ASL’s confidence tone at Sellafield

ASL Safety & Security have supplied a high-integrity building evacuation system (BES) to Sellafield Ltd at the company's nuclear processing facility in Cumbria. Sellafield currently performs multiple tasks geared towards decommissioning the UK's nuclear legacy as well as fuel recycling, manufacture and waste management.

As a key safety system at this nuclear-licensed site, the equipment is required to be entirely dual redundant, with emphasis placed on a design that meets key objectives for a robust architecture, unaffected by environmental and electromagnetic factors as defined in BS EN 61000-6-4 and BS EN 61000-6-2. The system also meets the stringent BS5839:8 standard for voice alarm systems.

Nuclear facilities have unusual requirements and safety is so critical at this location that a ‘confidence tone' is broadcast at 15-second intervals around the clock. The presence of these regular pips reassures personnel that the evacuation system is functioning correctly. If an event is activated manually by criticality incident detectors or activity-in-air monitors specific to a building, a distinct warning tone is broadcast within 300 milliseconds and the location in question is evacuated. At the same time, "Keep Out!" warning beacons are triggered throughout the evacuation zone. Local residents are automatically contacted by telephone and can also ring a number to hear a description of various emergency sirens.

Failure of any of the components will not affect the operation of the system as a whole. The amplifiers employed are ASL's M400 rack-mounted main frame units which use the company's unique class-D adaptive technology to minimise power consumption, meaning a reduced sizing requirement for battery back-up. The system features dual power supplies, routers and standby amplifiers modules with speaker line monitoring and automatic switching carried out via DC surveillance.