An occupier has a less onerous duty towards a person "in the exercise of his calling", such as a professional or somebody exercising a trade. Section 2(3)(b) of the Act provides that such a person "will appreciate and guard against any special risks ordinarily incidental to [his calling], so far as the occupier leaves him free to do so".Occupiers' Liability Act 1957 Section 2(3)(b) In Roles v Nathan 2 All ER 908 a pair of chimney sweeps were called to clean the flues of a boiler. The engineer warned them about the risk of carbon monoxide poisoning if the chimney sweeps cleaned the flues with the fires still lit, but they disregarded his warning and continued until they were overwhelmed by carbon monoxide and died. The Court of Appeal held that the occupier was not liable, because the chimney sweeps had been warned and a householder who calls in a specialist to deal with defective property can reasonably expect the specialist to guard against any obvious dangers.Bermingham (2008) p.160
