WHILE SLOWLY PULLING IN TO MY PARKING SPOT AT WORK, I APPLIED THE BRAKES TO STOP.TO MY AMAZMENT, THE BRAKE PEDEL WAS EXTREAMLY HARD. I HAD APPROX. 2 SECONDS TO REACT BEFORE I ROLLED INTO AN EXHUAST FAN ATTCHED TO A BUILDING. AFTER A FEW TAPS ON THE BRAKE PEDEL IT WAS STILL HARD AS STEEL.BY THIS TIME I HAD IMPACTED WITH THE EXHAUST FAN. THE DAMAGE TO MY TRUCK WAS BAD ENOUGH, HOWEVER THIS OUTCOME COULD HAVE BEEN FAR MORE SERIOUS IF A CO-WORKER WALKING OUT OF THE DOOR NEXT TO THE EXHAUST FAN WAS NOT AS QUICK THINKING AS HE WAS.