A worker who tried to rescue his colleague from a fatal blaze at a water sewage plant saw "his whole body catch fire", an inquest has heard.
Mick Jennings, 55, died in hospital following the blaze in Tadcaster, North Yorkshire, on 20 July 2015.
The jury at Selby Civic Centre heard sparks from a grinding tool he used caused the fire at a treatment tank.
David Jones recalled the moment his own thigh caught fire as he pulled Mr Jennings out of a well.
In a statement read out in court by Coroner Robert Turnbull, Mr Jones, who was not at the inquest, said he was working with Mr Jennings when he saw "sparks on Mick's right leg... He [Mr Jennings] went to pat it then his whole body caught fire".
Mr Jennings, a mechanical fitter for Yorkshire Water, was changing a drain valve in a 11ft (3.4m) deep well at the tank when the fire started, the jury heard.
Giving evidence, John Micklethwaite, from the Health and Safety Executive, said a valve was opened letting leaked oxygen in, which reacted with an angle grinder causing the fire.
Bolts holding the valve in place had corroded to such an extent that Mr Jennings could not remove them without using the grinding device, the inquest heard.
A risk assessment form had been filled and a permit had been granted to work on the Oxton Lane site.
Mr Jones said they had "no reason to suspect it was an oxygenated or explosive environment".
The inquest continues.