Factor of Safety


Definition - What does Factor of Safety mean?

A “factor of safety” (safety factor) is an engineering term used to describe how much stronger a system or structure is than it is required to be to fulfil its purpose under expected conditions.

In order to maximize the reliability of a load-bearing structure, the structure and its associated safety devices must be able to bear more weight than it would be subjected to under normal use. The amount of additional weight the structure must be capable of withstanding is described in terms of its safety factor (e.g., two times more weight than is expected during regular use = safety factor of 2).

Designing a safety system in this manner increases the probability that the system will continue to work properly if it is accidentally used improperly, or if it is exposed to unexpected additional stressors.

Safeopedia explains Factor of Safety

Using safety equipment with a high safety factor is an effective way to maximize the safety of workers by minimizing the potential of equipment failure. This is why fall safety equipment, such as personal fall arrest systems (PFAS), must be designed with a high safety factor; OSHA standard 1915.159 (fall arrest anchorages) requires any anchor point used as part of a PFAS to be able to support at least 5000 pounds per employee. The 5000 lbs requirement minimizes the likelihood that an individual will be able to fall with the force necessary to cause an anchoring point to fail.

The factor of safety requirements exist because it is impossible to predict all of the variables that a given safety system or structure will experience during use. By designing the system to be safer than it “needs to be”, manufacturers can ensure that their equipment does not fail due to the presence of an unforeseen variable (e.g., temperature).

A simple calculation for safety factor is; Factor of Safety = Actual Breaking Strength (lbs) / Normal Working Load (lbs).

The term “actual breaking strength” refers to the amount of load that will cause the system to fail. Thus, for OSHA standard 1915.159, breaking strength must be at minimum 5000 lbs. For non-critical equipment, the factor of safety is often 2, while components whose failure could cause serious injury or death typically have a safety factor of at least 4. The required factor may be higher if the equipment is going to be used in harsh conditions.

The real-world factor of safety calculations must account for the material being used, such as whether it is a rigid or ductile material. When determining the factor of safety for a system, the factor of safety for the entire system is determined by the component with the lowest factor of safety rating.

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