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..-:' :-.~'-':0r1i~"::-\ir;:~~~~::~~;~~~2"'-.~,;;_.; . --,.- .- . ;- f'-": ."' '.--~' ~.. ,1'. ":~""~..... .~"'-...,.~...~~ .................~-- '~--- P_03 ...--- .....- ... .~.--- GF~NERAI.J COMMENTS , In tbe event that, for reasons of simplicity of installation, desire for additjonal shielding, or economics as determined by the cUent, shieldIng in excess of the minimum thickness specified in this report may be used; however, shielding installed as specified in this report win satisfy the con, servative requirements of the Florida Control of Radiation Hazard Rogula. tions and the NCRP. . . .. .' l~HE L~:AD TAB QUESTION There is a general instruction provided for the installation of lead shielded gypsum board which causes unnecessary problems for the installers and degrades the strength of the finished instalhltion. On several previous jobs, I have seen instructions to install lead disks of thickness equal to the lead shielding behind the gypsum board to cover the screws used to secure the gypsum boards to the studs. In order to make the disks fit flush with the surface of the board, it is necessary to indont the area of the disk with a hammer or other instrument which often tears tbe paper surface which I am told significantly adversely affects the strength of the finished installation. Since the steel or iron used in the man ufacturc of the screw used to attach the gypsum board to the stud has only slightly less shielding capabili- ty than the lead on the back of the gypsum board (it takes less then half again as much thickness to achieved similar protection), the-:"3~rew itself, being much more than ten times the length of the lead sheet it penetrates, more than adequately shields the hole created by the screw. The net result of this is, lead disks to cover the drywall screws are NQI needed when steel or iron screws are used to attach the gypsum board to studs.