The verifications carried out in the previous steps define requirements according to inputs from hazard analysis in conjunction with data from testing, but nowhere are the effects of an impact on the system evaluated. As such, performance criteria should be applied that are based on information collected during system certification and MEL testing, but which are not evaluated or classified under the ETAG 27 guideline.
As an example, the appearance of gaps that can open near post locations are considered. Such gaps occur when inflexible nets are used in areas where deformation is constrained by attachment points. In some cases the situation is so extreme that intentional failure points (or break-away elements) are required in order to prevent the primary net from failing. Not only is this an indication of the deformability of the primary net but it also points out areas were projectiles may potentially pass through the system relatively unimpeded. To help classify this, the allowable opening and attachment method is defined according to the consequence class as shown below. For example, a site rated with a consequence class of CC3 may not use systems with break-away for attaching the nets to the bearing ropes. In addition, the opening must not be greater or equal to 0.2 m after an MEL impact. If such an opening exists during testing, then the system is disallowed due to safety concerns.
Also specified are allowable failures/ruptures of key components which are otherwise acceptable by the ETAG 27 certification process. For example, no rupture or failure of the primary nets, bearing ropes or retaining ropes or of any strand of these ropes is allowed during an MEL test for a site with a CC3 rating.
The information necessary to carry out the evaluation of performance criteria is vital and must be documented during certification according to ETAG 27. However, it is not displayed on standard certification documentation though a conscientious manufacturer should provide unaltered copies of the original documentation from the certification process to support claims.
Consequence Class 1
Consequence Class 2
Consequence Class 3Next Step
What level of risk is there?
How is a design block selected?
What system capacity is sufficient?
What system height is required?
How is an anchor verified?
What other performance criteria are there?
How can the system be safely adapted to a site?
What recommended maintenance protocols exist?