Then one day he accidentally kicked the wall with his metal shoe tip.
It made a sound like that from kicking a tight-stretched section of tin and it seemed to him it gave a little from the impact, as tin would do. He realized for the first time how thin it was—how deadly, dangerously thin.
According to the specifications he had read it was only one-sixteenth of an inch thick. It was as thin as cardboard.
He sat down with pencil and paper and began calculating. The bubble had a surface area of 146,500 square inches and the internal air pressure was fourteen pounds to the square inch. Which meant that the thin metal skin contained a total pressure of 2,051,000 pounds.
Two million pounds.
The bubble in which he sat was a bomb, waiting to explode the instant any section of the thin metal weakened.
It was supposed to be an alloy so extremely strong that it had a high safety factor but he could not believe that any metal so thin could be so strong. It was all right for engineers sitting safely on Earth to speak of high safety factors but his life depended upon the fragile wall not cracking. It made a lot of difference.
The next day he thought he felt the hook to which the exerciser spring was attached crack loose from where it was welded to the wall. He inspected the base of the hook closely and there seemed to be a fine, hairline fracture appearing around it.