Underbody Cooling: Fire Isolator Watermist Applicator 26 as a Critical Tool for EV Thermal Runaway
Electric vehicle fires caused by lithium-ion batteries in thermal runaway remain one of the toughest challenges for first responders. One proven method for this phenomenon is underbody cooling, where water is applied directly under the vehicle to reduce battery temperatures. The Fire Isolator Watermist Applicator 26 (FI-WMA26) is specifically designed for this purpose, giving first responders a practical solution in situations where direct access to the battery is impossible. The FI-WMA26 can also be placed next to the car, to produce a water mist like a water curtain.
Why underbody cooling and watermist matters
EV batteries are usually mounted deep in the undercarriage, shielded by protective casings and the passenger compartment above. This design makes it extremely difficult for firefighters to reach the cells with conventional water streams, even though cooling the pack is the fastest way to slow or stop thermal runaway. Underbody cooling with the FI-MWA26 bridges this gap, targeting the heat zone from below and buying responders valuable time.
Water remains the global standard (but not in the traditional way)
The NFPA, supported by fire testing from the Fire Protection Research Foundation (FPRF), identifies water as one of the most effective agents to cool lithium-ion batteries in thermal runaway, not to extinguish the battery. Firefighters are trained to apply “copious amounts of water” directly to the battery case while using thermal imaging to monitor heat. But in the real world, applying that guidance is often impossible, since the battery is rarely accessible from above. This is where underbody cooling becomes the most viable option.
How the Watermist Applicator 26 works
The FI-WMA26 is a lightweight (10kg) aluminum tool that can be maneuvered under or beside a burning EV. It sprays a fine water mist directly against the vehicle’s underside, cooling the battery zone and suppressing toxic vapors. At the same time, it creates a protective barrier between the responder and the heat. Tested to EN IEC 60900:2018 and EN IEC 61010-1 + A1:2019, the Watermist Applicator 26 is already a trusted tool in demanding environments such as parking garages and ferries.
When underbody cooling isn’t enough
External underbody cooling alone is not sufficient to stop thermal runaway. That is the reason we deploy potassium nitrate aerosol units under the blanket. These aerosol units not only prevent deflagration of gasses and vapor, but also kick down the flames coming from the battery and as a result, a dramatic drop in temperature is witnessed. In order to fully stop the thermal runaway, Fire Isolator offers the EV FireGun (FI-FIREGUN), which penetrates the battery housing and floods the pack from within. Delivering 40 liters of water per minute at two bar directly to the cells, the FireGun drastically reduces the risk of reignition and ensures deeper cooling at the source of the fire.
The FireGun, together with the Watermist Applicator 26, forms part of the broader FIRE⚡️ISOLATOR Concept—a comprehensive strategy for EV fire response. This multi-layered approach also includes our Fire Blanket Ultimate, a certified high-temperature resistant fire blanket designed to isolate the vehicle and contain flames. Used in combination, the Ultimate Fire blanket and Watermist Applicator make cooling more efficient by suppressing toxic vapors since the water mist applicator can also be placed next to the car to produce a water mist, moer as a water curtain. Alongside Aerosol Units and Thermal Imaging cameras, these elements give responders a tested and practical system to manage even the most challenging EV fire scenarios.
Please note: the Watermist Applicator 26 was later renamed from 36 to 26, we are showing you the same product.