3.3.2 Operation and Maintenance
When working on high-voltage systems, always ensure that the main switch is in the “off” position and tag it and/or lock it in that position so that no one else can turn the vehicle on.
Always assume that high-voltage electrical components are live, even when the vehicle main switch is in the off position. Use a volt meter to check before touching any electrical component.
Always use appropriate personal protective equipment, such as high-voltage gloves, when working on high-voltage systems. Follow the safety recommendations in the manufacturer’s service manual.
Never wear jewelry when working around high-voltage systems.
Always reinstall high-voltage covers and barriers. Reapply high-voltage labels if they are removed or damaged.
Do not ignore warnings from the ground fault monitoring system. Follow instructions in the service manual to isolate and repair the source of the fault. Unrepaired ground faults can cause shocks or electrocution to vehicle occupants or service technicians.
High-voltage electrical cables are designed with special shielding and insulation, and the exterior cover should be made from orange colored material. Always replace high-voltage wiring and harnesses with parts as specified by the manufacturer. Do not manufacture your own high-voltage harnesses or substitute non-approved parts.
Remember that high voltage will always be present inside a traction battery or ultracapacitor pack (if vehicle has a hybrid-electric drive system) even when the main switch is off or automatic shutdown has occurred. Special tools and procedures are required to work safely inside the battery/ultracapacitor pack. Do not open the battery/ultracapacitor pack cover unless you have been trained to work safely with live high voltage.
Monday, June 9, 2014
3.3.1 Design
All electrical cables that carry greater than 30 VAC or 60 VDC should be considered high-voltage cables and should be permanently identified with orange covering material, and be located to preclude casual contact by vehicle operators and maintenance personnel. No high voltage cables should be routed through the passenger compartment.
Any part or connector energized with high voltage during normal operations should be located behind a cover or in an enclosure labeled with the hazardous voltage symbol. See Figure 18. Removal of the cover should require removal of special fasteners and/or should trigger an interlock system that de-energizes the high-voltage components. If the cover or enclosure is made of conductive material, it should be grounded to the vehicle chassis.
The electrical system should include an automatic disconnect function that isolates both poles of any high-voltage source (fuel cell stack and/or high voltage battery pack) from other system components.
The connectors used should be “fail safe” so that they will open if the control signal is lost due to a system fault. This automatic disconnect function should be triggered by the following:
• Turning off the main switch
• By automatic system shutdown (due to a hydrogen sensor detecting a leak, or other system fault that shuts off the hydrogen fuel supply)
All high-voltage components should be designed with adequate electrical isolation to prevent “current leakage” between them and other electrical components or the chassis. The vehicle control system should include a ground fault monitoring system that can detect leakage current and set a warning light and/or take other action (up to automatic system shutdown) when a current above a set threshold is detected.
All electrical cables that carry greater than 30 VAC or 60 VDC should be considered high-voltage cables and should be permanently identified with orange covering material, and be located to preclude casual contact by vehicle operators and maintenance personnel. No high voltage cables should be routed through the passenger compartment.
Any part or connector energized with high voltage during normal operations should be located behind a cover or in an enclosure labeled with the hazardous voltage symbol. See Figure 18. Removal of the cover should require removal of special fasteners and/or should trigger an interlock system that de-energizes the high-voltage components. If the cover or enclosure is made of conductive material, it should be grounded to the vehicle chassis.
The electrical system should include an automatic disconnect function that isolates both poles of any high-voltage source (fuel cell stack and/or high voltage battery pack) from other system components.
The connectors used should be “fail safe” so that they will open if the control signal is lost due to a system fault. This automatic disconnect function should be triggered by the following:
• Turning off the main switch
• By automatic system shutdown (due to a hydrogen sensor detecting a leak, or other system fault that shuts off the hydrogen fuel supply)
All high-voltage components should be designed with adequate electrical isolation to prevent “current leakage” between them and other electrical components or the chassis. The vehicle control system should include a ground fault monitoring system that can detect leakage current and set a warning light and/or take other action (up to automatic system shutdown) when a current above a set threshold is detected.
3.3 HIGH VOLTAGE SYSTEMS
Any voltage greater than 30 VAC or 60 VDC can harm humans through electric shock and is considered “hazardous voltage” (SAE, 2002).
Hydrogen fuel cells produce electricity at nominal voltages of 300 to 600 VDC, which is used to power an electric drive system that operates at similar voltages (often after conversion to alternating current). The drive system may be designed with a hybrid-electric configuration. If so, there will also be a high-voltage battery pack installed on the vehicle.
Hydrogen fueled ICEs do not produce electricity directly, but hydrogen ICE vehicles may also be designed with a hybrid-electric drive configuration. If so, they will also include a high-voltage battery pack and other high-voltage electrical components.
Any voltage greater than 30 VAC or 60 VDC can harm humans through electric shock and is considered “hazardous voltage” (SAE, 2002).
Hydrogen fuel cells produce electricity at nominal voltages of 300 to 600 VDC, which is used to power an electric drive system that operates at similar voltages (often after conversion to alternating current). The drive system may be designed with a hybrid-electric configuration. If so, there will also be a high-voltage battery pack installed on the vehicle.
Hydrogen fueled ICEs do not produce electricity directly, but hydrogen ICE vehicles may also be designed with a hybrid-electric drive configuration. If so, they will also include a high-voltage battery pack and other high-voltage electrical components.
Tuesday, June 3, 2014
3.2.2 Operation and Maintenance
Anyone who will operate or maintain liquid hydrogen-fueled vehicles should receive hydrogen safety training. At a minimum, this training should cover the characteristics of hydrogen and liquid hydrogen, operation of onboard safety systems, liquid hydrogen fueling operations, and actions to take in an emergency.
During maintenance, never substitute fuel system replacement parts that have not been specifically tested and certified for use with liquid hydrogen. Lines that will carry liquid hydrogen must be well-insulated with the outer layer of insulation vapor sealed. O-rings or other seals used in connections between liquid hydrogen lines must be made of special materials that can withstand liquid hydrogen temperatures without breaking. Substituting seals made of different materials can result in liquid hydrogen leaks.
When working on the liquid hydrogen fuel system, always wear personal protective equipment, including safety glasses and a full face shield, loose fitting insulated or leather gloves, leather boots ankle height or higher, a long-sleeved shirt, and long pants without cuffs. Pant legs should be worn outside of the boots.
Never loosen any joint in the hydrogen fuel system while the connected components are under pressure (gaseous hydrogen lines) or contain liquid hydrogen. Never disturb the insulation on liquid hydrogen lines or cryotanks while they contain liquid hydrogen. Shut down the system, isolate and vent components as directed in the manufacturer’s service manual. Torque all joints to the levels specified in the manufacturer’s service manual. Do not over tighten. Overtorquing can cause leaks.
Air must never be allowed to enter the hydrogen fuel system. If exposed to the atmosphere, any component that will carry liquid hydrogen (including cryotanks and lines) must be purged with helium before being refilled with liquid hydrogen. Nitrogen must not be used because the residual nitrogen in the lines could liquefy and freeze when exposed to liquid hydrogen. This could potentially plug pressure relief valves and other system valves. Alternatively, components can be purged of air with nitrogen and the nitrogen can be purged with gaseous hydrogen before refilling with liquid hydrogen. See the manufacturer’s service manual for specific purging procedures.
Periodically check all connections in the hydrogen fuel system for leaks using procedures outlined in the manufacturer’s service manual. Tighten or repair all leaking joints, no matter how small the leak.
Leak checks should also be conducted after repair or replacement of any fuel system lines or valves.
Periodically check the exterior surface of liquid hydrogen cryotanks and fuel lines for cuts or damage to the exterior insulation layer. All damage that breeches the vapor barrier must be repaired.
Periodically check and calibrate hydrogen sensors in accordance with the schedule and procedures in the manufacturer’s service manual.
Periodically check operation of the fan in the hydrogen diffuser and any ventilation fans, in accordance with the schedule and procedures in the manufacturer’s service manual.
Do not ignore warning lights or alarms. Do not attempt to override automatic system shutdown unless absolutely necessary (e.g., to move vehicle off railroad tracks).
Always make sure that the main switch is off before servicing the vehicle. Before working on the fuel cell system or liquid hydrogen storage system also disconnect the vehicle’s 12/24-VDC battery.
Do not walk on liquid hydrogen cryotanks or expose them to damage from impact or abrasion.
Always electrically ground and bond the vehicle when fueling. Connect the ground strap or cable at the fuel station if one is provided.
Before fueling, check that the onboard fuel port is free of dirt and debris. Always replace the fuel port dust cover after fueling.
Do not smoke or use a cell phone when servicing or fueling the vehicle.
The manufacturer of the liquid hydrogen cryotank will specify a minimum ullage13 space required in each tank. During fueling, this ullage space must be maintained and tanks should not be overfilled.
Anyone who will operate or maintain liquid hydrogen-fueled vehicles should receive hydrogen safety training. At a minimum, this training should cover the characteristics of hydrogen and liquid hydrogen, operation of onboard safety systems, liquid hydrogen fueling operations, and actions to take in an emergency.
During maintenance, never substitute fuel system replacement parts that have not been specifically tested and certified for use with liquid hydrogen. Lines that will carry liquid hydrogen must be well-insulated with the outer layer of insulation vapor sealed. O-rings or other seals used in connections between liquid hydrogen lines must be made of special materials that can withstand liquid hydrogen temperatures without breaking. Substituting seals made of different materials can result in liquid hydrogen leaks.
When working on the liquid hydrogen fuel system, always wear personal protective equipment, including safety glasses and a full face shield, loose fitting insulated or leather gloves, leather boots ankle height or higher, a long-sleeved shirt, and long pants without cuffs. Pant legs should be worn outside of the boots.
Never loosen any joint in the hydrogen fuel system while the connected components are under pressure (gaseous hydrogen lines) or contain liquid hydrogen. Never disturb the insulation on liquid hydrogen lines or cryotanks while they contain liquid hydrogen. Shut down the system, isolate and vent components as directed in the manufacturer’s service manual. Torque all joints to the levels specified in the manufacturer’s service manual. Do not over tighten. Overtorquing can cause leaks.
Air must never be allowed to enter the hydrogen fuel system. If exposed to the atmosphere, any component that will carry liquid hydrogen (including cryotanks and lines) must be purged with helium before being refilled with liquid hydrogen. Nitrogen must not be used because the residual nitrogen in the lines could liquefy and freeze when exposed to liquid hydrogen. This could potentially plug pressure relief valves and other system valves. Alternatively, components can be purged of air with nitrogen and the nitrogen can be purged with gaseous hydrogen before refilling with liquid hydrogen. See the manufacturer’s service manual for specific purging procedures.
Periodically check all connections in the hydrogen fuel system for leaks using procedures outlined in the manufacturer’s service manual. Tighten or repair all leaking joints, no matter how small the leak.
Leak checks should also be conducted after repair or replacement of any fuel system lines or valves.
Periodically check the exterior surface of liquid hydrogen cryotanks and fuel lines for cuts or damage to the exterior insulation layer. All damage that breeches the vapor barrier must be repaired.
Periodically check and calibrate hydrogen sensors in accordance with the schedule and procedures in the manufacturer’s service manual.
Periodically check operation of the fan in the hydrogen diffuser and any ventilation fans, in accordance with the schedule and procedures in the manufacturer’s service manual.
Do not ignore warning lights or alarms. Do not attempt to override automatic system shutdown unless absolutely necessary (e.g., to move vehicle off railroad tracks).
Always make sure that the main switch is off before servicing the vehicle. Before working on the fuel cell system or liquid hydrogen storage system also disconnect the vehicle’s 12/24-VDC battery.
Do not walk on liquid hydrogen cryotanks or expose them to damage from impact or abrasion.
Always electrically ground and bond the vehicle when fueling. Connect the ground strap or cable at the fuel station if one is provided.
Before fueling, check that the onboard fuel port is free of dirt and debris. Always replace the fuel port dust cover after fueling.
Do not smoke or use a cell phone when servicing or fueling the vehicle.
The manufacturer of the liquid hydrogen cryotank will specify a minimum ullage13 space required in each tank. During fueling, this ullage space must be maintained and tanks should not be overfilled.
Wednesday, May 28, 2014
3.2.1 Design
The exterior of the vehicle should be marked with diamond-shaped labels that say “Liquid Hydrogen” in white letters on a blue background (see Figure 16). For commercial vehicles, one label should be located on the rear of the power unit and one label should be located on each side of the power unit cab, below the DOT numbers. The hydrogen labels should be legible from fifty feet in day light.
All cryotanks used to hold liquid hydrogen must be permanently marked “hydrogen,” securely mounted to the vehicle, and protected from damage by road debris.
All liquid hydrogen cryotanks must have a safety pressure relief valve installed. The outlet(s) from the valve(s) should empty into a hydrogen diffuser, whose outlet is located at or above the top surface of the vehicle. The hydrogen diffuser should be designed to mix the exiting hydrogen gas with enough air that under normal operations, the resultant flow will have a hydrogen concentration less than 25 percent of the lower flammable limit.
Each liquid hydrogen cryotank should have a manual shutoff valve installed that will allow that cylinder to be isolated from the rest of the fuel system for maintenance.
Each liquid hydrogen cryotank should be equipped with a liquid level gauge that can be read from the vehicle cab and a pressure gauge that can be read locally on or near the tank.
While certification standards for on-vehicle liquid hydrogen tanks have not yet been finalized, at a minimum, tanks should be tested/certified in the same way that current liquefied natural gas (LNG) tanks are tested.
For each tank design, this includes a 10-foot and a 30-foot drop test of a full tank to ensure that the tank will not leak even if subjected to a severe crash, and a 20-minute flame test to ensure that the tank will not immediately vent even if impacted by a fire (SAE, 1997).
The fuel system should include one or more electrically activated valves that will isolate the hydrogen cryotank(s), individually or as a group, from the rest of the system when closed. These valve(s) should “fail safely” so that they will close if the control signal is lost due to a system fault.
All liquid and gaseous hydrogen fuel lines should be securely mounted to the vehicle and routed away from heat sources. To the extent possible, fuel line connections should be minimized since leaks are most likely at joints. Fuel lines should not be routed through the passenger compartment.
All components of the fuel system that will come into contact with liquid hydrogen, including cryotank(s), fill lines, valves, and sealing materials should be constructed of materials that have been tested to be compatible with the low temperatures of liquid hydrogen. All gaseous hydrogen fuel lines and valves (downstream of the cryotank heat exchanger) shall be constructed of materials that have been tested to be compatible with hydrogen and not subject to hydrogen embrittlement.
All components of the fuel system and engine system that will carry or contain liquid or gaseous hydrogen should be electrically grounded and bonded to the vehicle chassis to preclude the buildup of static electricity.
All components of the fuel system that will carry or contain liquid hydrogen must be well-insulated, labeled, and be located to prevent casual contact by vehicle operators or maintenance personnel. The outer insulating layer must be vapor sealed to prevent air infiltration. Any fuel line that may be isolated between two closed valves with residual liquid hydrogen still inside (i.e., a fill line) must contain a pressure relief valve to vent hydrogen that vaporizes as the line heats up. These valve(s) should vent to a common plenum, with the pressure relief valve(s) on the liquid hydrogen cryotank(s).
Any compartment into which hydrogen could leak (from a fuel line connection or valve or from the fuel cell stack) should be ventilated such that gaseous hydrogen cannot collect in concentrations greater than 25 percent of hydrogen’s lower flammable limit. Hydrogen carrying components should not be located such that hydrogen can leak into the passenger compartment under any circumstance. Because fuel cell stacks can develop internal leaks over time, they will likely be installed in their own enclosure, which will have both ventilation holes and a ventilation fan to force air through the enclosure to flush out any leaked hydrogen so that it can not collect.
One or more hydrogen sensors should be installed on the vehicle. The number and location of these sensors will depend on the hydrogen fuel and engine system design. These hydrogen sensor(s) should be connected to the vehicle control system to provide an alarm and automatic system shutdown if a hydrogen concentration greater than a preset threshold is detected. This threshold could be anywhere from 25 percent to 50 percent of the lower flammable limit for hydrogen (1–2 percent hydrogen concentration).
The fuel system may also have an excess flow valve installed that is designed to close off fuel flow and trigger an automatic system shutdown when flow in excess of a set threshold is detected. The threshold is set to be greater than the maximum flow that could be used by the fuel cell or hydrogen ICE at full power. Flows greater than this amount indicate that there is probably a leak in the system.
The vehicle may also have an inertial crash sensor installed that can automatically trigger a vehicle shutdown when a crash is detected. Some vehicles may include a switch to override automatic shutdown and allow the vehicle to continue to operate for a short time. This switch should only be used in case of extreme emergency, for example, to move the vehicle out of high-speed traffic or off of a railroad track.
The vehicle control system should be configured so that automatic system shutdown can be triggered by detection of leaked hydrogen, excess fuel flow, a vehicle crash, or other system fault. Automatic system shutdown should include closing valve(s) to isolate hydrogen in the hydrogen storage cylinders, disconnecting traction power, and de-energizing high voltage equipment. During system shutdown, hydrogen should be vented from all other fuel and engine system components.
The control system should include a single main on/off switch that allows the vehicle operator to shut down the fuel cell system, disconnect traction power, de-energize high voltage equipment, and shut off the hydrogen fuel supply (isolating all hydrogen in the liquid hydrogen cryotank(s)). This switch should be located in the passenger cab easily accessible to the operator, similar to a conventional ignition switch.
The vehicle control system should include an interlock to the vehicle fueling port such that fueling cannot begin unless the fuel cell system is shutdown and the vehicle traction system is de-energized so that the vehicle cannot move.
The on board liquid hydrogen filling receptacle must be electrically bonded to the vehicle chassis, and some method must be provided to electrically connect the vehicle chassis to the fuel station ground during fueling. This can be done through the fueling nozzle (preferred) or with a separate ground strap.
A dust cap permanently mounted to the vehicle should be provided for the onboard fuel filling port, to keep out dirt and debris when the vehicle is not being fueled.
The vehicle fuel system should include fittings and other provisions necessary to safely remove hydrogen fuel from the liquid hydrogen cryotank(s) and purge them with nitrogen or helium as required for maintenance.
After system shutdown, hydrogen will typically be vented from the vehicle’s low-pressure gaseous fuel system and fuel cell stack. The outlet for this venting hydrogen should be at or above the top surface of the vehicle. If, under normal operations, venting hydrogen will achieve concentrations greater than 25 percent of the lower flammable limit (1 percent hydrogen concentration), the hydrogen should vent through a hydrogen diffuser. The same hydrogen diffuser can be used for both this function and to diffuse hydrogen released through the fuel system pressure relief valve(s).
The exterior of the vehicle should be marked with diamond-shaped labels that say “Liquid Hydrogen” in white letters on a blue background (see Figure 16). For commercial vehicles, one label should be located on the rear of the power unit and one label should be located on each side of the power unit cab, below the DOT numbers. The hydrogen labels should be legible from fifty feet in day light.
All cryotanks used to hold liquid hydrogen must be permanently marked “hydrogen,” securely mounted to the vehicle, and protected from damage by road debris.
All liquid hydrogen cryotanks must have a safety pressure relief valve installed. The outlet(s) from the valve(s) should empty into a hydrogen diffuser, whose outlet is located at or above the top surface of the vehicle. The hydrogen diffuser should be designed to mix the exiting hydrogen gas with enough air that under normal operations, the resultant flow will have a hydrogen concentration less than 25 percent of the lower flammable limit.
Each liquid hydrogen cryotank should have a manual shutoff valve installed that will allow that cylinder to be isolated from the rest of the fuel system for maintenance.
Each liquid hydrogen cryotank should be equipped with a liquid level gauge that can be read from the vehicle cab and a pressure gauge that can be read locally on or near the tank.
While certification standards for on-vehicle liquid hydrogen tanks have not yet been finalized, at a minimum, tanks should be tested/certified in the same way that current liquefied natural gas (LNG) tanks are tested.
For each tank design, this includes a 10-foot and a 30-foot drop test of a full tank to ensure that the tank will not leak even if subjected to a severe crash, and a 20-minute flame test to ensure that the tank will not immediately vent even if impacted by a fire (SAE, 1997).
The fuel system should include one or more electrically activated valves that will isolate the hydrogen cryotank(s), individually or as a group, from the rest of the system when closed. These valve(s) should “fail safely” so that they will close if the control signal is lost due to a system fault.
All liquid and gaseous hydrogen fuel lines should be securely mounted to the vehicle and routed away from heat sources. To the extent possible, fuel line connections should be minimized since leaks are most likely at joints. Fuel lines should not be routed through the passenger compartment.
All components of the fuel system that will come into contact with liquid hydrogen, including cryotank(s), fill lines, valves, and sealing materials should be constructed of materials that have been tested to be compatible with the low temperatures of liquid hydrogen. All gaseous hydrogen fuel lines and valves (downstream of the cryotank heat exchanger) shall be constructed of materials that have been tested to be compatible with hydrogen and not subject to hydrogen embrittlement.
All components of the fuel system and engine system that will carry or contain liquid or gaseous hydrogen should be electrically grounded and bonded to the vehicle chassis to preclude the buildup of static electricity.
All components of the fuel system that will carry or contain liquid hydrogen must be well-insulated, labeled, and be located to prevent casual contact by vehicle operators or maintenance personnel. The outer insulating layer must be vapor sealed to prevent air infiltration. Any fuel line that may be isolated between two closed valves with residual liquid hydrogen still inside (i.e., a fill line) must contain a pressure relief valve to vent hydrogen that vaporizes as the line heats up. These valve(s) should vent to a common plenum, with the pressure relief valve(s) on the liquid hydrogen cryotank(s).
Any compartment into which hydrogen could leak (from a fuel line connection or valve or from the fuel cell stack) should be ventilated such that gaseous hydrogen cannot collect in concentrations greater than 25 percent of hydrogen’s lower flammable limit. Hydrogen carrying components should not be located such that hydrogen can leak into the passenger compartment under any circumstance. Because fuel cell stacks can develop internal leaks over time, they will likely be installed in their own enclosure, which will have both ventilation holes and a ventilation fan to force air through the enclosure to flush out any leaked hydrogen so that it can not collect.
One or more hydrogen sensors should be installed on the vehicle. The number and location of these sensors will depend on the hydrogen fuel and engine system design. These hydrogen sensor(s) should be connected to the vehicle control system to provide an alarm and automatic system shutdown if a hydrogen concentration greater than a preset threshold is detected. This threshold could be anywhere from 25 percent to 50 percent of the lower flammable limit for hydrogen (1–2 percent hydrogen concentration).
The fuel system may also have an excess flow valve installed that is designed to close off fuel flow and trigger an automatic system shutdown when flow in excess of a set threshold is detected. The threshold is set to be greater than the maximum flow that could be used by the fuel cell or hydrogen ICE at full power. Flows greater than this amount indicate that there is probably a leak in the system.
The vehicle may also have an inertial crash sensor installed that can automatically trigger a vehicle shutdown when a crash is detected. Some vehicles may include a switch to override automatic shutdown and allow the vehicle to continue to operate for a short time. This switch should only be used in case of extreme emergency, for example, to move the vehicle out of high-speed traffic or off of a railroad track.
The vehicle control system should be configured so that automatic system shutdown can be triggered by detection of leaked hydrogen, excess fuel flow, a vehicle crash, or other system fault. Automatic system shutdown should include closing valve(s) to isolate hydrogen in the hydrogen storage cylinders, disconnecting traction power, and de-energizing high voltage equipment. During system shutdown, hydrogen should be vented from all other fuel and engine system components.
The control system should include a single main on/off switch that allows the vehicle operator to shut down the fuel cell system, disconnect traction power, de-energize high voltage equipment, and shut off the hydrogen fuel supply (isolating all hydrogen in the liquid hydrogen cryotank(s)). This switch should be located in the passenger cab easily accessible to the operator, similar to a conventional ignition switch.
The vehicle control system should include an interlock to the vehicle fueling port such that fueling cannot begin unless the fuel cell system is shutdown and the vehicle traction system is de-energized so that the vehicle cannot move.
The on board liquid hydrogen filling receptacle must be electrically bonded to the vehicle chassis, and some method must be provided to electrically connect the vehicle chassis to the fuel station ground during fueling. This can be done through the fueling nozzle (preferred) or with a separate ground strap.
A dust cap permanently mounted to the vehicle should be provided for the onboard fuel filling port, to keep out dirt and debris when the vehicle is not being fueled.
The vehicle fuel system should include fittings and other provisions necessary to safely remove hydrogen fuel from the liquid hydrogen cryotank(s) and purge them with nitrogen or helium as required for maintenance.
After system shutdown, hydrogen will typically be vented from the vehicle’s low-pressure gaseous fuel system and fuel cell stack. The outlet for this venting hydrogen should be at or above the top surface of the vehicle. If, under normal operations, venting hydrogen will achieve concentrations greater than 25 percent of the lower flammable limit (1 percent hydrogen concentration), the hydrogen should vent through a hydrogen diffuser. The same hydrogen diffuser can be used for both this function and to diffuse hydrogen released through the fuel system pressure relief valve(s).
3.2 LIQUID HYDROGEN SYSTEMS
Liquid hydrogen storage on vehicles is much less common than high-pressure compressed hydrogen storage. If your vehicle does store liquid hydrogen onboard, many of the design and operating considerations listed in Section 3.1 will apply, but since liquid hydrogen is stored at very low temperatures, the additional considerations listed below will also apply.
Liquid hydrogen storage on vehicles is much less common than high-pressure compressed hydrogen storage. If your vehicle does store liquid hydrogen onboard, many of the design and operating considerations listed in Section 3.1 will apply, but since liquid hydrogen is stored at very low temperatures, the additional considerations listed below will also apply.
3.1.2 Operation and Maintenance
Anyone who will operate or maintain hydrogen-fueled vehicles should receive hydrogen safety training. At a minimum, this training should cover the characteristics of hydrogen, operation of onboard safety systems, hydrogen fueling operations, and actions to take in an emergency.
During maintenance, never substitute fuel system replacement parts that have not been specifically tested and certified for use with hydrogen (for example, lines, valves, and regulators designed for use with natural gas).
While they may look and function the same, they may be subject to hydrogen embrittlement. In addition, compressed natural gas fuel systems typically operate at lower pressures (maximum 3,600 psi) than hydrogen fuel systems.
Periodically check all connections in the hydrogen fuel system for leaks using procedures outlined in the manufacturer’s service manual. Tighten or repair all leaking joints, no matter how small the leak. Leak checks should also be conducted after repair or replacement of any fuel system lines or valves.
Never loosen any joint in the fuel system while the connected components are under pressure. Shut down the system and isolate and vent components as directed in the manufacturer’s service manual. Torque all joints to the levels specified in the service manual. Do not over tighten. Overtorquing can cause leaks.
Air must never be allowed to enter the hydrogen fuel system. If exposed to the atmosphere, some components, particularly hydrogen fuel cylinders, must be purged with nitrogen before being refilled with hydrogen. See the manufacturer’s service manual for specific purging procedures.
Periodically check the exterior surface of hydrogen fuel cylinders for nicks, dents, and cuts that could weaken the structure. See the manufacturer’s service manual for information on the allowable level of wear and damage before cylinders need to be replaced. The Federal Motor Vehicle Safety Standards applicable to natural gas fuel cylinders (FMVSS 304, 49 CFR 571.304) specify that a visual inspection by a “qualified container inspector”11 must be conducted “at least every 36 months or 36,000 miles or at the time of re-installation.” The inspection procedures for damage assessment are outlined in pamphlet C-612 from the
Compressed Gas Association. While standards specifically applicable to hydrogen cylinders have not yet been developed, at a minimum, the requirements applicable to natural gas fuel cylinders should be followed.
Local laws and regulations may require more frequent cylinder inspections, for example, in conjunction with annual registration safety inspections. The fuel system, including the high-pressure storage tanks, should also be visually inspected after any accident, and be retested or replaced as required.
Periodically check and calibrate hydrogen sensors in accordance with the schedule and procedures in the manufacturer’s service manual.
Periodically check operation of the fan in the hydrogen diffuser and any ventilation fans in accordance with
the schedule and procedures in the manufacturer’s service manual.
The fuel system will likely include a coalescing filter to remove any oil that might carry over into the hydrogen fuel from the fuel station compressor. Check and empty or replace this filter periodically in accordance with the schedule and procedures in the manufacturer’s service manual.
Do not ignore warning lights or alarms. Do not attempt to override automatic system shutdown unless absolutely necessary (e.g., to move vehicle off of railroad tracks).
Always make sure that the main switch is off before servicing the vehicle. Before working on the fuel cell system or gaseous hydrogen storage system, also disconnect the vehicle’s 12/24-VDC battery and close the manual fuel valves to isolate hydrogen in the storage cylinders.
Do not try to repair damaged fuel lines—replace them.
Do not walk on hydrogen fuel cylinders or expose them to damage from impact or abrasion. Do not allow strong chemicals, such as battery acid or metal cleaning solvents, to contact the hydrogen fuel cylinders.
Always electrically ground and bond the vehicle when fueling and defueling. Connect the ground strap or cable at the fuel station if one is provided.
Before fueling, check that the onboard fuel port is free of dirt and debris. Always replace the fuel port dust cover after fueling.
Do not smoke or use a cell phone when servicing or fueling the vehicle.
If the vehicle must be defueled for servicing of the hydrogen fuel system, the rate of fuel release must be carefully controlled. Follow the instructions in the manufacturer’s service manual. Unless the hydrogen storage tanks will be removed, always leave a small amount of pressure in the tanks so that the internal pressure is a few psi above atmospheric pressure. Any time tank pressure falls below atmospheric, it is possible for air to enter, and the tank must be purged with nitrogen before refilling with hydrogen.
Anyone who will operate or maintain hydrogen-fueled vehicles should receive hydrogen safety training. At a minimum, this training should cover the characteristics of hydrogen, operation of onboard safety systems, hydrogen fueling operations, and actions to take in an emergency.
During maintenance, never substitute fuel system replacement parts that have not been specifically tested and certified for use with hydrogen (for example, lines, valves, and regulators designed for use with natural gas).
While they may look and function the same, they may be subject to hydrogen embrittlement. In addition, compressed natural gas fuel systems typically operate at lower pressures (maximum 3,600 psi) than hydrogen fuel systems.
Periodically check all connections in the hydrogen fuel system for leaks using procedures outlined in the manufacturer’s service manual. Tighten or repair all leaking joints, no matter how small the leak. Leak checks should also be conducted after repair or replacement of any fuel system lines or valves.
Never loosen any joint in the fuel system while the connected components are under pressure. Shut down the system and isolate and vent components as directed in the manufacturer’s service manual. Torque all joints to the levels specified in the service manual. Do not over tighten. Overtorquing can cause leaks.
Air must never be allowed to enter the hydrogen fuel system. If exposed to the atmosphere, some components, particularly hydrogen fuel cylinders, must be purged with nitrogen before being refilled with hydrogen. See the manufacturer’s service manual for specific purging procedures.
Periodically check the exterior surface of hydrogen fuel cylinders for nicks, dents, and cuts that could weaken the structure. See the manufacturer’s service manual for information on the allowable level of wear and damage before cylinders need to be replaced. The Federal Motor Vehicle Safety Standards applicable to natural gas fuel cylinders (FMVSS 304, 49 CFR 571.304) specify that a visual inspection by a “qualified container inspector”11 must be conducted “at least every 36 months or 36,000 miles or at the time of re-installation.” The inspection procedures for damage assessment are outlined in pamphlet C-612 from the
Compressed Gas Association. While standards specifically applicable to hydrogen cylinders have not yet been developed, at a minimum, the requirements applicable to natural gas fuel cylinders should be followed.
Local laws and regulations may require more frequent cylinder inspections, for example, in conjunction with annual registration safety inspections. The fuel system, including the high-pressure storage tanks, should also be visually inspected after any accident, and be retested or replaced as required.
Periodically check and calibrate hydrogen sensors in accordance with the schedule and procedures in the manufacturer’s service manual.
Periodically check operation of the fan in the hydrogen diffuser and any ventilation fans in accordance with
the schedule and procedures in the manufacturer’s service manual.
The fuel system will likely include a coalescing filter to remove any oil that might carry over into the hydrogen fuel from the fuel station compressor. Check and empty or replace this filter periodically in accordance with the schedule and procedures in the manufacturer’s service manual.
Do not ignore warning lights or alarms. Do not attempt to override automatic system shutdown unless absolutely necessary (e.g., to move vehicle off of railroad tracks).
Always make sure that the main switch is off before servicing the vehicle. Before working on the fuel cell system or gaseous hydrogen storage system, also disconnect the vehicle’s 12/24-VDC battery and close the manual fuel valves to isolate hydrogen in the storage cylinders.
Do not try to repair damaged fuel lines—replace them.
Do not walk on hydrogen fuel cylinders or expose them to damage from impact or abrasion. Do not allow strong chemicals, such as battery acid or metal cleaning solvents, to contact the hydrogen fuel cylinders.
Always electrically ground and bond the vehicle when fueling and defueling. Connect the ground strap or cable at the fuel station if one is provided.
Before fueling, check that the onboard fuel port is free of dirt and debris. Always replace the fuel port dust cover after fueling.
Do not smoke or use a cell phone when servicing or fueling the vehicle.
If the vehicle must be defueled for servicing of the hydrogen fuel system, the rate of fuel release must be carefully controlled. Follow the instructions in the manufacturer’s service manual. Unless the hydrogen storage tanks will be removed, always leave a small amount of pressure in the tanks so that the internal pressure is a few psi above atmospheric pressure. Any time tank pressure falls below atmospheric, it is possible for air to enter, and the tank must be purged with nitrogen before refilling with hydrogen.
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