[Seth Ben-Ezra]

Unfortunately, the game sets any roll where half or more of the dice turn up 1 as a critical failure. This means that when players roll 1 die they have a 10% chance of a critical failure occurring, and when they roll 2 dice they have a 20% chance of a critical failure occurring.

Actually, the chance of rolling a single 1 on 2d10 is 9%. Figure it like this:

--the chance of rolling something other than a 1 on 1d10 is 90%

--therefore, the chance of rolling something other than a 1 on 2d10 is .9*.9=.81=81%. Therefore, there's a 100%-81%=9% chance of rolling at least one 1 on 2d10.