To ensure the needed level of performance by emergency response vehicles, EPA has issued a direct final rule that authorizes manufacturers of engines for these vehicles to install devices that allow vehicle operators to decrease the effectiveness of air pollution control equipment so that vehicle performance will not be compromised during an emergency. Emergency vehicles are defined in the rule as ambulances or fire trucks.

The rule amends EPA’s regulations for heavy-duty diesel engines, which set limits on NOx and PM in vehicle exhaust. To meet the PM standard, manufacturers install diesel particulate filters (DPF) into their engines. DPFs capture and combust non-metallic PM in a process called regeneration. In some DPFs, a successful regeneration depends on drivers modifying the way to drive, for example, by idling or reducing speed. Also, an engine’s computer may limit the vehicle’s speed, torque, and power when a plugged DPF is detected.

NOx emissions in modern heavy duty diesel vehicles are generally controlled with selective catalytic reduction (SCR), whereby a fluid to reduce NOx is injected into the exhaust. When the fluid supply is low, a dashboard light notifies the driver. If the fluid level is not restored, the vehicle’s computer may cut back on speed, torque, and power to induce operators to maintain the SCR.

EPA notes that it has not regulated emissions from emergency vehicles any differently than those from non-emergency vehicles. One existing provision allows for use auxiliary emission control devices (AECD), which will deactivate the emission control devices, but only when deactivation is necessary to protect the vehicle, engine, or emission control system during limited modes of operation. Any other type of mechanism used to disable regulated emission control system is called a defeat device and is prohibited by the CAA and EPA regulations.

But the Agency has been informed by emergency response entities that engine features intended to ensure the proper use and maintenance of DPF and SCR were so limiting the performance of emergency vehicles that an indirect risk to public health and safety was occurring. For example, several fire chief’s informed the Agency that when computers in fire trucks directed the engine to regenerate the DPF, power was diverted from the capacity of the truck to pump water to extinguish a fire.

Accordingly, in the direct final rule, EPA is revising the definition of a defeat device to exclude AECD’s that apply only for engines on emergency vehicles, where the need for an AECD is justified in terms of preventing the vehicle or equipment from loosing speed, torque, or power due to abnormal conditions of the emission control system or in terms of preventing such abnormal condition from occurring during operation related to emergency response.

The Agency is also requiring that engine families sold for installation in an emergency vehicle and equipped with one or more approved emergency vehicle AECDs be labeled as such to ensure that they are installed in emergency vehicles only.

EPA’s direct final rule revising required for heavy duty emergency vehicles was published in the June 8, 2012, FR.