National Emission Standards for Hazardous Air Pollutants (NESHAP) (US)
The purpose of the NESHAPs regulation is to limit public exposure to hazardous air pollutants known or suspected of causing cancer, and hazardous pollution that have other serious health effects such as birth defects, and which are known or suspected of producing adverse ecological consequences.
In an effort to control as best as possible these hazardous air pollutants, strict pollution control technology standards are enforced for all new air pollution emitting facilities established after 1990. These standards are called Maximum Achievable Control Technology (MACT) standards. A MACT standards is established by EPA on an industry by industry basis through the examination of emissions among the best performing firms/facilities within an industry. The MACT standard is the minimum level of emissions performance allowable. The EPA sets MACT standards separately for existing sources and new sources of air pollution. The EPA may modify MACT standards when it is economically feasible to do so. Economically feasible means that the EPA can require newer air pollution controls that are more effective and efficient when those controls do not pose a financial burden.
The MACT standards is applied either to an individual major source emitter or to an area where several emitters are located. A major source emitter is defined as a facility that emits 10 tons per years of any individual HAP, or which emits 25 tons of a combination of HAPS. The same rule can be applied to a group of facilities that emit HAPs located in an area identified by the US EPA. In the latter case (the area case), an area HAP source is one that emits less than 10 tons per year of any individual HAP, or less than 25 tons of a combination of HAPs.