Height safety device vs. fall arrester: What really is safe on a flat roof
Retractable type fall arresters and energy absorbers fulfill the same basic function in a PPE fall arrest system: they connect the harness to the anchorage point and limit the fall energy in the event of a fall. However, their mode of operation, area of application, and requirements for the fall clearance differ fundamentally. Anyone who chooses the wrong system endangers themselves in an emergency.
How an energy absorber works
An energy absorber (standard: EN 354 + EN 355) is a connecting lanyard with an integrated energy absorber. In its normal state, the lanyard is folded to a length of typically 1.5 to 2 meters. In the event of a fall, the connection is suddenly loaded, the energy absorber webbing tears open in a controlled manner, and absorbs the kinetic energy of the fall. The maximum arresting force is limited to less than 6 kN – a value that the human body can survive.
The crucial disadvantage: The extended energy absorber webbing lengthens the system by up to 1.75 meters. Together with the harness length and the free space below the anchorage point, this results in a total fall clearance of often 6 meters or more. Anyone working on a flat roof with only 3 meters of fall height can hit the ground with an energy absorber – despite the system being deployed.
How a retractable type fall arrester works
A retractable type fall arrester (standard: EN 360) functions like a safety line with an automatic retraction unit. During normal movement, the device pays out and retracts the line – similar to a car seat belt. In the event of a fall, the unit locks immediately and holds the falling person within a few centimeters.
The result: The free fall is only a few centimeters, the arresting force is significantly lower than with an energy absorber, and the required fall clearance is minimal. Retractable type fall arresters are therefore often the better choice on flat roofs and in situations with limited free space below the anchorage point.
Direct comparison
Fall clearance: Energy absorber requires up to 6 m, retractable type fall arrester only approx. 1 m – this is the crucial practical difference.
Freedom of movement: Energy absorbers have a fixed maximum length. Retractable type fall arresters automatically pay out and retract the line – more freedom of movement, no swinging with excess line.
Price: Energy absorbers are significantly cheaper to purchase. Retractable type fall arresters cost more, but offer more comfort and safety with regular use.
Use after a fall: An activated energy absorber is used up and must be replaced. A retractable type fall arrester can be inspected after a fall and, if necessary, reused – observe manufacturer's instructions.
When to use which system?
Energy absorbers are suitable for work at great heights with sufficient free space below the anchorage point – e.g., on tall industrial buildings, bridges, or masts. They are often unsuitable on low flat roofs because the fall clearance is insufficient.
Retractable type fall arresters are the right choice on flat roofs and wherever the free space below the anchorage point is limited. They are also suitable for people who need to move a lot, as the automatic retraction of the line minimizes tripping hazards.
PPE fall arrest accessories and advice at Gerüstexpress
In the Gerüstexpress range, you will find mobile anchor points for use with PPE fall arrest systems on flat roofs. If you have any questions about the correct PPE fall arrest configuration for your application, we will be happy to advise you.
Frequently asked questions
Can I use an energy absorber on a flat roof?
Only if there is sufficient fall clearance. This is often not the case with typical flat roofs with a fall height of 3–5 m. When in doubt: choose a retractable type fall arrester.
How long does a retractable type fall arrester last?
Manufacturer-dependent, typically 10 years from the date of manufacture. After every fall, the device must be inspected – even if it appears externally undamaged.
Do I have to replace the energy absorber after a fall?
Yes, always. An activated energy absorber has used up its energy absorption capacity and must not be reused.
