The ductwork in buildings can harvest all manner of debris, as it is out of sight the air conditioning system is often neglected, as a consequence of this the risk of fire and illness throughout the building is increased.
Ducting is the perfect transport for fire. As air blows through the ducting system it transports dust and debris throughout; should a fire occur it will spread at a frightening pace.
The debris build up can also manifest itself into such substances as mould, given the illnesses and the bacteria it can cause it's not ideal to have it flowing throughout the building via the air conditioning system, especially as we move into a more hygiene concerned workplace.
Cleaning the ducting can also prevent serious illnesses such as legionnaires disease as water can build in AHU's (air handling unit), not to mention it falls under the Health & Safety at Work Act 1974, The Workplace Heath, Safety & Welfare Regulations 1992 and the The Occupiers Liability Act 1984.