Leak detection apparatus

Apparatus for detecting leaks of fluid from a pressurised container or a pipe (1) includes a secondary jacket (2) formed around the container or pipe (1) and filled with a liquid. A reservoir (5) containing the liquid is connected to the jacket (2) by a pipe (4) such that the hydrostatic pressure of the detection fluid in the jacket (2) is less than the fluid pressure in pipe (1) or container. The reservoir (5) is provided with level detecting means such as two floats (6, 7) which actuate associated switches (8, 9) if the level of liquid in the reservoir (5) rises or falls by more than a predetermined amount.