3T stands for ‘Through The Trap Door’ and is an approved method of assembly by the HSE that reduces the risk of the assembler falling. Using this method, the assembler sits on the platform trap-door to add or remove any guard rails above. This system protects the assembler from standing on an unprotected platform. Once guard-rails are secured in position the assembler can climb onto the platform and continue constructing the next level.
AGR stands for ‘Advanced Guard Rail’ which are rails that can be assembled on the next level above the one on which the assembler is standing. There are two types of system available known as ‘additional’ or ‘integral’. The ‘additional’ system means that as each level is assembled, a permanent guard rail is added in place of the AGR, which is moved up to the level above. The ‘integral’ system forms the advanced guard-rail as part of the tower structure so it remains in the same position until the tower is dismantled.
Which is the safer system?
This is a subjective question but if you are using the AGR system correctly, means you are never exposed to the danger of falling by standing on an unguarded platform. However, whilst the 3T system is more cost effective, if used according to the instructions is also a tried and tested method approved by the HSE for erecting tower scaffolds safely.
AGR systems are generally more expensive because there is more material used, more welding and cast components in each level. The positive part is there are less overall components and it is harder to build incorrectly but does limit the height flexibility.
TB Davies Contractor Towers are available in both 3T and AGR options. TB Davies AGR towers use the ‘integral’ system described above. The webpage below contains videos of the both tower systems being erected so you can see the difference in each structure.
When using either of these methods make sure the person in charge is competent to do the work in hand and they know what they are doing. PASMA (Prefabricated Access Suppliers’ & Manufacturers’ Association) are the body that represent the mobile tower industry in the UK and run the only recognised industry standard training scheme for inspecting, erecting and dismantling towers. Please find additional information on the PASMA Tower Courses.