The UK has an extensive collection of records of exposure to compressed air in tunnelling which are analysed periodically. The paper assesses occupation as a risk factor in tunnelling Decompression Illness (DCI) and is based on a batch of records covering around 120000 exposures derived from almost 2400 men on 34 contracts dating from the mid 1980s along with records of over 400 cases of acute DCI. For the study, the workforce was divided into four defined occupational categories covering "shift production workers" such as miners; "shift skilled" which included trades such as fitters and electricians; "regular supervisory" which covered staff and intermittent supervisory which included visitors. The incidence of DCI was determined together with the proportion of each category experiencing DCI. The study showed the extent to which shift workers experienced the majority of DCI events compared with their supervisory colleagues on a contract. The paper argues that bends rate - the commonly accepted measure of DCI incidence does not adequately identify the impact of DCI on shift workers from exposure to compressed air. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. "Reprinted with permission from Elsevier".