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Emission-Control Overrides for CI Engines in Emergency Situations [US]

On November 6th, 2015, the Environmental Protection Agency (EPA) proposed amendments to the performance standards for Stationary Ignition Internal Combustion Engines, also known as CI engines.

Many new model CI engines from 2014 or 2015 are designed to reduce power and prevent excess air pollutant emissions when routine maintenance is not carried out.  The amendments would allow operators to override the emission-control feature, ensuring the engine remains fully operational in emergency situations.

The proposed rule also requires operators to report situations where they temporarily override the emission-control feature to the CI engine manufacturer.

Pollutants and safety concerns

CI engines, which typically burn diesel to generate electricity, produce air pollutants such as:

  • carbon monoxide (CO)
  • nitrogen oxides (NOx)
  • non-methane hydrocarbons (NMHC)
  • particulate matter (PM)

Many new CI engines have features that shut down the engine when NOx emission-control equipment is not operating.  This raises safety concerns as operators rely on these engines in life-threatening situations, such as when back-up generators are used to restore power to hospitals.

Features of the proposed regulations

These proposed regulations would allow manufacturers to design CI engines with controls that can be removed temporarily in emergency situations to ensure the CI engine remains fully operational.  The EPA is proposing to define a “qualified emergency situation” as one in which “the condition of an engine’s emission controls poses a significant direct or indirect risk to human life.”


The proposed regulations would require operators who override the emission controls to report the incident to the engine manufacturer within 60 days.  Manufacturers would then be required to annually report this information to the EPA.

Operators who purchase engines with this override feature (known as auxiliary emission-control devices or AECDs) would receive manufacturer instructions on how to activate this function and satisfy the criteria detailed in the proposed new performance standards for CI engines.

Public comments

The EPA is accepting public comments on the proposed new source performance standards for stationary compression ignition internal combustion engines until December 21st, 2015 at the Federal eRulemaking Portal:  http://www.regulations.gov

If any member of the public contacts the EPA requesting a public hearing by November 13th, 2015, the hearing will be held on November 23rd, 2015.

Red-on-line EHS Legalist


Proposed Rule: Standards of Performance for Stationary Compression Ignition Internal Combustion Engines, Federal Register, 80 FR 68808, November 6th, 2015.

40 CFR 60, Subpart IIII

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