What should you immediately do when a flashback occurs?

When a flashback occurs, the immediate action to take is to shut off the oxygen needle valve. This is crucial because a flashback indicates that the flame has traveled back into the torch and is potentially igniting gas within the torch body or supply lines. By shutting off the oxygen supply first, the oxidizer is removed, which helps to extinguish the flame and prevent further combustion. The oxygen is a key factor in burning, so cutting it off quickly can avert a dangerous situation.

While other actions such as shutting off the acetylene needle valve, closing the torch pressure valve, or turning off the gas supply might also be important to ensure safety and prevent re-ignition, addressing the oxygen source immediately is the most critical step in controlling the flashback and ensuring a rapid response to the emergency.