Abbott and Mason Building and Joinery Contractors exposed an elderly resident's possessions to asbestos when carrying out renovation work at sheltered housing in West Bridgeford, Nottinghamshire.
The Mansfield firm was prosecuted by the Health and Safety Executive (HSE) after it removed asbestos insulation boards which had been used to box in pipework without taking precautions required under the Control of Asbestos Regulations 2006.
It was fined £20,000 and ordered to pay more than £5,000 costs.
A female resident at the property was exposed to asbestos, as were many of her possessions, which had to be destroyed.
The contractors also left the asbestos materials outside in the open air, risking contaminating the general public.
Both partners in the firm had received asbestos awareness training, but had failed to remove the asbestos safely.
If asbestos fibres are inhaled it can lead to the development of an asbestos related illness such as mesothelioma (an asbestos related cancer), lung cancer, asbestosis or pleural thickening.
Mesothelioma can be caused by inhalation of just one asbestos fibre. However, not everyone exposed to asbestos will develop an asbestos related illness and anyone concerned they may have been exposed, should seek medical advice from their GP.
Shoosmiths's partner Sara Hunt said: "In the UK, more than 2,000 people a year die from asbestos related illnesses.
"The asbestos regulations are intended to protect employees and the public from the dangers of asbestos exposure. It's crucial that the HSE continues to prosecute anyone who breaches these regulations if further deaths from asbestos related illness are to be prevented."