This Technical Specification gives guidance for the assessment of conformity of compounds, products, joints and assemblies in accordance with the applicable part(s) of EN 1555 intended to be included in the manufacturer"s quality plan as part of the quality management system and for the establishment of certification procedures. It is recommended that the quality management system conforms to or is no less stringent than the relevant requirements to EN ISO 9001 . NOTE 1 – If certification is involved, the certification and inspection body is preferably compliant with EN 45011 , EN 45012  or EN ISO/IEC 17020 , as applicable. In conjunction with Parts 1 to 5 of EN 1555 (see Foreword), this Technical Specification is applicable to polyethylene (PE) plastics piping systems for the supply of gaseous fuels. It is applicable to PE pipes, fittings, and valves, their joints and to joints with components of other materials intended to be used under the following conditions: a) a maximum operating pressure, MOP, up to and including 10 bar ); b) an operating temperature of 20 °C as reference temperature. NOTE 2 – For other operating temperatures, derating coefficients can be used; see EN 1555-5. For mechanical fittings conforming to ISO 10838-1 , ISO 10838-2  or ISO 10838-3 , as applicable, guidance for assessment of conformity is not given in this part of EN 1555. When requested, a quality plan based on the tests mentioned in ISO 10838-1 , ISO 10838-2  or ISO 10838-3 , as applicable, should be set up in agreement between user and manufacturer. EN 1555 covers a range of maximum operating pressures and gives requirements concerning colours and additives. NOTE 3 – It is the responsibility of the purchaser or specifier to make the appropriate selections from these aspects, taking into account their particular requirements and any relevant national regulations and installation practices or codes.