Safety System Design for Mitigating Risks of Intended Hydrogen Releases from Thermally Activated Pressure Relief Device of Onboard Storage

All vehicular high-pressure hydrogen tanks are equipped with thermally-activated pressure relief devices (TPRDs), required by Global Technical Regulation. This safety device significantly reduces the risk of tank catastrophic rupture by venting the hydrogen pressure outside. However, the released flammable hydrogen raises additional safety problems. Japan Automobile Research Institute has demonstrated that in the vehicle fire event, once the TPRD opens, the hydrogen fires will engulf the whole vehicle, making it difficult for the drivers and passenger to evacuate from the vehicle. This paper designs a new safety system to solve the evacuation problem. The safety system includes a rotatable pressure relief device with a motor, a sensory system that consists of infrared sensors, ultrasonic radar and temperature sensors, a central control unit and an alarm device. The new design of the pressure relief device allows the system actively adjusting the release direction towards void open space outside the vehicle to minimize the risks of hydrogen fires. The infrared sensors located at the roof of the vehicles collect info inside the vehicle and the ultrasonic radar detect the region outside the vehicle. Temperature sensors tell when to trigger the alarm and set the motor in standby mode, and the central control unit determines where to rotate based on the info from the infrared sensors and ultrasonic radars. A control strategy is also proposed to operate the safety system in an appropriate way. The cost-benefit analysis show that the new safety system can significantly reduce the risks of intended hydrogen releases from onboard pressure relief devices with total cost increases by less than 1% of the vehicle cost, making it a good cost-effective engineering solution.