However, as a result of an upset on the distillation column the amount of contaminant in the incoming stream rose to 9% and the flash point fell. If this incoming liquid had been added to the base of the tank, the usual practice when adding liquid to a tank, the change in the composition of the liquid would have had little effect on the composition of the vapour. But the tank was fitted with a swing arm so that liquid could be withdrawn from any level. This swing arm was stuck in the fully raised position and could not, therefore, be used for withdrawing liquid from the tank which was one-third full. The swing arm was therefore being used for delivery and the normal delivery line into the base of the tank was being used for