His apparent lenient handling of striking miners at the colliery in 1832 further strained relationships, especially as he disagreed with the treatment of the men by John Wood the underviewer and he was dismissed at the end of 1832.
As viewer of the St Lawrence Main and Shield Field collieries, he gave evidence on child labour to the Children's Employment Commission that reported in 1842.
He was a prolific author producing books, pamphlets, and practical papers on the coal trade and mining engineering, many covering safety topics.
In particular he emphasised the need for adequate underground air-flow rate to neutralize gases, and promoted developments such as the use of barometers to monitor changes; cast-iron equipment; improved boiler safety valves and wire rope.
He asked for regulations, but "as few and as simple" as possible; said that further advances in legislation should be made as "the state of opinion" ripened and argued for high technical and scientific qualifications for the inspectors and for the development of Schools of Mines.
Dunn urged miners to contact him if they were anxious about the condition of their pits, stressing that he did not have the power to enter and inspect mines uninvited.
This was a revision of a book first published in 1852 and provided a checklist of good practice; noted the appropriate duties of managers and discussed the role of inspection.
Dunn was one of the founder members of the management committee of the Newcastle upon Tyne Joint Stock Banking Company established in 1836.
In 1835 he produced a pamphlet in association with the engineer Robert Hawthorn setting out the advantages of a railway between Newcastle and Morpeth, intended to form the first phase of a rail link with Edinburgh.
Though he had some financial involvement in mines Dunn never seems to have become a partner in any of the major North East colliery companies, unlike people such as Nicholas Wood who became rich men.