This International Standard describes product screening. A proper product screen is actually a process, not a test. As a process, it is maintained and constantly validated to ensure it achieves the purpose for which it was defined. This process is applied to a product in order to induce products with a known failure mechanism, to fail in a controlled situation before the product is deployed in the field. If this process is properly applied, then all infant mortality failures in the field, associated with the failure mechanism(s) for the screen, will be eliminated. Figure 1 shows the classical "bathtub" three-region curve of failure rates for most products. Although the failure rates of passive optical components have not been conclusively shown to follow this curve, it is useful for illustrative purposes. Screening is known for some products as a proof stress or in the case of electronics, as a "burn-in process". When applied to a product, it will normally affect the failure rate applied during the infant mortality portion of the product life cycle. If the screen is properly chosen, it will induce a portion of the infant mortality failures caused by the chosen failure mechanism(s) to occur in the manufacturing cycle, earlier than would normally be seen in the unscreened population shown in the dashed line. Also, it should be noted that a properly applied screen does not weaken or degrade the wear-out or end of life performance of a product population. In any case, the screen should also not affect the middle region of normal life utilization.