7 The plaintiff contends that there is only one feasible explanation for the events that occurred. That explanation was advanced in an injury/incident report compiled by the defendant's staff in March 1999, in a report compiled for the defendant by a consultant chemical engineer, Dr Cockshutt, in March 2001, and by an expert witness called to give evidence for the plaintiff, Mr Dreher. Mr Dreher is a risk engineer with qualifications and experience in chemical engineering. The explanation is essentially as follows. Accepting that practically all the water that was at the bottom of TA248B was drained therefrom through the tap at the bottom of that vessel before its contents were transferred to RE357, a significant quantity of water must have been present, mixed with the toluene that was transferred to RE357, and must have settled to the bottom of RE357 when that vessel's contents were**,** unusually**,** left standing for some hours without agitation before the distillation process was commenced. When heat was applied to the sides of RE357, but not the bottom, the toluene began to boil, but the water below it did not. The boiling point of a liquid depends upon the pressure of the air or gas above that liquid. The higher the pressure, the higher the boiling point will be. The effect of the toluene boiling was to increase the pressure in the head of RE357 as the toluene boiled. The effect of the increased pressure was to increase the boiling point of the water under the toluene. After the operator closed off the supply of steam that was heating RE357, the pressure in the head of that vessel began to fall. It fell until the water began to boil. The water was superheated, ie, it was a liquid but its temperature was above 100oC. The toluene was still boiling when the water started to boil. When two different liquid compounds boil in a closed vessel, the pressure in the head of that vessel is increased by the sum of the pressures exerted by each boiling compound. When water boils, it expands dramatically. Thus, when the superheated water began to boil, with the toluene boiling simultaneously, the pressure in the head of RE357 increased so dramatically that the rupture disc ruptured, the gasket around the access lid blew out, and the access lid buckled.