California Air Resources Board

Potential Amendments to TP-901, Test Procedure for Determining Permeation Emissions from Small Off-Road Engine Fuel Tanks as of June 9, 2020.

This page consists of material released as part of the development process for the Proposed Amendments to the Small Off-Road Engine (SORE) Regulations.

For the Proposed Amendments and other rulemaking documents that the Board will consider for adoption during the public hearing in December 2021, please refer to the SORE rulemaking page.

(Note: The potential amendments are shown in underline to indicate additions and strikeout to indicate deletions from the existing regulatory text.)

Small Off-Road Engine Evaporative Emissions Test Procedure

TP-901

Test Procedure for Determining Permeation Emissions from Small Off-Road Engine Fuel Tanks

Adopted: July 26, 2004

Amended:  September 18, 2017

Amended:  May 6, 2019

Amended: MMMM DD, YYYY

California Environmental Protection Agency

Air Resources Board

Small Off-Road Engine Evaporative Emissions Test Procedure

TP-901

Test Procedure for Determining Permeation Emissions

from Small Off-Road Engine Fuel Tanks

A set of definitions common to all Certification and Test Procedures is in title 13, California Code of Regulations, section 2752 et seq.

For the purpose of this procedure, the term "CARB" refers to the California Air Resources Board, and the term "Executive Officer" refers to the CARB Executive Officer, or his or her authorized representative or designate.

1.  APPLICABILITY

This Test Procedure, TP-901, is used by the Air Resources Board to determine the permeation rate from fuel tanks of spark-ignited small off-road engines and equipment. Small off-road engines (SORE) are defined in title 13, California Code of Regulations (CCR), section 2401 et seq. This Test Procedure is proposed pursuant to Section 43824 of the California Health and Safety Code (CH&SC) and is applicable in all cases where engines or equipment with fuel tanks subject to the permeation emission standard in title 13, Cal. Code Regs., section 2754, 2755 or 2757 are sold, supplied, offered for sale, or manufactured for use in the State of California.

1.1   Requirements to Comply with All Other Applicable Codes and Regulations

Certification of a fuel tank or evaporative emission control system by the Executive Officer does not exempt the fuel tank or evaporative emission control system from compliance with other applicable codes and regulations such as state and federal safety codes and regulations.

1.2  Safety

This test procedure involves the use of flammable materials and shall only be used by or under the supervision of those familiar and experienced in the use of such materials.  Appropriate safety precautions shall be observed at all times while performing this test procedure. 

2.  PRINCIPLE AND SUMMARY OF TEST PROCEDURE

This test procedure uses the corrected daily mass change or reactive organic gas (ROG) emissions measured by a flame ionization detector (FID) of five identical fuel tanks to calculate the permeation rate of each fuel tank.  Prior to permeation testing of the fuel tanks, durability testing and preconditioning are performed.  Durability testing exposes the fuel tanks to pressure and vacuum extremes, ultraviolet radiation, fuel sloshing, and fuel cap installation cycles.  After durability testing, the fuel tanks are filled with fueland allowed to precondition to maximize the permeation emissions.

After preconditioning, the fuel tanks are placed in a temperature-controlled enclosure and exposed to a constant temperature of 40 ± 2 °C.  The permeation rate is determined by one of two methods.  In the first, described in section 11 of this test procedure, the mass change of each fuel tank is measured daily and corrected using an identical reference tank that does not contain fuel to calculate the permeation rate.  In the second, described in section 12 of this test procedure, the ROG emissions from each tank are measured by a FID.

3.  BIASES AND INTERFERENCES

To ensure the losses attributed to permeation are accurately quantified during this test procedure, the tanks must remain exposed to the constant 40 ± 2 °C temperature for each 24-hour (± 30 minutes) period.

Certification test fuel as specified in section 6 of this procedure is required for both preconditioning and testing.

4.  SENSITIVITY AND RANGE

The range of mass measurement of filled tanks is approximately 100 grams to 32,000 grams, depending on tank volume. For mass measurements more than 6200 grams, the minimum sensitivity of the balance must be 0.1 grams.  For mass measurement between 1000 and 6200 grams, the minimum sensitivity of the balance must be 0.01 grams.  For mass measurements less than 1000 grams, the minimum sensitivity of the balance must be 0.001 grams.

5.  EQUIPMENT

(a)       A handheld, thermostatically-controlled, Teflon-coated aluminum hot plate (handheld fusion welder) and coupons of the same material as the tank.  Both the hand held fusion welder and coupons must be of sufficient diameter to completely cover the opening(s) of the tank (optional).

(b)(a)   A balance that meets the requirements of section 4 above.

(c)(b)   A vented enclosure with a temperature conditioning system capable of controlling the internal enclosure air temperature to within ± 2.0 °C over the duration of the test.  Data confirming this performance shall be recorded at a rate no slower than once every 5 minutes.

(d)(c)   A barometric pressure transducer capable of measuring atmospheric pressure to within ± 2.0 millimeters of mercury.

(e)(d)   A temperature instrument capable of measuring ambient temperature to within ± 0.2°C.

(f)(e)    A relative humidity measuring instrument capable of measuring the relative humidity (RH) accurately to within ± 2 percent RH (optional).

(g)(f)    Instrumentation meeting the requirements of section 4 of TP-902, adopted July 26, 2004, and last amended May 6, 2019, (if permeation testing will be performed according to section 12 of this test procedure).

6.  CERTIFICATION TEST FUEL

Testing according to this procedure shall be conducted using 1) LEV III Certification Gasoline as defined in part II, section A.100.3.1.2 of the California 2015 and Subsequent Model Criteria Pollutant Exhaust Emission Standards and Test Procedures and 2017 and Subsequent Model Greenhouse Gas Exhaust Emission Standards and Test Procedures for Passenger Cars, Light Duty Trucks, and Medium-Duty Vehicles, as last amended September 2, 2015, or 2) the gasoline defined in 40 CFR Part 1060.520(e).

The fuel specified in part II, section A.100.3.1.1 of the California 2015 and Subsequent Model Criteria Pollutant Exhaust Emission Standards and Test Procedures and 2017 and Subsequent Model Greenhouse Gas Exhaust Emission Standards and Test Procedures for Passenger Cars, Light Duty Trucks, and Medium-Duty Vehicles, as last amended September 2, 2015, may be used as an alternative test fuel to certify fuel tanks for use on engines and equipment through model year 2019.

7.  CALIBRATION PROCEDURE

All instruments and equipment used in this procedure shall be calibrated at the interval specified by the manufacturer.

The balance listed in section 5(b) shall be calibrated annually per the balance manufacturer’s instructions using National Institute of Standards and Technology (NIST)-traceable mass standards.  The NIST-traceable mass standards shall be calibrated annually by an independent organization.

The instrumentation for measuring permeation emissions according to section 12 of this test procedure must be calibrated as specified in section 4 of TP-902.

8.  DURABILITY DEMONSTRATION

A durability demonstration is required prior to permeation testing.  These durability tests are designed to ensure the fuel tank assembly meets the permeation emission standard throughout the useful life of the equipment.  A durability demonstration consists of the following tests:

8.1  Pressure Test

The Pressure A pressure test shall be performed without fuel and prior to any other portion of the durability demonstration or preconditioning of the fuel tank.  Determine the fuel tank system’s design pressure and vacuum limits under normal operating and storage conditions considering the influence of any associated pressure/vacuum relief components.  To do this, measure the pressure limits using a fuel tank from an evaporative emission control system that is not used for any other portion of this test procedure by installing a pressure transducer in the fuel tank.  The fuel tank used for these pressure measurements shall be identical to those tested in the remainder of this test procedure.  In a 49 ± 3 °C environment with compressed air of no less than 21 °C, pressurize the fuel tank with compressed air to measure the maximum pressure and use a vacuum pump to measure minimum pressure.  Record measurements on the test report.  A pressure test is not required if the fuel tank pressure limits do not exceed gauge pressures of + 1.0 or – 1.0 kPa that persist for at least one minute.

A pressure test shall be performed by sealing each fuel tank and cycling the pressure between + 13.8 and − 3.4 kPa ( + 2.0 and − 0.5 psig) for 10,000 cycles at a rate of 60 seconds per cycle.  If normal operating or storage conditions cause pressure changes greater than + 13.8 or – 3.4 kPa to accumulate in the fuel tanks, cycle the pressure in the fuel tanks between the actual high and low pressure limits experienced during normal operation or storage.  If the fuel tanks have no features that would cause positive or negative pressure to accumulate during normal operation or storage, then a pressure test is not required. The tank pressure test shall be performed in a 49 + 3 °C environment with compressed air of no less than 21 °C.

Tanks that have a secondary operation for drilling holes for insertion of fuel line and grommet system may have these eliminated for purposes of durability and permeation testing.

8.2  Slosh Test

A slosh test shall be performed by filling each fuel tank to 50 percent of its nominal capacity with the fuel specified in section 6 of this procedure and rocking it from an angle deviation of + 15° to −15° from level at a rate of 15 cycles per minute for a total of one million total cycles.  As an alternative to rocking the fuel tank, use a laboratory sample orbital shaker table or similar device to subject the tank to a centripetal acceleration of at least 2.4 meter·second^-2 at a frequency of 2 ± 0.25 cycles per second for one million cycles.  Seal all openings in each fuel tank as they would be sealed when installed on a production engine during slosh testing.  A plug, cap, or coupon may be used to seal any openings to which a hose or tube is normally attached.

8.3 Ultraviolet Radiation Exposure

A sunlight-exposure test shall be performed by exposing each fuel tank to an ultraviolet light of at least 24 W·m^-2 
(0.40 W·hr·m^-2·min^-1) on the tank surface for at least 450 hours. Alternatively, each fuel tank may be exposed to direct natural sunlight for at least 450 daylight hours.  The ultraviolet radiation exposure test may be omitted if no part of the fuel tank, including the filler neck and fuel cap, will be exposed to light when installed on an engine.

8.4  Fuel Cap Installation Cycles

The following test is optional:  Installation cycles shall be performed with fuel caps intended for use with the fuel tanks by putting each fuel cap on and taking it off 300 times. Tighten the fuel cap each time in a way that represents typical usage.

8.5  Fuel Cap and Tether Spill Test

Fill the fuel tank to its nominal capacity with fresh test fuel as specified in Section 6 of this procedure.  Install the fuel cap.  Loosen the fuel cap completely.  Once the fuel cap is completely loosened, remove it and fully extend the tether, if one is used, within 2 seconds.  If no tether is connected to the fuel cap, remove the fuel cap to a height of 15 centimeters above the top of the fill neck within 2 seconds.  Note any dripping, spraying or leaking of fuel from any part of the fuel cap or tether on the test report.  Reinstall the fuel cap.

9.  PRECONDITIONING PROCEDURE

After performing the durability tests, fill each tank to its nominal capacity with the fuel specified in section 6 of this procedure and install a production fuel cap expected to have permeation emissions at least as high as the highest-emitting fuel cap that will be used with fuel tanks from the evaporative family.  Place the tanks in a suitable vented enclosure. Record the preconditioning start date on the data sheet.  Soak the tanks at a temperature that never falls below 38 °C for not less than 140 days. Accelerated preconditioning of the tanks shall not be less than 70 days and can be accomplished by soaking the tanks at an elevated temperature.

Data documenting that permeation emissions from the fuel tanks will not increase with further preconditioning must be provided for tanks soaked less than 140 days as follows:  seal each fuel tank as described in section 10 of this test procedure, and either 1) perform a gravimetric permeation test on each fuel tank as described in section 11 of this procedure, and calculate the coefficient of determination, r², as described in section 11.(a)(8) of this test procedure; or 2) perform two permeation tests with a FID, as described in section 12 of this procedure, on each fuel tank separated by at least 15 days, and calculate the permeation rate as described in section 14.2 of this test procedure.  The coefficient of determination for a gravimetric permeation test used to demonstrate that permeation emissions from the fuel tanks will not increase with further preconditioning must be equal to or greater than 0.95 without any rounding.  The permeation rate measured in the second of two permeation tests with a FID separated by at least 15 days that are used to demonstrate permeation emissions from the fuel tanks will not increase with further preconditioning must be no greater than the permeation rate measured in the first test. Fuel tanks shall continue to be preconditioned at a temperature that never falls below 38 °C between permeation tests.  The time of the durability demonstration in section 8.2 through 8.4 of this procedure may be counted as part of the preconditioning procedure if the ambient temperature remains within the specified temperature range, the same fuel cap is used throughout the durability demonstration and preconditioning period, and each fuel tank is at least 50 percent full; fuel may be added or replaced as needed to conduct the specified durability tests.  Record fuel fill amount and dates on the test report if fuel is added or replaced.  Drain the fuel tank and refill with fresh fuel to nominal capacity fifteen days prior to ending preconditioning.  The tank must not be empty for more than 15 minutes.  Record date and time the tank is emptied and refilled with fresh fuel on the test report.

10.  SEALING PROCEDURE

(a)       After preconditioning, remove the tanks from the enclosure to a well-ventilated area.  Record the preconditioning end date on the data sheet.Remove the cap and empty the tanks.  The tanks must not remain empty for more than fifteen minutes.  Immediately refill each tank to its nominal capacity with the fuel specified in section 6 of this procedure.  Place each unsealed tank in a heated enclosure and allow it to equilibrate to 40 ± 2 °C for a minimum of two hours. After the fuel temperature has equilibrated to 40 ± 2 °C, sealSeal each tank with the same fuel cap used for the durability demonstration and preconditioning procedure or by fusion welding a coupon over the fuel fill neck opening to make a seal.

            If the fuel tank is not sealed using the fuel cap orfusion welding, good engineering practices should be used to seal the tank.  The technique used to seal tanks described in SAE 920164 “Permeation of Gasoline-Alcohol Fuel Blends Through High-Density Polyethylene Fuel Tanks with Different Barrier Technologies” may be used. 

(b)       A reference tank is required to correct for buoyancy effects that may occur during testing only if the fuel tanks will be tested using the gravimetric permeation test in section 11 of this test procedure.  Prepare the reference tank as follows:

(1)       Obtain a sixth identical fuel tank that has not previously contained fuel or any other contents that might affect its mass stability.

(2)       Fill the reference tank with enough glass beads (or other inert material) so the mass of the reference tank is approximately the same as the test fuel tanks greater than the mass of the lightest test fuel tank and less than the mass of the heaviest test fuel tank when filled with fuel. Considering the performance characteristics of the balance to be used, use good engineering judgment as defined in 40 CFR Part 1060.801 to determine how similar the mass of the reference tank needs to be to the mass of the test tank.

(3)       Ensure that the inert material is dry.

(4)       Seal the reference tank in the same manner as the test fuel tanks were sealed.

11.  GRAVIMETRIC PERMEATION TEST

(a)       Perform the following steps to test the fuel tanks for permeation emissions:

(1)       Determine the fuel tank's internal surface area in square-meters, accurate to at least three significant figures.  The tank internal surfaces are those surfaces that are subjected to liquid fuel or fuel vapor under normal operating conditions and have an opposing surface through the wall section that is exposed to the atmosphere.  Internal webs and strengthening structures not in communication with the atmosphere are not considered internal surfaces for the purposes of this testing.

(2)       Weigh each sealed test fuel tank and record the mass, date, relative humidity (optional), barometric pressure, and time on the data sheet (Figure 1) or a similar data sheet. Place the reference tank on the balance and tare it so it reads zerorecord the mass. Place each sealed test fuel tank on the balance and record the difference between the test fuel tank and the reference tank the mass. This value is M₀ for each fuel tank. Take this measurement directly afterwithin 15 minutes of sealing each test fuel tank as specified in section 10 of this procedure.

(3)       Carefully place each fuel tank within a temperature-controlled room or enclosure within 30 minutes of weighing it. Do not spill or add any fuel.

(4)       Close the room or enclosure as needed to control temperatures and record the time. Steps may be taken to prevent an accumulation of hydrocarbon vapors in the room or enclosure that might affect the degree to which fuel permeates through the fuel tanks. This might simply involve passive ventilation to allow fresh air exchanges.

(5)       Ensure that the measured temperature in the room or enclosure stays within the temperature range specified in paragraph (a)(7) of this section.

(6)       Leave the tank in the room or enclosure for the duration of the test run.

(7)       Hold the temperature of the room or enclosure at 40 ± 2 °C; measure and record the temperature at least every five minutes.  Record the time when each fuel tank is removed from the room or enclosure.

(8)       Measure mass loss daily by retaring the balance using the reference tank and weighing each sealed test fuel tank and the reference tank. Record the mass, date, relative humidity (optional), barometric pressure, and time on the data sheet. Calculate the cumulative mass loss in grams for each measurement using the equation in section 14(a) of this procedure. Calculate the coefficient of determination, r², based on a linear plot of cumulative weight loss vs. test days. Use the equation in 40 CFR 1065.602(k), with cumulative weight loss represented by y_i and cumulative time represented by y_ref. The daily measurements must be at approximately the same time each day. Return each fuel tank to the temperature-controlled room or enclosure within 30 minutes of removing it for weighing.  Up to two daily measurements may be omitted in any seven-day period. Test for ten full days, then determine when to stop testing as follows:

(i)         Testing of a fuel tank may be stopped after the measurement on the tenth day if r² is at or above 0.95 or if the measured permeation rate is less than 50 percent of the applicable standard and the upper limit of the 95 percent confidence interval, as calculated in section 14(d) of this procedure, of the mean permeation rate for the fuel tank is below the applicable standard.

(ii)        If, after ten days of testing, r² is below 0.95 and the measured permeation rate is more than 50 percent of the applicable standard or the upper limit of the 95 percent confidence interval of the mean permeation rate for the fuel tank is above the applicable standard, continue testing for a total of 20 days or until r² is at or above 0.95. If r² is not at or above 0.95 within 20 days of testing, discontinue the test and precondition the fuel tank further until it has stabilized permeation emission levels, then repeat the testing.

(9)       RecordCalculate the difference in mass between the reference tank and each test fuel tank for each daily measurement. This value is M_i, where i is a counter representing the number of days elapsed.

(10)     Determine the final permeation rate based on the cumulative mass loss measured on the final day of testing using the equation in section 14(e). Round this result to the same number of decimal places as the emission standard.

12.  PERMEATION TEST WITH FLAME IONIZATION DETECTOR

(a)       Perform the following steps to test each fuel tank for permeation emissions:

(1)       Determine the fuel tank's internal surface area in square-meters, accurate to at least three significant figures.  The tank internal surfaces are those surfaces that are subjected to liquid fuel or fuel vapor under normal operating conditions and have an opposing surface through the wall section that is exposed to the atmosphere.  Internal webs and strengthening structures not in communication with the atmosphere are not considered internal surfaces for the purposes of this testing.

(2)       Place the fuel tank in an enclosure meeting the requirements of section 4 of TP-902 that is equilibrated to 40 ± 2 °C, and close the enclosure within 15 minutes of sealing the fuel tank as specified in section 10 of this procedure.

(3)       Purge the enclosure to reduce the reactive organic gas concentration and perform a 24-hour permeation test at a constant temperature of 40 ± 2 °C.  Measure the reactive organic gas emissions from the fuel tank using a flame ionization detector meeting the requirements of section 4 of TP-902.

13.  RECORDING DATA

Record data on data sheet shown in figure 1 or a similar data sheet.

14.  CALCULATIONS

(a)       The cumulative daily mass loss in grams for each test fuel tank is calculated for each 24-hour cycle as follows:

            cumulative mass loss = M₀ – M_i

Where

M₀       = initial difference in mass between a test fuel tank and the reference tank;

M_i        = difference in mass between a test fuel tank and the reference tank after permeation testing for i days.

(b)       Calculate the daily mass loss as follows:

            daily mass loss = M_i – M_i-1

Where

M_i-1      = difference in mass between a test fuel tank and the reference tank after permeation testing for (i – 1) days.

(c)        Calculate the daily permeation rate, P_i, for a test fuel tank as follows:

            Pi = daily mass loss/(SA∙1 day)

Where

            SA       = the internal surface area of the fuel tank

(d)       Calculate the upper limit of the 95 percent confidence interval for the mean permeation rate of each test fuel tank as follows:

            Upper limit of 95 percent CI = P̅+(ts/N^0.5)

Where

P̅         = mean daily permeation rate for a test fuel tank;

t           = Student’s critical t value for 95 percent confidence (e.g., 2.262 for 10 measurements);

s          = sample standard deviation of the mean,

N         = number of measurements.

(e)       Calculate the final permeation rate, P, for a test fuel tank tested according to section 11 of this test procedure as follows:

            P = cumulative mass loss/(SA∙i)

Where

i           = number of days of permeation testing for a test fuel tank.

(f)        Calculate the permeation rate for a fuel tank tested according to section 12 of this test procedure as described in section 5.5 of TP-902 for diurnal emissions, using the actual test volume of the fuel tank assembly as tested instead of the volume of an engine or equipment unit.

15.  ALTERNATIVE TEST PROCEDURES

Test procedures, other than specified above, shall only be used if prior written approval is obtained from the CARB Executive Officer. In order to secure the CARB Executive Officer's approval of an alternative test procedure, the applicant is responsible for demonstrating to the CARB Executive Officer's satisfaction that the alternative test procedure is equivalent to this test procedure.

16.  FIGURES

Figure 1.  Data Sheet

Tank Manufacturer:   

Tank I.D:        

Tested By:     

Water Bath Test (pass/fail):   

Tank Internal Surface Area (meter²):

Full Tank Data

Wl = (W_if – D_f), D_f = (W_ff + D_e), D_e = (W_ie – W_fe)

Reference Tank Data