When o-rings fail, there are clear traces that allow conclusions about the damage-causing mechanisms. Even the fact that there are no traces can be seen as a valuable hint to the future proceeding.The damaged seal itself is examined thoroughly to find the damage-causing mechanisms. Therefore, first of all its dimensions are being measured, afterwards the seal is examined visually or under a microscope Sooty or sticky surfaces or cracks are hints for a chemical attack. Visible damage is however is a hint of too much mechanical or physical stress. Brittleness of the o-ring can occur due to ageing or a chemical attack. Changes in hardness and density compared to new condition are other characteristics that allow specific conclusions concerning changes of the material.