Report on fires in gas-powered buses in Horgvegen, Ranheim, Trondheim on 17 December 2016, and at Flatåstoppen Trondheim on 23 november 2016

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Description

English translation now available.

On the morning of December 17, 2016, it began to burn in a gas-powered local bus that ran on a route with three passengers aboard the Horgenvegen road in Trondheim. SHT initiated an investigation. It became known that a similar fire had occurred with another bus of the same type at Flatåstoppen in Trondheim on November 23, 2016. No people were injured. SHT has examined both fires and has found similarities.

The Accident Investigation Board Norway`s investigation has shown that LED light technology can present a firerisk that can be challenging to handle and have major consequences. As a result of the survey, the AIBN believes that the regulations for the design of electrical installations in vehicles do not adequately protect fire safety.

The bus driver was informed about the fire by a passing vehicle, at a time when the bus had stopped at a bus stop. The bus driver evacuated the passengers, secured the bus and attempted to extinguish the fire, but this had no effect. The fire departement was called upon and eventually quenched the fire before it spread to the rest of the bus.

The gas-powered bus was the second bus of the same type that caught fire in a short period of time in the Trondheim area. The AIBN mainly investigated the fire on December 17, but found similarities with the fire on November 23, 2016.

Both fires have probably started in the LED lights that illuminated the rear license plate on the buses.

AIBN investigated and tested several new and used license plate lights, as well as conducted short-circuit tests of licence plate lights of the same type.

AIBN's investigation of the used LED-lights revealed cracks that were not compatible with normal influence of forces from attachment or normal use. The sign lights have most likely had cracks that created intrusion of moisture in the lights. Moisture with subsequent irradiation in circuit board components in LED light is therefore a likely source of ignition in both fires.

The investigation revealed weaknesses in the production of LED-lights, the electrical system and fuses in the busses, and the regulations for the design of electrical installations in busses.

Safety recommendation

Safety recommendation ROAD No 2017/10T

Two bus fires in Trondheim in 2016 started in the LED lights that illuminated the rear license plate on the buses. The lights have in all likelihood had cracks that stem from an error in production, which allowed moisture intrusion into the lights. The wiring of the lights was secured with a 15 A fuse, too high to prevent a flammable short circuit and far above what the light manufacturer recommends.

The Accident Investigation Board Norway recommends that Solaris Norway review and improve the dimensioning of the electrical system on existing and corresponding buses, so that fuse rates will be an effective barrier against fire in case of component failures.

Safety recommendation ROAD No 2017/11T

The investigation of two bus fires in Trondheim in 2016 showed that the bus's original incandescent bulbs in the license plate lights, were replaced with new LED lights, which have other features and different construction. The wiring of the license plate lights was secured with a 15 A fuse, far above the current required by an LED light and what the light manufacturer recommends. The Vehicle Regulations, and ECE 107, describe that the electrical system, is to be dimensioned according to the capacity of fuses and wiring, but also that several wires can be secured by a single fuse or switch. However, the rule does not specify the rest capacity for a single-fuse circuit, or multi consumer circuit.

The Accident Investigation Board Norway recommends that the Norwegian Public Roads Administration follow up the requirements of the current regulations on the design of fuses and circuits, so that this will be an effective barrier to fire in the event of errors in all types of (LED) electrical components.

Location
Horgvegen, Ranheim, Trondheim and Flatåstoppen, Trondheim
Occurrence date
17.12.2016
Accident type
Fire in vehicle
Road class
Local road
County
Sør-Trøndelag
Police Disctrict
Sør-Trøndelag
Vehicle type
Bus or coach
Type of Transportation
Passenger transport
Road region
Central Region
Accident category
Ulykke med buss
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