Final answer:
Before lighting a gas-fired boiler, it's most important to purge the boiler to reduce flammable gas concentrations. Other steps like checking the water level, fuel valves, and ensuring vents are open are also important but come after purging for safe ignition.
Step-by-step explanation:
The most important step before lighting a gas-fired boiler is to make sure the boiler is purged. Purging ensures that any flammable gas concentrations are reduced, providing a safe environment before ignition. This procedure helps in preventing any potential explosion that could occur if excess gas is ignited. It is also essential to check that vents and chimneys are working properly to maintain a well-ventilated space and to prevent the accumulation of gases.
While all steps listed are important for safe operation, such as ensuring the water level and having all manhole covers shut, checking that fuel valves are ready for start-up, and making sure that steam drum vents are open, the act of purging the boiler is fundamental and precedes other considerations for a secure ignition process. Moreover, when handling equipment associated with boilers or flames, such as Bunsen burners in a laboratory setting, it's critical to be alert and adhere to safety practices, like wearing appropriate protective gear, ensuring good ventilation, and keeping flammable substances away from open flames.