High standards for temporary edge protection
June 1st 2005 December 2004 finally saw the arrival of the much needed Temporary Edge Protection Systems Standard EN13374. Overshadowed somewhat by the Work At Height Regulations, EN13374 has been many years in the making, but it is here to engender best practice, to reduce injury and ultimately save lives, and it should serve us well. Indeed, it is the largest and most important single point of reference for temporary edge protection and will have an enormous effect on the construction industry, especially as many systems are yet to comply with it. The scope of the standard is broad, covering temporary edge protection systems for use during construction or maintenance of buildings and other structures. It includes edge protection for flat or inclined surfaces and specifies energy absorption capacities. But it doesn’t include impact by vehicles, containment of bulk materials, and the protection from falling objects of the general public. The industry usually groans at such documents and the cost of sending employees on courses to try to decipher the detail and to spell out the key points. This article simplifies the main aspects of the standard and which systems currently comply with the different classes of the Standard.
The Standard. A Class Act. The standard has three “Classes” of edge protection, A, B, and C. Each has an approximate description of the intended range of applications, particular geometry regarding heights, gaps, and levels of containment, and a set of performance criteria. It is well worth making reference to the actual standard to get a full understanding of the performance criteria. Interestingly these Classes fall neatly into the following roofing categories: Class A for flat slabs, Class B for pitched or standard sloping roofs, and Class C for the large bay sizes found in today’s sheeting and cladding systems.
Class A. Designed to resist fundamentally static loads only and intended for use on mostly flat surfaces: - The system should be erected perpendicular to the surface (vertical +/- 15º).
- The height of the principle guardrail should be 1000mm.
- If the system includes an intermediate guardrail it should be designed “so as not to permit a sphere of 470mm diameter to pass through.”
- If it does not include an intermediate guardrail, it should be designed to prevent a sphere of 250mm from passing through.
- If the system includes a toe board, it shall be minimum 150mm in height, and not have any gaps that will permit a 20mm sphere through below.
- The maximum deflection of the top guardrail, at any point, must not exceed 55mm when subjected to a horizontal load of 0.3kN (this can be evidenced by test or calculation)
- Class A edge protection must also be checked for ultimate limit state for combined loading and maximum wind loading, demonstrated by calculation or testing.
The key point here is that these performance criteria will apply to all Class A systems, irrespective of the span between supports. They will also apply to all Class A systems irrespective of the surface profile depth. Both have serious implications for the current practice using tube and fitting.
Flat Slabs The Flat Slab application has been championed from Sweden with the development of the Combisafe Steel Mesh Barrier. This concept has been enthusiastically embraced within the concrete frame market as it readily combines with table form systems and progressive erection. The original product has been much copied and much cloned, and the mesh barrier system solution is undoubtedly the way forward for Class A. Complete compliance with the new standard, the high level of containment from the mesh barriers, the ease and simplicity of erection, and the flexibility and adjustability of the modular design, all prove why this system is fast becoming the flat slab edge protection solution of choice.
Class B Designed to resist both static loads and low dynamic impacts, such as those of a person stumbling down an incline. Intended for use on shallow inclines such as modern house build construction. The main geometry limitations are the same as Class A, however : - The extent of infill must be such that at no point can a sphere of 250mm pass through it, so we are looking at a minimum of three tubes and a toe board in “tube and fitting” speak.
- The static load / performance test applied to Class A, must also be passed by Class B (55mm deflection at 0.3kN horizontal worst position load), however the Class B systems must also pass a low dynamic performance test. This involves 1.1kJ at low level, and 0.5kJ on all higher parts.
- Compliance with this dynamic test is best evidenced by a 50 kg sphericonical “swing bag” test for this purpose.
Pitched Roofs Pitched roofs are more complex, and the performance requirements for Class B are technically the hardest to meet, as they combine a requirement for stiffness with the need to absorb energy. The key here is to ensure that both the energy absorption (swing bag test) and the containment principles (250mm containment) are followed, and that the scaffold has taken the potential dynamic load into account. There are a number of solutions that do not rely on scaffolding, and again Combisafe is at the forefront of development with the Steel Mesh Barrier.
Class C This class has been designed to resist major dynamic or impact loads. The idea is to catch and contain, or “to cocoon” the worker. It is intended for use on steeply sloping roofs, and in areas where there is an opportunity for a high dynamic impact. The main geometry is as before, however: - A sphere of 100mm diameter must not pass through.
- The system must be between vertical and perpendicular to the working surface.
- There is no static load requirement, and no deflection limit for this Class, however there is a high dynamic impact test, involving 2.2kJ at the “worst location” within 200mm of the working surface. This is evidenced with a rolling cylinder test, which uses a 75kg rubber coated cylinder rolling down a 5m ramp inclined at 60º.
- The system must deflect more than 200mm (to absorb the impact slowly), and the cylinder must be contained. This is essentially the same test as a System U safety net to EN1263-1.
Sheeted Roofs Large bay sizes and lightweight components make it very difficult to find adequate structural capacity to support any form of edge protection load.The Combisafe Net Barrier System, in short a ‘cocoon netting’ concept is the latest product to address the problem and it seems to be working. The advantages are increased span up to 10 metres, simple light components, total roofer protection, a high degree of wind blown debris containment, and a high level of access control. The idea of edge protection being only provided by a flexible net takes a bit of getting used to, but most who have tried it have been pleasantly surprised by how quickly they become confident in the system. The system prevents the roofers from gaining access other than by the prescribed route, and links seamlessly with the safety netting below to totally contain the roofing activity in a cocoon.
The Point Of Impact The impact that this Standard will make on accepted current practice in construction, cannot be overstated. It puts the design responsibility back to the system designers, it includes specific performance criteria that must be met, and it sets a level of containment for all Classes. The combination of correctly installed safety nets below, and compliant edge protection at the sides, will make it very difficult for a roofer to fall.
These EN performance criteria will be challenging and, as with most change, the Standard will not necessarily be popular at first. If the industry embraces this change and adopts this common point of reference, the edge protection playing field will become more level, and the level of safety for roofers will dramatically increase.
All these system solutions address the two key questions. “Will it do the job?” and “Will it be erected correctly?” The first question will be answered by EN13374 certification. By “systemising” edge protection the problem of “on-site improvisation” is removed and to help many, including Combisafe, have in-house training courses for both installers and inspectors.
It looks like the new EN13374 is going to make a difference for the better. Many aspects will affect companies so the best thing to do is to look into the detail now so you can meet the standard. More articles from Combisafe International Limited: |
