What Does
Fall Arrest System Mean?
A fall arrest system is any device that is designed to stop (or arrest) a worker’s fall, preventing them from reaching the ground or other hazards below them. They are typically part of a broader fall arrest plan.
Although the term “fall arrest system” includes both general and personal fall arrest systems (PFAS), when used without specification it typically refers to the latter.
For either type of system to be effective, it must be properly anchored and be able to withstand at least twice the impact force of a falling worker.
Since they don’t prevent falls but only limit the harm caused by them, fall arrest systems are considered the last line of defense for people working at heights.
Safeopedia Explains Fall Arrest System
Falls from height are one of the leading causes of occupational injuries and fatalities. According to the Bureau of Labor Statistics (BLS), there were 700 work-related deaths due to falls to a lower level in 2022.
Employers must protect workers from fall hazards by implementing various fall protection measures, such as guardrails and safety nets. Where those don’t offer sufficient protection, a fall arrest system is required to protect workers in the event of a fall.
The Occupational Safety and Health Administration (OSHA) requires fall protection whenever employers are doing work:
- At an elevation of four feet in general industry
- At an elevation of five feet in shipyards
- At an elevation of six feet in construction
- At an elevation of eight feet in longshoring operations
- Over dangerous equipment and machinery, regardless of fall distance
An Overview of Personal Fall Arrest Systems
As the name implies, a personal fall arrest system is one that is worn on the user’s body (as opposed to a general fall arrest system such as a safety net).
The various components of a PFAS include the following.
Full Body Harness
The full body harness is the wearable part of the PFAS. It includes shoulder and thigh straps, along with a D-ring to connect it to the other components of the fall arrest system.
The harness is designed to distribute the force of the fall and minimize injury to the body. It also ensures that a worker will remain suspended in an upright position after a fall.
Shock-Absorbing Lanyard
The shock-absorbing lanyard is the device that connects the body harness to the anchor point. It’s also the component of the PFAS that bears the greatest force during a fall.
This lanyard is a short, flexible rope with connectors at either end. It must be made of wire rope, flexible rope, or a webbing strap and be no longer than six feet. The lanyard must be able to support a tensile load of 5,000 pounds or more.
In addition to the rope, the lanyard is also equipped with a deceleration device that slows the fall, as well as an internal or external shock absorber that reduces the fall arrest force exerted on the worker in the event of a fall.
Self-Retracting Lifeline
A self-retracting lifeline (SRL) is similar to a lanyard but does not hang freely. Instead, it retracts automatically into its housing and limits the freefall distance to less than two feet.
An SRL must be able to support a minimum tensile load of 3,000 lbs. The friction-controlled mechanism in the lifeline provides a smoother stop, limiting fall forces to approximately 900 lbs.
Self-retracting lifelines are rarely compatible with shock-absorbing lanyards and they should not be connected together.
Anchorage
Anchorages (or anchor points) allow the system to be tied to a secure structure, such as concrete building elements, I-beams, or roofs.
OSHA standard 191.140(b) defines an anchorage as “a secure point of attachment for equipment such as lifelines, lanyards, or deceleration devices.”
Anchor points must be able to support 5,000 pounds per worker in order to accommodate the force of the fall without failure. Less support is permissible, but only with a margin of safety, meaning that the anchorage must be able to withstand at least twice the expected force of a fall.
Rope Grabs
A rope grab is a deceleration device that travels along a vertical lifeline and automatically engages and locks into place to arrest a fall.
OSHA Requirement for Fall Arrest Systems
Requirements for fall protection systems are provided in OSHA 29 CFR 1910.140.
OSHA specifies the tensile load criteria for various components of a PFAS in 1915.159:
- Vertical lifelines and lanyards: 5,000 pounds (22.24 kN)
- Self-retracting lifelines and lanyards that limit free fall distances to two feet or less: 3,000 pounds (13.34 kN)
- Self-retracting lifelines and lanyards that do not limit free fall distance to two feet or less: 5,000 pounds (22.24 kN)
- Ripstitch, tearing, and deforming lanyards: 5,000 pounds (22.24 kN)
- D-rings and snap hooks: 5,000 pounds (22.24 kN) and proof-tested to a minimum tensile load of 3,600 pounds (16 kN) without cracking, breaking, or being permanently deformed
- Anchor points: 5,000 pounds (22.25 kN) per employee
OSHA’s regulations for anchor points rely on quality standards for fall protection equipment set by the American National Standards Institute (ANSI) standard Z359.18.
Post-Fall Considerations
When a fall is arrested and a worker is suspended in their safety harness, they are not yet safe from harm. Workers in this situation can suffer from suspension trauma, a potentially fatal condition caused by the increased pressure placed on the heart during vertical suspension.
After a fall, a suspended worker should:
- Try to move their legs and push against any footholds (like the relief straps attached to their harness)
- Try to get their legs as high and as horizontal as possible
- Be rescued in under 10 minutes
- Be placed in a horizontal position gradually to avoid a potential cardiac arrest
The Hierarchy of Fall Protection
When implementing fall protection methods, safety professionals should follow the hierarchy of hazard controls. Begin with the most effective method and then apply less stringent ones only if the risks have not been sufficiently mitigated.
Here is the hierarchy of fall protection, in order from the most effective control method to the least.
- Elimination: Changing the process or relocating the task so the worker is no longer exposed to a fall hazard
- Hazard Reduction: Reduce exposure to hazards by minimizing the amount of time workers spend near leading edges and other fall risks
- Passive Fall Protection: Physical barriers like guardrails and warning lines used to prevent or discourage workers from going near fall hazards
- Fall Restraint Systems: Wearable systems that tether the worker and prevent them from reaching nearby fall hazards
- Administrative Controls: Work practices, training, controlled access zones (CAZ), and other methods to ensure that worker are aware of the fall hazards around them and know how to work safely at heights
- Personal Fall Arrest Systems: Used to secure the worker so they are less likely to be harmed (or are harmed less severely) if a fall does happen
Fall Arrest Vs. Fall Restraint
Fall arrest and fall restraint systems are similarly named but protect workers in different ways.
Fall Restraint Systems
Fall restraint systems (such as a safety harness and lanyard) use a tie-off system to restrict the user from reaching fall hazards. They are often referred to as travel restraint systems because they limit the distance an employee can wander.
These systems can either include a fixed attachment point or a horizontal lifeline along which the lanyard can move. The latter gives more freedom of movement while still preventing workers from getting too close to leading edges.
Fall restraint systems are preferred over fall arrest systems since they can prevent falls from occurring and keep workers from coming into contact with fall hazards.
Fall Arrest Systems
Fall arrest systems (such as a safety harness and a self-retracting lifeline) are designed to stop a fall in progress. The goal of these systems is not to prevent a fall from taking place but to prevent a falling worker from reaching the ground below.
These are less effective than fall restraint systems, since they cannot prevent falls from happening. The force of the fall arrest and the subsequent suspension trauma can also result in injuries.
Despite these disadvantages, they may nevertheless be required in situations where fall restraint is not feasible or practical. Leading edge work, for instance, must be done in close proximity to fall hazards, making a restraint system pointless but making a fall arrest system essential.
How to Set Up a Fall Arrest System
Before workers tie off, it’s important to ensure that the fall arrest system is set up properly and suitable for the task. This will involve:
- Selecting an appropriate anchor point (or installing one if there are none available on the structure)
- Calculating the fall clearance to ensure that the PFAS has enough room to deploy and arrest the fall before the worker comes into contact with a surface on the lower level
- Ensuring that each component of the PFAS is appropriate for the application and has been properly inspected
While not part of the PFAS system, it’s also important to draft a fall rescue plan. After a fall has been arrested, the worker should not remain suspended in their harness for more than ten minutes. This will require a rapid response, which is unlikely to happen unless there is a clear and effective procedure in place for retrieving them quickly and safely.
Safety professionals should also be mindful of the pendulum effect when setting up a fall arrest system. This occurs when a fall arrest leaves the worker swinging, which can cause them to hit a wall, equipment, or other obstructions.
Calculating Fall Clearance
The fall clearance is the total distance needed to ensure that the fall arrest system can fully deploy and prevent a worker from hitting the ground below (bottoming out).
Calculating the fall clearance is somewhat complex and takes these factors into consideration:
- Deceleration Distance: The maximum length that a lanyard will stretch to slow down the fall (should not exceed 3.5 feet)
- D-Ring Shift: The distance the D-ring moves and the harness shifts as it is jerked upward when the fall is arrested (assumed to be one foot)
- Back D-Ring Height: The distance between the D-ring and shoe sole when the harness is worn (defaults to 5 feet for workers 6 feet and shorter, but may have to be adjusted for taller workers)
- Safety Factor: Additional distance (3 feet) added to ensure adequate clearance between the worker and the lower level during a fall arrest
The formula to calculate fall clearance is:
Lanyard Length + Deceleration Distance + Height of the Worker + Safety Factor
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