Venting holes were opened on the side of the galleries, and mechanical hatches made of iron were installed, along with an electric railway into the upper tunnel.
Mechanical iron hatches were installed, along with an electric railway into the upper tunnel. Venting holes were opened on the side of the galleries.
Venting holes were opened on the side of the galleries. Mechanical iron hatches were installed, along with an electric railway into the upper tunnel.
Venting holes were opened on the side of the galleries. Mechanical iron hatches were installed, along with an electric railway into the upper tunnel.