S1. Scope. This standard specifies requirements for compressed hydrogen storage systems used in motor vehicles.

S2. Purpose. The purpose of this standard is to reduce deaths and injuries occurring from fires that result from hydrogen fuel leakage during vehicle operation and to reduce deaths and injuries occurring from explosions resulting from the burst of pressurized hydrogen containers.

S3. Application. This standard applies to each motor vehicle manufactured on or after September 1, 2028, that is equipped with compressed hydrogen gas as a fuel source to propel the vehicle. The standard does not apply to vehicles that are only equipped with cryo-compressed hydrogen storage systems and/or solid-state hydrogen storage system to propel the vehicle.

S4. Definitions.

BPO means the vehicle manufacturer-supplied median burst pressure for a batch of new containers.

Burst means to break apart or to break open.

Burst pressure means the highest pressure achieved for a container tested in accordance with S6.2.2.1 of this standard.

Check valve means a valve that prevents reverse flow.

Closure devices mean the check valve(s), shut-off valve(s), and thermally-activated pressure relief device(s) that control the flow of hydrogen into and/or out of a CHSS.

Container means a pressure-bearing component of a compressed hydrogen storage system that stores a continuous volume of hydrogen fuel in a single chamber or in multiple permanently interconnected chambers.

Container attachments mean non-pressure bearing parts attached to the container that provide additional support and/or protection to the container and that may be removed only with the use of tools for the specific purpose of maintenance and/or inspection.

Compressed hydrogen storage system (CHSS) means a system that stores compressed hydrogen fuel for a hydrogen-fueled vehicle, composed of a container, container attachments (if any), and all closure devices required to isolate the stored hydrogen from the remainder of the fuel system and the environment.

Cryo-compressed hydrogen storage system means a system that stores hydrogen by compressing it to high pressure while simultaneously cooling it to very low temperatures, allowing for a higher density of hydrogen storage compared to standard compressed hydrogen systems.

Hydrogen fuel system means the fueling receptacle, CHSS, fuel cell system or internal combustion engine, fuel lines, and exhaust systems.

Nominal working pressure (NWP) means the settled pressure of compressed gas in a container or CHSS fully fueled to 100 percent state of charge and at a uniform temperature of 15 °C.

Normal milliliter means a quantity of gas that occupies one milliliter of volume when its temperature is 0 °C and its pressure is 1 atmosphere.

Pressure relief device (PRD) means a device that, when activated under specified performance conditions, is used to release hydrogen from a pressurized system and thereby prevent failure of the system.

Service life (of a container) means the time frame during which service (usage) is authorized by the vehicle manufacturer.

Shut-off valve means a valve between the container and the remainder of the hydrogen fuel system that must default to the “closed” position when unpowered.

Solid-state hydrogen storage system means a system that stores hydrogen at ambient temperatures and low pressures within solid materials that can either physically absorb the hydrogen gas or chemically combine with it.

State of charge (SOC) means the density ratio of hydrogen in the CHSS between the actual CHSS condition and that at NWP with the CHSS equilibrated to 15 °C, as expressed as a percentage using the equation 1 to this section, where ρ is the density of hydrogen (g/L) at pressure (P) in MegaPascals (MPa) and temperature (T) in Celsius ( °C) as listed below in Table 1 or linearly interpolated therein:

Equation 1 to § 571.308 S4

Thermally-activated pressure relief device (TPRD) means a non-reclosing PRD that is activated by temperature to open and release hydrogen gas.

TPRD sense point means instrumentation that detects elevated temperature for the purpose of activating a TPRD.

S5. Requirements.

S5.1. Requirements for the CHSS. Each vehicle CHSS shall include the following functions: shut-off valve, check valve, and TPRD. Each vehicle CHSS shall have a NWP of 70 MPa or less. Each vehicle container, closure device, and CHSS shall meet the applicable performance test requirements listed in table 2 to this section.

S5.1.1. Tests for baseline metrics.

S5.1.1.1. Baseline initial burst pressure. The vehicle manufacturer shall immediately and irrevocably specify upon request, in writing and within 15 business days: whether the primary constituent of the container is glass fiber composite. When a new container with its container attachments (if any) is tested in accordance with S6.2.2.1 of this standard, both of the following requirements shall be met:

(a) The burst pressure of the container shall not be less than 2 times NWP.

(b) The burst pressure of the container having glass-fiber composite as a primary constituent shall not be less than 3.5 times NWP.

S5.1.1.2. Baseline initial pressure cycle test. When a new container with its container attachments (if any) is hydraulically pressure cycled in accordance with S6.2.2.2 of this standard to any pressure between 125.0 percent NWP and 130.0 percent NWP,

(a) Containers for vehicles with a GVWR of 10,000 pounds or less

(1) Shall not leak nor burst for at least 7,500 cycles, and

(2) Thereafter shall not burst for an additional 14,500 cycles. If a leak occurs while conducting the test as specified in S5.1.1.2(a)(2), the test is stopped and not considered a failure.

(b) Containers for vehicles with a GVWR of over 10,000 pounds

(1) Shall not leak nor burst for at least 11,000 cycles, and

(2) Thereafter shall not burst for an additional 11,000 cycles. If a leak occurs while conducting the test as specified in S5.1.1.2(b)(2), the test is stopped and not considered a failure.

S5.1.2. Test for performance durability. A new container shall not leak nor burst when subjected to the sequence of tests in S5.1.2.1 through S5.1.2.6. Immediately following S5.1.2.6, and without depressurizing the container, the container is subjected to a burst test in accordance with S6.2.2.1(c) and (d) of this standard. The burst pressure of the container at the end of the sequence of tests in this section shall not be less than 0.8 times the BPO value specified by the vehicle manufacturer. The sequence of tests and the burst pressure test are illustrated in figure 1 to S5.1.2. The vehicle manufacturer shall immediately and irrevocably specify upon request, in writing and within 15 business days: the BPO of the container.

S5.1.2.1. Drop test. The container with its container attachments (if any) is dropped once in accordance with S6.2.3.2 of this standard in any one of the four orientations specified in that section. Any container with damage from the drop test that prevents further testing of the container in accordance with S6.2.3.4 of this standard shall be considered to have failed to meet the test for performance durability requirements. In the case of an asymmetric container, the vehicle manufacturer shall immediately and irrevocably specify upon request, in writing, and within 15 business days: the center of gravity of the container.

S5.1.2.2. Surface damage test. The container, except if an all-metal container, is subjected to the surface damage test in accordance with the S6.2.3.3 of this standard. Container attachments designed to be removed shall be removed and container attachments that are not designed to be removed shall remain in place. Container attachments that are removed shall not be reinstalled for the remainder of S5.1.2; container attachments that are not removed shall remain in place for the remainder of S5.1.2.

S5.1.2.3. Chemical exposure and ambient-temperature pressure cycling test. The container is exposed to chemicals in accordance with S6.2.3.4 and then hydraulically pressure cycled in accordance with S6.2.3.4 of this standard for 60 percent of the number of cycles as specified in S5.1.1.2(a)(1) or (b)(1) as applicable. For all but the last 10 of these cycles, the cycling pressure shall be any pressure between 125.0 percent NWP and 130.0 percent NWP. For the last 10 cycles, the pressure shall be any pressure between 150.0 percent NWP and 155.0 percent NWP.

S5.1.2.4. High temperature static pressure test. The container is pressurized to any pressure between (or equal to) 125 percent NWP and 130 percent NWP and held at that pressure no less than 1,000 and no more than 1,050 hours in accordance with S6.2.3.5 of this standard and with the temperature surrounding the container at any temperature between 85.0 °C and 90.0 °C.

S5.1.2.5. Extreme temperature pressure cycling test. The container is pressure cycled in accordance with S6.2.3.6 for 40 percent of the number of cycles specified in S5.1.1.2(a)(1) or (b)(1) as applicable. The pressure for the first half of these cycles equals any pressure between 80.0 percent NWP and 85.0 percent NWP with the temperature surrounding the container equal to any temperature between −45.0 °C and −40.0 °C. The pressure for the next half of these cycles equals any pressure between 125.0 percent NWP and 130.0 percent NWP and the temperature surrounding the container equal to any temperature between 85.0 °C and 90.0 °C and the relative humidity surrounding the container not less than 80 percent.

S5.1.2.6. Residual pressure test. The container is hydraulically pressurized in accordance with S6.2.3.1 of this standard to a pressure between 180.0 percent NWP and 185.0 percent NWP and held for any duration between 240 to 245 seconds.

Figure 1 to § 571.308 S5.1.2. Performance Durability Test; (for Illustration Purposes Only)

S5.1.3. Test for expected on-road performance. When subjected to the sequence of tests in S5.1.3.1, the CHSS shall meet the permeation and leak requirements specified in S5.1.3.2 and shall not burst. Thereafter, the container of the CHSS shall not burst when subjected to a residual pressure test in accordance with S5.1.3.3. Immediately following the test specified in S5.1.3.3, and without depressurizing the container, the container of the CHSS is subjected to a burst test in accordance with S6.2.2.1(c) and (d) of this standard. The burst pressure of the container at the end of the sequence of tests in this section shall not be less than 0.8 times the BPO specified by the vehicle manufacturer under S5.1.2.

S5.1.3.1. Ambient and extreme temperature gas pressure cycling test. The CHSS is pressure cycled using hydrogen gas for 500 cycles under any temperature and pressure condition for the number of cycles as specified in table 3 to S5.1.3.1, and in accordance with the S6.2.4.1 of this standard test procedure. A static gas pressure leak/permeation test performed in accordance with S5.1.3.2 is conducted after the first 250 pressure cycles and after the remaining 250 pressure cycles.

S5.1.3.2. Extreme temperature static gas pressure leak/permeation test. When tested in accordance with S6.2.4.2 of this standard after each group of 250 pneumatic pressure cycles in S5.1.3.1, the CHSS shall not discharge hydrogen more than 46 millilitres per hour (mL/h) for each litre of CHSS water capacity.

S5.1.3.3. Residual pressure test. The container of the CHSS is hydraulically pressurized in accordance with S6.2.3.1 to any pressure between 1.800 times NWP and 1.850 times NWP and held at that pressure for any duration between 240 to 245 seconds.

S5.1.4. Test for service terminating performance in fire. When the CHSS is exposed to the two-stage localized or engulfing fire test in accordance with S6.2.5 of this standard, the container shall not burst. The pressure inside the CHSS shall fall to 1 MPa or less within the test time limit specified in S6.2.5.3(o) of this standard. Any leakage or venting, other than that through TPRD outlet(s), shall not result in jet flames greater than 0.5 m in length. If venting occurs though the TPRD, the venting shall be continuous.

S5.1.5. Tests for performance durability of closure devices. All tests are performed at ambient temperature of 5 °C to 35 °C unless otherwise specified.

S5.1.5.1. TPRD requirements. The TPRD shall not activate at any point during the test procedures specified in S6.2.6.1.1, S6.2.6.1.3, S6.2.6.1.4, S6.2.6.1.5, S6.2.6.1.6, S6.2.6.1.7, and S6.2.6.1.8 of this standard.

(a) A TPRD subjected to pressure cycling in accordance with S6.2.6.1.1 of this standard shall be sequentially tested in accordance with S6.2.6.1.8, S6.2.6.1.9, and S6.2.6.1.10 of this standard;

(1) When tested in accordance with S6.2.6.1.8, the TPRD shall not exhibit leakage greater than 10 normal milliliters per minute (NmL/hour).

(2) When tested in accordance with S6.2.6.1.9 of this standard, the TPRD shall activate within no more than 2 minutes of the average activation time of three new TPRDs tested in accordance with S6.2.6.1.9;

(3) When tested in accordance with S6.2.6.1.10 of this standard, the TPRD shall have a flow rate of at least 90 percent of the highest baseline flow rate established in accordance with S6.2.6.1.10;

(b)(1) A TPRD shall activate in less than ten hours when tested at the vehicle manufacturer's specified activation temperature in accordance with S6.2.6.1.2 of this standard;

(2) When tested at the accelerated life temperature in accordance with S6.2.6.1.2 of this standard, a TPRD shall not activate in less than 500 hours and shall not exhibit leakage greater than 10 NmL/hour when tested in accordance with S6.2.6.1.8 of this standard;

(c) A TPRD subjected to temperature cycling testing in accordance with S6.2.6.1.3 of this standard shall be sequentially tested in accordance with S6.2.6.1.8(a)(3), S6.2.6.1.9, and S6.2.6.1.10 of this standard;

(1) When tested in accordance with S6.2.6.1.8(a)(3) of this standard, the TPRD shall not exhibit leakage greater than 10 NmL/hour;

(2) When tested in accordance with S6.2.6.1.9 of this standard, the TPRD shall activate within no more than 2 minutes of the average activation time of three new TPRDs tested in accordance with S6.2.6.1.9;

(3) When tested in accordance with S6.2.6.1.10 of this standard, the TPRD shall have a flow rate of at least 90 percent of the highest baseline flow rate established in accordance with S6.2.6.1.10;

(d) A TPRD subjected to salt corrosion resistance testing in accordance with S6.2.6.1.4 of this standard shall be sequentially tested in accordance with S6.2.6.1.8, S6.2.6.1.9, and S6.2.6.1.10 of this standard;

(1) When tested in accordance with S6.2.6.1.8 of this standard, the TPRD shall not exhibit leakage greater than 10 NmL/hour;

(2) When tested in accordance with S6.2.6.1.9 of this standard, the TPRD shall activate within no more than 2 minutes of the average activation time of three new TPRDs tested in accordance with S6.2.6.1.9;

(3) When tested in accordance with S6.2.6.1.10 of this standard, the TPRD shall have a flow rate of at least 90 percent of the highest baseline flow rate established in accordance with S6.2.6.1.10;

(e) A TPRD subjected to vehicle environment testing in accordance with S6.2.6.1.5 of this standard shall not show signs of cracking, softening, or swelling, and thereafter shall be sequentially tested in accordance with S6.2.6.1.8, S6.2.6.1.9, and S6.2.6.1.10 of this standard. Cosmetic changes such as pitting or staining are not considered failures.

(1) When tested in accordance with S6.2.6.1.8 of this standard, the TPRD shall not exhibit leakage greater than 10 NmL/hour.

(2) When tested in accordance with S6.2.6.1.9 of this standard, the TPRD shall activate within no more than 2 minutes of the average activation time of three new TPRDs tested in accordance with S6.2.6.1.9,

(3) When tested in accordance with S6.2.6.1.10 of this standard, the TPRD shall have a flow rate of at least 90 percent of the highest baseline flow rate established in accordance with S6.2.6.1.10;

(f) A TPRD subjected to stress corrosion cracking testing in accordance with S6.2.6.1.6 of this standard shall not exhibit visible cracking or delaminating;

(g) A TPRD shall be subjected to drop and vibration testing in accordance with S6.2.6.1.7 of this standard. If the TPRD progresses beyond S6.2.6.1.7(c) to complete testing under S6.2.6.1.7(d), it shall then be sequentially tested in accordance with S6.2.6.1.8, S6.2.6.1.9, and S6.2.6.1.10 of this standard.

(1) When tested in accordance with S6.2.6.1.8 of this standard, the TPRD shall not exhibit leakage greater than 10 NmL/hour.

(2) When tested in accordance with S6.2.6.1.9 of this standard, the TPRD shall activate within no more than 2 minutes of the average activation time of three new TPRDs tested in accordance with S6.2.6.1.9,

(3) When tested in accordance with S6.2.6.1.10 of this standard, the TPRD shall have a flow rate of at least 90 percent of the highest baseline flow rate established in accordance with S6.2.6.1.10;

(h) One new TPRD subjected to leak testing in accordance with S6.2.6.1.8 of this standard shall not exhibit leakage greater than 10 NmL/hour;

(i) Three new TPRDs are subjected to a bench top activation test in accordance with S6.2.6.1.9 of this standard. The maximum difference in the activation time between any two of the three TPRDs shall be 2 minutes or less.

S5.1.5.2. Check valve and shut-off valve requirements. This section applies to both check valves and shut-off valves.

(a) A valve subjected to hydrostatic strength testing in accordance with S6.2.6.2.1 of this standard shall not leak to an extent that prevents continued pressurization in accordance with S6.2.6.2.1(c) nor burst at less than 250 percent NWP;

(b) A valve subjected to leak testing in accordance with S6.2.6.2.2 of this standard shall not exhibit leakage greater than 10 NmL/hour;

(c)(1) A check valve shall meet the requirements when tested sequentially as follows:

(i) The check valve shall reseat and prevent reverse flow after each cycle when subjected to 13,500 pressure cycles in accordance with S6.2.6.2.3 of this standard to any pressure between 100.0 and 105.0 percent NWP and at any temperature between 5.0 °C and 35.0 °C;

(ii) The same check valve shall reseat and prevent reverse flow after each cycle when subjected to 750 pressure cycles in accordance with S6.2.6.2.3 of this standard to any pressure between 125.0 and 130.0 percent NWP and at any temperature between 85.0 °C and 90.0 °C;

(iii) The same check valve shall reseat and prevent reverse flow after each cycle when subjected to 750 pressure cycles in accordance with S6.2.6.2.3 of this standard to any pressure between 80.0 and 85.0 percent NWP and at any temperature between −45.0 °C and −40.0 °C;

(iv) The same check valve shall be subjected to chatter flow testing in accordance with S6.2.6.2.4 of this standard;

(v) When tested in accordance with S6.2.6.2.2 of this standard, the same check valve shall not exhibit leakage greater than 10 NmL/hour;

(vi) When tested in accordance with S6.2.6.2.1 of this standard, the same check valve shall not leak to an extent that prevents continued pressurization in accordance with S6.2.6.2.1(c), nor burst at less than 250 percent NWP, nor burst at less than 80 percent of the burst pressure of the new unit tested in accordance with S5.1.5.2(a) unless the burst pressure of the valve exceeds 400 percent NWP.

(2) A shut-off valve shall meet the requirements when tested sequentially as follows:

(i) The shut-off valve shall be subjected to 45,000 pressure cycles in accordance with S6.2.6.2.3 to any pressure between 100.0 and 105.0 percent NWP and at any temperature between 5.0 °C and 35.0 °C;

(ii) The same shut-off valve shall be subjected to 2,500 pressure cycles in accordance with S6.2.6.2.3 of this standard to any pressure between 125.0 and 130.0 percent NWP and at any temperature between 85.0 °C and 90.0 °C;

(iii) The same shut-off valve shall be subjected to 2,500 pressure cycles in accordance with S6.2.6.2.3 of this standard to any pressure between 80.0 and 85.0 percent NWP and at any temperature between −45.0 °C and −40.0 °C;

(iv) The same shut-off valve shall be subjected to chatter flow testing in accordance with S6.2.6.2.4 of this standard;

(v) When tested in accordance with S6.2.6.2.2 of this standard, the same shut-off valve shall not exhibit leakage greater than 10 NmL/hour;

(vi) When tested in accordance with S6.2.6.2.1 of this standard, the same shut-off valve shall not leak to an extent that prevents continued pressurization in accordance with S6.2.6.2.1(c), nor burst at less than 250 percent NWP, nor burst at less than 80 percent of the burst pressure of the new unit tested in accordance with S5.1.5.2(a) unless the burst pressure of the valve exceeds 400 percent NWP.

(d) A valve subjected to salt corrosion resistance testing in accordance with S6.2.6.1.4 of this standard shall be tested sequentially in accordance with S6.2.6.2.2 followed by S6.2.6.2.1 of this standard.

(1) When tested in accordance with S6.2.6.2.2 of this standard, the valve shall not exhibit leakage greater than 10 NmL/hour;

(2) When tested in accordance with S6.2.6.2.1 of this standard, the valve shall not leak to an extent that prevents continued pressurization in accordance with S6.2.6.2.1(c), nor burst at less than 250 percent NWP, nor burst at less than 80 percent of the burst pressure of the new unit tested in accordance with S5.1.5.2(a) unless the burst pressure of the valve exceeds 400 percent NWP.

(e) A valve subjected to vehicle environment testing in accordance with S6.2.6.1.5 of this standard shall not show signs of cracking, softening, or swelling and shall be tested sequentially in accordance with S6.2.6.2.2 followed by S6.2.6.2.1 of this standard. Cosmetic changes such as pitting or staining are not considered failures.

(1) When tested in accordance with S6.2.6.2.2 of this standard, the valve shall not exhibit leakage greater than 10 NmL/hour;

(2) When tested in accordance with S6.2.6.2.1 of this standard, the valve shall not leak to an extent that prevents continued pressurization in accordance with S6.2.6.2.1(c), nor burst at less than 250 percent NWP, nor burst at less than 80 percent of the burst pressure of the new unit tested in accordance with S5.1.5.2(a) unless the burst pressure of the valve exceeds 400 percent NWP;

(f) A shut-off valve shall have a minimum resistance of 240 kΩ between the power conductor and the valve casing, and shall not exhibit open valve, smoke, fire, melting, or leakage greater than 10 NmL/hour when subjected to electrical testing in accordance with S6.2.6.2.5 followed by leak testing in accordance with S6.2.6.2.2 of this standard;

(g) A valve subjected to vibration testing in accordance with S6.2.6.2.6 of this standard shall be tested sequentially in accordance with S6.2.6.2.2 followed by S6.2.6.2.1 of this standard.

(1) When tested in accordance with S6.2.6.2.2 of this standard, the valve shall not exhibit leakage greater than 10 NmL/hour;

(2) When tested in accordance with S6.2.6.2.1 of this standard, the valve shall not leak to an extent that prevents continued pressurization in accordance with S6.2.6.2.1(c), nor burst at less than 250 percent NWP, nor burst at less than 80 percent of the burst pressure of the new unit tested in accordance with S5.1.5.2(a) unless the burst pressure of the valve exceeds 400 percent NWP.

(h) A valve shall not exhibit visible cracking or delaminating when subjected to stress corrosion cracking testing in accordance with S6.2.6.1.6 of this standard.

S5.1.6. Labeling. Each vehicle container shall be permanently labeled with the information specified in paragraphs S5.1.6(a) through (g). Any label affixed to the container in compliance with this section shall remain in place and be legible for the vehicle manufacturer's recommended service life of the container. The information shall be in English and in letters and numbers that are at least 6.35 millimeters ( 1/4 inch) high.

(a) The statement: “If there is a question about the proper use, installation, or maintenance of this compressed hydrogen storage system, contact ______,” inserting the vehicle manufacturer's name, address, and telephone number. The name provided shall be consistent with the vehicle manufacturer's filing in accordance with 49 CFR part 566.

(b) The container serial number.

(c) The statement: “Manufactured in ______,” inserting the month and year of manufacture of the container.

(d) The statement “Nominal Working Pressure ______MPa (_____psig),” Inserting the nominal working pressure which shall be no greater than 70 MPa.

(e) The statement “Compressed Hydrogen Gas Only.”

(f) The statement: “Do Not Use After ______,” inserting the month and year that mark the end of the vehicle manufacturer's recommended service life for the container.

(g) The statement: “This container should be visually inspected for damage and deterioration after a motor vehicle accident or fire, and either: (i) at least every 12 months when installed on a vehicle with a GVWR greater than 4,536 kg, or (ii) at least every 36 months or 36,000 miles, whichever comes first, when installed on a vehicle with a GVWR less than or equal to 4,536 kg.”

S6. Test procedures.

S6.1. [Reserved]

S6.2. Test procedures for compressed hydrogen storage.

S6.2.1. Unless otherwise specified, data sampling for pressure cycling under S6.2 shall be at least 1 Hz.

S6.2.2. Test procedures for baseline performance metrics.

S6.2.2.1. Burst test. (a) The container is filled with a hydraulic fluid.

(b) The container, the surrounding environment, and the hydraulic fluid are at any temperature between 5.0 °C and 35.0 °C.

(c) The rate of pressurization shall be less than or equal to 1.4 MPa per second for pressures higher than 1.50 times NWP. If the rate exceeds 0.35 MPa per second at pressures higher than 1.50 times NWP, then the container is placed in series between the pressure source and the pressure measurement device.

(d) The container is hydraulically pressurized until burst and the burst pressure of the container is recorded.

S6.2.2.2. Pressure cycling test. (a) The container is filled with a hydraulic fluid.

(b) The container surface, or the surface of the container attachments if present, the environment surrounding the container, and the hydraulic fluid are at any temperature between 5.0 °C and 35.0 °C at the start of testing and maintained at the specified temperature for the duration of the testing.

(c) The container is pressure cycled at any pressure between 1.0 MPa and 2.0 MPa up to the pressure specified in the respective section of S5. The cycling rate shall be any rate up to 10 cycles per minute.

(d) The temperature of the hydraulic fluid entering the container is maintained and monitored at any temperature between 5.0 °C and 35.0 °C.

(e) The vehicle manufacturer may specify a hydraulic pressure cycle profile within the specifications of S6.2.2.2(c). Vehicle manufacturers shall submit this profile to NHTSA immediately and irrevocably, upon request, in writing, and within 15 business days; otherwise, NHTSA shall determine the profile. At NHTSA's option, NHTSA shall cycle the container within 10 percent of the vehicle manufacturer's specified cycling profile.

S6.2.3. Performance durability test.

S6.2.3.1. Residual pressure test. The container is pressurized smoothly and continually with hydraulic fluid or hydrogen gas as specified until the pressure level is reached and held for the specified time.

S6.2.3.2. Drop impact test. The container is drop tested without internal pressurization or attached valves. The surface onto which the container is dropped shall be a smooth, horizontal, uniform, dry, concrete pad or other flooring type with equivalent hardness. No attempt shall be made to prevent the container from bouncing or falling over during a drop test, except for the vertical drop test, during which the test article shall be prevented from falling over. The container shall be dropped in any one of the following four orientations described below and illustrated in figure 2 to S6.2.3.2.

(a) From a position within 5° of horizontal with the lowest point of the container at any height between 1.800 meters and 1.820 meters above the surface onto which it is dropped. In the case of a non-axisymmetric container, the largest projection area of the container shall be oriented downward and aligned horizontally;

(b) From a position within 5° of vertical with the center of any shut-off valve interface location upward and with any potential energy of between 488 Joules and 538 Joules. If a drop energy of between 488 Joules and 538 Joules would result in the height of the lower end being more than 1.820 meters above the surface onto which it is dropped, the container shall be dropped from any height with the lower end between 1.800 meters and 1.820 meters above the surface onto which it is dropped. If a drop energy of between 488 Joules and 538 Joules would result in the height of the lower end being less than 0.100 meters above the surface onto which it is dropped, the container shall be dropped from any height with the lower end between 0.100 meters and 0.120 meters above the surface onto which it is dropped. In the case of a non-axisymmetric container, the center of any shut-off valve interface location and the container's center of gravity shall be aligned vertically, with the center of that shut-off valve interface location upward;

(c) From a position within 5° of vertical with the center of any shut-off valve interface location downward with any potential energy of between 488 Joules and 538 Joules. If a potential energy of between 488 Joules and 538 Joules would result in the height of the lower end being more than 1.820 meters above the surface onto which it is dropped, the container shall be dropped from any height with the lower end between 1.800 meters and 1.820 meters above the surface onto which it is dropped. If a drop energy of between 488 Joules and 538 Joules would result in the height of the lower end being less than 0.100 meters above the surface onto which it is dropped, the container shall be dropped from any height with the lower end between 0.100 meters and 0.120 meters above the surface onto which it is dropped. In the case of a non-axisymmetric container, the center of any shut-off valve interface location and the container's center of gravity shall be aligned vertically, with the center of that shut-off valve interface location downward;

(d) From any angle between 40° and 50° from the vertical orientation with the center of any shut-off valve interface location downward, and with the container center of gravity between 1.800 meters and 1.820 meters above the surface onto which it is dropped. However, if the lowest point of the container is closer to the ground than 0.60 meters, the drop angle shall be changed so that the lowest point of the container is between 0.60 meters and 0.62 meters above the ground and the center of gravity is between 1.800 meters and 1.820 meters above the surface onto which it is dropped. In the case of a non-axisymmetric container, the line passing through the center of any shut-off valve interface location and the container's center of gravity shall be at any angle between 40° and 50° from the vertical orientation. If this specification results in more than one possible container orientation, the drop shall be conducted from the orientation that results in the lowest positioning of the center of the shut-off valve interface location.

Figure 2 to § 571.308 S6.2.3.2. The Four Drop Orientations; (for Illustration Purposes Only)

S6.2.3.3. Surface damage test. The surface damage test consists of surface cut generation and pendulum impacts as described below.

(a) Surface cut generation: Two longitudinal saw cuts are made at any location on the same side of the outer surface of the unpressurized container, as shown in Figure 3, or on the container attachments if present. The first cut is 0.75 millimeters to 1.25 millimeters deep and 200 millimeters to 205 millimeters long; the second cut, which is only required for containers affixed to the vehicle by compressing its composite surface, is 1.25 millimeters to 1.75 millimeters deep and 25 millimeters to 28 millimeters long.

(b) Pendulum impacts: Mark the outer surface of the container, or the container attachments if present, with five separate, non-overlapping circles each having any linear diameter between 100.0 millimeters and 105.0 millimeters, as shown in Figure 3. The marks shall be located on the side opposite from the saw cuts, or located on a different chamber in the case of a container with more than one chamber. Within 30 minutes following preconditioning for any duration from 12 hours to 24 hours in an environmental chamber at any temperature between −45.0 °C and −40.0 °C, impact the center of each of the five areas with a pendulum having a pyramid with equilateral faces and square base, and the tip and edges being rounded to a radius of between 2.0 millimeters and 4.0 millimeters. The center of impact of the pendulum shall coincide with the center of gravity of the pyramid. The energy of the pendulum at the moment of impact with each of the five marked areas on the container is any energy between 30.0 Joules and 35.0 Joules. The container is secured in place during pendulum impacts and is not pressurized above 1 MPa.

Figure 3 to § 571.308 S6.2.3.3. Locations of Surface Damage for S6.2.3.3(a) and Pendulum Impacts for S6.2.3.3(b); (for Illustration Purposes Only)

S6.2.3.4. Chemical exposure and ambient temperature pressure cycling test. (a) Each of the 5 areas preconditioned by pendulum impact in S6.2.3.3(b) is exposed to any one of five solutions:

(1) 19 to 21 percent by volume sulfuric acid in water;

(2) 25 to 27 percent by weight sodium hydroxide in water;

(3) 5 to 7 percent by volume methanol in gasoline;

(4) 28 to 30 percent by weight ammonium nitrate in water; and

(5) 50 to 52 percent by volume methyl alcohol in water.

(b) The container is oriented with the fluid exposure areas on top. A pad of glass wool approximately 0.5 centimeters thick and 100 millimeters in diameter is placed on each of the five preconditioned areas. A sufficient amount of the test fluid is applied to the glass wool to ensure that the pad is wetted across its surface and through its thickness for the duration of the test. A plastic covering shall be applied over the glass wool to prevent evaporation.

(c) The exposure of the container with the glass wool is maintained for at least 48 hours and no more than 60 hours with the container hydraulically pressurized to any pressure between 125.0 percent NWP and 130.0 percent NWP. During exposure, the temperature surrounding the container is maintained at any temperature between 5.0 °C and 35.0 °C.

(d) Hydraulic pressure cycling is performed in accordance with S6.2.2.2 at any pressure within the specified ranges according to S5.1.2.3 for the specified number of cycles. The glass wool pads are removed and the container surface is rinsed with water after the cycles are complete.

S6.2.3.5. Static pressure test. The container is hydraulically pressurized to the specified pressure in a temperature-controlled chamber. The temperature of the chamber and the container surface, or the surface of the container attachments if present, are held at the specified temperature for the specified duration.

S6.2.3.6. Extreme temperature pressure cycling test. (a) The container is filled with hydraulic fluid for each test;

(b) At the start of each test, the container surface, or the surface of the container attachments if present, the hydraulic fluid, and the environment surrounding the container are at any temperature and relative humidity (if applicable) within the ranges specified in S5.1.2.5 of this standard and maintained for the duration of the testing.

(c) The container is pressure cycled from any pressure between 1.0 MPa and 2.0 MPa up to the specified pressure at a rate not exceeding 10 cycles per minute for the specified number of cycles;

(d) The temperature of the hydraulic fluid entering the container shall be measured as close as possible to the container inlet.

S6.2.4. Test procedures for expected on-road performance.

S6.2.4.1. Ambient and extreme temperature gas pressure cycling test. (a) In accordance with table 3 to S5.1.3.1 of this standard, the specified ambient conditions of temperature and relative humidity, if applicable, are maintained within the test environment throughout each pressure cycle. When required in accordance with table 3 to S5.1.3.1, the CHSS temperature shall be in the specified initial system equilibration temperature range between pressure cycles.

(b) The CHSS is pressure cycled from any pressure between 1.0 MPa and 2.0 MPa up to any pressure within the specified peak pressure range in accordance with table 3 to this section. The temperature of the hydrogen fuel dispensed to the container is controlled to within the specified temperature range within 30 seconds of fueling initiation. The specified number of pressure cycles are conducted.

(c) The ramp rate for pressurization shall be greater than or equal to the ramp rate given in table 4 to S6.2.4.1(c) according to the CHSS volume, the ambient conditions, and the fuel delivery temperature. If the required ambient temperature is not available in table 4 to this section, the closest ramp rate value or a linearly interpolated value shall be used. The pressure ramp rate shall be decreased if the gas temperature in the container exceeds 85 °C.

(d) The de-fueling rate shall be any rate greater than or equal to the intended vehicle's maximum fuel-demand rate. Out of the 500 pressure cycles, any 50 pressure cycles are performed using a de-fueling rate greater than or equal to the maintenance de-fueling rate.

S6.2.4.2. Gas permeation test. (a) A CHSS is filled with hydrogen gas to any SOC between 100.0 percent and 105.0 percent and placed in a sealed container. The CHSS is held for any duration between 12 hours and 24 hours at any temperature between 55.0 °C and 60.0 °C prior to the start of the test.

(b) The permeation from the CHSS shall be determined hourly throughout the test.

(c) The test shall continue for 500 hours or until the permeation rate reaches a steady state. Steady state is achieved when at least 3 consecutive leak rates separated by any duration between 12 hours and 48 hours are within 10 percent of the previous rate.

S6.2.5. Test procedures for service terminating performance in fire. The fire test consists of two stages: a localized fire stage followed by an engulfing fire stage. The burner configuration for the fire test is specified in S6.2.5.1. The overall test configuration of the fire test is verified using a pre-test checkout in accordance with S6.2.5.2 prior to the fire test of the CHSS. The fire test of the CHSS is conducted in accordance with S6.2.5.3.

S6.2.5.1. Burner configuration. (a) The fuel for the burner shall be liquefied petroleum gas (LPG).

(b) The width of the burner shall be between 450 millimeters and 550 millimeters.

(c) The length of the burner used for the localized fire stage shall be between 200 millimeters and 300 millimeters.

(d) The length of the burner used for the engulfing fire stage shall be in accordance with S6.2.5.3(m).

(e) The burner nozzle configuration and installation shall be in accordance with table 5 to S6.2.5.1. The nozzles shall be installed uniformly on six rails.

S6.2.5.2. Pre-test checkout. (a) The pre-test checkout procedure in this section shall be performed to verify the fire test configuration for the CHSS tested in accordance with S6.2.5.3.

(b) A pre-test container is a 12-inch Schedule 40 Nominal Pipe Size steel pipe with end caps. The cylindrical length of the pre-test container shall be equal to or longer than the overall length of the CHSS to be tested in S6.2.5.3, but no shorter than 0.80 m and no longer than 1.75 m.

(c) The pre-test container shall be mounted over the burner:

(1) At any height between 95 millimeters and 105 millimeters above the burner;

(2) Such that the nozzles from the two center rails are pointing toward the bottom center of the pre-test container; and

(3) Such that the container's position relative to the localized and engulfing zones of the burner is consistent with the positioning of the CHSS over the burner in S6.2.5.3.

(d) For outdoor test sites, wind shielding shall be used. The separation between the pre-test container and the walls of the wind shields shall be at least 0.5 meters.

(e) Temperatures during the pre-test check-out shall be measured at least once per second using 3.2 millimeter diameter or less K-type sheath thermocouples.

(f) The thermocouples shall be located in sets to measure temperatures along the cylindrical section of the pre-test container. These thermocouples are secured by straps or other mechanical attachments within 5 millimeters from the pre-test container surface. One set of thermocouples consists of:

(1) One thermocouple located at the bottom surface exposed to the burner flame,

(2) One thermocouple located mid-height along the left side of the cylindrical surface,

(3) One thermocouple located mid-height along the right side of the cylindrical surface, and

(4) One thermocouple located at the top surface opposite to the burner flame.

(g) One set of thermocouples shall be centrally located at the localized fire zone of the CHSS to be tested as determined in S6.2.5.3. Two additional sets of thermocouples shall be spread out over the remaining length of the engulfing fire zone of the CHSS to be tested that is not part of the localized fire zone of the CHSS to be tested.

(h) Burner monitor thermocouples shall be located between 20 millimeters and 30 millimeters below the bottom surface of the pre-test container in the same three horizontal locations described in S6.2.5.2(g). These thermocouples shall be mechanically supported to prevent movement.

(i) With the localized burner ignited, the LPG flow rate to the burner shall be set such that the 60-second rolling averages of individual temperature readings in the localized fire zone shall be in accordance with the localized stage row in the table below.

(j) With the entire burner ignited, the LPG flow rate to the burner shall be set such that the 60-second rolling averages of individual temperature readings shall be in accordance with the engulfing stage row in table 6 to S6.2.5.2.

S6.2.5.3. CHSS fire test. (a) The CHSS to be fire tested shall include TPRD vent lines.

(b) The CHSS to be fire tested shall be mounted at any height between 95 millimeters and 105 millimeters above the burner.

(c) CHSS shall be positioned for the localized fire test by orienting the CHSS such that the distance from the center of the localized fire exposure to the TPRD(s) and TPRD sense point(s) is at or near maximum.

(d) When the container is longer than the localized burner, the localized burner shall not extend beyond either end of the container in the CHSS.

(e) The CHSS shall be filled with compressed hydrogen gas to any SOC between 100.0 percent and 105.0 percent.

(f) For outdoor test sites, the same wind shielding shall be used as was used for S6.2.5.2. The separation between the CHSS and the walls of the wind shields shall be at least 0.5 meters.

(g) Burner monitor temperatures shall be measured below the bottom surface of the CHSS in the same positions as specified in S6.2.5.2(h).

(h) The allowable limits for the burner monitor temperatures during the CHSS fire test shall be established based on the results of the pre-test checkout as follows:

(1) The minimum value for the burner monitor temperature during the localized fire stage (TminLOC) shall be calculated by subtracting 50 °C from the 60-second rolling average of the burner monitor temperature in the localized fire zone of the pre-test checkout. If the resultant TminLOC exceeds 600 °C, TminLOC shall be 600 °C.

(2) The minimum value for the burner monitor temperature during the engulfing fire stage (TminENG) shall be calculated by subtracting 50 °C from the 60-second rolling average of the average of the three burner monitor temperatures during the engulfing fire stage of the pre-test checkout. If the resultant TminENG exceeds 800 °C, TminENG shall be 800 °C.

(i) The localized fire stage is initiated by starting the fuel flow to the localized burner and igniting the burner.

(j) The 10-second rolling average of the burner monitor temperature in the localized fire zone shall be at least 300 °C within 1 minute of ignition and for the next 2 minutes.

(k) Within 3 minutes of the igniting the burner, using the same LPG flow rate as S6.2.5.2(i), the 60-second rolling average of the localized zone burner monitor temperature shall be greater than TminLOC as determined in S6.2.5.3(h)(1).

(l) After 10 minutes from igniting the burner, the engulfing fire stage is initiated.

(m) The engulfing fire zone includes the localized fire zone and extends in one direction towards the nearest TPRD or TPRD sense point along the complete length of the container up to a maximum burner length of 1.65 m.

(n) Within 2 minutes of the initiation of the engulfing fire stage, using the same LPG flow rate as S6.2.5.2(j), the 60-second rolling average of the engulfing burner monitor temperature shall be equal or greater than TminENG as determined in S6.2.5.3(h)(2).

(o) The fire testing continues until the pressure inside the CHSS is less than or equal to 1.0 MPa or until:

(1) A total test time of 60 minutes for CHSS on vehicles with a GVWR of 10,000 pounds or less or;

(2) A total test time of 120 minutes for CHSS on vehicles with a GVWR over 10,000 pounds.

S6.2.6. Test procedures for performance durability of closure devices.

S6.2.6.1. TPRD performance tests. Unless otherwise specified, testing is performed with either hydrogen gas with a purity of at least 99.97 percent, less than or equal to 5 parts per million of water, and less or equal to 1 part per million particulate, or with an inert gas. All tests are performed at any temperature between 5.0 °C and 35.0 °C unless otherwise specified.

S6.2.6.1.1. Pressure cycling test. A TPRD undergoes 15,000 internal pressure cycles at a rate not exceeding 10 cycles per minute. The table below summarizes the pressure cycles. Any condition within the ranges specified in table 7 to this section may be selected for testing.

(a) The first 10 pressure cycles shall be from any low pressure of between 1.0 MPa and 2.0 MPa to any high pressure between 150.0 percent NWP and 155.0 percent NWP. These cycles are conducted at any sample temperature between 85.0 °C to 90.0 °C.

(b) The next 2,240 pressure cycles shall be from any low pressure between 1.0 MPa and 2.0 MPa to any high pressure of between 125.0 percent NWP and 130.0 percent NWP. These cycles are conducted at any sample temperature between 85.0 °C to 90.0 °C.

(c) The next 10,000 pressure cycles shall be from any low pressure of between 1.0 MPa and 2.0 MPa to any high pressure between 125.0 percent NWP and 130.0 percent NWP. These cycles are conducted at a sample temperature between 5.0 °C to 35.0 °C.

(d) The final 2,750 pressure cycles shall be from any low pressure between 1.0 MPa and 2.0 MPa to any high pressure between 80.0 percent NWP and 85.0 percent NWP. These cycles are conducted at any sample temperature between −45.0 °C to −40.0 °C.

S6.2.6.1.2. Accelerated life test. (a) Two TPRDs undergo testing; one at the vehicle manufacturer's specified activation temperature, and one at an accelerated life temperature, TL, given in °C using equation 2 to this section, where β = 273.15 °C, TME is 85 °C, and Tf is the vehicle manufacturer's specified activation temperature in °C.:

Equation 2 to § 571.308 S6.2.6.1.2

(b) The TPRDs are placed in an oven or liquid bath maintained within 5.0 °C of the specified temperature per S6.2.6.1.2(a). The TPRD inlets are pressurized with hydrogen to any pressure between 125.0 percent NWP and 130.0 percent NWP and time until activation is measured.

S6.2.6.1.3. Temperature cycling test. (a) An unpressurized TPRD is placed in a cold liquid bath maintained at any temperature between −45.0 °C and −40.0 °C. The TPRD shall remain in the cold bath for any duration not less than 2 hours and not more than 24 hours. The TPRD is removed from the cold bath and transferred, within five minutes of removal, to a hot liquid bath maintained at any temperature between 85.0 °C and 90.0 °C. The TPRD shall remain in the hot bath for any duration not less than 2 hours and not more than 24 hours. The TPRD is removed from the hot bath and, within five minutes of removal, transferred back into the cold bath maintained at any temperature between −45.0 °C and −40.0 °C.

(b) Step (a) is repeated until 15 thermal cycles have been achieved.

(c) The TPRD remains in the cold liquid bath for any duration not less than 2 and not more than 24 additional hours, then the internal pressure of the TPRD is cycled with hydrogen gas from any pressure between 1.0 MPa and 2.0 MPa to any pressure between 80.0 percent NWP and 85.0 percent NWP for 100 cycles. During cycling, the TPRD remains in the cold bath and the cold bath is maintained at any temperature between −45.0 °C and −40.0 °C.

S6.2.6.1.4. Salt corrosion resistance test. (a) Each closure device is exposed to a combination of cyclic conditions of salt solution, temperatures, and humidity. One test cycle is equal to any duration not less than 22 and not more than 26 hours, and is in accordance with table 8 to S6.2.6.1.4.

(b) The apparatus used for this test shall consist of a fog/environmental chamber as defined in ISO 6270-2:2017(E) (incorporated by reference, see § 571.5), with a suitable water supply conforming to Type IV requirements in ASTM D1193-06 (Reapproved 2018) (incorporated by reference, see § 571.5). The chamber shall include a supply of compressed air and one or more nozzles for fog generation. The nozzle or nozzles used for the generation of the fog shall be directed or baffled to minimize any direct impingement on the closure devices.

(c) During “wet-bottom” generated humidity cycles, water droplets shall be visible on the samples.

(d) Steam generated humidity may be used provided the source of water used in generating the steam is free of corrosion inhibitors and visible water droplets are formed on the samples to achieve proper wetness.

(e) The drying stage shall occur in the following environmental conditions: any temperature not less than 60 °C and not greater than 65 °C and relative humidity no more than 30 percent with air circulation.

(f) The impingement force from the salt solution application shall not remove corrosion and/or damage the coatings of the closure devices.

(g) The complex salt solution in percent by mass shall be as specified in S6.2.6.1.4(g)(1) through (5):

(1) Sodium Chloride: not less than 0.08 and not more than 0.10 percent.

(2) Calcium Chloride: not less than 0.095 and not more than 0.105 percent.

(3) Sodium Bicarbonate: not less than 0.07 and not more than 0.08 percent.

(4) Sodium Chloride must be reagent grade or food grade. Calcium Chloride must be reagent grade. Sodium Bicarbonate must be reagent grade. For the purposes of S6.2.6.1.4, water must meet ASTM D1193-06 (Reapproved 2018) Type IV requirements (incorporated by reference, see § 571.5).

(5) Either calcium chloride or sodium bicarbonate material must be dissolved separately in water and added to the solution of the other materials.

(h) The closure devices shall be installed in accordance with the vehicle manufacturer's recommended procedure and exposed to the 100 daily corrosion cycles, with each corrosion cycle in accordance with table 8 to S6.2.6.1.4.

(i) For each salt mist application, the solution shall be sprayed as an atomized mist, using the spray apparatus to mist the components until all areas are thoroughly wet and dripping. Suitable application techniques include using a plastic bottle, or a siphon spray powered by oil-free regulated air to spray the test samples. The quantity of spray applied should be sufficient to visibly rinse away salt accumulation left from previous sprays. Four salt mist applications shall be applied during the ambient stage. The first salt mist application occurs at the beginning of the ambient stage. Each subsequent salt mist application should be applied not less than 90 and not more than 95 minutes after the previous application.

(j) The time from ambient to the wet condition shall be any duration not less than 60 and not more than 65 minutes and the transition time between wet and dry conditions shall be any duration not less than 180 and not more than 190 minutes.

S6.2.6.1.5. Vehicle environment test. (a) The inlet and outlet connections of the closure device are connected or capped in accordance with the vehicle manufacturer's installation instructions. All external surfaces of the closure device are exposed to each of the following fluids for any duration between 24 hours and 26 hours. The temperature during exposure shall be any temperature between 5.0 °C and 35.0 °C. A separate test is performed with each of the fluids sequentially on a single closure device.

(1) Sulfuric acid: not less than 19 and not more than 21 percent by volume in water;

(2) Ethanol/gasoline: not less than 10 and not more than 12 percent by volume ethanol and not less than 88 and not more than 90 percent by volume gasoline; and

(3) Windshield washer fluid: not less than 50 and not more than 52 percent by volume methanol in water.

(b) The fluids are replenished as needed to ensure complete exposure for the duration of the test.

(c) After exposure to each fluid, the closure device is wiped off and rinsed with water.

S6.2.6.1.6. Stress corrosion cracking test. (a) All components exposed to the atmosphere shall be degreased. For check valves and shut-off valves, the closure device shall be disassembled, all components degreased, and then reassembled.

(b) The closure device is continuously exposed to a moist ammonia air mixture maintained in a glass chamber having a glass cover. The exposure lasts any duration not less than 240 hours and not more than 242 hours. The aqueous ammonia shall have a composition of between 19 weight percent and 21 weight percent ammonium hydroxide in water. Aqueous ammonia shall be located at the bottom of the glass chamber below the sample at any volume not less than 20 mL and not more than 22 mL of aqueous ammonia per liter of chamber volume. The bottom of the sample is positioned any distance not less than 30 and not more than 40 millimeters above the aqueous ammonia and supported in an inert tray.

(c) The moist ammonia-air mixture is maintained at atmospheric pressure and any temperature not less than 35 °C and not more than 40 °C.

S6.2.6.1.7. Drop and vibration test. (a) The TPRD is aligned vertically to any one of the six orientations covering the opposing directions of three orthogonal axes: vertical, lateral and longitudinal.

(b) A TPRD is dropped in free fall from any height between 2.00 meters and 2.02 meters onto a smooth concrete surface. The TPRD is allowed to bounce on the concrete surface after the initial impact.

(c) Any sample with damage from the drop that results in the TPRD not being able to be tested in accordance with S6.2.6.1.7(d) shall not proceed to S6.2.6.1.7(d) and shall not be considered a failure of this test.

(d) Each TPRD dropped in S6.2.6.1.7(a) that did not have damage that results in the TPRD not being able to be tested is mounted in a test fixture in accordance with vehicle manufacturer's installation instructions and vibrated for any duration between 30.0 minutes and 35.0 minutes along each of the three orthogonal axes (vertical, lateral and longitudinal) at the most severe resonant frequency for each axis.

(1) The most severe resonant frequency for each axis is determined using any acceleration between 1.50 g and 1.60 g and sweeping through a sinusoidal frequency range from 10 Hz to 500 Hz with any sweep time between 10.0 minutes and 20.0 minutes. The most severe resonant frequency is identified by a pronounced increase in vibration amplitude.

(2) If the resonance frequency is not found, the test shall be conducted at any frequency between 35 Hz and 45 Hz.

S6.2.6.1.8. Leak test. Unless otherwise specified, the TPRD shall be thermally conditioned to the ambient temperature condition, then checked for leakage, then conditioned to the high temperature condition, then checked for leakage, then conditioned to low temperature, then checked for leakage.

(a) The TPRD shall be thermally conditioned at test temperatures in each of the test conditions and held for any duration between 1.0 hour and 24.0 hours. The TPRD is pressurized with hydrogen at the inlet. The required test conditions are:

(1) Ambient temperature: condition the TPRD at any temperature between 5.0 °C and 35.0 °C; test in accordance with S6.2.6.1.8(b) at any pressure between 1.5 MPa and 2.5 MPa and then at any pressure between 125.0 percent NWP and 130.0 percent NWP.

(2) High temperature: condition the TPRD at any temperature between 85.0 °C and 90.0 °C; test in accordance with S6.2.6.1.8(b) at any pressure between 1.5 MPa and 2.5 MPa and then at any pressure between 125.0 percent NWP and 130.0 percent NWP.

(3) Low temperature: condition the TPRD at any temperature between −45.0 °C and −40.0 °C; test in accordance with S6.2.6.1.8(b) at any pressure between 1.5 MPa and 2.5 MPa and then at any pressure between 100.0 percent NWP and 105.0 percent NWP.

(b) Following conditioning at each of the specified test temperature ranges, the TPRD is observed for leakage while immersed in a temperature-controlled liquid at the same specified temperature range for any duration between 1.0 minutes and 2.0 minutes at each of the pressure ranges listed above. If no bubbles are observed for the specified time period, it is not considered a failure. If bubbles are detected, the leak rate is measured.

S6.2.6.1.9. Bench top activation test. (a) The test apparatus consists of either a forced air oven or chimney with air flow. The TPRD is not exposed directly to flame. The TPRD is mounted in the test apparatus according to the vehicle manufacturer's installation instructions.

(b) The temperature of the oven or chimney is at any temperature between 600.0 °C and 605.0 °C for any duration between 2 minutes and 62 minutes prior to inserting the TPRD.

(c) Prior to inserting the TPRD, pressurize the TPRD to any pressure between 1.5 MPa and 2.5 MPa.

(d) The pressurized TPRD is inserted into the oven or chimney, the temperature within the oven or chimney is maintained at any temperature between 600.0 °C and 605.0 °C, and the time for the TPRD to activate is recorded. If the TPRD does not activate within 120 minutes from the time of insertion into the oven or chimney, the TPRD shall be considered to have failed the test.

S6.2.6.1.10. Flow rate test. (a) At least one new TPRD is tested to establish a baseline flow rate.

(b) After activation in accordance with S6.2.6.1.9, and without cleaning, removal of parts, or reconditioning, the TPRD is subjected to flow testing using hydrogen, air or an inert gas;

(c) Flow rate testing is conducted with any inlet pressure between 1.5 MPa and 2.5 MPa. The outlet is at atmospheric pressure.

(d) Flow rate is measured in units of kilograms per minute with a precision of at least 2 significant digits.

S6.2.6.2. Check valve and shut-off valve performance tests. Unless otherwise specified, testing shall be performed with either hydrogen gas with a purity of at least 99.97 percent, less than or equal to 5 parts per million of water, and less than or equal to 1 part per million particulate, or with an inert gas. All tests are performed at any temperature between 5.0 °C and 35.0 °C unless otherwise specified.

S6.2.6.2.1. Hydrostatic strength test. (a) The outlet opening is plugged and valve seats or internal blocks are made to assume the open position.

(b) Any hydrostatic pressure between 250.0 percent NWP and 255.0 percent NWP is applied using water to the valve inlet for any duration between 180.0 seconds and 185.0 seconds. The unit is examined to ensure that burst has not occurred.

(c) The hydrostatic pressure is then increased at a rate of less than or equal to 1.4 MPa/sec until component failure. The hydrostatic pressure at failure is recorded.

S6.2.6.2.2. Leak test. Each unit shall be thermally conditioned to the ambient temperature condition, then checked for leakage, then conditioned to the high temperature condition, then checked for leakage, then conditioned to low temperature, then checked for leakage.

(a) Each unit shall be pressurized to any pressure between 2.0 MPa and 3.0 MPa and held for any duration between 1.0 hours and 24.0 hours in the specified temperature range before testing. The outlet opening is plugged. The test conditions are:

(1) Ambient temperature: condition the unit at any temperature between 5.0 °C and 35.0 °C; test at any pressure between 1.5 MPa and 2.5 MPa and at any pressure between 125.0 percent NWP and 130.0 percent NWP.

(2) High temperature: condition the unit at any temperature between 85.0 °C and 90.0 °C; test at any pressure between 1.5 MPa and 2.5 MPa and at any pressure between 125.0 percent NWP and 130.0 percent NWP.

(3) Low temperature: condition the unit at any temperature between −45.0 °C and −40.0 °C; test at any pressure between 1.5 MPa and 2.5 MPa and at any pressure between 100.0 percent NWP and 105.0 percent NWP.

(b) While within the specified temperature and pressure range, the unit is observed for leakage while immersed in a temperature-controlled liquid held within the same specified temperature range as the test condition for any duration between 1.0 minutes and 2.0 minutes at each of the test pressures. If no bubbles are observed for the specified time period, the sample passes the leak test. If bubbles are detected, the leak rate is measured.

S6.2.6.2.3. Extreme temperature pressure cycling test. (a) The valve unit is connected to a test fixture.

(b) For a check valve, the pressure is applied in six incremental pulses to the check valve inlet with the outlet closed. The pressure is then vented from the check valve inlet. The pressure is lowered on the check valve outlet side to any pressure between 55.0 percent NWP and 60.0 percent NWP prior to the next cycle.

(c) For a shut-off valve, the specified pressure is applied through the inlet port. The shut-off valve is then energized to open the valve and the pressure is reduced to any pressure less than 50 percent of the specified pressure range. The shut-off valve shall then be de-energized to close the valve prior to the next cycle.

S6.2.6.2.4. Chatter flow test. The valve is subjected to between 24.0 hours and 26.0 hours of chatter flow at a flow rate that causes the most valve flutter.

S6.2.6.2.5. Electrical Tests. This section applies to shut-off valves only.

(a) The solenoid valve is connected to a variable DC voltage source, and the solenoid valve is operated as follows:

(1) Held for any duration between 60.0 and 65.0 minutes at any voltage between 0.50 V and 1.5 times the rated voltage.

(2) The voltage is increased to any voltage between 0.5 V to two times the rated voltage, or between 60.0 V and 60.5 V, whichever is less, and held for any duration between 60.0 seconds and 70.0 seconds.

(b) Any voltage between 1,000.0 V DC and 1,010.0 V DC is applied between the power conductor and the component casing for any duration between 2.0 seconds to 4.0 seconds.

S6.2.6.2.6. Vibration test. (a) The valve is pressurized with hydrogen to any pressure between 100.0 percent NWP and 105.0 percent NWP, sealed at both ends, and vibrated for any duration between 30.0 and 35.0 minutes along each of the three orthogonal axes (vertical, lateral and longitudinal) at the most severe resonant frequencies.

(b) The most severe resonant frequencies are determined using any acceleration between 1.50 g and 1.60 g and sweeping through a sinusoidal frequency range from 10 Hz to 500 Hz with any sweep time between 10.0 minutes and 20.0 minutes. The resonance frequency is identified by a pronounced increase in vibration amplitude.

(c) If the resonance frequency is not found, the test shall be conducted at any frequency between 35 Hz and 45 Hz.

[90 FR 6281, Jan. 17, 2025]