like public garages, where many of these vehicles are stored. The NFPA is now conducting research to investigate the storage of electric vehicles inside parking structures to determine the required sprinkler flow that would help lower the risk for first responders and others.
As a result of this design challenge, transitional approaches have been developed to apply existing fire suppression concepts and approved design flow rates to structures housing electric vehicles. The most common approach has been to consider the fire risk to be similar to a warehouse used for storing plastic. The reason is that high water flow density is necessary in the design of the sprinkler systems in such warehouses, which is similar to the need for high water flow on electric battery fires.
This analogy with plastic warehouses also stems from the fact that today’s vehicles are made of more plastic than ever before and that sprinklers have proven effective in controlling fires in plastic warehouses. NFPA-13 has design criteria that provide water protection for warehouses that store plastic, listing three different types of sprinkler heads that are to be used. The design criteria for those sprinkler heads can be used to develop an appropriate engineering design that can fit with the needs of sprinkler systems in garage structures that store electric vehicles.
It is difficult to know the adequate water density for the sprinkler system before a NFPA standard for such sprinkler systems is published. The answer to this design challenge will be based on actual large-scale fire tests. In the meantime, as large a water flow as possible should be considered necessary to help extinguish electric battery fires and prevent further spreading.
Ahmed Ibrahim
Ahmed Ibrahim, PE is a senior fire protection engineer with Weston & Sampson in Foxborough, Mass.
