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Understanding Manufacturer Generator Allowances and Tiered EPA Emission Standards



Non-road compression-ignition engines, or diesel generators, are common emission sources utilized for electrical generation in a variety of industries. For purposes of emissions, the model year of the specific unit and the power rating (kW) are the two primary factors driving the exhaust emission standards for VOC, NOx, and CO. The emission standards were developed by the US EPA using a tiered approach. Manufacturers of the units are required to meet the specific Tier 1/2/3/4 emission standards based on the type of unit and power rating group.


Every now and again, you will come across a generator whose model year does not necessarily match a given tier on the approved EPA standards for one of several reasons. For example, we recently came across a generator that was manufactured in 2018 and was assumed to in compliance with Tier 4 emission standards based on the EPA standards. However, on the engine plate/sticker, there was a note saying that the generator was certified under 40 CFR 1039.625, which is an exemption for manufacturers.

40 CFR 1039.625 provides a “phase-in” allowance based on the number of engines produced by a company and based on the country the engines were manufactured in. In this specific instance, the manufacturer certified the unit met US EPA emission standards under 40 CFR §1039.625 and was a US EPA Tier 3 Engine.


When identifying the correct Tier for a nonroad compression-ignition engine, it is critical to complete your due diligence and not assume the emission factors are solely based on model year and the rated power. This could be overlooked quite easily, and if permitted incorrectly as Tier 4 when the unit is only meeting Tier 3 standards, the compliance demonstration could prove difficult once discovered, especially in urban and non-attainment regions.

Diesel Tier 1 2 3
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Source 1: e-CFR Electronic Code of Federal Regulations

Source 2: e-CFR Electronic Code of Federal Regulations


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