E.8.3 Add Iron Shoring [1791]

Time to learn: 21 days.
Time to use: 14 days.
Requires: ten workers [11] (not consumed)
Requires: ten iron [79]

Use of this skill adds iron shoring to a mine shaft. Normally the chance each month of a cave-in in a mine shaft is (depth/300)%. Iron shoring reduces this chance by 4.6%.