Sunderland-based Romag Ltd also ignored recommendations from its own safety advisors to cordon off a contaminated area and arrange for an emergency clean-up by specialists.

The incident was triggered by two fire alarm installers when they started some work at the firm’s Princess Building on Leadgate Industrial Estate in July 2011.

Consett Magistrates’ Court heard that the two subcontractors, who had been told the building was free from asbestos, unknowingly drilled through an asbestos insulation panel while installing fire sensors.

They then used a domestic vacuum cleaner to clean up the dust and debris and later used it in several parts of the building as they put up the sensors, spreading asbestos fibres around the premises.

The court was told the asbestos disturbance was discovered the next day but Romag Ltd failed to take any appropriate action for at least nine days, even though its own health and safety advisors had urged it to cordon off and lock down the area and arrange for an emergency clean-up and air clearance test.

HSE found the firm’s delay in taking action led to 180 workers and 16 visitors being put at risk of exposure to asbestos fibres.

When the clean-up was organised, a substantial amount of contaminated material was collected.

Romag Ltd, of Sunderland pleaded guilty to safety beaches and was fined £20,000 and ordered to pay £12,638 in costs.

After the hearing, HSE Inspector Paul Miller said: “Romag Ltd needlessly put at risk the health of nearly 200 people because they failed to identify the presence of asbestos before any work started and then compounded the failing by not acting quickly to clean the area properly.

“Any company that intends to do work to the fabric of a property built prior to the year 2000 must ensure that they have taken all reasonable steps to check whether asbestos is present before any work starts.

“That information must be then shared with anyone involved in the proposed work.”