Page 150 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

A Quick Guide to Welding and Weld Inspection

Permit-to-work
Many companies operate a written permit system for hot
work. The permit details the work to be carried out, how and
when it is to be done, and the precautions to be taken. A
written permit system is likely to result in a higher standard
of care and supervision and must be adhered to.
Tanks and drums
Flammable liquids and vapours such as petrol, diesel, fuel
oil, paints, solvents, glue, lacquer and cleaning agents are
found in many places of work. If welding or thermal cutting
is used on a tank or drum containing a flammable material
the tank or drum can explode violently. People have been
killed and seriously injured by such explosions. Tanks and
drums that are ‘empty’ usually still have residues in the
bottom, and in seams and crevices. Just a teaspoon of
flammable liquid in a drum can be enough to cause an
explosion when heated and turned into vapour.
You must never weld or thermally cut a drum or tank that
has contained or may have contained flammable material
unless you know it has been made safe. If it contains
flammable material, it will need thorough cleaning or inerting
(see the HSE guidance note CS15: The Cleaning and Gas
Freeing of Tanks Containing Flammable Residues). It may be
safer for a specialist company to carry out the work. If in
doubt, ask.

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Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200909QG Welding chap9.3d Page 134 of 134