The firm which owns the Rugby Cement plant has been fined £400,000 after its negligence led to cars and houses in nearby villages being covered with a potentially toxic dust.
Cemex UK Cement Limited had pleaded guilty at Rugby magistrates court to failing to comply with conditions of a pollution prevention and control permit.
And at Warwick Crown Court the firm was hit with a heavy fine and ordered to pay £12,429 costs after the Judge criticised its 'sloppy attitude' to the situation which emerged in October last year.
Barry Berlin, for the Environment Agency, said the company, part of a multi-national group, manufactures cement at the Rugby Cement works at Long Lawford, near Rugby.
It committed a serious breach of the regulations by failing to ensure that an external door at the top of the 150-foot tall 'reject clinker silo' was properly maintained.
"The door was hanging off two of its three hinges, which allowed a large amount of cement and clinker dust to escape into the atmosphere."
The dust was sticky, and could not easily be removed from the cars, window sills and windows on which it landed over a distance of 4.5 kilometres, particularly in nearby Long Lawford and Lawford Heath.
Mr Berlin pointed out that the dust is 'potentially very hazardous and toxic,' and when damp an alkaline solution is formed which can cause burning and ulceration to skin and eyes, as well as irritant contact dermatitis.
Although there is no evidence that people did suffer from those effects, it had presented a risk, he said.
The Environment Agency received ten complaints from people in the area about dust covering their cars and homes.
Because of the potential hazard to health Cemex was required to check all external doors at least once every shift, not simply look from the ground to see whether any dust was being emitted from the door at the top of the silo.
BT engineer Stephen Walsh was the first to notice there was a problem as he was walking his dog at 8.30am on October 14, and he contacted the Environment Agency when dust was still coming from the silo two hours later.
At 1.10pm Cemex employ-ees were told and found the door was off its top two hinges and with a section of cladding missing, there was still a one-inch gap when it was closed.
Despite that, the kiln was re-started at 2pm and by midnight 175 tonnes of reject clinker had been produced, and large amounts of clinker dust escaped and was carried on light 7 mph winds all over the Rugby area.
Lucie Allen, defending, said there was no adverse impact to the health of people in the area, and although it was conceded there would have been a risk, it did not materialise in this case.
She said that although the door was wide open at one point, it was then closed, leaving a one-inch gap, and only low concentrations of the dust were involved.
"The breach by not properly checking the doors, for which the company is being prosecuted, was aggravated by something beyond its control in that there was a kiln flash," which she said resulted in more reject clinker being produced.
By the time a maintenance meeting was held at 3.30 and the contractors were instructed to repair the door, they could not start the work until the next morning for health and safety reasons because they were at the end of their shift.