To limit the probability that accumulation of combustible deposits in a chimney, flue or flue pipe will go unnoticed, which could lead to a fire in the chimney, flue, or flue pipe, which could lead to the spread of fire to other parts of the building, which could lead to harm to persons.
To limit the probability that dangerous conditions [e.g. excessive corrosion, deposits, damage, etc.] will go unnoticed, which could lead to malfunction of the appliance the chimney, flue or flue pipes serves or ignition of adjacent combustible materials, which could lead to fire, which could lead to harm to persons.