Tower Controller described a confused runway entry event when a fire truck entered the runway at the departure end; opposite to the landing aircraft.

Narrative

An Air Carrier was returning to land with an emergency. A truck from the Fire Department; plus four other vehicles set up on Taxiway E at their respective positions awaiting the arrival. The pilot requested that the emergency vehicles follow him down the runway upon arrival. I relayed this information to the lead vehicle from the Fire Department. Upon landing each of the vehicles entered the runway as the aircraft passed them up except for one truck who was part of the group of fire vehicles. This truck; who was at the departure end of the runway; turned on the runway and was driving head on with the aircraft as it rolled out. This is something that I have not seen happen in the many years of being here. My recommendations to prevent this from happening is to train the Fire Department of when they are suppose to enter the runway. This is an isolated incident and to recommend drastic changes because of this is totally unnecessary but the controllers voice on this is never heard and someone behind a desk will make this decision. These same procedures have been in effect for many years and they have worked well.