The incident happened during a refurbishment project at offices in Sentinel House, Nuffield Industrial Estate, Poole over a period of several weeks in 2009.
Bournemouth Crown Court heard that MJC Decorating & Refurbishing Ltd began removing ceilings at the two-story block without carrying out a suitable survey in advance to determine whether asbestos was present.
A visit to the site by an HSE inspector revealed widespread contamination and spread of asbestos both inside and outside the building. Investigations revealed that some material removed from the site as non-hazardous may have included asbestos-containing materials.
As a result, four employees and 14 agency staff working under the control of MJC, were exposed to asbestos dust and fibres that can cause respiratory problems and even incurable lung diseases.
MJC workers carried out the removal of asbestos insulation board ceiling over two weeks while wearing normal work clothes that became contaminated with asbestos fibres. This may have led to the exposure of many more members of the public during their journey to and from the site over this two week period.
MJC Decorating & Refurbishing Ltd, of London Road, North Cheam, Sutton, Surrey, pleaded guilty to three breaches of the Control of Asbestos Regulations 2006. It was fined a total of £45,000 and ordered to pay £36,943 in costs.
Speaking after the hearing, HSE inspector Helena Tinton said: "This was a very serious incident which carries severe risks for people's health.
"MJC's safety failings led to the needless exposure to dangerous asbestos fibres of its employees, agency staff and the wider public. The firm didn't carry out a suitable survey for asbestos material before the work started and failed to provide protection for workers on site.
"Regulations on dealing safely with asbestos have been in place for many years and are widely known in the industry.
"This totally needless incident would not have happened if MJC had carried out proper assessments and had trained staff on site."