745 Welding, Cutting, and Brazing Safety

Backfire and Flashback

Unless the system is thoroughly purged of air and all connections in the system are tight before the torch is ignited, the flame is likely to bum inside the torch instead of outside the tip. The difference between the two terms backfire and flashback is this:

Backfire

In a backfire, there is a momentary burning back of the flame into the torch tip. A backfire is characterized by a loud snap or pop as the flame goes out. A backfire is less serious. Usually you can light the flame again without difficulty. If backfiring continues whenever the torch is lit, check for these causes:

• overheated tip,
• gas working pressures greater than that recommended for the tip size being used,
• loose tip, or
• dirt on the torch tip seat.

Flashback

A hissing or squealing sound usually accompanies a flashback. At the same time, the flame at the tip becomes smoky and sharp pointed. A flashback can have the same causes as a backfire.

It may also indicate improper handling or something radically wrong either with the torch, such as a distorted or cracked torch head. When a flashback occurs, immediately shut off the torch oxygen valve and then close the acetylene valve.

You can stop the flashback at once if you close the oxygen valve immediately.

In most instances, backfires and flashbacks result from carelessness. You can avoid these difficulties by making certain that:

• all connections in the system are clean and tight;
• torch valves are closed (not open or merely loosely closed) when the equipment is stowed;
• the oxygen and acetylene working pressures used are those recommended for the torch employed; and
• the system is purged of air before the apparatus is used.

Purging the system of air is especially necessary when you incorporate the newly connected hose and torch, or a new cylinder, into the system.

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