Flashbacks and backfires
When welding or flame cutting, the flame could burn back into the blowpipe with a
sharp bang. This means that there has been a flashback.
There are three different types of flashbacks:
1. Limited flashback
2. Backfire
3. Complete flashback
In a limited flashback the flame burns back into the blowpipe causing a typical sharp
bang or several successive bangs while the flame alternately goes out and re-ignites.
In a backfire the flame continues to burn in the blowpipe, which might heat the blowpipe
to a point that some parts of it start to melt. Typically in this type of backfire there
is a whistling noise from the blowpipe and there is also a possibility of smoke coming
out of the blowpipe.
A complete flashback is the most dangerous type of the flashbacks. There is a risk
that the acetylene could start to decompose in the welding hose and even in the acetylene
cylinder or network. (Extremely flammable hydrocarbons, fine carbon and heat
could be generated.)
16. WELDING AND FLAME CUTTING
The nozzle or blowpipe
is defective
The nozzle is
blocked by spatter
The nozzle is
over-heated
The hoses are
leaking
The hoses are
damaged
The hoses have not been
purged well enough before
lighting the blowpipe
The gas flow is not sufficient
(e.g. one of the distribution
valves is closed)
The gas pressures
are wrong
79