Yorkshire Water workman died of burns.

A Yorkshire Water workman died after being engulfed in a fireball in which he received 86 per cent burns, an inquest heard.

A mechanical engineer, Michael Edward Jennings, 55, was working in a well at a Yorkshire Water Treatment plant in Tadcaster, North Yorkshire, when sparks created by his angle grinder reacted with oxygen which had leaked into an unused effluent treatment tank used by Sam Smiths brewery.

The inquest heard that Mr Jennings, from Holme-on-Spalding-Moor, had been sent into the 3.4 metre deep well on July 20, 2015 to remove the valve but eight bolts holding it in place had corroded to such an extent he could not remove them without an angle grinder.

The inquest heard the plant is made up of three lanes and effluent from the Tadcaster brewery is treated with oxygen in each lane to dilute it before the waste is released into the River Wharfe.

Lane one was decommissioned in 2008 when two breweries which had previously used the facility decided to treat their waste themselves leaving Sam Smiths as the only brewery using the plant.

Mr Jennings, who had worked for Yorkshire Water since April 2010, was in the well alone and two other Yorkshire Water maintenance fitters, David Jones and Nathan Horsefield, were assisting him above ground.

They had followed a three-stage risk assessment procedure, but had not accounted for using an angle grinder underground in what was technically regarded as a ‘confined space.’

Mr Jones and Mr Jennings were later joined by Mr Horsefield, a trainee and former miner, with 15 years’ experience.

They started to remove the valve at 11am on Monday, July 20, and had first checked for noxious gases by placing an alarmed monitor in the well.

Health and safety executive inspector, John Micklethwaite, said the monitor’s alarm sounded when more than 23.5per cent oxygen was detected in the well.

When Mr Jennings started to work on removing the valve, the gas and oxygen levels were normal. The alarm sounded at 11.43am although records showed it was turned off at 11.48am.

Data retrieved from the monitor showed that the fire which resulted in Mr Jennings’ horrific injuries which led to his death two days later in Pinderfields Hospital, Wakefield, happened about 11.57am.

Mr Micklethwaite told the inquest that a near miss had happened in September 2014 in the same lane when workmen tried to remove its pumps.

The workmen had taken off a manhole cover to access the area, but the alarm on their gas monitors had sounded immediately and they were forced to ventilate it overnight until it was safe to enter.

This was reported to a line manager and the procedure for reporting ‘near misses’ was followed, but it is unclear whether warnings were put in place to alert other workmen.

Coroner, Robert Turnbull, said he was satisfied sufficient changes had been made to help prevent any future deaths.

A Health and Safety Executive inquiry is continuing into Mr Jennings' death.

In a statement, Yorkshire Water chief executive, Richard Flint, said: "Mick was a popular colleague and his tragic death has had a profound impact on everyone at Yorkshire Water."