An engine fire in a bus can be devastating. Due to flammable material and the typically large quantities of diesel, hydraulic oil, often operating under high pressures in the immediate area, an ignited engine fire could lead to a rapid and disastrous series of events with financial and operational consequences. However, the most important resource of any company is the human workforce, who along with the passengers are put at great danger in the event of a bus fire.
Fogmaker International AB develops, manufactures and markets fire-suppression systems for engine compartments using high-pressure watermist technology. Fogmaker International AB has more than 160,000 installations in buses and heavy vehicles in more than 50 countries worldwide. Buses are our main application and we have been implementing fire-suppression systems in bus engine compartments since 1995.
Fogmaker’s manufacturing and R&D facility is located in Växjö, Sweden where we manufacture all our products, 93% of which are exported. We are approved according to ISO9001:2015 and ISO14001:2015 and since June 2018 we have been certified according to IATF 16949, which is a requirement for long-term suppliers of fire-suppression systems to the automotive market.
Fogmaker high-pressure watermist fire suppression is a professional and reliable system approved to many international standards including R107, SPCR183/SP 4912, SBF-128, AS 4587 and FM. High-pressure watermist has excellent cooling performance and oxygen displacement. For example, the cooling effect of watermist is outstanding with a temperature decrease of around 700°C within 10 seconds. At the same time, a decrease in the oxygen level occurs due to the expansion of the watermist into steam. A small amount of foam additive prevents hydrocarbon vapours from re-igniting. Fogmaker systems can be installed in any engine compartment or enclosed area where they can quickly detect and suppress fire.
The fire-suppression system is very simple and robust and there is no need for electronics, electrically powered sensors or batteries. In the event of a fire, a thermoplastic tube melts and activates the distribution system, which spreads a mist of micro water droplets within the protected area. Therefore, the system remains ready to activate even if the vehicle power supply is switched off or has failed for some reason. The system also brings low life-cycle costs for the operator or machine owner because of its simplicity and cost-efficient servicing, e.g. if the system is activated, it can be restored easily by a recharge of the extinguisher and there is no need to dismount or replace the extinguisher with a new one. Because of its simplicity the system is also service friendly for bus operators and it is easy to clean the engine compartment after activation, which helps to limit the downtime of the vehicle. Fogmaker has a global network for service via its Partners who are certified according to the Fogmaker Training Academy programme.
We all know that bus operations are extremely sensitive to unscheduled downtime. A fire in the engine compartment of a bus can be devastating for the driver and passengers but also results in unwanted downtime or, worse, complete destruction of the bus. High-pressure watermist is a superior suppression technique for engine compartments and limits the consequences of a bus fire. This is an important aspect when protecting the bus where the effectiveness of the system means that damage to the vehicle will be small and result in low repair costs. The investment in an efficient high-pressure watermist system will only be a very small part of the total investment needed when procuring new buses. Throughout the world, different organisations have found the need for installation of automated fire-suppression systems in the engine compartment to be an important fire-safety measure. Furthermore, some insurance companies and individual bus operators already require fire-suppression systems and the trend is set to continue in light of new legislation such as UN ECE R107. Today there are about 50 countries which have signed this legislation, both within and outside Europe, with others sure to follow. In practice UN ECE R107 requires that from 2021 every new bus exceeding 22 passengers must be fitted with an OEM homologated fire-suppression system. R107 will be introduced step by step during 2018–19 for coaches and will finally also include city buses during 2020–21.
Most bus fires start in the engine compartment. A fire in an engine compartment is hard to detect and it is almost impossible to suppress it with a portable extinguisher. The safety requirement for automatic fire-suppression systems in vehicles has existed in many places around the world for several years, and in more and more countries, insurance companies and operators are adding it to the specification list. But an important question to keep in mind is what are the physical aspects of a fire? Heat, oxygen and fuel all must be foreseen and attacked. These three elements of a fire are often symbolised by the fire triangle. Only taking out one corner of the triangle can be enough to kill a fire. However, the complex nature of a vehicle-engine fire means there can be no guarantees. Re-ignition, or re-flash, of fires occur. Therefore, a triple-action fire-suppression system, attacking all three elements simultaneously, is the safest and most logical method for minimising equipment downtime, maintaining business continuity and protecting human life. At the same time, the fire-suppression system must constantly be ready to act, independent of human interaction, vehicle position and vehicle activity. Considering all these aspects, it is proven, after more than 130,000 bus installations of Fogmaker, that high-pressure watermist is a superior suppression technique in bus engine compartments.
Electrification of buses, which is a clear trend and seems to be the obvious future solution for the drivetrain of many bus types, is a challenge for automatic fire-suppression systems, due to the use of Li-ion batteries which cannot be ignored in terms of fire risk. A fire in a bus containing Li-ion batteries where the fire starts in, or spreads to, the battery pack could result in an extremely intense battery fire. This kind of battery fire will be almost impossible to extinguish using the kind of automatic fire-suppression systems that are normally installed in buses today. One strategy is to delay the fire to allow time to evacuate passengers from the electric bus. The extremely good cooling effects of water make this possible by reducing the temperature of the battery pack and increasing the timeframe for evacuation.
Since fire-suppression systems were introduced to buses the installations have normally been retrofitted to existing vehicles, but now it is increasingly common for installations to be carried out on the production line and this practice is sure to continue as R107 is implemented. This gives better quality control of the installation since each bus type will receive a customised installation depending on vehicle and engine compartment design where the distribution system of the watermist in the engine compartment is optimised by the use of pre-bended pipes and nozzles. The design of the distribution system must be carried out based on a careful risk assessment to define the most important fire hazards and therefore the most efficient design and layout of the system. The same procedure could also be used when retrofitting a large number of older buses in cooperation with bus operators and transport authorities.
Even with a fire-suppression system installed in a bus the general maintenance procedure of the engine compartment is extremely important to fulfil. Poor maintenance and cleaning of the engine, engine compartment, hydraulics and so on will make the vehicle more prone to catch fire and also make it more difficult for the fire-suppression system to work properly. Another factor that will influence the performance of the fire-suppression system is if changes in the engine compartment are made because of technical updates, or if additional components are mounted in the engine compartment. These kinds of changes can affect the distribution system, piping and nozzles in such a way that installed nozzles could be unintentionally blocked from reaching the fire hazard spots. Even worse, the nozzles could be completely covered by, for example, a newly installed hose or other component such as an additional alternator that was not fitted at the time of the risk assessment and design of the fire-suppression system. These potential issues can be identified during normal servicing of the engine and engine compartment. Unfortunately, these problems are not so uncommon and so it cannot be emphasised enough how important it is to be aware of any issues that may affect the performance of a fire-suppression system mounted in the engine compartment.
While a fire-suppression system is a very good investment, it doesn’t mean the root cause of the fire has been removed, and it is absolutely not any excuse to not carry out necessary maintenance of the vehicle. Also, a correct risk assessment and professional installation is essential for achieving the best possible function and performance of the system in combination with other fire-safety actions.
We should all be aware of that even if a lot of effort is put into designing the best possible fire-suppression system for the bus, including a very careful risk assessment. Of course, not all the countless fire scenarios that can occur in the vehicle can be extinguished, but the more careful the design, risk assessment and installation of the fire-suppression system, and in combination with general vehicle maintenance, the closer to 100% we will get.
The photo shows a Fogmaker International demonstration with a 2m3 box to represent the engine compartment of a bus. The demo was set up so that two nozzles were spraying diesel fuel into the compartment, which also had four nozzles in the top of the box that discharged the fire-suppression agent. The fuel was ignited and a fire grows inside the compartment. The temperature continues to increase and, when it reaches 170°C, the fuel line bursts. A massive fireball erupts, and the temperature quickly moves toward and passes 800°C. The agent is released, and the fire is extinguished almost immediately. The amount of fluid, which is 97% salt water and 3% foam additive, used in this demo is 400–500ml. On a typical bus, it would require 6.1 litres of extinguishing agent according to UN ECE R 107 with an engine-compartment reference volume of 4m3. The Fogmaker system attacks the three components of the chain reaction that causes a fire: heat, oxygen and fuel. The cooling is by far the most important factor when breaking the chain reaction, and water is the best agent for that purpose. During the evaporation process, the watermist cools the burnt gases and hot parts in the engine compartment. One 7.5-litre Fogmaker extinguisher generates up to 12m3 of steam, causing oxygen displacement, and supports the knockdown effect on the fire. A small amount of surfactant creates a coating, which isolates hot surfaces or fuel from oxygen. This prevents the fire.
For more information, go to www.fogmaker.com
About the Author
Lars Utterström is Sales and Marketing Manager at Fogmaker International headquarters in Sweden.
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