EE WAS ASSISTING OTHER EE CHANGE THE VALVE ON THE CEMENT LINE AT THE TOP OF THE SHIPPING SILOS. PLANT AIR PRESSURE HAD NOT BEEN SHUT OFF, SO WHEN VALVE WAS OPENED, CEMENT SPILLED OUT AND ONTO HEAD OF EE. THE DUST FELL BEHIND THE EE'S SAFETY GLASSES AND GOT INTO BOTH OF HIS EYES. ER PHYSICIAN IRRIGATED EYES AND PRESCRIBED ANTIBIOTIC DROPS.