Release from a hydrogen bus

A hydrogen and fuel cells bus experienced a hydrogen detection alarm in a city centre. This triggered the evacuation of the immediate surroundings and the towing of the vehicle to the maintenance garage.

The actions and corrective measures taken by the the bus manufacturer after the alarm are indicative of the long pathway still necessary before arriving to full deployment maturity of hydrogn-based mobility solutions.
A. Collected the vehicle (VH VIN 66242) from the city Depot
B. Review and analysis of the gydrogen exhaust set-up and the fuel cell cooling
systm
C. Re-built the bus to original set-up triggering fault/alarm
D. Installed measurement equipment (8 H2 concentration sensors) to measure hydrogen concentration in exhaust and under roof panels.
E. Installated 2 extra sensors to determine if the normal sensors (8) do not react to other gasses but only to hydrogen
F. Installed of additional dataloggers, for extra datalogging and evaluation of principalsystem.
G. Mapped the hydrogen flow via visualization of gas
H. Modifiedy the vehicle to resolve issues with high hydrogen concentration if necessary.
I. Brought vehicle back to the city and performed a thorough test on route to determine that sensors do not pick up any other gas concentrations that can trigger warning or alarm.
K. Modified the 2nd bus accordingly

It is important to use hydrogen sensors and detectors characterised by low cross-sensitivity to other gases. In this way, the risk of false alarm triggered by the presence of other gases is minimised. The accuracy, the alarm level and the location of the sensors are also relevant.

The bus manufacturer will:
1. Perform an analysis of hydrogen exhaust set up
2. Install measurement equipment (8 sensors) to measure the hydrogen concentration in exhaust and under roof panels.
3. Installation of 2 extra sensors to determine if normal sensors (8) do not react to other gasses (only Hydrogen)
4. Map the Hydrogen flow (stream) via visualization of gas