The importance of automatic fire suppression systems

This is the first of two articles to provide a background look at bus fires and to underline the importance of automatic fire suppression systems for buses and coaches. About 1% of all buses suffer some form of fire incident each year. Most of these fires occur in the vehicle’s engine compartment located at the rear of the bus or coach, making it difficult for the driver to discover the fire. Experience from Sweden – where the installation of detection and fire suppression systems is actively encouraged by the insurance industry – shows that the installation of an automatic fire suppression system is an important fire safety measure. The second part of this article will be published in Intelligent Transport Issue 6 2012.

High number of bus fires

Bus fires are an increasing worldwide problem. Even though accidents that cause injuries are fortunately quite uncommon, the potential risk of a disastrous event is still high, with several examples in recent years highlighting this. In the evening of 8 September 2009, the Atac bus depot in Rome, Italy, was enveloped in flames with 24 gas-fuelled buses destroyed. Only five months earlier, another Atac depot had burnt down, destroying 30 mini-buses. On 4 November 2008, on the motorway near Garbsen in Germany, a coach carrying a group of pensioners and children caught fire. The fire spread extremely rapidly, killing 20 of the passengers, many of them still held in their seats by their seat belts. On 25 December 2011, at a depot fire in Bottrop, Germany, almost 70 buses were destroyed to a value of approximately €17 million. The list of bus and coach fires that have resulted in major economic losses and, in the worst cases, in injuries or deaths, is long, with just a few examples stated above. The list of smaller bus fires is even longer. Reports from European countries show that the number of bus fires has almost doubled over the last 10 years.

A bus or coach can accommodate a large number of people – a double-decker bus may hold up to 90 passengers – a large portion of which are often children or the elderly. It is not uncommon for passengers with disabilities to travel by bus and walkers, prams and baggage can sometimes limit passage on emergency routes. In the case of a fire, the time available for evacuation is a critical factor, as fires sometimes progress very rapidly. A bus or coach fire in a road tunnel would aggravate the situation considerably. Poisonous gases may spread in the tunnel and chaotic traffic conditions may hinder road users when exiting the tunnel, potentially leading to catastrophic circumstances.

The general reaction to bus and coach fires tends to vary, and is partly dependent on how the question is seen politically. When, for example, three buses from different manu – facturers were totally destroyed by fires within one week in the summer of 2009 in Poland, it resulted in major political discussions which led to most of the large bus companies starting to install fire extinguishing-systems in their vehicles: a decision which puts Poland in the lead in the struggle against the rising number of bus and coach fires. Surprisingly enough, not much is heard or seen internationally about bus fires in the mass media, for understandable reasons: the operators do not want to scare the passengers.

Reasons for bus fires

The number of bus fires has increased since the late 1990s and this is primarily fires originating in the engine compartment of the vehicle. There are several reasons for this increase, including:

1. More stringent demands for low noise levels have resulted in more widespread use of engine compartment insulation and encapsulation. Sound proofing may keep the noise in, but will also maintain high engine compartment temperatures.
2. Lowered permissible emission levels have resulted in higher service temperatures in some engine components in order to increase the combustion efficiency of the engine. A turbo charger of a modern vehicle can reach a surface temperature in excess of 600°C. This temperature is much higher than the auto-ignition temperature of combustible liquids in engine com partments and causes a great possibility for any leakage of combustible liquid to ignite.
3. Higher engine compartment temperatures will reduce the life length of polymeric materials such as plastics, increasing the risk for cracking and leakage.
4. More widespread use of plastics in modern engine compartments compared to engines on old buses increases the amount of combustible materials which creates a risk of faster fire development.

Other reasons for the high number of bus fires are the heavy usage and limited maintenance time for buses in traffic. The average annual mileage of a bus is almost three times that of a truck, resulting in high levels of engine wear.

Fire safety regulations with good results

In 2004, Swedish insurance companies required all new buses with fire insurance to be equipped with an approved automatic fire suppression system. Combined with annual fire safety inspections of all insured buses, this has considerably reduced the insurance companies’ cost for bus fire claims. The actions have reduced the number of reported bus fires, but even more significantly, reduced the cost for every bus fire that occurs. From an average cost of $60,000 to $70,000 in 2002/2003, the average cost per bus fire in 2010 and 2011 have only been slightly more than $20,000. Even if a fire suppression system will not prevent a fire from occurring, it can dramatically reduce the impact of a fire by an early extinction or by suppressing and delaying the fire development to such an extent that the fire brigade – or sometimes even the bus driver – can put out any remaining fire in the engine compartment.

Figure 1: The average cost per bus fire claim. From 2004, fire supression systems were installed in all new vehicles

Figure 1 shows the average costs for bus fire claims in Sweden. Even though there is a normal variation of the costs through the years, the trend line shows a significant reduction of the average bus fire cost.

Different fire suppression systems

There are approximately 20 manufacturers of fire suppression systems for vehicles in Europe and the USA. They produce different kinds of fire suppression systems with various types of extinguishing agents. The most common agents are dry chemical (for example ABC- and BC-powder), water mist, foam, aerosol and clean agent (gaseous systems). The agents are distributed to the fire hazards in different ways, for example using nozzles, pressurised bursting tubes or suppression agent generators. The systems are also designed in different ways, with some systems designed to protect the entire engine compartment, while other systems focus on protecting fire hazard areas. Furthermore, the systems are equipped with different fire detection systems, including different types of thermal detectors as well as flame detectors. There is on-going research in the area of gas detection systems suitable for engine compartments. As a leakage of oil on a hot surface will create a steam of hydrocarbon vapour, this vapour could be detected before a fire has started with the detection system sending a signal to the driver that there are critical conditions in the engine compartment. It is a challenge to design a detection system which gives a quick detection but also avoids false alarms.

All fire suppression systems behave differently in terms of their fire fighting performance, and they all have their pros and cons with regard to their mode of extinguishment. Certain systems also have challenges concerning re-ignition protection. Most systems work well in confined spaces where the concentration of the extinguishing agent remains high for a long period of time, but have difficulty maintaining performance under the high airflow conditions often present in bus engine compartments. The variety of suppression technologies combined with the complicated task of extinguishing engine fires makes it important to demonstrate successful suppression tests in order to ensure that the firefighting performance is sufficient.

International standard for fire suppression systems – a new approach

There is currently no international standard for evaluating fire extinguishing systems in bus engine compartments, and as a consequence, the suppression manufacturers must verify and authenticate their systems using systems defined by relevant local or national transit authorities and insurance companies. This can be extremely difficult and does not typically allow for the comparison of different suppression systems.

On behalf of the National Road Authority in Sweden, SP Technical Research Institute of Sweden has prepared an international test method that can be used when specifying requirements for the efficacy and function of a bus fire suppression system. The objectives of this project are:

• Creation of a safer environment for passengers and bus drivers worldwide, in particular with respect to safe escape for vulnerable passengers, i.e. those with disabilities, the elderly and children
• Reducing the loss of property
• Designing a standard that will evaluate the firefighting performance of different suppression systems in a well-defined, objective and comparable way.

About the author

Jonas Brandt is a Project Manager at SP Technical Research Institute of Sweden. Having studied fire protection engin – eering and with a background as a bus driver, Jonas has a special interest in the field of bus fire safety.

Further reading: In Intelligent Transport Issue 6 2012 (December2012) Jonas Brandt will focus on the new test method (SP method 4912) and the challenges in designing a new international standard. To guarantee you receive this edition of Intelligent Transport, become a subscriber today by contacting Karen Hutchinson directly via email at [email protected] or by visiting our website at www.eurotransportmagazine.com