Welding operations have been the cause of numerous serious fires over the years. Many serious accidents have been caused by cutting or welding being performed on closed drums, tanks or other receptacles containing flammable vapours. A most unusual accident is on record concerning the explosion of a drum which was known to be entirely gas free, having been used to carry water for some time. Investigation revealed that the drum was being used as a stand during welding operations and when the operator first opened the acetylene valve sufficient acetylene entered the drum through the open bung hole to provide an explosive concentration which ignited when the torch was lit.
Another case is on record of a welder standing on an empty petrol drum on the sixth floor of a building under construction. The sparks from the torch fell into the drum causing it to explode, hurling the operator to his death.
It has been argued that fires caused through welding operations receive undue publicity due to the fact that they are invariably known causes as against most other large loss fires that occur the causes of which are generally listed as undetermined. Whilst this may be the case it must also be obvious that such fires are without doubt the result of carelessness or neglect.
Contributory factors
A study of reports received over the years show that the following factors contributed towards fires caused by cutting or welding:
1. Contractors who are unfamiliar with the premises and hazards which may exist often do not exercise the same degree of caution as would plant personnel.
2. Welding visors or goggles prevent the operator from seeing where sparks may fall.
3. Failure to remove or cover combustible goods in the vicinity of welding or cutting operations.
4. Failure to check for combustible materials on the reverse side of the object being welded. (A large ocean liner was burnt out and capsized when welding being carried out on a steel bulkhead ignited kapok lifebelts in an adjoining cabin).
5. The absence of fire-fighting equipment in the vicinity of the welding operations.
Precautionary measures
Every factory should have a person designated as being responsible for ensuring that hazardous activities of this nature are carried out under strict supervision. This should include a suitable hot work permit system. The following general precautions should be observed:
1. The welding appliance should not be removed from the workshop area to the other parts of the factory without the permission of the designated official. This official should ensure that precautionary measures are observed.
2. The area where hot work is to be carried out should be inspected.
3. All combustible material in the vicinity is either removed, damped down or suitably protected. A check should be carried out for any openings or cracks below the working area which may cause sparks to ignite materials at lower levels.
4. Outside contractors should be given strict instructions as to the procedures to be adopted and particularly hazardous areas should be pointed out to them.
5. Fire extinguishers and hose-reels should be provided near the site of welding or cutting operations and operators should be experienced in the handling of such equipment.
6. When welding or cutting operations are carried out in particularly hazardous areas it is advisable to have a person standing by with a fire extinguisher.
7. A small fire extinguisher, possibly of the dry powder type, should be fitted to the welding trolley itself.
8. Leaking tubing, badly fitting valves and regulators and loose connections are all sources of danger and the cause of many fires. Regular maintenance of equipment is essential.
9. Empty drums which have contained flammable liquids should not be stored in the vicinity of welding or cutting operations.
10. Empty containers which have held flammable liquids should be thoroughly degassed, preferably by the application of steam, if they are to be welded or cut.
11. Buildings in which welding or cutting operations are carried out should be well ventilated in order that flammable or explosive gases and vapours may not accumulate.
Maintenance of welding equipment
All welding equipment should be kept clean and in good working order and should be regularly inspected. Rubber hoses should be red for acetylene and black for oxygen and should be checked for cuts, cracks, burns and worn parts. Copper alloys of high copper content react with acetylene to form an explosive compound (cuprous acetylide), and tubing of these metals should not, therefore, be used for acetylene.
Hot work permit
It is recommended that no cutting, welding or other hot work be carried out on factory premises unless the operator has received a clearance in the form of a certificate which must be signed by the responsible official.
Reference: Fire Protection Association of Southern Africa.
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