Leak detection system and method

1. A leak detector adapted to detect a leak of a first gas or vapor by detecting a change in at least a physical property of a second gas or vapor, wherein the detector includes at least one sensor for detecting changes in the physical property of the second gas or vapor, the sensor including a radiation source and a detector for measuring or monitoring a change in absorption of radiation by the second gas or vapor.

2. A leak detector as claimed in claim 1 , wherein the physical property of the second gas or vapor is at least one of a concentration, a pressure, or a property dependent upon at least one of a concentration or a pressure.

3. A leak detector as claimed in claim 1 , wherein the leak detector is arranged to detect a leak of the first gas or vapor by detecting a reduction in concentration of the second gas or vapor that is caused by displacement due to the leak of the first gas or vapor.

4. A leak detector as claimed in claim 1 , wherein the second gas or vapor is located outside a vessel and the detector is arranged to detect the leak of the first gas or vapor from within the vessel.

5. A leak detector as claimed in claim 1 , wherein the second gas or vapor comprises at least one of water or carbon dioxide.

6. A leak detector as claimed in claim 1 , wherein the first gas or vapor comprises at least one of oxygen, nitrogen, helium, natural gas, or butane.

7. A leak detector as claimed in claim 1 , wherein the leak detector is operable to sense leaks at two or more locations.

8. A leak detector as claimed in claim 1 , wherein the leak detector is adapted to detect a leak by comparing a signal that is dependent on a physical property of the second gas or vapor at a first location with at least one corresponding signal that is dependent on a physical property of the second gas or vapor at one or more other locations.

9. A leak detector as claimed in claim 1 , wherein the leak detector comprises a plurality of sensors for detecting changes in a physical property of the second gas or vapor.

10. A leak detector as claimed in claim 1 , further comprising a quantum cascade laser.

11. A leak detector as claimed in claim 10 , wherein the quantum cascade laser comprises a pulsed, chirped quantum cascade laser.

12. A leak detector as claimed in claim 1 , wherein the detector includes at least one sensor that comprises a source of radiation and a detector for measuring or monitoring at least one of a change in an absorption characteristic or a change in absorption lineshape of the second gas or vapor at one or more infrared wavelengths.

13. A method for detecting a leak of a first gas or vapor by detecting a change in at least a physical property of a second gas or vapor by measuring or monitoring a change in absorption of radiation by the second gas or vapor.

14. A method as claimed in claim 13 , wherein the physical property of the second gas or vapor comprises at least one of a concentration, a pressure, or a property dependent upon at least one of a concentration or a pressure.

15. A method as claimed in claim 13 , wherein the first gas or vapor is located inside a vessel.

16. A method as claimed in claim 15 , wherein the second gas or vapor is located outside the vessel.

17. A method as claimed in claim 13 , further comprising detecting at least partial displacement of the second gas or vapor by the first gas or vapor.

18. A method as claimed in claim 13 , further comprising measuring the physical property of the second gas or vapor at two or more locations.

19. A method as claimed in claim 18 , further comprising comparing the physical property of the second gas or vapor at a first location with the physical property of the second gas or vapor at one or more other locations.

20. A method as claimed in claim 13 , further comprising at least one of measuring or monitoring at least one of a change of an absorption characteristic or a change in absorption lineshape of the second gas or vapor.

21. A method as claimed in claim 20 wherein the at least one of a change in an absorption characteristic or a change in absorption lineshape is measured at one or more infrared wavelengths.

22. A method as claimed in claim 20 further comprising measuring absorption of the output of a quantum cascade laser.

23. A method as claimed in claim 22 , wherein the quantum cascade laser comprises a pulsed quantum cascade laser.