A spokesperson for the Cruise Lines International Association says other air quality depends on the requirements of the nation where a ship was built.
VOA: special.2009.07.14
Many ship's captains fell in love with the town and built homes there.
VOA: standard.2010.03.15
In 2010, the IMO adopted rules that require any large cruise shipbuilt after July 1 of that year to have a separate, redundant system able to maintain the ship's propulsion, steering and so forth in case one engine is disabled by fire.