Using Liquids

Once the new brush is created and the lava texture is
applied, it's time to make it sting.  Make another brush
with the exact width and length as the lava but only make
it a couple of units thick.  Make sure it's resting right on
top of the lava brush and use the 'trigger' texture to cover
it.  This can be found in the 'common' section of your
texture menu.  With the texture applied and the brush
still selected right-click on the wireframe window and
choose 'trigger' then 'trigger_hurt'.


  

Hit the 'n' key to bring up the entity menu and in the
key field enter 'dmg' and in the value field enter '20'
This will cause the player to take twenty health points
every second contact is made with the lava.  If you want
instant death just increase the value to 200 since it's
the maximum health status.  

  

'Trigger_hurt' is also used in hell fog or the killing abyss
in space maps.  You can use it on any kind of brush. Above
You can see the joy of standing in a cool tub of water and
the agony of lava.  Ouch!