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Safer Buses with Fire Extinguishing Systems

by Marcus
Safer Buses with Fire Extinguishing Systems

Safer Buses with Fire Extinguishing Systems

The Department of Fire Technology is currently developing a system for testing and certification of fire extinguishing systems for installation in the engine compartments of buses and coaches. The objective is the development of an international standard, and a range of parties in Europe, Asia and the USA is involved. At the beginning of the year Inger Wiklund of the Swedish Firefighters magazine, wrote an in depth article on the work. With permission, the article is reproduced in its entirety.

A serious fire being tested in the engine compartment test rig at the start of the project.

Every year, over one per cent of Sweden’s buses and coaches experience some form of fire incident. Nevertheless, the requirements for fire safety on buses are low. Scientists at SP Fire Technology are tackling the problems from a number of sides: the most recent project is development of a new standard for testing fire extinguishing systems for use in buses. Manufacturers from all over the world are participating in the project: when the Swedish Firefighters magazine visited SP, two scientists from Kidde Research were working there.

In 2011, when about 50 Swedish youngsters were travelling in a double decker coach on a German autobahn on their way to a Christian camp, a fire started in the engine compartment. Although most of them were asleep, they all escaped from the coach and no-one was physically injured.

– Nevertheless, the coach was completely enveloped in flames by the time the fire service arrived, says Jonas Brandt, a fire protection engineer and scientist at SP in Bors, who points out that Swedish buses and coaches, whether in urban traffic or on long-distance routes, are worked very hard.

– On average, a Swedish bus or coach travels almost three times as far as a commercial vehicle, which means that there is considerable engine wear. And maintenance is not always of the best, he notes.

The number of fires in buses is also increasing dramatically throughout the world. About 140 fire incidents in buses are reported in Sweden each year, which is a doubling since the end of the 1990s, according to statistics from the Swedish Bus and Coach Federation.

– Over one per cent of Sweden’s buses or coaches experience some form of fire incident each year. For any given vehicle, there is a 10 % risk that it will be involved in a fire incident sometime during its life time. In comparison with goods vehicles, the risk of a fire occurring in a bus or coach is almost ten times as high, says Jonas Brandt.

The worst scenario

Luckily, we have been spared any fatal fires in buses or coaches in Sweden since the 1970s.

– In most cases, the passengers have escaped from the vehicle in time. However, as bus and coach fires are so common, there is a substantial potential risk of a serious accident occurring. The nightmare scenario is that of a coach fire occurring in a tunnel during rush hour. The responsibility for preventing fires in buses and coaches therefore cuts across all aspects of society, notes Jonas Brandt.

Several bus or coach fires with fatal outcomes have occurred in other countries in recent years. Consider a fire in Germany in 2008:

– The fire is thought to have started in the lavatory, and resulted in an explosion like flashover. Twenty persons died, many without even having managed to undo their seat belts. The fire was found to have been due to an electrical fault.

Safer Buses with Fire Extinguishing Systems

Henrik Fredriksson lights the pans of heptane.

Inadequate requirements

Despite the risks, the fire safety requirements for the interiors of buses and coaches are much less strict than those applicable to other forms of public transport in Sweden. In comparison with trains and ships, fire safety requirements for buses and coaches are relatively low.

– The rail sector has always had high safety requirements, but we would welcome higher safety requirements for buses and coaches as well, says Jonas Brandt.

But changes are afoot. In 2005, the Swedish National Road Administration, together with the Norwegian Public Roads Administration, stated that this was an area that needed further work. They commissioned SP to investigate the fire safety of buses, with the objective that the results of the work could be used to tighten up European safety requirements for buses and coaches. The project ran for five years, and was very comprehensive, including identification of risk areas and the drafting of proposals to reduce the number of fire incidents.

In one trial carried out during the project, a fire was started in the engine compartment of a bus. The progress of the fire was surprisingly rapid: after only four to five minutes, the entire passenger compartment was full of toxic fire gases.

– The fire was so fierce – about 15 MW – that there was a risk of damage to the test hall, so that the trial had to be stopped when half the bus had burnt.

As the results of this work clearly show that present safety requirements are inadequate, the Group de Rapporteurs Sécurité Générale (GRSG) at the United Nations Economic Commission for Europe has taken the initiative to develop new and stricter fire safety requirements for buses and coaches.

New standard for extinguishing systems

In 2011, SP started work on developing a new standard for testing fire extinguishing systems in buses: a project to which the Swedish Transport Agency has contributed funding.

– Fire extinguishing systems are intended for installation in the engine compartments of the vehicles, which is where most bus fires start, and so installation of a reliable and effective fire extinguishing system is an important safety enhancing measure, says Jonas Brandt.

A reference group has been established for the project, consisting of representatives from the bus manufacturing industry, bus operating companies, manufacturers of fire fighting systems, fire investigators and others. The fire and rescue service is also represented, from such as the Södra älvsborg Fire & Rescue Services and others. Several groups from the major bus manufacturers, Volvo and Scania, have visited SP during the tests.

– There are about 15 manufacturers of fire extinguishing systems for buses in the USA and Europe, which means that there is a substantial need for a standard – with interest being surprisingly high from all quarters.

One problem is the fact that information on bus fires is not gathered in one place. SP is interested in collecting this information:

– What happened in the fire? How did the driver and passengers react? Was there an automatic fire extinguishing system in the engine compartment? I would be grateful for all information like this from the fire and rescue services around the country. Anyone who has such material should get in touch with me by phone on or by email to Jonas.Brandt@sp.se, he says.

Tests must be realistic

One requirement for a European standard is that the tests should be both repeatable and reproducible, so that they can be performed by all test institutes in Europe, and not just at SP.

– The test must be repeatable, so that approval does not depend on whether the test personnel have had a good or a bad day, says Jonas Brandt.

He emphasises that it is important that tests should reflect real conditions, and that the standard that is developed should put the manufacturers on the right path.

– The manufacturers of fire extinguishing systems could modify their systems in order better to meet the requirements of the standard, but if the tests themselves are not realistic they may make changes to their equipment which actually degrade the performance of the system in a real fire. A good standard recognises and specifies reality, so that when changes are made in order to meet the requirements of the standard they result in improved systems.

A test rig simulates an engine compartment

In order to be able to compare and test fire extinguishing systems, the scientists have built a 4 m3 test rig that represents the engine compartment of a bus. The bus manufacturers have contributed with drawings to authenticate its design.

– In order to make the tests repeatable; so that all fire extinguishing systems are tested under the same conditions, we perform the tests in a test rig instead of in a real engine compartment. As there are so many different types of bus engine compartment, we have looked at many variants and constructed a rig having the properties that encourage a fire and make extinguishing more difficult, as typically encountered in a bus engine compartment, explains Jonas Brandt.

As most engine compartments include large fans, the test rig includes a fan to create conditions more difficult for the extinguishing system by supplying oxygen to the fire and ventilating away the extinguishant. In an actual engine compartment the engine components, such as pipes and containers, make it more difficult for the extinguishant to reach the fire. A number of obstructions, such as pipes and baffles, have therefore been installed in the test rig to represent these obstructions. Another difficulty is presented by oil escaping onto hot surfaces, and re igniting the fire after it appears to have been extinguished. In this way, the ability of the system to prevent fire re ignition is tested.

-Insulation material that has absorbed oil is also difficult to extinguish. In addition, the systems must be capable of withstanding effects such as corrosion and temperature changes.

Safer Buses with Fire Extinguishing Systems

Eight kilos of powder are sufficient to extinguish most of the fires in the SP tests.

No miracle solution

Jonas Brandt and the other scientists at SP have found that if a bus or coach is being driven at full speed it is difficult for some extinguishing systems to work, while others are more robust.

– It’s important that manufacturers and operators understand that fire extinguishing systems are not some form of miracle problem solver. They can extinguish fires only under certain conditions, such as being correctly installed, he says, and explains that, when systems are being installed, they must identify the risk areas in the engine compartment and position the system nozzles to protect the common risk areas.

If a fire should occur in an unexpected position in the engine compartment it is not certain that a fire extinguishing system would be able to deal with it. And if the vehicle operator subsequently fits additional items, such as heat shields, that block the extinguishing system nozzles, the result can be a serious degradation of the performance of the system.

– Nevertheless, it’s important to emphasise that a fire extinguishing system can gain time to ensure that all the passengers can evacuate the vehicle. It can save lives, and reduce the severity of the fires so that the fire services can get to the site and fully extinguish the fire, emphasises Jonas Brandt.

However, much work remains to be done, and it could be several years before a standard has been accepted and won legal status in UNECE.

Stop the engine

If a bus catches fire, the driver should turn off the engine and isolate the battery in order to reduce the risk of a fire spreading. He/she should not open the engine compartment cover, as that would risk the fire flaring up. There is also a risk that the gas prop that supports the engine compartment cover could come loose and shoot away like a rocket due to the compressed gas inside it.

– Some buses have a small hole in the engine compartment cover to enable the fire to be fought using a manual extinguisher, explains Jonas Brandt, and points out that the driver must not drive on once the fire has been put out, as it could re ignite.

Safer Buses with Fire Extinguishing Systems

This picture shows how effective the powder is in extinguishing the fire.

Good for all parties

At the beginning of February, when the Swedish Firefighters magazine visited SP, nine manufacturers from all over the world had tested their extinguishing systems at SP, ranging from foam and powder systems to gas and sprinkler systems.

– The best feature of this project is that several manufacturers come back to us once they have improved their systems in order to retest them, says Jonas Brandt.

At the time of our visit, two scientists from Kidde Research in Slough are at SP: Robert G. Dunster and Paul Weller. Together with the SP team, they aim to perform 20 tests.

– Kidde has several effective extinguishing systems. Powder extinguishers are good in many ways; they are water soluble and have little environmental impact. However, there is a risk of re ignition, which can occur up to five minutes later. This is because although the powder suppresses the fire, it does not cool hot surfaces, explains Robert Dunster, who points out that the tests performed at SP benefit the entire sector, and not just Kidde.

– It’s difficult for us manufacturers to know with whom we should talk among the operators and public authorities in order to spread information on how the various systems work. It’s therefore all to the good that representatives from all those concerned should come to SP during this project, he continues.

Robert Dunster points out that if the wrong system is sold, the entire sector suffers for it, and so it’s in everybody’s interest that the systems should work.

– When they come here, customers can see how the systems are tested and therefore get a better understanding not only of what a fire extinguishing system on a bus must do, but also of the importance of training personnel to use such systems.

Robert Dunster is writing a report, based on the approximately 400 tests that have been carried out on Kidde’s own outdoor test rig and on the results from the SP tests. The results were presented at the StandarDays conference, arranged by CENELEC on 17th and 18th April.

850 C

This afternoon has been reserved for fire tests, the first of which is of a powder system. The preparations before each individual test are meticulous and time-consuming. The container holds 8 kg of powder, and the Kidde scientists decide to mount the nozzle on the roof of the test rig.

They set up their cameras and instruments while Jonas Brandt and his helpers pour diesel oil and heptane into ten fireproof pans and position them in the engine compartment. SP’s Henrik Fredriksson then puts on protective clothing and breathing apparatus, before lighting the pans with an LPG burner, whereupon all those without protective clothing are moved to the control room to watch a cascade of powder being released. The fire gases have a temperature of about 850 C, but this is reduced to about 100 C within 30 seconds.

Think again

This is followed by two tests with a gas system; one with the nozzles facing the top of the compartment and one with them discharging from the back, in order to investigate how important the position of the nozzles is for effectiveness. Both positions put the fire out quickly, and the Kidde scientists are very pleased with the results.

The final test of the day uses a new powder, with the nozzle transferred from the top of the compartment to the rear wall. However, this time the system does not manage to extinguish the fire: instead, Henrik Fredriksson has to use a manual fire extinguisher. However, this is what the scientists had expected.

– This was the most difficult scenario, with the nozzle in the worst possible place for attempting to extinguish the fire. The results are as logical as they are interesting, and we need to do more work on this arrangement, perhaps adding another kilo of powder. And we’ll aim the nozzle differently next time, says Robert Dunster.

– Your tests are great, Jonas, they don’t miss anything, adds Paul Weller.

– Yes, we would never have got these results by computer modelling. We’ll have to think about what we’ve learnt – it’s our responsibility to get it right, emphasises Robert Dunster.

Safer Buses with Fire Extinguishing Systems

From the left: Robert Dunster and Paul Weller from Kidde Research, and Jonas Brandt, fire protection engineer and scientist at SP Technical Research Institute of Sweden.

A new method of testing fire extinguishing systems for use in buses and coaches has been developed by SP Fire Technology: SP Method 4912. In October, SP will launch a voluntary quality marking scheme, P marking, for fire extinguishing system manufacturers. The P symbol shows that the system has met the requirements of SP Method 4912, and that its components meet various standardised tests, such as relating to mechanical properties and corrosion resistance. Quality marked systems are subject to an annual manufacturing inspection by SP in order to ensure that the approved quality is being maintained. SP Method 4912 and the P marking system are in great demand on the market, and have been developed as a result of close cooperation between manufacturers, users and public authorities.


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