Nooses.

[atomic1fire]

In muncher station (formerly known as cogmap) you could convert the engine's mixture room into a gas chamber. Especially if you just set the room on fire, then open the space doors to let all the fire out before you add a new prisoner. You might need a fire suit (to keep from getting burned) before doing that though.

You could perform station gas chamber executions and be a service to the engineers by just toasting the dead bodies in the furnaces when you are done.