Comparative fire suppression testing of drencher systems: Gasoline vs. battery electric vehicles
A test series was conducted involving two pairs of geometrically similar gasoline-fuelled and battery electric vehicles. The intent was to simulate a vehicle fire in a ro-ro space of a ship and investigate the fire suppression performance of its drencher system. The results indicate that a fire in a battery electric vehicle does not seem to be more challenging than a fire in a gasoline-fuelled vehicle for a drencher system designed in accordance with current international recommendations.
Water spray systems (often referred to as “drencher systems”) are typically installed to protect ro-ro and special category spaces on ships. A “special category space” is a space where the vehicles are driven on board and to which passengers have access. The drencher system consists of deluge sections with open water spray nozzles at the ceiling, and the sections are manually operated by the crew in case of fire. Concerns have been raised about whether these drencher systems are able to control a fire in an electric vehicle or if the design of the system in terms of water flow rates defined in the international recommendations needs to be increased.
The objective of the tests was to compare the fire suppression performance of a drencher system for fires involving gasoline-fuelled and battery electric vehicles in test conditions as equivalent as possible.
The arrangement of the tests
Two pairs of vehicles, i.e., a total of four vehicles, were used in the tests. Each pair of vehicles was chosen to be as similar as possible, except for the powertrain. A drencher system consisting of four open water spray nozzles was used in each of the four tests. The nozzles were installed about 5 m above the floor, and the system design in terms of the water discharge density (10 mm/min) corresponds to the design recommendations in MSC.1/Circ.1430/Rev.2, “Revised Guidelines for the Design and Approval of Fixed Water-Based Fire-Fighting Systems for Ro-Ro Spaces and Special Category Spaces” from 2020.
The plan was to initiate fire in such a way that the liquid fuel or the battery pack was involved at the initial stage of the fire. This was done by making a mechanical penetration of the fuel tank and the battery, combined with small fire ignition sources that ensured that fire ignition occurred. The application of water was manually initiated at a total heat release rate of about 1.5 MW. This threshold was chosen to ensure that the fire had indeed involved the vehicle at a time when continued fire growth was to be expected. Water was discharged for 30 minutes. Thereafter, the post-application fire regrowth was documented by allowing the vehicle to be completely consumed in the fire.
The tests were conducted under a large-scale calorimeter in order to measure the heat release rate from the fire. Additionally, the temperature above the vehicle, the surface temperature on steel sheet screens to the sides of the vehicle (simulating adjacent vehicles), the heat radiation at the long side of the vehicle, and finally the surface temperature of Plate Thermometers in front of and behind the vehicle were measured.
Very different fire scenarios
The fire scenarios of the two types of vehicles were quite different. The gasoline fuel spill fire associated with the gasoline-fuelled vehicle tests developed rapidly, and the application of water was initiated after about a minute. The fire in the battery pack of the battery electric vehicles developed slower, involved other combustibles gradually, and the application of water was initiated after more than twelve minutes and sixteen minutes, respectively.
Figure 1: The fire size at the most intense stage in the first pair of vehicles: The gasoline-fuelled at about 03:30 [min:s] and the corresponding battery electric vehicle at about 19:00 [min:s], viewed from a position behind the vehicle.
Figure 2: The fire size at the most intense stage in the second pair of vehicles: The gasoline-fuelled at about 04:00 [min:s] and the corresponding battery electric vehicle at about 24:40 [min:s], viewed from a position behind the vehicle.
The drencher system controlled the fire, irrespective of the type of vehicle. The control of the fire was measured as a reduction of temperatures above the vehicle, the surface temperatures of adjacent steel sheet screens, the surface temperature of Plate Thermometers, and reduced heat radiation. Fire control was also documented by a reduction of the heat release rate during water application and clear fire regrowth with significant fire sizes once the application was terminated. The overall conclusion from the tests is that a fire in a battery electric vehicle does not seem to be more challenging for the current drencher system design than a fire in a gasoline-fuelled vehicle of comparable size. During the tests, one concern was raised – a flammable liquid spill fire could involve adjacent vehicles due to its intensity and as the liquid spill could spread under adjacent vehicles.
The tests were conducted in the LASH FIRE project
The tests are described in the report D10.4, “Large-scale validation of the new fire test standard for alternative fixed fire-fighting systems,” that can be downloaded at www.lashfire.eu. The LASH FIRE project was running from September 2019 to August 2023 and was founded by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 814975. The information in this article reflects only the author’s view, and the Agency is not responsible for any use that may be made of the information it contains.
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Magnus Arvidson
magnus.arvidson@ri.se
