Designing effective roof fall arrest systems is no easy task
Designing a safe system for working on domestic or other small scale buildings is one of those activities that architects and engineers are regularly called upon to do.
Like all construction projects this has to be done in the minimum of time – with the minimum of cost.
There is much to consider, but thankfully there are many new products now available to make this easier and safer.
In most cases the aim of a Fall Arrest system is to provide safe access for staff to distinct points on the roof, usually mechanical equipment or the edged of the roof to enable the cleaning of gutters and the like.
In all but the most utilitarian of the buildings, the owner is not be keen to have the appearance of the building downgraded by the appearance of walk ways or horizontal life lines in silhouette against the or other parts of the building.
The first step is the provision of safe easy to use access. Where the expectation is that there will be a need for a lot of regular access to a roof, there is a range of fixed ladder systems that can be permanently installed.
These range for conventional appearing ladders, to ladders like the Miller Pivotloc, which is a ladder that folds in on itself. This enables a ladder to be provided in a way that effectively makes the ladder invisible, when it is not in use.
For situations where a temporary ladder is used there are also surface mount brackets that will secure the ladder whilst the climber ascends and in the case of some of the newer models provides a rated fall arrest anchorage point.
As the worker reaches the edge of the roof, he should now be able to reach his next anchorage point, so that as he climbs onto the roof he is connected through the entire movement.
The development of a surface mount fall arrest anchorage points for metal roofs, has resulted in a very compact and low profile units that can comply with AS/NZS 1891 Part 4 as anchorage points.
Some units can be used as simple individual fall arrest points, bases for permanent horizontal lifeline intermediate supports or end anchorages for temporary horizontal life lines. When specifying these units it is necessary to make sure that they are compatible with the roofing profile.
Technical files for surface mount anchorage points such as the MILLERFIX available from
These surface mount units come with a closed cell neoprene weather proofing seal, they are usually also fitted by using heavy duty mandrel style rivets (also fitted with a weather proof seals).
The positioning and orientation of the rivet lines will be set out in the instructions, these
should be closely followed.
Providing the positioning of Fall Arrest anchorage points for fall areas such as the edges of roofs, must be done very carefully.
It is generally recognised that the safest method for this type of work is Restraint, (see
AS/NZS 1891-4 Appendix F and Miller Working in Restraint Guidelines AUNZ 1000/2009).
When positioning an anchorage point for Restraint work near an edge, it is recommended that the shortest distance between the edge and the anchorage point is 1m longer than the lanyard the operator will be supplied with (assuming the anchorage is at foot level).
For example, if the worker was to be equipped with a 2m Lanyard the anchorage point should be 3m from the edge.
Technically this is known as “Total Restraint.” The next level up the hierarchy is “Restraint Technique.”
This is where the lanyard has length adjustability, and the operator is sufficiently trained so that he can be relied upon to adjust his lanyard to the appropriate length to keep him out of trouble.
All of the above is assuming that the surface the person is working on is effectively level and there is not any contaminate such as saw dust, water, grease, oil or ice that would affect his footing on the surface.
Whilst it is always desirable and preferable that the anchorages are positioned so that a person connected to them will always work in Restraint, there are times where the system design has to take in the possibility of a free fall.
In this circumstance the employer has an obligation, to make sure that a suitable rescue plan is in place.
If there is a risk of free fall, usually the safest method of connection between the operators harness and the anchorage point is a compact fall arrester.
The reason for this is that the compact fall arrester (such as the Miller TurboLite or the Miller Scorpion), will continuously monitor the about of material that is paid out, minimising the amount of slack material in the connection.
This will minimise the degree of the freefall. If there is a risk that during the fall the connection part of the fall arrester may come in contact with sharp edge.
There is a range of compact fall arresters that are designed to sustain the impact even if the person falls over a sharp edge.
These have been tested against the new European Standard for Fall Arresters, a very serve test that simulates the line of the fall arrester being drawn both across and along the a sharp edge.
If there is a need for the roof worker to walk along the roof, even going around structures on the roof, and there is a fall risk where he is walking.
Consideration should be given to installing a permanent horizontal life line, this is a 8mm stainless steel wire that is supported along its length, usually just off the roof surface.
The operators can connect to the line, walk along next to it, where the line is supported, the intermediate is designed to let the operators shuttle pass through, there are both internal and external corner units so the wire and the operators path can be directed around equipment or obstructions on the roof.
Permanent lines like this have the advantage of being very low profile, and not providing being an eyesore.
There is some engineering involved in establishing the required strength of the structure supporting the line, typically the intermediate supports need to be able to sustain a force of 12 kN, the end posts and the corners twice the in line force.
Each system manufacturer can provide either a program or a spreadsheet to allow the
calculation of the in-line force.
System variables that effect the calculation of the in-line force are, number of people, system overall length, length of intermediate spans and numbers of corners.
Most lines require an in line energy absorber, to make sure the line is installed with to the appropriate pretension and that in the event of a fall that the peak force in the system will not go above a safe level for the system as a whole.
Selecting the right system and parts to provide a safe and secure working environment for working on roofs is important, manufacturers of fall arrest and other safety equipment are keen to supply, technical files and other information to assist.
Sperian Protection Australia Pty Ltd
Ph: 03 9565 3509