Abstract: A bursting disc orientation device comprises a cut-away portion (7) on a predetermined one collar (2) of the bursting disc unit and cooperable with the cut-away portion, a projection (8) e.g. in the form of an arm of an angle bracket (9) secured to the periphery, or integral therewith, of that pipe flange (5) against which the said one collar (2) is required to bear. Thus, the unit can be prevented from being located between the pipe flanges of the bursting disc unit in other than a predetermined orientation in which the projection (8) is located in the cut-away portion (7). This improves the safety of the device.