Here's the dimension of the steel sheets that TEPCO laid on the floor of the high-radiation area in the reactor building for the Reactor 3 (information from Mainichi Japanese):
Dimension: 3 meters x 1.5 meters x 2 centimeters (or 9.84 feet x 4.92 feet x 0.79 inch)
Total number of sheets: 51
Workers also filled the gap between the sheets with thin steel sheets.
So, as the sheets are doubled, 4 centimeters of steel to protect the workers (organic and inorganic) from the very high radiation supposedly coming from the water in the basement.
No news yet on the radiation levels that the organic workers measured on July 8.