line. Do not store nylon line in strong sunlight. Cover it with tarpaulins.

As a final precaution, line should NEVER be exposed to lime, acids, or other chemicals, or even stored in a room containing chemicals. Even the fumes may severely damage the line.

Overloading a line poses a serious safety threat to personnel It is also likely to result in heavy losses through damage to material and equipment. To avoid overloading, you must know the strength of the line with which you are working. This involves three factors: breaking strength, safe working load, and safety factor.

The term breaking strengfh refers to the tension at which the line will break apart when an additional load is applied. The breaking strength of the various lines has been determined through tests made by line manufacturers, and tables have been established to provide this information. In the absence of a manufacturer's table, a rule of thumb for finding the breaking strength of manila line is as follows:

C squared x 900 = BS

In this rule, C = circumference in inches and BS = breaking strength in pounds. The circumference is squared and the figure obtained is then multiplied by 900 to find BS. With a 3-inch line, for example, you will get a BS of 8,100 pounds. This was figured as follows:

3 x 3 x 900 = 8,100 lb

When the line is measured in centimeters, the breaking strength can be figured in kilograms. The same equation is used with only the constant being changed to 64.8 (vice 900). The breaking strength in kilograms is figured as follows:

7.5 cm x 7.5 cm x 64.8 = 3,645 kg

The breaking strength of manila line is higher than that of an equal-size sisal line. This is because of the difference in strength of the two fibers. The fiber from which a particular line is constructed has a definite bearing on its breaking strength.

Briefly defined, the safe working load of a line is the load that can be applied without causing damage to the line. Remember that the safe working load of a line is considerably less than the breaking strength. A wide margin of difference between breaking strength and safe working load is necessary to allow for such factors as additional strain imposed on the line by jerky movements in hoisting or bending over sheaves in a pulley block

You may not always have a chart available to tell you the safe working load for a particular size line. Fortunately, there is a rule of thumb with which you can determine the safe working load (SWL).

SWL = C squared x 150

SWL = the safe working load in pounds

C = the circumference of the line in inches

To determine the SWL, simply take the circumference of the line, square it, and then multiply by 150. For example, for a 3-inch line, here is how the rule works:

3 x 3 x 150= 1,350 lb

Thus the safe working load of a 3-inch line is 1,350 pounds.

In the metric system, the rule is as follows:

SWL = C squared x 10.8

SWL = the safe working load in kilograms

C = the circumference of the line in centimeters

Substituting in the equation for a 3-inch line the centimeter equivalent of 3 inches (3 inches = 7.5 cm), the formula becomes the following:

7.5 cm x 7.5 cm x 10.8 = 607.5 kg

Thus the safe working load of a line 7.5 cm in circumference is equal to 607.5 kg.

NOTE: 10.8 is the metric constant equivalent to 150 in the decimal system.

If the line is in good shape, add 30 percent to the calculated SWL. If it is in bad shape, subtract 30 percent from the SWL. In the example given above for the 3-inch line, adding 30 percent to the 1,350 pounds would give you a safe working load of 1,755 pounds. On the other hand, subtracting 30 percent from the 1,350 pounds would leave you a safe working load of 945 pounds.

Continue ReadingIntegrated Publishing, Inc. |