The OAPC specifies two ways in which the requirements on emissions from construction machines can be met. The first is that construction machine manufacturers can provide evidence that their machines comply with the limit levels for particles in accordance with the OAPC. Based on the current status of technology, this is only possible if a particle filter has already been installed at the factory. Alternatively, the requirements of the OAPC can be met by retrofitting a machine with a tested and approved filter system. The Particle Filter List thus consists of two parts:

• a list of particle filter system types with a filtering rate of at least 97%, in particular for ultrafine particles; they have passed a rigourous technical test and are suitable for retrofitting diesel engines of construction machines, other non-road mobile machines and appliances, stationary systems and heavy motor vehicles; 
• a list of engine types which are OAPC conform, i.e. which have been tested with their in-built particle reduction system in accordance with Directive 97/68/EC (so-called original equipment manufacturer (OEM) machines) and have been certified as meeting the requirements of the OAPC.       

The main purpose of these two lists is to provide the authorities responsible for the enforcement of the OAPC with a helpful tool, but they can also be used as a source of information concerning efficient and reliable particle filter systems for the retrofitting of diesel engines. Experience to date has shown that with the right choice and proper maintenance of the particle filter systems included in the FOEN filter list it is possible to find a technically reliable solution for effectively eliminating soot emissions from diesel engines.

Included in the lists are types of particle filter systems and engines which have been issued a certificate of conformity to the effect that they meet the requirements of the Ordinance on Air Pollution Control (OAPC). Both lists are updated regularly.

Engines compliant with the newest European emission regulations for heavy duty (EURO VI) and light duty (EURO 6) vehicles satisfy the requirements on construction machines according to annex 4 section 31 of the OAPC.