CFR > Title 49 - Transportation > SUBTITLE B—Other Regulations Relating to Transportation > CHAPTER V—NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION (Parts 501–599) > PART 571—FEDERAL MOTOR VEHICLE SAFETY STANDARDS > SUBPART B—Federal Motor Vehicle Safety Standards (§571.101 to §571.500) > 571.303—Standard No. 303; Fuel system integrity of compressed natural gas vehicles.

571.303—Standard No. 303; Fuel system integrity of compressed natural gas vehicles.

S1. Scope. This standard specifies requirements for the integrity of motor vehicle fuel systems using compressed natural gas (CNG), including the CNG fuel systems of bi-fuel, dedicated, and dual fuel CNG vehicles.
S2. Purpose. The purpose of this standard is to reduce deaths and injuries occurring from fires that result from fuel leakage during and after motor vehicle crashes.
S3. Application. This standard applies to passenger cars, multipurpose passenger vehicles, trucks and buses that have a gross vehicle weight rating (GVWR) of 10,000 pounds or less and use CNG as a motor fuel. This standard also applies to school buses regardless of weight that use CNG as a motor fuel.
S4. Definitions.
Bi-fuel CNG vehicle means a vehicle equipped with two independent fuel systems, one of which is designed to supply CNG and the second to supply a fuel other than CNG.
CNG fuel container means a container designed to store CNG as motor fuel onboard a motor vehicle.
CNG fuel system means all components used to store or supply CNG to a vehicle's engine.
Dedicated CNG vehicle means a vehicle equipped with one fuel system and designed to operate on CNG.
Dual-fuel CNG vehicle means a vehicle which is fueled by two fuels simultaneously, one of which is CNG and the second is a fuel other than CNG.
High pressure portion of a fuel system means all the components from and including each CNG fuel container up to, but not including, the first pressure regulator.
Service pressure means the internal pressure of a CNG fuel container when filled to design capacity with CNG at 20 °Celsius (68 °Fahrenheit).
S5. General requirements.
S5.1Vehicle requirements.
S5.1.1Vehicles with GVWR of 10,000 pounds or less. Each passenger car, multipurpose passenger vehicle, truck, and bus with a GVWR of 10,000 pounds or less that uses CNG as a motor fuel and that is manufactured on or after September 1, 1995 shall meet the requirements of S6, except S6.4.
S5.1.2Schoolbuses with a GVWR greater than 10,000 pounds. Each schoolbus with a GVWR greater than 10,000 pounds that uses CNG as a motor fuel and that is manufactured on or after September 1, 1995 shall meet the requirements of S6.4.
S5.2Fuel system pressure drop: barrier crash.
(a) For all vehicles, the pressure drop in the high pressure portion of the fuel system, expressed in kiloPascals (kPa), in any fixed or moving barrier crash from vehicle impact through the 60 minute period following cessation of motion shall not exceed:
(1) 1062 kPa (154 psi), or
(2) 895 (T/VFS ); whichever is higher

Code of Federal Regulations

where T is the average temperature of the test gas in degrees Kelvin, stabilized to ambient temperature before testing, where average temperature (T) is calculated by measuring ambient temperature at the start of the test time and then every 15 minutes until the test time of 60 minutes is completed; the sum of the ambient temperatures is then divided by five to yield the average temperature (T); and where VFS is the internal volume in liters of the fuel container and the fuel lines up to the first pressure regulator.
(b) For bi-fuel or dual fuel CNG vehicles, the test requirement in S5.2(a) shall apply to the CNG fuel system, and the test requirement of Standard No. 301 shall apply to the other fuel system, if that standard is applicable.
S5.3Each CNG vehicle shall be permanently labeled, near the vehicle refueling connection, with the information specified in S5.3.1 and S5.3.2 of this section. The information shall be visible to a person standing next to the vehicle during refueling, in English, and in letters and numbers that are not less than 4.76 mm (3/16 inch) high.
S5.3.1The statement: “Service pressure _______________ kPa (______ psig).”
S5.3.2The statement “See instructions on fuel container for inspection and service life.”
S5.4When a motor vehicle is delivered to the first purchaser for purposes other than resale, the manufacturer shall provide the purchaser with a written statement of the information in S5.3.1 and S5.3.2 in the owner's manual, or, if there is no owner's manual, on a one-page document. The information shall be in English and in not less than 10 point type.
S6.Test requirements: fuel system integrity. Each vehicle with a GVWR of 10,000 pounds or less shall meet the requirements of any applicable barrier crash test. A particular vehicle need not meet further requirements after having been subjected to a single barrier crash test.
S6.1Frontal barrier crash. When the vehicle traveling longitudinally forward at any speed up to and including 30 mph impacts a fixed collision barrier that is perpendicular to the line of travel of the vehicle, or at any angle up to 30 degrees in either direction from the perpendicular to the line of travel of the vehicle, with 50th percentile test dummies as specified in part 572 of this chapter at each front outboard designated seating position and at any other position whose protection system is required to be tested by a dummy under the provisions of Standard No. 208, under the applicable conditions of S7, the fuel pressure drop shall not exceed the limits of S5.2.
S6.2Rear moving barrier crash. When the vehicle is impacted from the rear by a barrier moving at any speed up to and including 30 mph, with test dummies as specified in part 572 of this chapter at each front outboard designated seating position, under the applicable conditions of S7, the fuel pressure drop shall not exceed the limits of S5.2.
S6.3Lateral moving barrier crash. When the vehicle is impacted laterally on either side by a barrier moving at any speed up to and including 20 mph with 50th percentile test dummies as specified in part 572 of this chapter at positions required for testing to Standard No. 208, under the applicable conditions of S7, the fuel pressure drop shall not exceed the limits of S5.2.
S6.4Moving contoured barrier crash. When the moving contoured barrier assembly traveling longitudinally forward at any speed up to and including 30 mph impacts the test vehicle (schoolbus with a GVWR exceeding 10,000 pounds) at any point and angle, under the applicable conditions of S7, the fuel pressure drop shall not exceed the limits of S5.2.
S7.Test conditions. The requirements of S5 and S6 shall be met under the following conditions. Where a range of conditions is specified, the vehicle must be capable of meeting the requirements at all points within the range.
S7.1General test conditions. The following conditions apply to all tests.
S7.1.1Each fuel storage container is filled to 100 percent of service pressure with nitrogen, N2. The gas pressure shall stabilize to ambient temperature before testing may be conducted.
S7.1.2After each fuel storage container is filled as specified in S7.1.1, the fuel system other than each fuel storage container is filled with nitrogen, N2, to normal operating pressures. All manual shutoff valves are to be in the open position.
S7.1.3In meeting the requirements of S6.1 through S6.4, if the vehicle has an electrically driven fuel pump that normally runs when the vehicle's electrical system is activated, it is operating at the time of the barrier crash. If the vehicle has any high pressure electric shutoff valve that is normally open when the electrical system is activated, it is open at the time of the barrier crash. Furthermore, if any electric shutoff valve prevents sensing of system pressure by the pressure transducer when closed, it must be open for both the initial pressure measurement and the pressure measurement 60 minutes after the vehicle ceases motion from impact. Any valve shall be open for a period of one minute to equalize the system pressure.
S7.1.4The parking brake is disengaged and the transmission is in neutral, except that in meeting the requirements of S6.4, the parking brake is set.
S7.1.5Tires are inflated to manufacturer's specifications.
S7.1.6The vehicle, including test devices and instrumentation, is loaded as follows:
(a) A passenger car, with its fuel system filled as specified in S7.1.1 and S7.1.2, is loaded to its unloaded vehicle weight plus its rated cargo and luggage capacity weight, secured in the luggage area, plus the necessary test dummies as specified in S6, restrained only by means that are installed in the vehicle for protection at its seating position.
(b) A multipurpose passenger vehicle, truck, or bus with a GVWR of 10,000 pounds or less, whose fuel system is filled as specified in S7.1.1 and S7.1.2, is loaded to its unloaded vehicle weight, plus the necessary test dummies as specified in S6, plus 136.1 kilograms (kg.) (300 pounds (lb.)), or its rated cargo and luggage capacity weight, whichever is less, secured to the vehicle and distributed so that the weight on each axle as measured at the tire-ground interface is in proportion to its GAWR. Each dummy shall be restrained only by means that are installed in the vehicle for protection at its seating position.
(c) A schoolbus with a GVWR greater than 10,000 pounds, whose fuel system is filled as specified in S7.1.1 and S7.1.2, is loaded to its unloaded vehicle weight, plus 54.4 kg. (120 lb.) of unsecured weight at each designated seating position.
S7.1.7The ambient temperature is not to vary more than 5.6 °C (10 °F) during the course of the test.
S7.1.8The pressure drop measurement specified in S5.2 is to be made using a location on the high pressure side of the fuel system in accordance with the vehicle manufacturer's recommendation.
S7.2Lateral moving barrier crash test conditions. The lateral moving barrier crash test conditions are those specified in S8.2 of Standard No. 208, 49 CFR 571.208.
S7.3Rear moving barrier test conditions. The rear moving barrier test conditions are those specified in S8.2 of Standard No. 208, 49 CFR 571.208, except for the positioning of the barrier and the vehicle. The barrier and test vehicle are positioned so that at impact—
(a) The vehicle is at rest in its normal attitude;
(b) The barrier is traveling at any speed up to and including 30 mph with its face perpendicular to the longitudinal centerline of the vehicle; and
(c) A vertical plane through the geometric center of the barrier impact surface and perpendicular to that surface coincides with the longitudinal centerline of the vehicle.
S7.4Moving contoured barrier test conditions. The moving contoured barrier crash test conditions are those specified in S7.5 of Standard No. 301, 49 CFR 571.301.
[59 FR 19659, Apr. 25, 1994; as amended at 60 FR 2543, Jan. 10, 1995; 60 FR 57948, Nov. 24, 1995]