Flames produce heat; the rising, whirring air is plain to see, and distorts the graphics in the background.
Another example of flames can be seen in Shadowgrounds. The hotter the fire produced by the flamethrower, the more the air and flames swirl.
Water surfaces are the most popular PixelShader effects; the environment is reflected in warped surfaces. Each shot with the laser across water in Shadowgrounds produces light reflections in the waves.
Gas is simulated by distorting both the background environment and objects. If the character stumbles into poisonous fumes, the resulting queasiness sets the entire screen shaking.
Splinter Cell requires different view filters to represent night vision and thermal images.