safety bulletin #033

SAFETY BULLETIN # 033

SAFETY IN WELDING OR CUTTING (PART 2)

ELECTRICAL CONSIDERATIONSA.ACCEPTABLE VOLTAGE AND THE HUMAN BODY

The voltages of a part of an electrical system which are generally accepted as unlikely to have harmful effects if touched by a person under normal dry conditions are:

42 volts in the case of alternating current, and 110 volts in the case of direct current. With ALTERNATING current welding, the voltage between the electrode holder and the job, is only about 25 volts during welding. However, when there is no load on the welding transformer, the voltage rises to between 70 to 80 volts. Therefore, welding transformers should be equipped with an automatic device which effectively limits the secondary voltage to a maximum of 42 volts if the welding current (arc) is interrupted.

With DIRECT current, welding voltages are normally below 110 volts. Therefore, direct current welding is highly recommended, particularly for work in confined, warm or humid places.

B.GENERAL PRECAUTIONS

It should be realized that electric arc welding cannot be neglected as a potential hazard. Therefore, the following precautions should always be taken:

(1)The welder should wear gloves at all times, and particularly in the "NO LOAD" situation when changing electrodes.

It should be noted that welding gloves are leather (chrome tanned) which, when wet, are good conductors. The use of a quiver is recommended when changing electrodes.

(2)The electrode, electrode holder or cable lug should never be touched. Electrode holders with a completely insulated head should always be used. Uninsulated cable lugs should not be permitted.

(3)If the welder is in close contact with the material being welded (laying on it, inside it, etc.), he should use a wooden cradle when welding in a sitting, supine, or prone position. The cradle should always be dry and not contaminated with flammable products.

NB:

If a welder is in very humid surroundings or in a confined space with metal walls where he has to work in a cramped position and may be perspiring heavily, a large part of his body is in close contact with the metal parts around him, thus forming a conductive connection. In this situation, a fatal current may easily pass through his body if he should accidentally touch part of the electrode holder in a "NO LOAD" condition.

(4)A reliable return cable from the work to the transformer should be fitted.

NB:

Bolted steel structure or flanged pipelines should not be used for return leads as:

The paint between bolted connections will give high resistance resulting in a poor weld.

Sparks may be produced in an area away from the immediate vicinity of the weld which may not be covered by the Work Permit and may not be gas free.

Special consideration should be given to the location and position of the welder. An electric shock may cause him to make a reflex movement from which an accident could result.

C.PORTABLE EQUIPMENT

(1)Service Cables and Connectors

Only approved, insulated connectors of a capacity at least equal to that of the cable should be used to connect or splice one length of cable to another. Where connections are effected by means of cable lugs, these should be fastened together by more than one bolt to give good electrical contact. The exposed metal parts of the lugs should be completely insulated.

It is not normally recommended to use cable clamps.

(2)Return Leads

The return lead should be an integral part of the welding equipment, which should be as close as possible to the work to minimize the length of the lead. However, when welding in tank farm areas, it is normal practice to leave the welding machines in roadways.

NB:

The frame of the welding machine itself should be earthed.

(3)Cable Protection

Cables should be kept out of water and coiled when not in use.

Where traffic lanes have to be crossed, the cable should be protected or run overhead to avoid vehicles running over it.

Page 1 of 2Page 2 of 2