WARNING. The distances given in this annex are for illustration only. They should not under any
circumstances be used in the setting up of an actual fall arrest system. The manufacturer’s instructions for the particular equipment to be used should always be consulted.
F.1 System based on an energy absorbing lanyard
Table F.1 gives an example of the calculation of the minimum free space requirements when a fall arrest system based on an energy absorbing lanyard of 2.0 m, or of 1.5 m, overall length is to be used in the situations shown in Figure 32 (see 9.7.2). The anchor point and ground level have been used as the datum points. This example illustrates the limitations of using a fall arrest system based on an energy absorbing lanyard in terms of the relatively large amount of free space required, and also the need to place the anchor point overhead wherever possible to give a shorter free fall distance and thus a smaller free space
requirement.
NOTE Where an energy absorbing lanyard is used, the free fall distance is the distance the user travels from the onset of the fall to the point at which the energy absorbing lanyard begins to arrest the fall. The greater the free fall distance the more the energy absorber has to extend to absorb the energy of the fall and hence the greater the free space requirement.
Table F.1 — Example of calculation of minimum free space requirements for a fall arrest system based on an energy absorbing lanyard
F.2 System based on a retractable type fall arrester
Table F.2 gives an example of the calculation of the minimum free space requirement when a fall arrest system based on a retractable type fall arrester is to be used in the situation shown in Figure 33 (see 9.7.3). The walkway and ground level have been used as the datum points.
NOTE With a retractable type fall arrester the free fall distance is much less than with an energy absorbing lanyard.
Table F.2 — Example of calculation of minimum free space requirement for a fall arrest system based on a retractable type fall arrester
Distance Description Measurement
m
Anchor point above usera
[see Figure 32a)]
Anchor point at shoulder level
[see Figure 32b)]
Anchor point at foot level
[see Figure 32c)]
2 m
lanyard lanyard1.5 m lanyard2 m lanyard1.5 m lanyard2 m lanyard1.5 m A Length of lanyard + Length
of extended energy absorber 2.0 + 0.25 1.5 + 0.2 2.0 + 0.75 1.5 + 0.5 2.0 + 1.75 1.5 + 1.25 B Harness stretch distance +
Distance between the connection point of the lanyard on the harness and the user’s feet
2.0 2.0 2.0 2.0 2.0 2.0
C Safety clearance 1.0 1.0 1.0 1.0 1.0 1.0
A + B
+ C Minimum free space requirement 5.25 4.7 5.75 5.0 6.75 5.75 a Anchor point above user but still with sufficient slack in the lanyard to allow the user to bend down in order to reach work areas
at walkway level.
Distance
(see Figure 33) Description Measurementm
A Free fall distance + Brake operation distance + Harness
stretch distance 1.5
B Safety clearance 1.0
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F.3 Systems based on a vertical anchor line (rigid or flexible)
Table F.3 gives an example of the calculation of the minimum free space requirements when one of the fall arrest systems based on a vertical anchor line, as shown in Figure 34, is to be used (see 9.7.4). In the case of the rigid anchor line (see Figure 34a) the ladder rung on which the user is standing and ground level have been used as datum points. In the case of the flexible anchor line (see Figure 34b) the walkway and ground level have been used as datum points.
Table F.3 — Example of calculation of minimum free space requirements for fall arrest systems based on a vertical anchor line
F.4 System based on a horizontal anchor line and an energy absorbing lanyard
WARNING. The calculation of the free space requirement when arresting a fall by the use of a flexible
horizontal anchor line is extremely complex and takes account of numerous factors. This calculation should only be undertaken by system manufacturers, or by competent persons authorized to use software issued by the manufacturer. Software issued by one manufacturer should never be used to perform calculations for another manufacturer’s system.
Table F.4 gives examples of the calculation of the minimum free space requirements when a fall arrest system based on a horizontal anchor line at shoulder height and an energy absorbing lanyard of 2.0 m overall length is to be used by a single user in the situations shown in Figure 31 (see 9.7.5). The anchor line level and ground level have been used as the datum points.
Table F.4 — Example of calculation of minimum free space requirements for fall arrest systems based on a horizontal anchor line and an energy absorbing lanyard
Distance Description Measurement
m
Rigid anchor line
[see Figure 34a)] Flexible anchor line[see Figure 34b)]
A Free fall distance + Fall arrester operation distance + Length of extended energy absorber (if included in system) + Anchor line extension distancea + Harness extension distance
1.5 2.5
B Safety clearance 1.0 1.0
A + B Minimum free space requirement 2.5 3.5
a Applies only to the system with a flexible anchor line.
Distance Description Measurement
m
Single span horizontal anchor line, 10 m span
[see Figure 31b)] Multi-span horizontal anchor line, 3 m span [see Figure 31c)] Horizontal rail, fixed at intervals
[see Figure 31a)]
A Length of lanyard + Length of extended energy absorber + “V”-deflection of anchor linea
4.5 3.0 2.75
B Harness stretch distance + Distance between the connection point of the lanyard on the harness and the user’s feet
2.0 2.0 2.0
C Safety clearance 1.0 1.0 1.0
A + B + C Minimum free space
requirement 7.5 6.0 5.75