1 Memorize these steps: (1) Shut the cylinder or mains gas valve immediately. (2) Open windows and doors — ventilation is the most important step. (3) Do not switch anything electrical on OR off — even a light switch; the tiny spark inside it is enough. (4) No lighters or open flames, obviously. (5) Leave the room and call us on 16062 from outside. If the smell is strong and widespread, call the national gas emergency line (129) first, then us.