Abstract: The accident site was the Vista (concrete) batch plant. At about 8:00 a.m. on April 5, 1993, a cement-storage silo with a defective pressure relief device was being filled with cement powder by compressed air transport from a powder truck. The indicator alarm system that warns of overfilling the silo was inoperative. Furthermore, a rope system that indicates the level of cement in the silo was either jammed or was misinterpreted by the powder truck driver who proceeded to fill the silo. Consequently, the silo was overfilled with pressurized cement powder that blew away an unsecured hatch cover of the silo and created a large dense cloud of cement dust. This dust cloud engulfed a mixer truck driver, Employee #1, who was located near the base of the silo in her truck. Employee #1 suffered a delayed, disabling, and chronic respiratory illness from the acute and severe exposure to Portland cement dust.