Choice of a denominator for occupational injury rates: A study of the development of a Swedish iron-ore mine

This study is concerned with the longitudinal representation of injury risk obtained using alternative injury-rate denominators-hours worked and produ ction volume. It investigates injury risks at the underground extraction ph ase in a Swedish iron-ore mine. Six stages of mining development are define d, and three risk measures are employed: average injury rates (AIRs) by sta ge, injury rate ratios (IRRs) by stage, and annual injury rates (AnIRs). Th e two denominators give a quite different representation of injury risk at the early stages of the development of the mine, but tend increasingly to p rovide a similar picture (similar ratios) at later stages. It is concluded that automated production processes, as opposed to mechanized ones, tend to make hours worked and production volume interchangeable denominators. Choi ce of appropriate denominator may depend upon whether the individual or the production process is in focus.