The use of a fall arrest system is a sign that a worker will be operating in an area of very high risk. It is important that the system is setup and used in a way that will best protect the user.
In the order of preferences when it comes to fall protection and height safety systems, fall arrest is close to the bottom. To be working in a fall arrest environment is to be in a situation where it is known that a free fall is possible. It cannot be prevented, restrained or otherwise removed as a potential outcome in the event of an incident
Given this, it is extremely important that fall arrest systems be designed and used in a manner that best protects the operator. Making this difficult is the reality that the system only comes into action once a fall has occurred.
What is a fall?
Under the Work Health and Safety Regulation 2017 (NSW), a PCBU must manage the risks to health and safety associated with a “fall by a person from one level to another that is reasonably likely to cause injury to the person or any other person”.
That is very broad, however, and only looks at falls from a risk management perspective.
When it comes to fall arrest systems, “falls” are classified by the distance a worker will free fall before the slack is taken up and the arrest action starts.
Shock absorbers
Every fall arrest system will involve the use of a personal shock absorber. The shock absorber works to absorb the forces generated while slowing down a worker from free fall. This helps a worker avoid a sudden stop at the end of their lanyard.
They do this by deforming or deploying to decelerate a fall victim in a steady manner that does not place excessive force on their body. In a similar manner to how the crumble zones on a car operate in a collision, or the padding around a football goal post.
Types of falls
In a perfect world, the typical distance a worker could fall would be zero millimetres. However, that is simply unrealistic. If there is a need for people to be off the ground, the risk a fall can exists. Strictly speaking, even tripping over one’s own feet on flat ground could be considered a type of fall.
When discussing fall arrest, though, falls come in a couple of different categories.
A fall environment where a worker could free fall up to 600mm before the arrest system activates is what is referred to as a “limited free fall”. A fall of this type is unlikely to generate forces necessary to severely injure a worker, or even deploy their shock absorber.
Environments with a potential free fall distance of greater than two metres becomes what is classified as a “high risk work”. As a result, sites must have a written safe work method statement that implements controls measures to reduce the severity of the potential fall. This reduction occurs by taking action to reduce both the likelihood of the fall occurring and the severity of the outcome should the fall occur.
Safe fall clearances for fall arrest systems
The Australian standard AS/NZS 1891.5 (2000) contains the requirements for the manufacture of lanyard assemblies and pole straps, along as specifying testing and labelling requirements.
Table 4.1 within this standard provides the calculations for working out the minimum fall clearances required when working in fall arrest. This considers the length of the lanyard, weight of the operator and the extension a shock absorber will have during deployment.
In a situation where a worker is likely to free fall up to 600mm before being arrested, the minimum distance they should be from the ground is at least 3.4 metres.
This distance includes the required one metre of residual clearance and assumes an operator height of 1.8m.
At the other extreme, a situation where a two-metre free fall is possible requires that a worker be nearly seven metres above the ground.
This considers the two metres of free fall, plus two-metre extension of the shock absorber (a maximum design length), the 1.8m tall operator and one metre residual fall clearance.
2m + 2m + 1.8m + 1m = 6.8m
As mentioned above, any situation where a free fall distance is greater than two metres requires additional control measures to be implemented to reduce that.
Solving the fall arrest equation
All the above calculations run off the assumption any potential fall from height would be straight down and that the area immediately beneath the operator is clear of any obstructions.
Any worker in an environment where either of these assumptions are not being met is being placed at even greater risk. And working in fall arrest is already a work method that carries substantial risk.
As ever, there are solutions that should be fully investigated and assessed prior to implementing fall arrest. The hierarchy of control should be used to guide these decisions. A complete risk assessment and safe work documentation should also be completed.
Anywhere any person is working at height and there is a risk of a fall there must also be a comprehensive and well-practised rescue plan in place and the equipment needed to perform that rescue must be available on site.
Your partners in protecting people
Since 2003 Height Safety Engineers have been designing, installing and inspecting safe access and fall protection systems across a variety of industries.
Our team bring their decades of real-world high risk work experience to every job. Start your safety journey with HSE by calling 1300 884 978, emailing enquiries@heightsafety.net or completing the contact form on the right-hand side of this page.
