A system comprises a fluid supply line 5 having a fluid flow cut-off valve 40 arranged serially with a fluid pipe 20. The cut off valve is actuatable from an open position to a closed position by a change of pressure at an actuation input that crosses a threshold pressure. The fluid supply line has an actively bunded section 50 comprising a sleeve 60 around the fluid pipe to form a pressure-tight space V, which may be a vacuum space. The pressure tight space is in fluid communication with the actuation input, so that the cut-off valve is maintained in its open position by maintenance of a pressure in the pressure-tight space. The change of pressure may be an increase or decrease in pressure towards atmospheric pressure. The system may comprise a heat sensor 16 in sealed fluid communication with a capillary tube 18, the other end of the capillary tube being in fluid communication with the pressure-tight space. The system may comprise a fluid supply tank, such as a fuel tank 30, and a fluid consuming or dispensing device, such as a boiler 10. The system may be retrofitted.
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