Sajid,
I have never come across any such number, but I have heard doctors say that anything above 15,000 is absolutely critical and anything above 10,000 needs immediate action. As this is a sample measure of how much iron there is in the blood stream, one could say that it is highly probable the organ damage starts to happen at these levels. However, it is possible, though not probable, that ferritin levels could be high for some one without having caused damage to the body organs.
Poirot