29 Nov 2011
The Story
The NASC have now officially stated that the tables in Volume Two of TG20:08 are outdated and that the entire code is under review. For those people using TG20:08 on a daily basis this is old news. The new Eurocode BS-EN-1991 has been in existence since 2005 and replaced BS 6399 on 31st March 2010 when BS 6399 was officially withdrawn by the BSI.
Earlier in the year the NASC launched 'Appendix H' which was a re-write of the tables in TG20:08 Volume One using the new European wind code. However, the tables in TG20:08 Volume Two were not considered and continued to be used even though the code upon which they were based had been withdrawn.
Originally the NASC stated:
"Due to the impending review of TG20:08 Volume 2, which is necessary following the introduction of the European Wind Code and the publication of BS EN1991-1-4:2005 A1:2010 (European Wind) and the National Annexe to BS EN1991-1-4:2005 A1:2010, all the safe height tables, text and diagrams associated with wind loading covered in TG20:08 Volume 2 are no longer valid and the tables detailed below should not be used, with immediate effect."
"The NASC are currently reviewing the data associated with the wind load calculations and intend to issue revised data shortly. Until this time the NASC advises all users of TG20:08 - Volume 2 that the safe heights identified in the tables mentioned above will have to be determined from first principles."
This would have posed a significant challenge for the NASC members and the industry in general who are using TG20:08, meaning a large number of previously acceptable scaffold configurations would now require design.
The NASC stance has now changed somewhat and they are no longer stating that the tables are 'invalid' and 'should not be used' - the insistence on first principle design did seem like a knee-jerk reaction. The new article on the NASC website is copied below:
"Following the introduction of the European Wind Code and the publication of BS EN1991-1-4:2005 A1:2010 (European Wind) and the National Annexe to BS EN1991-1-4:2005 A1:2010, the NASC has undertaken a review of all the safe height tables, text and diagrams associated with wind loading covered in TG20:08 Volume 2 as shown below.
Tables being reviewed: Table 29 – 31 (Pages 154 – 159) Safe heights for Basic independent tied scaffolds fully ledger braced with fully loaded inside boards. Safe heights for Basic independent tied scaffolds part ledger braced. Appendix A - Tables of maximum safe height for fully ledger braced Basic Scaffolds Appendix B - Tables of maximum safe height for part ledger braced Basic Scaffolds with line of ties at alternate lifts. Table 34 – 36 (Pages 165 – 168) Tables A1 – A24 (Pages 172 – 219) Tables B1 – B12 (Pages 222 – 233)
The NASC are currently completing the final review of the data associated with the wind load calculations and intend to issue the revised data shortly.Until this time the NASC advises all users of TG20:08 - Volume 2 that scaffolds erected using the current safe height tables in TG20:08 remain safe and do not require further calculation or review."
The whole situation does leave a couple of questions unanswered. Firstly, why didn't the NASC state this publicly at the beginning of the year when this situation arose? Secondly, why were the wind calculations in TG20:08 not completed using Eurocode BS-EN-1991-1-4 in the first place?
For those people worried about the situation and wondering which code of practice they should be using for the erection of scaffolding, the advice of 48.3 is this: continue to use TG20:08 Volume One with Appendix H and continue to use TG20:08 Volume 2 as suggested by the NASC. The tables in Volume Two although outdated, have not become unsafe overnight. You do not need to suddenly get a design completed for these scaffolds. If you are in any doubt you can contact the NASC for advice, contact details are on their website.
The article on the NASC website can be found here: http://www.nasc.org.uk/TG20_Launch
