Calculations show that the tank would have begun to overflow at about 05:20. There is evidence suggesting that a high-level switch, which should have detected that the tank was full and shut off the supply, failed to operate. The switch failure should have triggered an alarm, but it too appears to have failed. Forty-one minutes later, an estimated of petrol would have spilled down the side of the tank through the roof vents onto the ground inside a bund walla semi-enclosed compound surrounding several tanks.