What causes a flashback in welding?

A flashback in welding primarily results from grossly unequal pressures of gases or a severed hose. When the pressure of the oxygen and acetylene in the hoses is not balanced, it can lead to a situation where the flame travels back into the hoses or the torch. This is particularly dangerous as it can cause the flame to ignite the gases within the hoses, potentially leading to an explosion or severe injury.

Maintaining equal pressures ensures that the gases flow correctly and that the torch operates safely. A severed hose can disrupt the gas flow, causing a sudden drop in pressure that can trigger a flashback. The design of many torches includes flashback arrestors to help prevent this dangerous situation by stopping flames that try to travel backwards into the hoses.

In contrast, while improper torch operation and high temperatures can lead to other hazards, they are not the primary causes of flashbacks. Unequal heating of the gas may affect the welding process, but it does not directly lead to flashbacks as the pressure-related issues do.