What does Tier 1, 2, 3 or 4 means ?

Background

Tier 1-4 Standards is the United States federal exhaust emissions standards for diesel engines of  heavy equipment which were adopted in 1994 for engines over 37 kW (50 hp). The standard is applicable to all the heavy equipment engine manufacturer namely who signed the Environmental Protection Agency (EPA) regulations for Emissions for Compression-Ignition (Diesel) Engines.

Tier 1-3 Emission Standards

The 1998 heavy equipment  diesel engine regulations were put forward into a  3-tiered progression. Each tier level involved a phase-in (by horsepower rating) over several years. Tier 1 standards were phased-in from 1996 to 2000. The more stringent Tier 2 standards took effect from 2001 to 2006, and yet more stringent Tier 3 standards phased-in from 2006 to 2008,  Tier 3 standards applied only for engines from 37-560 kW.

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