Once you're on fire, how do you put yourself out?

When you are on fire, an indicator will appear on your screen. If you roll once, the indicator will go lower, but it will not go away. If you roll 3 or 4 times as fast as you can, you should put yourself out.

If you start rolling before the indicator reaches the top, you will take no damage.

There are water barrels randomly scattered throughout the map. Smash one open.

Careful, though, as there usually aren't many per map.