While playing in Casual/Ranked Multiplayer with a Thermite operator and you are attacking, use Thermite on a reinforced wall, which is a wall with spikes on it. You can also use it on the other side (blue) of the reinforced wall if you breach the enemy base. However, if you place the Thermite on a reinforced wall with electrical shocks emitting from it, you will take damage and your Thermite will be destroyed. You can see if the wall is charged by scanning for electronics or touching it and seeing if you take damage. The Thermite will also not work if the enemy team has a signal disruptor next to the reinforced wall.