The rule for this can be found under the "Action Cards" section in the 3rd paragraph.
Three Action Cards are dealt to each player at the beginning of the game. After placing a tile next to a village, a player may draw one Action Card for each new lava flow in contact with the village, even if the village is protected by a wall in that location or the
village is not owned by any player. A player may also draw an Action Card on each turn if his village has entered or passed the second Danger Zone on the Burn Meter.
Another clarification about the Action Cards from Stratus Games is:
The deck of Action Cards is shuffled and reused when depleted. This is not explicitly stated in the rules, but will be clarified in future versions.
This point has been stated explicitly in the recently released video tutorial: