The development of the EASE model.

The estimation and assessment of substance exposure (EASE) model has been under development and in use since the early 1990s. It is a general model that can be used to predict workplace exposure to any substance hazardous to health. The current EASE model (version 2.0) has been used widely in the risk assessment of new and existing chemicals by the UK Health and Safety Executive (HSE) and other regulatory agencies. EASE has also been distributed globally to over 200 users and therefore may have been used for many other purposes. Despite widespread use of the model, neither the development of its structure nor its underlying concepts and principles have been published in the open literature. Using surviving documentary evidence and discussions with key personnel, the creation and development of the model from 1992 to 2002 is described. The role of the HSE's National Exposure Database (NEDB) as the principal data source for the development of the model output exposure ranges is described. A number of problems and limitations of the model have been identified and the description of the model's development provides some explanation of their presence.