A mill where four workers were killed in an explosion had a "superficial" risk assessment and a build-up of dangerous wood dust, an expert has told a court.
Cleaner Dorothy Bailey, 62, maintenance fitter Derek William Barks, known as Will, 51, mill worker Derek Moore, 62, and chargehand Jason Shingler, 38, died in the explosion at the Wood Treatment Ltd mill in Bosley, Cheshire, on July 17 2015.
Wood Treatment Ltd and mill owner George Boden, 65, deny their manslaughter.
Giving evidence at the Nightingale court at Chester Town Hall on Tuesday, principal safety inspector Sam Summerfield told the jury there was a "very large gap" between the procedures which should have been carried out at the mill and what actually happened.
He told the court it was likely the explosion was caused by an "initiating incident" within the mill and then there was a secondary blast, caused by a build-up of wood dust.
He said: "There is evidence that we have seen and heard in regard to accumulation of amounts of dust within the mill over an extended period of time.
"It wasn't everywhere all the time but for long periods of time there was enough there."
Mr Summerfield told the court wood dust was a dangerous substance, but the court has heard evidence from former workers of "mounds" of sawdust in areas.
When asked about the control measures in place to stop an explosion, Mr Summerfield said: "Overall, the picture is not good."
He said the risk assessment the mill had in place was "superficial" and there was no evidence there had been any consideration of safety processes when changes were made to the plant after it was bought by Boden and his two brothers in 2008.
Mr Summerfield said the housekeeping regime within the mill, where Mrs Bailey was the only cleaner, was not sufficient and there was evidence it was not effective.
He told the court a change in the raw material used at the mill could have affected the rate the machinery eroded and temporary repairs made to equipment were likely to fail after a short period of time.
He also said evidence of activations of a Firefly system, which alerted staff when it detected sparks within the mill, showed controls to stop ignition sources were failing.
Wood Treatment Ltd has admitted a health and safety offence, but denies four counts of corporate manslaughter.
Boden, of Church Road, Stockport, denies four counts of gross negligence manslaughter and a health and safety offence.
Mill manager Peter Shingler, 57, of Tunstall Road, Bosley, and operations manager Phil Smith, 59, of Raglan Road, Macclesfield, both deny a health and safety offence.