| Obscuration Gauge |
| A form of dust gauge which relies on the soiling of a reference surface by deposited dust. Two examples are the Sticky Pad, and the Glass Slide. |
| ODPM |
| See Office of the Deputy Prime Minister. |
| Office of the Deputy Prime Minister (ODPM) |
| Office of the Deputy Prime Minister. This WAS the UK government office responsible for policy on housing, planning, devolution, regional and local government and the fire service. In 2006 its responsibility for Planning has taken up by the Department for Communities and Local Government (DCLG). |
| Open side setting (OSS) |
| This is the point where the crushing surfaces are the furthest apart at the product discharge outlet. See closed side setting (CSS). |
| Opencast |
| This refers to a type of surface mining, where the rock which is required (often coal) lies below a covering (or overburden) of rock which has to be removed. This is often blasted, dug and then ?cast? out of the way, so that the valuable mineral can be extracted. |
| Orthogonally |
| Three directions all at right angles to each other. In the case of monitoring, the directions are vertical and two horizontal. |
| OSS |
| Open Side Setting. This is the point where the crushing surfaces are the furthest apart at the product discharge outlet. See closed side setting (CSS). |
| Overburden |
| Material (usually unconsolidated) overlying the desired mineral deposit that has to be removed to access the deposit. |
| Overpressure |
| This is the term used for the pressure waves which travel through the air from a blast. |