Board Thread:General Discussion/@comment-34256877-20190423040750/@comment-31797469-20190423154056

Based on thousands of tries with 0 or 10 torches a few years ago by User:BunsenH, the base chance is 1% if no torches, and 11% with 10 torches.

Probably, the chance is 2% with one torch, or more generally (1 + Number of Torches) %