The driver who hit them is also a member of the same fire department, who was driving a dually pick-up truck.
It happened at 2055 hours when the on-duty firefighters were stopped on the small two-lane road to check out their front tires.
Louise Volunteer Fire Chief Tommy Johnston said the three men all responded to the same fire call minutes before. He said Henderson and his partner were in a fire tanker truck while the other firefighter was in his personal pick-up truck.
Johnston says Henderson and his partner left the fire scene first and drove up FM-647 where they had to turn around. The third firefighter left the scene shortly after, driving up the same road and did not see the fire tanker truck parked in the roadway, or the two men standing outside of it.
Troopers say the emergency lights on the fire tanker truck were not on, but the headlights were. Henderson was initially transported by LifeFlight to Memorial Hermann Hospital with severe injuries.