4 Steps to Calculating Fall Arrest Distance
Miscalculating fall arrest distance can have serious consequences.
Whether you are working in a cradle, on scaffolding or performing any other type of work at heights, the fall arrest system is of no help if you reach the ground before your fall is stopped. Although it sounds obvious, we unfortunately see all too often inadequate fall arrest systems.
The source of the problem is usually a lack of training or a solution developed without the assistance of a qualified person. Miscalculating the fall arrest distance always leads to the same result: injuries or death.
Many workers don’t fully understand how a fall arrest system works and don’t adjust the system according to the actual data of the situation. Often, when adding the length of the safety harness, the lanyard, the anchorage as well as the height of the worker, the total length can cause injuries. Therefore, to learn how to efficiently calculate the fall distance and leave the necessary clearance is crucial.
The Components of a Fall Arrest System
A fall arrest system (personal protective equipment for working at heights) is essentially composed of three integral elements: a body harness, a fall-arrest device (lifeline, shock absorber, carabiner, connector, cable, etc.) and an anchorage system.
The greater the free fall distance, the more energy the fall will produce and the more violent will be the shock. The free fall is the distance travelled during a fall before the fall arrest system is triggered. It is important to minimize the free fall distance (maximum of 1.8 meter according to the CSTC). In order to achieve this, the user must, whenever possible, attach his lanyard to an anchorage connection point just above his shoulders. In case of a fall, this will reduce the impact force, the risks of contact with an obstacle and the injury severity while facilitating emergency and rescue operations.
Specific anchorage points should be located directly above the user – “above” in order to reduce the fall distance and “directly” to minimize the pendular movements. The risk of swing fall increases in direct relation with the horizontal distance between the user’s harness and his anchorage connection point. For that reason, anchors (on the roof) must not be spaced more than 3 meters (10 feet) in between on a right angle from the building’s facade, and applied along the traction axis corresponding to the worker’s potential fall. Also, the angle created by the offset must not be over 22 degrees.
Four Factors to Be Taken into Consideration When Calculating the Fall Arrest Distance
1. Length of the lanyard, the harness and the anchorage connector
For an untrained worker, a lanyard of six feet may seem enough when working at a height of 10 or 12 feet. Still, the length of the harness and the anchorage connectors must be added. A fixed anchor is easy to calculate as the only distance to add is the ring. However, when the anchor is part of a horizontal lifeline, the calculation is more complex. Horizontal lifelines are not tight in their initial design and can stretch in the event of a fall. This collapse must be taken into account. Calculating the collapse may be as simple as tightening the rope to calculate the distance, but determining the collapse during a fall is more complicated. The force applied on a lifeline will pull it farther than you could measure when only tightening the line. In average, calculate about 3% of the total length of the tight line to 15% of the length of a lifeline using a shock absorber. Ideally, an engineer should calculate the collapse for a fall according to the number of people attached to the lifeline.
2. Deceleration distance
We often forget the deceleration device. When deployed, it adds 3.5 feet more to the length of the lanyard. Also, the harness can stretch so the anchorage point is moved higher than the head during a fall. In this example, the distance to be considered is not 6 feet, but 10.5 feet.
3. Height of the worker
Although apparently simple, this information is often overlooked when calculating the fall arrest distance. It is imperative to take the height of the worker under the anchorage point into account. A fall arrest system that stops a worker at 12 feet is not efficient when the lowest level is 14 feet, unless the worker is less than 2 feet tall, which is highly unlikely! On average, at least 5 feet must be added to the calculation to take into account the person’s height.
4. The safety factor
The section 8 of the CSA Z259.16-04 standard: Design of Active Fall-Protection Systems, offers the necessary guidelines to evaluate the required clearance underneath the worker using a fall protection anchorage system. In most cases, the required minimum clearance for using a harness as a fall prevention device must be greater than 4.5 meters (15 feet).
Calculation of the required fall arrest distance (measured from a rigid anchorage point)
Calculate the free fall distance Free fall distance = Length of the lanyard + Height of back D-ring – Height of the anchor
Calculate the total fall distance Total fall distance = free fall distance + deceleration distance (shock absorber) + D-ring slide
Calculate the minimal required fall clearance Minimal required fall clearance = total fall distance + safety distance factor + height of suspended worker (between the feet and D-ring)
Add the safety factor before the nearest obstruction.
This post originally appeared on SPI Health and Safety's blog. It has been republished with permission.
More from AD Safety Network
- When should you consider using custom molded earplugs?
- At what height do falls become deadly?
- Who should be responsible for rescuing fallen workers?
- What kind of training do loading dock workers need?
- How often should I inspect a loading dock?
- How is wind chill calculated?
- What is the difference between occupational safety and process safety?
- Why should rubber insulating gloves be tested?
- What happens if I tie off at the foot level with a personal SRL?
- Why is testing with a NAIL4PET accredited lab important?
- What kind of face protection do I need when using a chainsaw?
- What is the permissible exposure limit (PEL) for silica?
- What is silica and why is it hazardous?
- What is 'Table 1' and why is it so important?
- Video Q&A - What is a safety policy?
- What kind of fire extinguisher is best for your work site?
- How do I choose the right respirator and mask for working with silica?
- Can I wear fall protection equipment over my rainwear or winter gear?
- When do I need a cage ladder?
- What types of gloves protect your hands from hazardous chemicals?
- How come I still got hurt while wearing flame-resistant clothing?
- What dangers do workers face when working outside in the winter?
- How do I win over my most reluctant employees?
- What kinds of jobs should use disposable safety gloves?
- Is it true that safety shouldn't be a top priority?
- When are employers allowed to conduct drug and alcohol tests on their employees?
- How can I get employees more involved in the risk assessment plan?
- What are some of the indirect costs of accidents?
- How often do fire extinguishers need to be inspected?
- What is the best way to store rubber safety gloves?
- How much voltage protection is needed for safety gloves used in electrical work?
- What is the difference between a safety valve and a release valve?
- When do workers have the right to refuse to work?
- What is the most overlooked item when designing Lockout/Tagout (LOTO) procedures?
- What are some of the misconceptions about heat stress and what should we do to address them?
- What tools should I tether when working at heights?
- What types of gas should I watch out for when working in a confined space?
- How do you create a culture of safety in your workplace?
- What is the difference between industrial safety and industrial hygiene?
- What is the best kind of gas detector to use in confined spaces?
- Is it important to get PPE assessments by trained professionals?
- What is a fault tree analysis?
- What kind of respirator cartridge should I use?
- What are the safety benefits of a whistleblower program?
- What type of safety record-keeping and recording should we be doing?
- What makes a hi-vis safety vest ANSI compliant?
- Why is it important to have air sampling done to determine my PELs?
- What is the life expectancy of fall protection equipment?
- What are hot work and cold work permits?
- What are some basic fall protection rules that each of my workers need to understand?
- How much clearance do I need to safely use a Leading Edge SRL?
- What is the difference between an acute hazard and a chronic hazard?
- What’s the difference between a bump test, a calibration check, and a full calibration?
- Is there any legislation regulating lone worker safety I should know about before hiring?
- What kind of fire extinguisher and accessories should be kept on hand on a factory floor?
- What can companies do to reduce their lost time injury frequency rates?
- Video Q&A - What's your safety network like?
- Video Q&A - What are the 3 levels of safety?
- Video Q&A - How do you treat a near miss?
- Does body weight affect falls differently?
- What ages are most affected by falls?
- Why do workers take risks?
- What Is the Difference Between OHSAS 18001 and 18002?
- What is the difference between lost time injury and medical treatment case?
- What is the difference between occupational health and safety and workplace health and safety?
- What is the difference between occupational health and occupational safety?
- What is the difference between a lost time injury and a disabling injury?