When you ignite a gas stove, you need to "hold" or press and hold the control knob in for a few seconds before the flame ignites for safety reasons. This process is known as "purging the gas line."
The main reason for this safety measure is to ensure that any accumulated gas from a previous attempt to ignite the stove is safely purged before the flame ignites. If there is air in the gas line or if the stove was recently turned off, the gas may have dissipated, leaving the line empty. When you turn on the gas and press the control knob, it allows fresh gas to flow into the gas line.
By holding the control knob for a few seconds, you allow the new gas to replace any air or old gas in the line. This helps prevent the potential risk of a sudden ignition or a flash fire that could occur if the accumulated gas or air mixture ignites all at once. Holding the control knob gives the gas a chance to reach the igniter or pilot light and establish a steady flow before igniting.
Additionally, some gas stoves have a safety feature called a thermocouple or flame sensor. This device detects the presence of a flame. If the thermocouple does not sense a flame after the gas is released, it automatically shuts off the gas supply to prevent the release of unburned gas, which could be dangerous.
By holding the control knob while igniting the stove, you give the thermocouple or flame sensor enough time to register the presence of the flame, ensuring that the gas supply remains open for continued cooking.
Overall, holding the control knob when igniting a gas stove is a simple safety measure to prevent potential hazards associated with gas accumulation and to ensure a safe and reliable ignition process.