How to make an instant death sector?

How can I make it so that when a player touches lava or whatever he instantly dies rather then getting hurt?

I'm using Skulltag: Doom in Hexen format.

You can use a Actor Touches Floor thing (number 9999), and give it a thing special of ThingDamage with 255 damage. Just put it in all sectors you want the player to be killed.

Use sector type 115. No need for workarounds.