Do we have any medical evidence that all health impacts would be identified within 30 years? The impacts from other incidents have turned up much later. Was the number just pulled from a hat? You can always exceed an international convention; you simply can't be “less than”. The convention says that it's at least 30 years. There's no reason that you can't say 50.
Evidence of meeting #35 for Natural Resources in the 41st Parliament, 2nd Session. (The original version is on Parliament’s site.) The winning word was proposed.
A recording is available from Parliament.