The scientific justification of the ACR test and Factors of Safety
The background to the ACR test is decribed in the report ďHuman Impact Loads On RoofsĒ by A. Maitra. Details of the factors of safety implicit in the test can be found in paragraph 16.
Application of the ACR Test to glazed assemblies
Following the publication of the Red Book (ACR[M]001:2000) ACR has been asked several times about the application of the test to glazing. The correspondence has, predominantly, come in two forms:
- A comment that the test should not apply to glazed assemblies, and
- A question asking whether it applied to glazed assemblies and, if not, why?.
The Committee always responds as follows:
When the ACR developed the test, there was no input from the glazing industry. Consequently, the ACR were not aware of the special circumstances, which may be connected with glazed assemblies. Therefore, the ACR test does not require any preliminary drops of sharp low-weight objects onto the assembly1. Neither does it require any post-test loading of the impacted assembly2. This is because on most industrial types of roof, rescue of the fallen person would be possible without going on to the damaged assembly.
Note 1: Impact of sharp low-weight objects, eg, tool-boxes dropped on end, can have a significant effect on the impact strength of glass.
Note 2: On industrial roofs, the purlin spacing is unlikely to exceed 1.8m. This means that a person who has fallen and cannot self-rescue, can be rescues by someone working entirely from an undamaged area of roof.
With many glazed assemblies, the spacing of the supports is much greater, which means that the rescuer could have to work from within the damaged area.Therefore, the ACR recognises that the test, as specified, may not be applicable to glazed assemblies.
However, ACR would stress the point that the drop test specified in the Red Book represents the forces that a 100kg person falling from standing to seated would apply to the surface he/she has fallen on. This force would not be different for glazed assemblies and should be the one that is applied as the definitive test for non-fragility, regardless of any additional requirement to pre-test and post-load.
The background to the development of the ACR test can be found in the report ďHuman Impact Loads on RoofsĒ . Readers are also advised that a working group sponsored by the Centre for Window and Cladding Technology [CWCT], in Bath, is developing a test applicable to glazed assemblies [Technical Note TN 42].
Application of the ACR Test to GRP Rooflights
The NATIONAL ASSOCIATION OF ROOFLIGHT MANUFACTURERS (NARM) have produced a GUIDANCE NOTE (ref:2004/1 -Test for Fragility of Roofing Assemblies (ACR[M]001:2000) - Application to GRP Profiled Rooflight Sheeting)
This Guidance Note sets out guidelines on the application of ACR[M]001:2000 -Test for Fragility of Roofing Assemblies ( the Red book) to GRP Profiled Rooflight Sheeting, together with recommendations for GRP sheet weights to use in order to achieve the desired levels of performance in various applications.
A copy of the guidance note can be can be found at www.narm.org.uk/home/pdfs/guidancenotespath2004.pdf
How should the Red book test be referenced in manufacturers literature
The ACR recommends that the correct and preferred method for manufacturers/suppliers to use to reference the Red Book test when referring to the non fragility aspects/classification of their products is :
" Tested and Classified to ACR(M) 001: ( insert year/version number of the red book used for the actual testing) Red Book ( compliant with the current edition)."
The actual test originally defined in ACR (M) 001: 2000 has remained unchanged throughout each subsequent revision of the Red Book - the various revisions merely seek to clarify aspects of the interpretation of itís correct application.
When a new version of the Red Book is issued it automatically supersedes the preceding version which becomes obsolete and is withdrawn.
The latest version of the Red Book WILL always be used to validate any claims regardless of which version was current / used at the time of actual testing. When a new version of the Red Book is issued manufacturers MUST check that the interpretation of the Red Book used at the time of testing is still valid in accordance with the new version.
If the interpretation is still valid then the products may continue to claim compliance to the Red Book without further testing.
If the interpretation used is invalid then compliance with the Red Book may no longer be claimed and retesting must be done using the correct interpretation as detailed in the latest version of the document.
Note: By claiming compliance with the Red Book all manufacturers and suppliers MUST accept and agree to these stipulations otherwise the ACR will withdraw itís permission for any reference to itís publication/test being used by them.
The ACR recommends that the preferred method of reference indicated above should be used in any future publications/ material.
Existing printed literature which contain a wrong method of reference may continue to be used but should be revised to use the preferred reference method as soon as reasonably practicable.
The ACR recommends however that more easily amended transient publicity material such as websites, adverts, flyers etc. should be brought up to date as soon as possible.
Note: Merely using a wrong method of reference does not invalidate the classification claim of any product provided the above principles & requirements are met and should not give cause to raise a complaint against the product under the ACR complaints procedure. Where a wrong method of referencing is found being used Clients/Purchasers should satisfy themselves, by enquiry to the manufacturer/supplier, that the above procedure has been carried out.
[See also ACRís Legal Page re acceptable use of the Red Book]
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