The son of a man killed in an explosion at a chemical plant in Norwich was working alongside him when the accident happened, an inquest has heard.
Robert Cranston, 46, suffered serious injuries when flammable gas ignited causing an explosion as he was working to repair a tank at Briar Chemicals on Sweet Briar Road.
He died later the same day at the Norfolk and Norwich University Hospital
Mr Cranston, who had worked at the Briar plant for three years as a contractor involved in steel fabrication and pipe fitting, had been using a grinder and welding when the explosion occurred on July 27, 2018.
The first day of an inquest into his death heard his son had started work as an apprentice at the plant just months before the accident, and had been working alongside his father on the day providing “fire watch.
They were part of a team replacing a steel ring on a large glass lined chemical tank that they were told had been drained and flushed.
In a statement read at the inquest, Owen Cranston said they had been issued with “hot work” permits to carry out the work after safety checks and gas monitoring designed to ensure it was safe.
He said he was keeping watch at ground level while his father wearing a gas mask fitted to an air tank worked at the top of a scaffold.
He said: “There was a very loud bang and I felt a blast of air. I can only describe it as a jet blast coming out of an aircraft engine immediately before take off.”
He was told to raise the fire alarm. “When I ran back to the vessel I could see dad’s welding mask on the ground. At first I thought he had got clear but as I got close I could see there was blood running down his face,” he said.
A Health and Safety Executive report read at the inquest stated: “It is likely that there was some gas vapour directly around the vessel which ignited while the ‘hot works’ were ongoing. This then ignited the internal content of the vessel causing the explosion.
“Later analysis of the chemicals were carried out both immediately after the explosion and three days later. These tests show that there was an upper layer of Toluene in the vessel which was greater than 99pc concentration.”
Norfolk area coroner Yvonne Blake told the inquest jury they would hear evidence that tests of valves showed they had leaked up to 22kg of Toluene, a chemical used in the production of herbicides, into the tank.
She added that evidence would also be heard about the use of gas monitors. “There was no monitor calibrated to detect Toluene and the configuration of the monitor used would have given an artificially low reading,” she said.
“If the monitor suitable for testing Toluene had been used it would have alarmed within eight seconds as opposed to the gas monitor that was used which would take nearly seven minutes to alarm.
“A gas monitor was used before Mr Cranston began the work. It was switched on for a period of two minutes 18 seconds. The monitor did not alarm or display a non-zero reading.”
Gordon Wilcox, who at the time of the accident was a supervisor at Briar Chemicals, was one of three people who had issued the “hot work” permit to Mr Cranston.
He told the inquest gas monitoring prior to issuing the permit had concentrated on possible hazards from nearby drains because he did not think flammable vapours would be inside the tank.
He said: “Obviously with the work that Rob was doing, grinding and welding, you could get sparks being an ignition source carried across into the drain.”
He added: “My thoughts were that the vessel had been completely washed out, cleaned out, water had been put into the bottom part of the vessel, so we weren’t considering the inside of the vessel to be a hazard.”
The inquest is expected to last nine days.