Recent shifts in the transport industry towards green energy have led to an increase in electric, hybrid electric and hydrogen vehicles on the road. Public transport has seen a rise in the number of clean energy buses on the roads, and questions regarding the safety of the vehicles have been raised.

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.

One such question was that of the effect of the quiet vehicles on other road users and the partially sighted. The answer to this question took the form of UNECE Regulation No. 138 for Quiet Road Transport Vehicle, as electric vehicles are much quieter than their ICE equivalents, and are almost silent at low speeds.

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 there are some challenges that lie in the difference between the fire risk of clean energy and traditional combustion engines.

Traditional fire suppression and how it works

Traditional combustion engines catch fire most often when they overheat or when there is a fuel leak. As we know, 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 a dry chemical extinguishing agent (dry powder) to suppress fires. 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 minimise damage to the vehicle.

Challenges when protecting clean energy vehicles

Clean energy vehicles pose a challenge, as the combustion properties of an electric engine are different to those of a traditional ICE equivalent. Hydrogen fuel cell-powered vehicles and Lithium-ion (Li-ion) battery-powered vehicles both pose a significant threat if ignited, and each acts differently.

Lithium-ion (Li-ion) battery vehicles

Electric and hybrid electric vehicles use Li-ion batteries and, should the battery pack ignite, produce an extremely intense fire that can spread quickly from cell to cell. The fire suppression systems currently installed on electric and hybrid buses are designed to contain the fire long enough 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 without producing smoke, making them almost invisible and 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.

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 and 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.

For hydrogen vehicles, as soon as a fire is detected the vehicle should be shut down in order 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?

Li-ion batteries have a short window where they are safe to 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 how the Li-ion battery cells respond to a range of variables, including temperature, fire, and explosion.


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. It is imperative that public transport vehicles 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. This momentum should push the industry forward over the next decade.

Take a look at our UNECE Regulation 107 Approved Fire Suppression System for buses and coaches, or give us a call at +44 (0)1423 326740 to find out what we can do for you.