A BUSINESS has revealed more details about a chemical reaction incident which stopped work for the day and left hundreds of people evacuated from their Derby homes.
Nuns Street Plating, where the incident happened, said it was the result of a chemical reaction which went wrong.
The company has apologised to the public for the widespread panic it caused.
The company said engineers had been advised to mix an incorrect measure of three chemical substances which caused a reaction.
And it was the first time the business – which has been operating for 25 years – has ever had an incident like this happen.
Today police remained outside the company, on Nuns Street, while a health and safety investigation took place.
Staff were not allowed back on the site and had to remain outside.
Jean Ditheridge, managing director at the business, said: "The three chemicals involved include two diluted acids and one soap inhibitor, and when mixed incorrectly, there is an unusual odour of fumes which an experienced plater would recognise immediately.
"Nuns Street Plating is a family run business and has served Derby's rail and engineering industries for over 25 years.
"Our team are professional qualified platers, which means we coat the components used in engineering fabrication processes.
"There is a chemical treatment involved in the plating procedure. However, as a rule this practice isn't dangerous and is highly unlikely to cause an incident."
The managing director continued: "As we work with chemicals, our team does follow a strict health and safety policy and we have all the relevant ISO accreditations for our services.
"Yesterday, for the first time, one of our engineers had been advised to mix an incorrect measure of three chemical substances which caused a reaction.
"However following our protocol, our engineer reacted immediately to diffuse the situation and make the area safe.
"As a precaution, he alerted the emergency services and when they arrived the risk was contained, and indeed no damage was caused and nobody was hurt.
"We do apologise for the huge inconvenience to local residents and thank the emergency services for their assistance."
People living on Mill Street, Bridge Street and Nuns Street were told to leave their homes while police waited for a bomb disposal team, which arrived from Chilwell Barracks at about 7.30pm last night, to assess the situation.
Those evacuated included University of Derby students who had only moved into their halls of residence hours before.
Paul Cocker, manager of Nuns Street Plating, said everybody at the factory was extremely concerned when the incident happened.
Mr Cocker said: "It was very worrying when we found out. At first, nobody knew what was happening.
"If something happens which is not quite right, we know to get out of the building as soon as possible.
"When you see all the fire engines, bomb squad and people talking about explosives then it is obviously worrying.
"We called the fire service and they arrived within five minutes.
"The incident was caused by a mistake.
"Nobody is perfect and accidents do happen. It was a miscalculation.
"But we did the right thing by calling 999. Nobody wants to see an incident like this, it's scary.
"When dealing with chemicals we have to follow a procedure when in a built-up area.
"We do a lot of business with Bombardier and people like that and they are still 100% with us. We are a vital link in their chain."
A spokeswoman for the University of Derby said: "Following the incident, it will be important that any lessons are learned by all involved, as this affected many local residents in the area around Nuns Street, including many of our students.
"We will continue to work with partners to understand any risks and try to ensure that we meet our priority for our students and staff to have a safe environment in which to live, study and work.
"I imagine the company has learned lessons from this," she added.
A police spokesman confirmed students returned to their homes at about 2.20am.
Many students who had only moved into their halls of residence hours earlier were part of the evacuation.
Daisy Giuliano, 20, is the president of the university's Student Union.
She said the students were disappointed to be held back from going out into the town, many of them arriving for their first day.
She said: "It was good bonding with people being outside in the street, especially because many have not seen each other before.
"There were no horror stories and people were safe.
"However, it was one girl's birthday and she was gutted not to be able to go out."
A spokesman for Derby City Council said: "Nuns Street Plating is situated on an industrial estate; the site has planning permission for this type of industrial process.
"The Health and Safety Executive is the enforcing authority for safety issues at such premises."