Considerations

The ratio of a material or structure's strength to its planned or expected stresses conveys its safety factor. If you have detailed knowledge of the material properties involved and can accurately predict the operating conditions, you can accept lower safety factors. If you understand the materials, but will use them under uncertain or unfamiliar operating conditions, engineers recommend higher safety factors.

Examples

Wire rope used with cranes operates as running rope (which travels around drums or sheaves) and standing rope. For these applications, safety factors of 3.5 and 3, respectively, rate as sufficient, according to engineering standards in U.S. government safety reports. Other applications, such as a wire rope supporting a passenger lift, might require a higher safety factor, the U.S. Bureau of Reclamation points out.

Benefits

If a wire rope breaks, materials and items being moved or secured may be damaged or lost. In some cases, injury or even death could result. The Bureau of Reclamation asserts that a sufficient safety factor helps prevent accidents.

source: ehow.com