Like electric vehicles, FCVs have ground fault indication systems, making it extremely difficult for a person to complete a circuit and be shocked. When the ground fault system (called a safety interlock system by some vehicle manufacturers) detects that the vehicle’s ground and battery are no longer insulated, a relay in the battery pack box opens to isolate high voltage in the vehicle electrical storage (either high voltage batteries or ultracapacitors), essentially shutting down the system.
For hydrogen handling, safe FCV design maintains two objectives:
1. Locking the high pressure hydrogen in the safest place, inside onboard vehicle storage tanks, during all non-fire vehicle safety incidents (or when the vehicle is off) – by employing in-tank solenoids that default to a closed position
2. Evacuating all the high pressure hydrogen quickly under conditions where it is unsafe to store, such as during fires - by employing a tank-integrated temperature activated pressure relief device (PRD/TRD)
Modern PRD/TRDs, integrated into all hydrogen tanks mounted on light-duty FCVs and FC buses, are the result of decades of learning from the CNG vehicle tank industry and consensus-based standards development organizations such as the Compressed Gas Association (CGA) and CSA America. The PRD/TRD consists primarily of a fusible metal plug made of material engineered to melt at a certain temperature (108 °C for H35 tanks). Design characteristics, such as the use of a low melting temperature metal, produce PRD/TRDs that open under high temperature conditions, such as a fire engulfing the tank, during which the fusible plug melts causing the PRD/TRD to open and rapidly release the contents of the tank.
The on-board hydrogen storage tanks are extremely strong, carbon-fiber wrapped tanks. Similar to CNG tanks, hydrogen tanks are put through a battery of extreme tests, including bonfire, pressure cycling, impact, burst and gunfire tests. The tanks must meet strict manufacturer guidelines and applicable DOT criteria for acceptable use on public roads. In addition, each tank is equipped with a thermally activated pressure relief device (PRD/TRD) that provides a controlled release of the tank contents if tank temperature, and therefore pressure, exceed allowable thresholds.
Unlike natural gas, which usually contains mercaptan, hydrogen cannot be colorized or odorized. Because hydrogen is such a small molecule and is so buoyant, no other substance can move and diffuse with hydrogen to effectively indicate a leak. In other words, by the time you smelled the odorant, the hydrogen might have already moved to another location and/or collected in concentrations above the lower flammability limit.
Yes. CaFCP vehicle manufacturer members subject fuel cell vehicle models to extensive safety testing prior to releasing them on public roads. Current testing employs both destructive and non-destructive evaluations and occurs at the component, system, and vehicle level.
