Describe the dangers associated with tunneling jobs, and explain how Jurgis is injured.

From the text:

"In a work thus carried out, not much thought was given to the welfare of the laborers. On an average, the tunneling cost a life a day and several manglings; it was seldom, however, that more than a dozen or two men heard of any one accident. The work was all done by the new boring machinery, with as little blasting as possible; but there would be falling rocks and crushed supports, and premature explosions--and in addition all the dangers of railroading. So it was that one night, as Jurgis was on his way out with his gang, an engine and a loaded car dashed round one of the innumerable right-angle branches and struck him upon the shoulder, hurling him against the concrete wall and knocking him senseless."