A trained operator was blending water, sand, anhydrite, lime, cement, pulverized fly ash, and powdered aluminum in a mixing chamber to produce material for making concrete building blocks. In the blending process, sand and water are mixed to form a slurry, and then the powders are dispensed automatically into the mix by a computer-controlled system. Finally, a slurry of glycol-coated aluminum powder is added in the last few seconds before the mix is discharged into a car, and then molds are filled from the car. Adding aluminum to the mixture results in a small amount of hydrogen gas evolution, which disperses from the car into the surrounding ventilated area and out through roof vents. In addition to being an ingredient of the mix, water also helps to keep the mixture cool.

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During a refueling event, the operator activated the fueling lever in the wrong sequence. The vehicle filled to proper pressure, but filled faster than normal. Under different circumstances, this could have resulted in overheating of the receiving fuel tank.