To limit the probability that, under in-service conditions, a lack of strength and corrosion resistance will lead to the corrosion of metal flue liners, which could lead to distortion and premature failure, which could lead to the ingress of condensed water vapour into the cavity between the chimney liner and the surrounding masonry, which could lead to damage to the masonry due to freeze-thaw stresses, which could lead to the collapse of the chimney, which could lead to harm to persons.