Recent shifts in the transport industry towards green energy have led to an increase in electric, hydrogen, and hybrid electric vehicles on the road. Public transport has seen a rise in the number of clean energy buses in use, and some questions regarding the safety of the vehicles have been raised.
fire suppression systems
One such question was that of the effect of the quiet vehicles on other road users and the partially sighted, which led to UNECE Regulation No. 138 for Quiet Road Transport Vehicles about their reduced audibility.
Another question that has been raised concerns the use of fire suppression systems on these new energy vehicles. As technology develops, clean energy vehicles are becoming increasingly safe, but some challenges lie in the difference between the fire properties of clean energy and traditional combustion engines.
Traditional fire suppression
Traditional combustion engines catch fire most often when they overheat or when there is a fuel leak
Traditional combustion engines catch fire most often when they overheat or when there is a fuel leak. Fire requires 3 essential components to ignite: fuel, heat, and oxygen. The diesel or hydraulic oil acts as fuel for the fire, the engine provides the heat, and the oxygen in the atmosphere completes the triangle.
Traditional fire suppression systems, including some UNECE R107, approved fire suppression systems, rely predominantly on dry chemical extinguishing agents (dry powder) to suppress fires.
how it works
These systems work because the dry chemical agent is dispersed from the nozzles and gets into every area of the engine compartment thanks to its excellent dispersion and coverage capabilities.
The dry powder coats the surfaces within the engine compartment, creating a barrier between the fuel and the oxygen. This suffocates a fire, suppressing it in a matter of seconds to minimize damage to the vehicle.
Challenges when protecting clean energy vehicles
Clean energy vehicles pose a challenge, as the combustion properties are different from those of a traditional engine.
Hydrogen fuel cell-powered vehicles and Lithium-ion (Li-ion) battery-powered vehicles both pose a significant threat if ignited and each act differently.
Lithium-ion (Li-ion) battery vehicles
Electric and hybrid electric vehicles use Li-ion batteries and, if the battery pack ignites, the resulting fire is intense
Electric and hybrid electric vehicles use Li-ion batteries and, if the battery pack ignites, the resulting fire is extremely intense and can spread quickly from cell to cell.
The fire suppression systems currently installed on electric and hybrid buses are designed to contain the fire to give the passengers and the driver time to evacuate, rather than to extinguish the fire completely.
Hydrogen fuel cell vehicles
Hydrogen cell vehicles in particular pose a unique fire risk. For hydrogen to ignite, oxygen and an ignition source are required. However, when ignited, pure hydrogen flames burn pale blue which makes them almost invisible and they do not produce smoke, making them incredibly difficult to detect visually.
Hydrogen firefighting protocols are similar to those of other gases. The gas should be eliminated, or, if this is not possible, the fuel should be allowed to burn out under controlled conditions.
1) Extinguishers
Small fires can be fought with dry powder agents, carbon dioxide, or halon extinguishers. If a hydrogen fire is extinguished, but the fuel source is not cut off, the resulting mixture may re-form to reignite.
Currently, hydrogen fires where the fuel source cannot be removed are fought by allowing the fire to burn out while preventing the spread of the fire and using copious amounts of water to cool the surroundings.
2) Dry chemical fire suppression system
For hydrogen vehicles, as soon as a fire is detected the vehicle should be shut down to shut the valves, eliminating the fuel source.
The installation of a dry chemical fire suppression system in hydrogen buses is recommended to contain the fire, reducing vehicle damage and allowing passengers and the driver to safely evacuate the vehicle.
What is being done to improve electric vehicle fire safety?
The testing creates safer batteries through tests examining the Li-ion battery cells' response to a range of variables
Li-ion batteries have a safe window of use. Outside of this window they are liable to self-heat and go into ‘thermal runaway’ mode, increasing the likelihood of fire. Stringent safety measures are put in place to monitor Li-ion batteries, shutting down the battery if unsafe conditions are detected.
The SP Technical Research Institute of Sweden (SP) is currently engaged in research surrounding the dangers and advancement of safety for electrified vehicles. The testing looks at creating safer batteries through tests examining the Li-ion battery cells' response to a range of variables, including temperature, fire, and explosion.
greener fuel sources
The rapid transition from the traditional internal combustion engine to newer, greener fuel sources has sparked changes in fire suppression, with investigations and experimentation into suppression systems for the new fuel sources underway.
The danger that the risk of fire on these vehicles poses cannot be overlooked and despite advances in the safety of electric and hydrogen vehicles, the damage done if a fire does start can be catastrophic.
Installation of fire suppression system
Public transport vehicles must have a fire suppression system installed, as not only does it mitigate damage to the vehicle, but most importantly it gives the passengers and the driver valuable time to evacuate the vehicle. For passengers with reduced mobility, this extra time can make all the difference.
The future looks bright for public transport vehicles, with constant and continual innovation in the field of fire suppression and the safety of clean fuel sources, and this momentum should push the industry forward in the next decade.