This part of ISO 22621 specifies a code of practice dealing with polyamide (PA) piping systems, intended to be buried outside buildings and used for the supply of gaseous fuels. It is applicable to mains and service lines, the components of which are prepared for jointing by scraping and/or machining, and gives instructions for the design, storage, handling, transportation, laying conditions and fusion quality control of PA pipes and fittings up to and including 250 mm outside diameter, as well as subsequent joint testing, backfilling, pipe system testing, commissioning and decommissioning. The jointing methods covered by this part of ISO 22621 are butt fusion jointing and electrofusion jointing. No special precautions are necessary for areas exposed to the influence of mining and earthquakes other than those precautions mentioned in this part of ISO 22621.It is the responsibility of users of this part of ISO 22621 to take existing and new national regulations into account.