In this blog I give my top technical tips when working with multiple trades on installing shielding within large construction projects.
We’ve worked with a number of dry-lining contractors on large projects over the years, and one thing our experience has taught us is that close liaison between trades is essential in successfully installing radiation shielding.
All contractors need to be aware of the critical importance of shielding in lead-lined rooms and the role it performs in protecting people from harmful ionising radiation. For this reason it is essential that penetrations, either intended or unintended are reported immediately so they can be rectified.
To minimise errors on large construction sites we work with contractors to ensure that each board is carefully labelled with the lead code used, the board type and also the exact location it is to be placed. By taking this approach errors can be minimised and penetrations repaired, always of course in liaison with the projects main contractor.
Aside from logistics, sequencing and programme management, the planned handling of penetrations through shielded walls will lead to savings in cost management as well as the timely completion of works.
Here’s my top technical tips:
Shielding behind power boxes often creates issues when boxes are ‘back to back’ on each side of the partition. This makes effective shielding difficult if not impossible. When lead-lined boards are installed it is not always possible to determine the exact position of the power boxes. However, this problem can be overcome by using a lead-lined pattress which runs from stud to stud at 600mm centres. This will allow for horizontal adjustment of the box.
By using a lead-lined pattress, commonly 600mm wide x 300mm high, a shadow of at least 100mm can be created around the box. The thickness of the plywood is unimportant, in respect of shielding, but the lead used should be the same code as the lead-lined boards.
On large builds it is common for the dry-lining package to be separate from the joinery package. However, these two packages come together at doors and windows in shielded rooms. This fact needs to be taken into consideration at the commissioning stage. Liaison between the two trades will help identify problem areas at an early stage and enable the dry-lining work to be conducted efficiently and effectively, saving time for the joiners who follow.
It is recognised good practice to shield behind all vertical board joints with a lead fillet strip of the same thickness as that on the lead-lined boards. For the plain board joints this is usually a 50mm strip of lead running to the same height as the lead-lined boards. Whereas at the corners it is usually a 100mm strip of lead.
The structural opening for doors and windows will also require shielding. This can be achieved by trapping a 100mm lead fillet strip between the last stud and the boards, leaving about 50mm to return around the reveal. This ‘overlap’ will allow the on-coming joinery contractor sufficient lead to ensure continuous shielding across the structure interface. This technique should be applied at each side of an opening and also at the top. In the case of windows, the lower horizontal reveal will also require the same approach.
Air handling, gas and water supply all create potential penetration issues in a shielded room if they pass through a lead-lined wall. This problem is particularly acute when post installation adjustments have to be made. Labelling of the shielded wall, as discussed in the electrical section can help with this, as can frequent site liaison meetings. However, simply changing the method used to shield penetrations can give extra flexibility in the post installation stage.
The standard approach to shielding an air handling duct penetrating a lead-lined wall is to wrap the appropriate thickness of lead around the duct, returning on to the wall at least 25mm all around and coming out along the duct as far as the Radiation Protection Advisor (RPA) advises appropriate. This is typically a minimum of 150mm.
However, creating a horizontal baffle, above the finished ceiling level but below the duct, can increase the amount of flexibility the mechanical installation team has during their work. The baffle can be made from plywood with the appropriate thickness of lead attached, sized and positioned in accordance with advice from the RPA. This method allows for installation at a later stage and is less dependent on the ducting being in its final position.