CNG powered bus does not fit under viaduct |
Friday, December 21st 2018
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CNG powered bus does not fit under viaduct

News from Moditech Rescue Solutions BV

As promised, in this edition of the newsletter we will look at the experience of the Franeker Fire Brigade concerning a MAN City Lions CNG bus that did not fit under a viaduct and caused a lot of problems. What were the on-site experiences of this fire brigade and how did they proceed?

Furthermore, we would like to wish you a wonderful 2019. We thank you for the trust you have placed in us and are happy to be of service again in the new year!



In the background a MAN articulated bus with a CNG drive, which does not fit under the viaduct. In the foreground a number of CNG tanks and sheet material from the roof of the bus.

The video gives a good impression of what the emergency services found on site. Luckily nobody was injured. Below is a brief explanation from the Commander and Service Officer, their considerations and plan of action.

"When I arrived, I got four people breathing gas. On site, two men were instructed to explore the area with an explosion hazard gauge and two men were sent ahead to explore the bus. There were no injured people or people in the bus. The situation was reasonably stable. We looked up the number of CNG tanks that could be present in the Crash Recovery System. In total, 8 CNG tanks were indicated in the CRS."

"We examined the surroundings and closed the main road over the viaduct. Most of the knocked-off CNG tanks were empty by the time the fire brigade arrived. The safety valves on the tanks had been knocked off. One CNG tank was leaking through the pipe that had been torn off. The outflow was so small that it did not present any danger, so no action was taken to accelerate venting. This tank was later removed whilst leaking. After the incident officer arrived, the accident was cleared and I re-opened the road as well as the road over the viaduct. The video shows that the incident could have been much worse. Not a single gas tank ignited. Nevertheless, people could have been seriously injured by the flying gas tanks. These were spread out over a large distance, with one gas tank even reaching the other side of the water. The damage to a pole is also clearly visible, as well as the traces of a gas tank that flew away over a large distance. There’s no need for me to explain what you would have found had that pole been a person."

To be able to act safely in such a situation, you not only need personal protective equipment and an explosion hazard gauge, but also information about the vehicle involved. The commander was able to call up this vital information in the Crash Recovery System. As the commander pointed out, it was important to first establish what type of gas is involved, where the gas tanks are and how many are installed. By simply counting the number in the CRS image, it quickly becomes clear during the exploration of the area whether all the gas tanks have been located and accounted for.

After requesting the number plate, this vital information quickly became clear. Also clearly visible is the position and the number of gas tanks.

Image: CRS image MAN Lions City CNG

By clicking on the gas tanks and/or valves, the emergency responder can call up important information about these components. Zoom in to make clicking on these components easier. To zoom in on the image, place two fingers on the screen and spread them apart.

Image: CRS image zoomed in on the gas tanks and safety valves

Clearly visible, safety valves fitted to both sides of the tank. The valves at the bottom of the image are linked via the pipe network. These valves supply the drive with gas and are open when the drive is switched on. The valves at the top of the image are called pressure control devices. These are activated when overheating occurs (fire).

By clicking on the gas tanks, the emergency responder receives information about the:

  • Contents
  • Pressure
  • Position

The information sheet provides information about the type of gas and the pressure under which the gas is stored. In this case it is 200 bar.

ATTENTION! For more important safety information, there is a reference to the safety valve.

Image: CRS information sheet gas tank compressed natural gas CNG

Behind the safety valve the following information can be found:

  • The position
  • The various safety functions
  • The information is supported by images.

CRS information sheet; safety valve

The information sheet shows the different functions of the safety valve. This information sheet relates to the safety valves connected to the pipe network. By clicking on the buttons Image 1 and Image 2 the information is reinforced with clear images.


Images: CRS image of safety valve and safety valve of the vehicle concerned

The electromagnetic valve in red and the manual valve in yellow are clearly visible. The video also shows when this valve blows off under low pressure. When the valve and/or pipes are damaged, the gas is vented via the flow limiter, which significantly reduces the pressure. This process cannot be stopped once underway. This is unnecessary in the open air. As the Service Officer already indicated, the concentration was so low that this leakage did not pose any acute danger.

The safety valves on the other side of the tank are pressure control devices. These are activated at temperatures above 110 degrees Celsius. Due to the nature of this incident, a number of these pressure control devices had broken off, as a result of which the gas was vented under very high pressure. This explains the distribution of the gas tanks.

Images: On the left, pressure control device intact, on the right a gas tank where the pressure control device is broken off

- Jelle Rodenhuis - Commander of Franeker Fire Brigade (NL)
- Lambert Kesimaat - Officer of Friesland Fire Brigade (NL)
- Sander Bosma - Assen Fire Brigade (NL) (image material)

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