Much Ado About Safety Factors of Two

It’s time for another thrilling blog post about OSHA standards and requirements! This week, we will be discussing the definition and importance of safety factors when implementing a fall protection system in an industrial setting.

According to OSHA 1910.140(c)(13), anchorages “must be: capable of supporting at least 5,000 pounds (22.2 kN) for each employee attached; or designed, installed, and used, under the supervision of qualified person, as part of a complete personal fall protection system that maintains a safety factor of at least two.”

This OSHA requirement can be satisfied in one of two ways: you can install a fall protection system with anchorages that can hold 5,000 pounds if a “Competent Person” can verify the 5,000 pound strength. Or, you can use a system engineered by an OSHA-defined “Qualified Person” that can resist double the magnitude of the system’s maximum arresting force.

A “Safety Factor” is defined as how much of an overload any object can withstand during use. Often times, the material that comprises the equipment determines the amount of stress that the equipment can withstand. Engineers like to define the materials as either ductile or brittle. When a building material is ductile, this means that the material will deform to the type of pressure or force that is being exerted upon it before breaking. If a material is brittle, it will simply snap or break after having its maximum force exerted upon it.

Steel is n example of a ductile material. Steel’s chemical composition allows it to bend and mold (albeit slightly) with the direction of force that is exerted upon it. And the composition of steel is strong enough that it takes large amounts of force to even begin influencing its shape. An example of a brittle material is glass. When glass encounters a force it cannot withstand, glass will crack or shatter instead of deforming to the direction of the stress. Since our fall protection systems are made of steel, we focus on its ductile qualities.

Within the realms of ductile materials, there are two types of strengths: yield strength and ultimate strength. Yield strength is defined as the point of force where a ductile material begins to deflect (or bend) with stress. Ultimate strength is defined as the point of force at which a ductile material breaks in half.

In order to determine how much weight these materials can handle, engineers need to perform a series of calculations and strength tests to determine the quantitative amount of loading a component can handle. Once the loads have been determined, then fall protection engineers can design a product with enough material that it will handle the loadings with the least amount of deflection.

If we were to do a break-down of the calculations and numbers that go into determining the safety factor for a Rigid Lifelines fall protection system, the numbers would look like this:

• A human can withstand approximately 10 G-Forces before they will experience injury.
• Most average adults have a weight range of anywhere between 90 and 310 pounds—of course, there are exceptions, but this range is relatively inclusive.
• We engineer our systems so that a user will experience a maximum arresting force of 900 pounds.
• The Rigid Lifelines system is meant to handle a maximum arresting force, or capacity, of 900 pounds. Capacity is defined as the allowable load from the deceleration device and fall arrest system.
• The “design load” of our system is calculated by multiplying the capacity of the system by the OSHA-required safety factor of two.

Here’s the math:

(Deceleration-Device Capacity)(Service Factor)=Track Design Load

(900 lbs)(2)=1,800 pounds

In non-numerical terminology:

The track in a Rigid Lifelines fall arrest system is designed to handle double the magnitude of the maximum arresting force of our deceleration devices (SRL’s or Rip-Stitch Lanyards).

We re-enforce the steel in our systems to have a 2 to 1 ratio against bending. This results in about a 3 to 1 ratio against system failure.

The bottom line:

A fall protection system that meets OSHA requirements must either hold 5,000 pounds (per person) or a qualified fall protection engineer must develop a system that can withstand double the force/load of maximum arresting force of all workers using the system.

Stay Safe!

Hannah Addison