Fire Safety for Hydrogen Fuel Cell Vehicles

Issue 49: Fire Safety for Hydrogen Fuel Cell Vehicles

By Carl H. Rivkin, P.E.

Hydrogen fuel cell vehicles have been deployed at the prototype level in the US and other countries such as Japan and Germany. However, planned commercial deployment will occur in the near future, and it is therefore important to have a basic understanding of the safety issues that these vehicles present.

Hydrogen fuel cell vehicles present different hazards than gasoline powered vehicles do. These hazards require taking different safety measures than those employed on gasoline-powered vehicles. As with gasoline powered vehicles, these hazards can be addressed with both engineering and operator controls.

There are several ways of classifying hazards associated with hydrogen fuel cell vehicles. This article will group hazards into three areas: dispensing and operating, onboard hydrogen storage and use, and onboard electrical systems. This article does not address vehicles that employ hydrogen internal combustion engines, although these vehicles present many of the same hazards as hydrogen fuel cell vehicles.

A hydrogen fuel cell vehicle consists of the systems shown in Figure 1. A hydrogen fuel cell vehicle is an electric vehicle because it is powered by an electric motor. The fuel cell stack converts hydrogen into electricity that powers the motor. The term "stack" is used because the conversion device is composed of many fuel cells that operate in series to produce the electric current required to run the motor. A single fuel cell would not produce sufficient power to meet the required performance parameters.

Vehicles typically use Polymer Electrolyte Membrane (PEM) fuel cells, although there are other fuel cell technologies. Hydrogen is fed on the anode side of the fuel cell and oxygen is fed on the cathode side of the fuel cell. The PEM allows the hydrogen molecule that has separated into OH - and H + ions to have the OH - ion flow through the membrane and the H + ion to flow around the membrane in a circuit. PEM fuel cells require less time to power-up and operate at lower temperatures than other fuel cell technologies, which makes them suitable for vehicle applications.

Figure 1. Hydrogen Fuel Cell Vehicle Schematic (Source NREL)


Dispensing Operations

Dispensing gaseous hydrogen into fuel cell vehicles presents hazards that are different than dispensing gasoline; hydrogen is transferred into the vehicle at pressures that may exceed 10,000 psi (70 MPa). The dispensing nozzle must connect to the vehicle so that, unlike gasoline dispensing, it forms a closed, high-pressure system. Failures of the nozzle to lock to the vehicle should terminate the dispensing operation. However, there is still an opportunity to release hydrogen in the event of a nozzle failure or other leak.

The failure of the nozzle to adhere properly to the vehicle also presents the hazard of an unrestrained high-pressure hose proximate to the individual performing the fueling. This hazard is addressed primarily by engineering the nozzle system for very high reliability.

 

Hydrogen storage and use on-board the vehicle

Almost all hydrogen fuel cell vehicles use high-pressure gaseous storage systems to provide the hydrogen for the fuel cell stack. There are cryogenic /compressed hydrogen storage systems that are being developed, but the majority of vehicles that will be deployed relatively soon will use high pressure storage systems. These systems are typically either 5000 psi (35 MPa) or 10000 psi (70 MPa) systems.

Hydrogen storage systems are designed with sensor technologies that will shut down the system if a leak is detected. The leaks are typically detected by sensing a pressure drop in the system. If the system is exposed to fire, the pressure relief device (PRD) will function and relieve the contents of the tank. SAE J25781 states that the PRD should be installed to direct flow away from people, assuming the orientation of the vehicle is not changed from the routine orientation.

There is not standardized labeling system used on hydrogen fuel cell vehicles, although most vehicles have some type of label that indicates that hydrogen is on the vehicle.

The storage systems will also have to meet the Federal Motor Vehicle Safety Standards (FMVSS) for crash safety so that the systems will maintain their integrity after the specified crash conditions.

Electrical safety associated with electric motor and associated components

Hydrogen fuel cell vehicles use an electric motor to power the vehicle. This motor requires high voltage lines to run from the fuel cell, typically located in the center of the vehicle, to the electric motor located in the front of the vehicle. Hydrogen fuel cell vehicles would also typically employ a capacitor or battery to allow storage to start the vehicle and compensate for variation in fuel cell power output. There are a few basic safety rules that emergency responders should follow:

  • Never cut into hydrogen lines (No standard markings, most are silver (stainless steel))
  • Do not cut high-voltage cables (typically orange- 200-500 volts and 200-300 amps).

These lines typically run through the bottom of the vehicle so the general safety rule is to avoid cutting through the floor line of the vehicle.

Codes and Standards

There are fairly comprehensive codes and standards promulgated that address vehicle fueling and onboard vehicle safety. These codes and standards include:

  • International Fire Code2 that addresses hydrogen dispensing stations, storage, and aspects of the built environment.
  • NFPA 2, Hydrogen Technologies Code,3 that addresses almost all infrastructure elements of hydrogen storage, use, and handling including dispensing.
  • The SAE series of documents that include SAE J2578, Recommended Practice for General Fuel Cell Vehicle Safety,1 SAE J2579, Fuel Cell Systems in Fuel Cell and other Hydrogen Technologies,4 SAE J2600, Compressed Hydrogen Surface Vehicle Refueling Connection Devices,5 and SAE J2601.6
  • CSA America: HPRD 17 and HGV 4.2.8
  • ASME Boiler and Pressure Vessel Code (BPV),9 Section VIII Rules for the Construction of Pressure Vessels.

Carl H. Rivkin is with the National Renewable Energy Laboratory

Additional Resources

  1. SAE J2578, Recommended Practice for General Fuel Cell Vehicle Safety, SAE International, Warrendale, PA 2009.
  2. International Fire Code, International Code Council, Washington, DC, 2012.
  3. NFPA 2 Hydrogen Technologies Code, National Fire Protection Association, Quincy, MA, 2012.
  4. Technical Information Report for Fuel Systems in Fuel Cell and Other Hydrogen Vehicles, SAE International, Warrendale, PA 2009.
  5. SAE J2600, Compressed Hydrogen Vehicle Fueling Connection Devices, SAE International, Warrendale, PA 2002.
  6. SAE J2601, Fueling Protocols for Light Duty Gaseous Hydrogen Surface Vehicles, SAE International, Warrendale, PA 2010.
  7. HPRD1, Temporary Interim Requirement For Pressure Relief Devices For Compressed Hydrogen Vehicle Fuel Containers, Canadian Standards Association, Mississauga, Ontario, Canada, 2009.
  8. HGV 4.2, Temporary Interim Requirement For Hoses For Compressed Hydrogen Fuel Stations, Dispensers and Vehicle Fuel Systems, Canadian Standards Association, Mississauga, Ontario, Canada, 2009.
  9. ASME Boiler and Pressure Vessel Code, American Society of Mechanical Engineers, New York, 2010.
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