(a) This subpart specifies gaseous emission test procedures for Otto-cycle and diesel heavy-duty engines, and particulate emission test procedures for diesel heavy-duty engines.

(b) You may optionally demonstrate compliance with the emission standards of this part by testing hybrid engines and hybrid powertrains using the test procedures in 40 CFR part 1036, rather than testing the engine alone. If you choose this option, you may meet the supplemental emission test (SET) requirements by using the SET duty cycle specified in either § 86.1362 or 40 CFR 1036.510. Except as specified, provisions of this subpart and subpart A of this part that reference engines apply equally to hybrid engines and hybrid powertrains.

(c) The abbreviations and acronyms from subpart A of this part apply to this subpart.

[88 FR 4475, Jan. 24, 2023]

(a) This subpart specifies the equipment and procedures for performing exhaust-emission tests on Otto-cycle and diesel-cycle heavy-duty engines. Subpart A of this part sets forth the emission standards and general testing requirements to comply with EPA certification procedures.

(b) Use the applicable equipment and procedures for spark-ignition or compression-ignition engines in 40 CFR part 1065 to determine whether engines meet the duty-cycle emission standards in subpart A of this part. Measure the emissions of all regulated pollutants as specified in 40 CFR part 1065. Use the duty cycles and procedures specified in §§ 86.1333, 86.1360, and 86.1362. Adjust emission results from engines using aftertreatment technology with infrequent regeneration events as described in § 86.004-28.

(c) The provisions in §§ 86.1370 and 86.1372 apply for determining whether an engine meets the applicable not-to-exceed emission standards.

(d) Measure smoke using the procedures in subpart I of this part for evaluating whether engines meet the smoke standards in subpart A of this part.

(e) Use the fuels specified in 40 CFR part 1065 to perform valid tests, as follows:

(1) For service accumulation, use the test fuel or any commercially available fuel that is representative of the fuel that in-use engines will use.

(2) For diesel-fueled engines, use the ultra low-sulfur diesel fuel specified in 40 CFR part 1065 for emission testing.

(3) For gasoline-fueled engines, use the appropriate E10 fuel specified in 40 CFR part 1065; however, through model year 2021 you may instead use the appropriate E0 fuel specified in 40 CFR part 1065, with the exception that the E0 fuel must have sulfur concentration between 0.0015 and 0.008 weight percent and research octane of at least 93. Starting in model year 2022, you may certify up to 5 percent of your nationwide sales volume of engines certified under subpart A of this part in a given model year based on this E0 test fuel if those engines are certified with carryover data.

(f) You may use special or alternate procedures to the extent we allow them under 40 CFR 1065.10. In addition, for 2010 and earlier model year engines, you may use modified test procedures as needed to conform to the procedures that were specified at the time of emission testing for the model year in question.

(g) This subpart applies to you as a manufacturer, and to anyone who does testing for you.

(h) For testing conducted with engines installed in vehicles, including field testing conducted to measure emissions under Not-To-Exceed test procedures, use the test procedures and equipment specified in 40 CFR part 1065, subpart J.

(i) You may disable any AECDs that have been approved solely for emergency vehicle applications under paragraph (4) of the definition of “Defeat device” in § 86.004-2. The emission standards do not apply when any of these AECDs are active.

[79 FR 23703, Apr. 28, 2014, as amended at 79 FR 46371, Aug. 8, 2014]

(a) Generating transient test cycles. The heavy-duty transient engine cycles for Otto-cycle and diesel engines are listed in appendix I((f) (1), (2) and (3)) to this part. These second-by-second listings represent torque and rpm maneuvers characteristic of heavy-duty engines. Both rpm and torque are normalized (expressed as a percentage of maximum) in these listings.

(1) To unnormalize rpm, use the following equations:

(i) For diesel engines:

Where: Max Test Speed = the maximum test speed as calculated in 40 CFR part 1065.

(ii) For Otto-cycle engines:

Where: Max Test Speed = the maximum test speed as calculated in 40 CFR part 1065.

(2) Torque is normalized to the maximum torque at the rpm listed with it. Therefore, to unnormalize the torque values in the cycle, the maximum torque curve for the engine in question must be used. The generation of the maximum torque curve is described in 40 CFR part 1065.

(b) Example of the unnormalization procedure. Unnormalize the following test point, given Maximum Test speed = 3800 rpm and Curb Idle Speed = 600 rpm.

$$

(1) Calculate actual rpm:

$$

(2) Determine actual torque: Determine the maximum observed torque at 1829 rpm from the maximum torque curve. Then multiply this value (e.g., 358 ft-lbs) by 0.82. This results in an actual torque of 294 ft-lbs.

(c) Clutch operation. Manual transmission engines may be tested with a clutch. If used, the clutch shall be disengaged at all zero percent speeds, zero percent torque points, but may be engaged up to two points preceding a non-zero point, and may be engaged for time segments with zero percent speed and torque points of durations less than four seconds.

(d) Determine idle speeds as specified in 40 CFR 1065.510.

[70 FR 40438, July 13, 2005, as amended at 73 FR 37192, June 30, 2008; 79 FR 23704, Apr. 28, 2014]

The test procedures of this subpart N apply for supplemental emission testing, except as specified otherwise in this section.

(a) Applicability. This section applies to 2007 and later diesel heavy duty engines.

(b) Test cycle. (1) Perform testing as described in § 86.1362 for determining whether an engine meets the applicable standards when measured over the supplemental emission test.

(2) For engines not certified to a NOX standard or FEL less than 1.5 g/bhp-hr, EPA may select, and require the manufacturer to conduct the test using, up to three discrete test points within the control area defined in paragraph (d) of this section. EPA will notify the manufacturer of these supplemental test points in writing in a timely manner before the test. Emission sampling for these discrete test modes must include all regulated pollutants except particulate matter.

(3) For engines certified using the ramped-modal cycle specified in § 86.1362, perform the three discrete test points described in paragraph (b)(2) of this section as follows:

(i) Allow the engine to idle as needed to complete equipment checks following the supplemental emission test described in this section, then operate the engine over the three additional discrete test points.

(ii) Validate the additional discrete test points as a composite test separate from the supplemental emission test, but in the same manner.

(iii) Use the emission data collected during the time interval from 35 to 5 seconds before the end of each mode (excluding transitions) to perform the MAEL calculations in paragraph (f) of this section.

(c) The engine speeds A, B and C, referenced in the table in paragraph (b)(1) of this section, must be determined as follows:

Speed A = nlo + 0.25 × (nhi − nlo) Speed B = nlo + 0.50 × (nhi − nlo) Speed C = nlo + 0.75 × (nhi − nlo) Where: nhi = High speed as determined by calculating 70% of the maximum power. The highest engine speed where this power value occurs on the power curve is defined as nhi. nlo = Low speed as determined by calculating 50% of the maximum power. The lowest engine speed where this power value occurs on the power curve is defined as nlo. Maximum power = the maximum observed power calculated according to the engine mapping procedures defined in 40 CFR 1065.510.

(d) Determining the control area. The control area extends from the engine speed A to C, as defined in paragraph (c) of this section, and extends from 25 to 100 percent load.

(e) [Reserved]

(f) Maximum allowable emission limits. (1) For gaseous emissions, the 12 non-idle test point results and the four-point linear interpolation procedure specified in paragraph (g) of this section for intermediate conditions, shall define Maximum Allowable Emission Limits for purposes of § 86.007-11(a)(3) except as modified under paragraph (f)(3) of this section. Each engine shall have it's own Maximum Allowable Emission Limits generated from the 12 non-idle supplemental steady state test points from that engine. The control area extends from the 25% to the 75% engine speeds, at engine loads of 25% to 100%, as defined in paragraph (d) of this section. Figure 1 of this paragraph (f)(1) depicts a sample Maximum Allowable Emission Limit curve, for illustration purposes only, as follows:

(2) If the weighted average emissions, calculated according to paragraph (e)(6) of this section, for any gaseous pollutant is equal to or lower than required by § 86.007-11(a)(3), each of the 13 test values for that pollutant shall first be multiplied by the ratio of the applicable emission standard (under § 86.007-11(a)(3)) to the weighted average emissions value, and then by 1.10 for interpolation allowance, before determining the Maximum Allowable Emission Limits under paragraph (f)(1) of this section.

(3) If the Maximum Allowable Emission Limit for any point, as calculated under paragraphs (f)(1) and (2) of this section, is greater than the applicable Not-to-Exceed limit (if within the Not-to-Exceed control area defined in § 86.1370(b)), then the Maximum Allowable Emission Limit for that point shall be defined as the applicable Not-to-Exceed limit.

(g) Calculating intermediate test points. (1) For the three test points selected by EPA under paragraph (b)(2) of this section, the emissions must be measured and calculated as described in paragraph (e)(6)(i) of this section (except that n = 1 and WF = 1). The measured values then must be compared to the interpolated values according to paragraph (g)(3) of this section. The interpolated values are determined from the modes of the test cycle closest to the respective test point according to paragraph (g)(2) of this section.

(2) Interpolating emission values from the test cycle. The gaseous emissions for each regulated pollutant for each of the control points (Z) must be interpolated from the four closest modes of the test cycle that envelop the selected control point Z as shown in Figure 2 of this paragraph (g)(2).

(i) For these modes (R, S, T, U), the following definitions apply:

(A) Speed (R) = Speed(T) = nRT.

(B) Speed (S) = Speed(U) = nSU.

(C) Per cent load (R) = Per cent load (S).

(D) Per cent load (T) = Per cent load (U).

(ii) The interpolated value of the brake specific gaseous emissions of the selected control point Z(EZ) must be calculated as follows:

EZ = ERS + (ETU-ERS) * (MZ-MRS) / (MTU-MRS) ETU = ET + (EU-ET) * (nZ-nRT) / (nSU-nRT) ERS = ER + (ES-ER) * (nZ-nRT) / (nSU-nRT) MTU = MT + (MU-MT) * (nZ-nRT) / (nSU-nRT) MRS = MR + (MS-MR) * (nZ-nRT) / (nSU-nRT) Where: ER, ES, ET, EU = for each regulated pollutant, brake specific gaseous emissions of the enveloping modes adjusted according to the factors in(f)(2). MR, MS, MT, MU = engine torque of the enveloping modes. MZ = engine torque of the selected control point Z. nZ = engine speed of the selected control point Z.

(iii) Figure 2 follows:

(3) Comparing calculated and interpolated emission values. The measured brake specific gaseous emissions of the control point Z (XZ) must be less than or equal to the interpolated value (EZ).

[65 FR 59958, Oct. 6, 2000, as amended at 66 FR 5188, Jan. 18, 2001; 70 FR 40439, July 13, 2005; 71 FR 51487, Aug. 30, 2006; 73 FR 37192, June 30, 2008. Redesignated and amended at 79 FR 23704, Apr. 28, 2014]

(a) This section describes how to test engines under steady-state conditions. Perform ramped-modal testing as described in 40 CFR 1036.505 and 40 CFR part 1065, except as specified in this section.

(b) Measure emissions by testing the engine on a dynamometer with the following ramped-modal duty cycle to determine whether it meets the applicable steady-state emission standards in this part and 40 CFR part 1036:

[86 FR 34367, June 29, 2021, as amended at 88 FR 4476, Jan. 24, 2023]

(a) General. The purpose of this test procedure is to measure in-use emissions of heavy-duty diesel engines while operating within a broad range of speed and load points (the Not-To-Exceed Control Area) and under conditions which can reasonably be expected to be encountered in normal vehicle operation and use. Emission results from this test procedure are to be compared to the Not-To-Exceed Limits specified in § 86.007-11(a)(4), or to later Not-To-Exceed Limits. The Not-To-Exceed Limits do not apply for engine-starting conditions. Tests conducted using the procedures specified in this subpart are considered valid Not-To-Exceed tests (Note: duty cycles and limits on ambient conditions do not apply for Not-To-Exceed tests).

(b) Not-to-exceed control area for diesel heavy-duty engines. The Not-To-Exceed Control Area for diesel heavy-duty engines consists of the following engine speed and load points:

(1) All operating speeds greater than the speed calculated using the following formula, where nhi and nlo are determined according to the provisions in § 86.1360(c):

nlo + 0.15 × (nhi-nlo)

(2) All engine load points greater than or equal to 30% or more of the maximum torque value produced by the engine.

(3) Notwithstanding the provisions of paragraphs (b)(1) and (2) of this section, all operating speed and load points with brake specific fuel consumption (BSFC) values within 5% of the minimum BSFC value of the engine. For the purposes of this requirement, BFSC must be calculated under the general test cell conditions specified in 40 CFR part 1065. The manufacturer may petition the Administrator at certification to exclude such points if the manufacturer can demonstrate that the engine is not expected to operate at such points in normal vehicle operation and use. Engines equipped with drivelines with multi-speed manual transmissions or automatic transmissions with a finite number of gears are not subject to the requirements of this paragraph (b)(3).

(4) Notwithstanding the provisions of paragraphs (b)(1) through (b)(3) of this section, speed and load points below 30% of the maximum power value produced by the engine shall be excluded from the Not-To-Exceed Control Area for all emissions.

(5) [Reserved]

(6)(i) For petroleum-fueled diesel cycle engines, the manufacturer may identify particular engine-vehicle combinations and may petition the Administrator at certification to exclude operating points from the Not-to-Exceed Control Area defined in paragraphs (b)(1) through (5) of this section if the manufacturer can demonstrate that the engine is not capable of operating at such points when used in the specified engine-vehicle combination(s).

(ii) For diesel cycle engines that are not petroleum-fueled, the manufacturer may petition the Administrator at certification to exclude operating points from the Not-to-Exceed Control Area defined in paragraphs (b)(1) through (5) of this section if the manufacturer can demonstrate that the engine is not expected to operate at such points in normal vehicle operation and use.

(7) Manufacturers may petition the Administrator to limit NTE testing in a single defined region of speeds and loads. Such a defined region must generally be of elliptical or rectangular shape, and must share some portion of its boundary with the outside limits of the NTE zone. Under this provision testing would not be allowed with sampling periods in which operation within that region constitutes more than 5.0 percent of the time-weighted operation within the sampling period. Approval of this limit by the Administrator is contingent on the manufacturer satisfactorily demonstrating that operation at the speeds and loads within that region accounts for less than 5.0 percent of all in-use operation (weighted by vehicle-miles-traveled or other EPA-approved weightings) for the in-use engines of that configuration (or sufficiently similar engines). At a minimum, this demonstration must include operational data from representative in-use vehicles.

(c) [Reserved]

(d) Not-to-exceed control area limits. (1) When operated within the Not-To-Exceed Control Area defined in paragraph (b) of this section, diesel engine emissions shall not exceed the applicable Not-To-Exceed Limits specified in § 86.007-11(a)(4) when averaged over any time period greater than or equal to 30 seconds, except where a longer minimum averaging period is required by paragraph (d)(2) of this section.

(2) For engines equipped with emission controls that include discrete regeneration events and that send a recordable electronic signal indicating the start and end of the regeneration event, determine the minimum averaging period for each NTE event that includes regeneration active operation as described in paragraph (d)(2)(i) of this section. This minimum averaging period is used to determine whether the individual NTE event is a valid NTE event. For engines equipped with emission controls that include multiple discrete regeneration events (e.g., de-soot, de-NOX, de-SOX, etc.) and associated electronic signals, if an NTE event includes regeneration active operation on multiple regeneration signals, determine the minimum averaging period for each regeneration signal according to paragraph (d)(2)(i) of this section and use the longest period. This minimum averaging period applies if it is longer than 30 seconds. The electronic signal from the engine's ECU must indicate non-regeneration and regeneration operation. Regeneration operation may be further divided into regeneration pending and regeneration active operation. These are referred to as states 0, 1, and 2 for non-regeneration, regeneration pending, and regeneration active operation, respectively. No further subdivision of these states are allowed for use in this paragraph (d)(2). Where the electronic signal does not differentiate between regeneration pending and active operation, take the regeneration signal to mean regeneration active operation (state 2). A complete non-regeneration event is a time period that occurs during the course of the shift-day that is bracketed by regeneration operation, which is either regeneration active operation (state 2) or regeneration pending operation (state 1). A complete regeneration event is a time period that occurs during the course of the shift-day that is bracketed before and after by non-regeneration operation (state 0); a complete regeneration event includes any time in the event where regeneration is pending (state 1). The following figure provides an example of regeneration events during a shift-day:

(i) Calculate the minimum averaging period, tNTE,min, for each candidate NTE event as follows:

$$ Where: i = an indexing variable that represents periods of time within the candidate NTE event where the electronic signal indicates regeneration active operation (state 2). N = the number of periods of time within the candidate NTE event where the electronic signal indicates regeneration active operation (state 2). t2,NTE,i = the duration of the i-th time period within the candidate NTE event where the electronic signal indicates regeneration active operation (state 2), in seconds. RF = regeneration fraction over the course of the shift-day, as determined in paragraph (d)(2)(ii) of this section.

(ii) Calculate the regeneration fraction, RF, over the course of a shift-day as follows:

$$ Where: i = an indexing variable that represents complete regeneration events within the shift-day. j = an indexing variable that represents periods of time within the i-th complete regeneration event where the electronic signal indicates regeneration active operation (state 2). k = an indexing variable that represents complete non-regeneration events within the shift-day. N0 = the number of complete non-regeneration events within the shift-day. N12 = the number of complete regeneration events within the shift-day. N2,i = the number of periods of within the i-th complete regeneration event where the electronic signal indicates regeneration active operation (state 2). t0,k = the duration of the k-th complete non-regeneration event within the shift-day, in seconds. t12,i = the duration of the i-th complete regeneration event within the shift-day, in seconds, including time in those events where regeneration is pending (state 1). t2,i,j = the duration of the j-th time period within the i-th complete regeneration event where the electronic signal indicates regeneration active operation (state 2), in seconds. Note that this excludes time in each complete regeneration event where regeneration is pending (state 1).

(iii) If either N0 or N12 are zero, then RF cannot be calculated and all candidate NTE events that include regeneration active operation are void.

(iv) Compare the minimum averaging period for the candidate NTE event, tNTE,min, to the actual NTE duration, tNTE. If tNTE <tNTE,min the candidate NTE event is void. If tNTE ≥tNTE,min the candidate NTE event is valid. It can also therefore be included in the overall determination of vehicle-pass ratio according to § 86.1912.

(v) You may choose to not void emission results for a candidate NTE event even though we allow you to void the NTE event under paragraph (d)(2)(iii) or (iv) of this section. If you choose this option, you must include the results for all regulated pollutants that were measured and validated during the NTE event for a given NTE monitoring system.

(vi)(A) The following is an example of calculating the minimum averaging period, tNTE,min, for a candidate NTE event. See Figure 1 of this section for an illustration of the terms to calculate the regeneration fraction, RF. For this example there are three complete non-regeneration events and two complete regeneration events in the shift-day.

N0 = 3 N12 = 2

(B) The duration of the three complete non-regeneration events within the shift-day are:

t0,1 = 5424 s t0,2 = 6676 s t0,3 = 3079 s

(C) The sums of all the regeneration active periods in the two complete regeneration events are:

$$

(D) The duration of each of the two complete regeneration events within the shift-day are:

t12,1 = 8440 s t12,2 = 3920 s

(E) The RF for this shift-day is:

$$

(F) For this example, consider a candidate NTE event where there are two periods of regeneration active operation (state 2).

t2,NTE,1 = 37 s t2,NTE,2 = 40 s

(G) The minimum averaging period for this candidate NTE event is:

$$ tNTE,min = 320.0 s

(e) Ambient corrections. The measured data shall be corrected based on the ambient conditions under which it was taken, as specified in this section.

(1) For engines operating within the ambient conditions specified in § 86.007-11(a)(4)(ii)(a):

(i) NOX emissions shall be corrected for ambient air humidity to a standard humidity level of 50 grains (7.14 g/kg) if the humidity of the intake air was below 50 grains, or to 75 grains (10.71 g/kg) if above 75 grains.

(ii) NOX and PM emissions shall be corrected for ambient air temperature to a temperature of 55 degrees F (12.8 degrees C) for ambient air temperatures below 55 degrees F or to 95 degrees F (35.0 degrees C) if the ambient air temperature is above 95 degrees F.

(iii) No ambient air temperature or humidity correction factors shall be used within the ranges of 50-75 grains or 55-95 degrees F.

(iv) Where test conditions require such correction factors, the manufacturer must use good engineering judgement and generally accepted engineering practice to determine the appropriate correction factors, subject to EPA review.

(2) For engines operating within the ambient conditions specified in § 86.007-11(a)(4)(ii)(b):

(i) NOX emissions shall be corrected for ambient air humidity to a standard humidity level of 50 grains (7.14 g/kg) if the humidity of the intake air was below 50 grains, or to 75 grains (10.71 g/kg) if above 75 grains.

(ii) NOX and PM emissions shall be corrected for ambient air temperature to a temperature of 55 degrees F (12.8 degrees C) for ambient air temperatures below 55 degrees F.

(iii) No ambient air temperature or humidity correction factors shall be used within the ranges of 50-75 grains or for temperatures greater than or equal to 55 degrees F.

(iv) Where test conditions require such correction factors, the manufacturer must use good engineering judgement and generally accepted engineering practice to determine the appropriate correction factors, subject to EPA review.

(f) NTE cold temperature operating exclusion. Engines equipped with exhaust gas recirculation (EGR) whose operation within the NTE control area specified in paragraph (b) of this section when operating during cold temperature conditions as specified in paragraph (f)(1) of this section are not subject to the NTE emission limits during the specified cold temperature conditions.

(1) Cold temperature operation is defined as engine operating conditions meeting either of the following two criteria:

(i) Intake manifold temperature (IMT) less than or equal to the temperature defined by the following relationship between IMT and absolute intake manifold pressure (IMP) for the corresponding IMP:

$$ Where: P = absolute intake manifold pressure in bars. IMT = intake manifold temperature in degrees Fahrenheit.

(ii) Engine coolant temperature (ECT) less than or equal to the temperature defined by the following relationship between ECT and absolute intake manifold pressure (IMP) for the corresponding IMP:

$$ Where: P = absolute intake manifold pressure in bars. ECT = engine coolant temperature in degrees Fahrenheit.

(2) [Reserved]

(g) You may exclude emission data based on catalytic aftertreatment temperatures as follows:

(1) For an engine equipped with a catalytic NOX aftertreatment system, exclude NOX emission data that is collected when the exhaust temperature at any time during the NTE event is less than 250 °C.

(2) For an engine equipped with an oxidizing catalytic aftertreatment system, exclude NMHC and CO emission data that is collected if the exhaust temperature is less than 250 °C at any time during the NTE event.

(3) Using good engineering judgment, measure exhaust temperature within 30 cm downstream of the last applicable catalytic aftertreatment device. Where there are parallel paths, use good engineering judgment to measure the temperature within 30 cm downstream of the last applicable catalytic aftertreatment device in the path with the greatest exhaust flow.

(h) Any emission measurements corresponding to engine operating conditions that do not qualify as a valid NTE sampling event may be excluded from the determination of the vehicle-pass ratio specified in § 86.1912 for the specific pollutant.

(i) Start emission sampling at the beginning of each valid NTE sampling event, except as needed to allow for zeroing or conditioning the PEMS. For gaseous emissions, PEMS preparation must be complete for all analyzers before starting emission sampling.

(j) Emergency vehicle AECDs. If your engine family includes engines with one or more approved AECDs for emergency vehicle applications under paragraph (4) of the definition of “defeat device” in § 86.1803, the NTE emission limits do not apply when any of these AECDs are active. apply when any of these AECDs are active.

[65 FR 59961, Oct. 6, 2000, as amended at 66 FR 5188, Jan. 18, 2001; 70 FR 40441, July 13, 2005; 75 FR 68457, Nov. 8, 2010; 77 FR 34146, June 8, 2012. Redesignated and amended at 79 FR 23705, Apr. 28, 2014; 81 FR 73982, Oct. 25, 2016]

This section contains the measurement techniques to be used for determining compliance with the filter smoke limit or opacity limits in § 86.007-11(b)(1)(iv).

(a) For steady-state or transient smoke testing using full-flow opacimeters, use equipment meeting the requirements of 40 CFR part 1065, subpart L.

(1) All full-flow opacimeter measurements shall be reported as the equivalent percent opacity for a five inch effective optical path length using the Beer-Lambert relationship.

(2) Zero and full-scale (100 percent opacity) span shall be adjusted prior to testing.

(3) Post test zero and full scale span checks shall be performed. For valid tests, zero and span drift between the pre-test and post-test checks shall be less than two percent of full-scale.

(4) Opacimeter calibration and linearity checks shall be performed using manufacturer's recommendations or good engineering practice.

(b) For steady-state testing using a filter-type smokemeter, equipment meeting the requirements of ISO/FDIS-10054 “Internal combustion compression-ignition engines—Measurement apparatus for smoke from engines operating under steady-state conditions—Filter-type smokemeter” is recommended. Other equipment may be used provided it is approved in advance by the Administrator.

(1) All filter-type smokemeter results shall be reported as a filter smoke number (FSN) that is similar to the Bosch smoke number (BSN) scale.

(2) Filter-type smokemeters shall be calibrated every 90 days using manufacturer's recommended practices or good engineering practice.

(c) For steady-state testing using a partial-flow opacimeter, equipment meeting the requirements of ISO-8178-3 and ISO/DIS-11614 is recommended. Other equipment may be used provided it is approved in advance by the Administrator.

(1) All partial-flow opacimeter measurements shall be reported as the equivalent percent opacity for a five inch effective optical path length using the Beer-Lambert relationship.

(2) Zero and full scale (100 percent opacity) span shall be adjusted prior to testing.

(3) Post-test zero and full scale span checks shall be performed. For valid tests, zero and span drift between the pre-test and post-test checks shall be less than two percent of full scale.

(4) Opacimeter calibration and linearity checks shall be performed using manufacturer's recommendations or good engineering practice.

(d) Replicate smoke tests may be run to improve confidence in a single test or stabilization. If replicate tests are run, three additional tests which confirm to this section shall be run, and the final reported test results must be the average of all the valid tests.

(e) A minimum of thirty seconds sampling time shall be used for average transient smoke measurements. The opacity values used for this averaging must be collected at a minimum rate of 1 data point per second, and all data points used in the averaging must be equally spaced in time.

[65 FR 59962, Oct. 6, 2000. Redesignated at 79 FR 23706, Apr. 28, 2014; 88 FR 4478, Jan. 24, 2023]