Poisonous gases have been found seeping into a Bradford shop, according to an electrical shopping chain.
Maplin Electronics plans to take legal action against the landlord of its store in Hamm Strasse, amid claims environmental consultants discovered methane and "other poisons".
The store was closed in October when staff complained of nausea and headaches.
Since then the company has been operating a catalogue order service from a temporary cabin in the store car park.
Maplin retail director Graham Caldwell said the firm now planned to take legal action against the building's owners Carpet World - which has a shop next door - to recoup lost revenue caused by the store's closure.
And ventilation work is to be carried out so the premises can reopen later this month.
Mr Caldwell said: "There were traces of methane and other poisons found but it's rather sensitive since we are taking action against the landlords.
"We have lost trade because of the closure and we will be keen to tell people when we are open again."
More than half of the shop's ten staff had reported feeling unwell and were checked out by doctors.
Officers at Bradford Council's planning department were unable to say what the land beneath the building had been formerly used for but Maplin believes it was the site of a landfill tip.
Mr Caldwell said insurance loss adjusters had been appointed on behalf of the company.
A spokesman for Carpet World said the matter was being investigated.
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