Fall factors and forces

No matter what measures are in place to prevent it, there is still a possibility that a person could accidentally fall. When persons fall from a height, their bodies and equipment generate energy. The greater the fall distance, the greater the energy that they will produce. This energy is known as “fall force” or “impact force”, and it can be life-threatening if it is too great.

Fall factors are simple equations that are used to calculate what the forces would be if a person falls. The equation considers the type of fall arrest equipment that is used, as well as where the person was anchored to when they fell.

Fall factors and forces have a serious impact on the health and safety of people working at height and it’s important to understand them. Here, we explain some basic concepts.

How fall factors work

A fall factor is a ratio between the height that a worker falls and the free length of the worker’s lanyard that has been made available to absorb some of the forces of the fall. Values of fall factors are calculated between zero and two (anything higher than two would be considered as a fatal fall). This calculation is done by dividing the height of the fall by the length of the lanyard or rope that the person is connected to. The lower the value of the fall factor, the fewer impact forces are applied to the body of the person and the “safer” the fall. On the other hand, the higher the value, the greater the impact forces will be on the body and the more likely it is that serious injuries will be sustained.

Let’s assume a person who is working at height is using a double shock-absorbing lanyard, which is anchored above their head while they are working. To calculate the theoretical fall factor, we use the following equation:

The value of the lanyard is rounded off to 2 m (this factors in the lanyard’s length as well as a safety margin for any stretch in webbing that could happen after a fall). The lanyard is anchored above the worker’s head, so there will be little to no distance to fall. Putting these figures into the equation helps to calculate what the theoretical fall factor would be:

Therefore

FF = 0

We refer to these calculations as theoretical as they do not entirely cover real-life situations, because elements like rope stretch, deflection of wire rope and energy absorber deployment could all have an impact on the forces. However, a fall factor of zero is the most ideal position to minimise injury if a person should fall. Note: the fall factor is a way to indicate the severity of a fall – not an exact way to measure the impact forces.

At a fall factor of one it can be seen that the person’s lanyard was anchored at waist height/shoulder height, which allowed them to fall a small distance due to the extra slack in the lanyard’s webbing. This would have resulted in minor injuries, but possibly not be fatal. The person working with their lanyard anchored at their feet would be considered to be connected in a fall factor two position and would fall a great distance because of the large amount of slack in the webbing. This type of fall would theoretically result in major injuries and possibly even be fatal.

Two major elements play a role in determining what the fall factor would be or how serious the fall would be:

• The position of the person’s anchor point in relation to their harness connection, and
• The type of fall arrest device that is being used.

If you can identify and select these two elements correctly, you will be able to maintain a fall factor of zero when working at height.

Choosing the right equipment

Any person working at height will be connected to their anchor point through some kind of fall-arresting device, which can range from lanyards to mechanical locking devices (mobile fall arrestors) that grab onto the rope. Because there are multiple functions for each device, the choice depends on the person’s training and competence in using the equipment and selecting suitable anchor points.

Lanyards are a good choice when the anchor point is installed at a short distance away and the worker needs the additional length in the webbing to be able to move while working. Situations where lanyards would be appropriate include truck loading bays, with overhead anchors or lifelines, and walkways at a height where there are structural beams to anchor to.

Mobile fall arrestors have very little slack in movement, as they are designed to lock onto the rope or wire immediately following a fall. They are best used when the person is constantly working in a vertical position and is therefore exposed to a greater risk of falling. These devices are often seen being used on vertical lifeline systems installed on fixed ladders, where the person can attach directly to the front of the harness and climb up and down with ease.

Although fall factors are theoretical equations, applying them to real-life situations could save lives. Keeping this information in mind will assist in choosing the most appropriate configuration for fall protection systems and, where possible, strive to minimise the fall factor to a zero.

Stay safe up there!