Factor of Safety in Engineering

The Factor of Safety in Engineering

In engineering, the factor of safety (FoS) is an important concept, especially in the design phase. The factor of safety is also commonly referred to as the safety factor and is determined by using a formula.

What is the Factor of Safety in Engineering?

The factor of safety expresses how much stronger a system is than required. The factor of safety is the backbone of engineering systems including, structures and safety.

For reliability and safety reasons, it allows a system to undergo more stress than originally expected in the event of abnormal external circumstances.

Implementing a factor of safety requires the actual load-bearing capacity of the system or components needs to be identified or calculated. Secondly, the prescribed factor of safety for the system or component must be identified, according to the design standards for that system.

Determining the Factor of Safety

The first step of determining the factor of safety is determining the load-bearing capacity of the system. Depending on the system, this is calculated differently.

For example, the factor of safety for a single component will revolve around that material’s yield strength or ultimate tensile strength, depending on if the material is ductile or brittle.

The required (design factor) of safety is stated by law or by a standard.

For example, a column in a building will have a prescribed safety of factor, which must be taken into account when designing the structure and must meet the minimum value. For structural steelwork in buildings, a factor of safety between 4 and 6 is required.

Structural steelwork in buildings has a factor of safety between 4 and 6

Factor of Safety Formula

The other type of factor of safety is the realised factor of safety. The realised factor of safety is a measure of the reliability of the design. It is determined by the ratio of the capacity of the component to the actual load.

Factor of Safety Formula = load capacity / actual load

Why Is The Factor of Safety Important in Engineering?

As its name suggests, it is a vitally important aspect of engineering to maintain the safety and reliability of engineering systems and components. Safety is at the forefront of engineering and is a major consideration in the design phase.

In safety-critical components and systems, failure can be devastating, leading to injury and death.

Safety is critically important in engineering

Other considerations

The below factors help engineers design components effectively with safety in mind.

Cost: Implementing a factor of safety leads to greater costs predominantly because more material is required.
Stress concentration: Does the system have any stress concentrators i.e. holes, bends etc.
Maintenance: What kind of maintenance will be utilised? A more vigorous maintenance regime increase the likelihood of detecting defects.
Wear: Does the component or the system have tribological contacts? This will reduce the load capacity of the system.