Overhead Fall Arrest Systems
Kee Safety Singapore Pte Ltd
A leading supplier of fall protection solutions, safety railing systems, and safe access equipment for working at height
Imagine you're working high up, like on a truck or near machinery, and there's a risk of falling. That's where fall arrest systems come in—they keep you safe if you slip or trip.
Now, there are two main types: cable-based and track-based systems. Cable ones are like tight ropes you connect to, while track ones are like rails you slide along. Which one you need depends on stuff like where you're working, how many people need protection, and how the place is set up.
So basically, these systems make sure you don't take a tumble when you're working up high, and they come in different types to suit different situations.
This article explains the differences between the two types of fall protection.
Hierarchy of Fall Protection
When it comes to any task involving working at heights, understanding the Hierarchy of Fall Protection is crucial. It's a structured approach that guides us in prioritizing and selecting the most effective fall prevention systems.
At the top of the hierarchy is the ideal scenario: designing out the need for working at heights altogether. While this might seem like common sense, it's often overlooked. However, it's not always feasible.
Moving down the hierarchy, the next layer involves using collective equipment to protect workers, like guardrails and barriers. These measures provide a level of safety for multiple individuals simultaneously.
Finally, at the bottom of the hierarchy, we have measures to minimize the impact of a fall, such as fall arrest systems. These are used when all other options have been exhausted to reduce the distance and consequences of a potential fall.
Understanding and adhering to this hierarchy ensures that safety measures are implemented effectively, protecting workers from potential hazards at heights, and is crucial for any organization or team undertaking such tasks.
Selecting a fall arrest system
When we talk about fall arrest systems, the image that often comes to mind is a horizontal lifeline, particularly for those working near the roof's edge. These systems are crucial for reducing the impact of a fall and safely decelerating a worker over a specified distance. However, there are several factors to take into account, including the height of the anchor point in relation to the worker, the length of the lanyard, and the worker's weight. All of these elements affect the necessary free fall distance required to stop a fall safely and prevent the worker from hitting the ground or obstacles below.
While horizontal fall arrest systems are effective in many scenarios, there are situations where they aren't practical or where there simply isn't enough space for the required fall clearance. For example, imagine a worker on top of a dairy tanker or a maintenance technician walking on the wings of an airplane. In these cases, an overhead fall arrest system provides a viable alternative for ensuring worker safety.
What exactly is an overhead fall arrest system?
As with horizontal fall arrest, an overhead system provides continuous handsfree protection for the user and is ideal for low-clearance applications such as loading lorries, working on vehicles, aircraft, and trains, or for external building works such as fa?ade maintenance.
Where should you use an overhead fall arrest system?
Overhead fall arrest systems can be used in a wide range of industrial and commercial applications where fall clearance is a concern or when floor space needs to be kept clear and open for operational purposes. For example:
Overhead cable fall arrest systems
Overhead lifeline systems normally feature a highly tensioned cable that spans the work area and is fixed to anchor points at both ends. Permanently attached trollies allow users to travel and work freely whilst connected to the line without needing to disconnect from the system as they pass over intermediate brackets.
Overhead lifeline systems tend to be designed for up to 3 users and are ideal for situations where a fall arrest system needs to be mounted directly above a work area. The flexible design of these cable-based systems means they can cope with changes in height or direction and the fixation points can span large distances, meaning they are typically cost-effective and quick to install.
One big disadvantage of overhead cable systems is the larger fall clearance distance required in comparison to the rigid rail system.? The 8mm stainless steel wire rope that is typically used by these systems has a higher degree of flexibility and will, therefore, deflect more under load than a rigid rail system.? This in the industry is known as “sag” and there are two main types we refer to; one is initial sag and the other is dynamic sag.? Initial sag comes from the weight of the system trolley, self-retracting lifeline (SRL), and the weight of the wire rope.? Dynamic sag is caused by the impact load which is applied to the system in the event of a fall.? Initial sag is depicted below in point 1 and dynamic sag in point 3.
The image above represents a fall on a cable-based overhead fall protection system and rigid rail fall protection system.
Overhead rigid rail systems
Overhead rail systems house anchor points, known as travelers that run along the length of the rail, providing hands-free movement to multiple users at any one time. Like overhead cable systems, rigid rail fall protection allows workers to move freely around a wide working area. Their modular design can easily accommodate awkward layouts and be configured around obstacles such as ventilation systems, ducting, and pipework.
Rigid rail systems, by design, do not have any sags and, as such, can be used in lower clearance areas. Unlike cable fall protection, rigid rails have limited deflection, which limits free fall. During a fall arrest scenario with a cable lifeline, cable sag causes the traveler to slide to the center point of the nearest support. This motion can cause the worker to hit walls and nearby structures during or after a fall. In addition to reduced deflection rates, rigid rail systems are better suited than cable systems for accommodating multiple users.
Low clearance applications, such as working on top of containers and flatbed trucks, require the use of a rigid rail system and quick-stopping self-retracting lanyards. Performing maintenance on top of equipment used for manufacturing and distribution processes can also be hazardous. Often, the equipment has access points that require someone to work in an unsafe position. A rigid rail system can provide safe, consistent access to areas that would otherwise be considered high-risk and, therefore, unsafe.
The flexibility of these systems means they can be added to, moved, and reconfigured when necessary.? For example, some products can be erected externally as a stand-alone system with structurally sound footers and beams.
Before specifying an overhead rail, you need to be sure that the building can accommodate the anticipated load of the fall arrest system.? Traditional systems are fixed to primary steel, however more advanced models allow the protection to be attached directly to secondary steel.? Advanced models eliminate the need for additional beams, dramatically reduce the potential disruption on-site during installation, and therefore open up more opportunities for usage.?
So which overhead system is best – cable or rigid?
The simple answer to this is neither. Each system has its benefits, and which one you choose will depend on aspects, including the application, the environment, and how many workers need to be attached at any one time.
If the building’s layout requires a versatile system that can accommodate changes in direction around corners, for example, a cable system provides the perfect solution. As you would expect, a rigid rail system is restricted to a straight-line installation and would not be suitable in these cases.
When using an overhead cable system, you need to be aware of deflection that would occur in the event of a fall.? As cables are flexible, if someone falls more force is applied to both the person’s body and the anchor point during the process of arresting the fall.? As the system slows the persons fall, the cable will deflect under the additional load which will increase the distance before the fall is stopped.?? If other users are attached to the cable, the sudden system deflection and potential swinging pendulum effect caused by the person falling may cause other users to fall as well, putting an even greater strain on the cable and further increasing fall distance.
Deflection is, of course, something we consider when specifying an overhead cable system, but there are so many other influences that need to be thought about, such as the weight of any potential user and the equipment they will be carrying.? These can have serious implications when the fall distance is very limited or where there are obstructions, and this will determine the type of system that should be used.
For example, when it comes to aircraft maintenance, wings are close to the ground and can present issues with fall clearance.?? A rigid rail would be the better option in this application as it does not deflect in the same way, which means if a person does slip, their fall will be arrested within a shorter distance which significantly reduces the possibility of injury or expensive repairs to the aircraft.
An informed choice means assured safety
As you can see when properly designed, engineered, installed, and maintained, both cable and rigid rail overhead systems are capable of providing reliable and compliant fall protection solutions.
However, as with any safety-critical application, you need to make sure you have the right equipment and the knowledge to be able to use it effectively, not only for the safety of those carrying out the work but also for other people working in the same vicinity.? The word here is competence and any person designing, installing, or using these systems should be able to demonstrate they are suitably trained, and able to carry out the works.??
You should always seek professional advice from a competent person or company when specifying fall protection equipment. The correct specification will be based on several important factors. If you get any of these wrong, you could be putting both your workers and your business at risk.?
We at Kee Safety understand the complexities associated with designing effective and compliant fall protection systems and are very happy to provide advice and guidance to ensure the correct solutions are implemented and in line with your project-specific requirements.
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