40 CFR 90.118 - Certification procedure - service accumulation and usage of deterioration factors.
(2) The period sufficient to stabilize emissions may not exceed 12 hours.
(d) The manufacturer must maintain, and provide to the Administrator if requested, records stating the rationale for selecting a service accumulation period less than 12 hours and records describing the method used to accumulate hours on the test engine(s).
(e) For purposes of establishing whether Phase 2 engines comply with applicable exhaust emission standards or FELs, the test results for each regulated pollutant as measured pursuant to § 90.119 shall be multiplied by the applicable df determined under § 90.104 (g) or (h). The product of the two numbers shall be rounded to the same number of decimal places contained in the applicable standard, and compared against the applicable standard or FEL, as appropriate.