ANSI safety eye-wear standards include the following key features:
For the basic impact tests, lenses are tested separately (not mounted in a frame). For the high impact classification, the frame and lenses are tested together as a unit.
Non-prescription lenses used for high impact testing are considered to be structurally weaker than prescription lenses made of the same material; the prescription lenses are generally thicker.
Thinner prescription safety lenses are now allowed, if they meet the high impact testing requirements. (Previously, all prescription safety lenses had to have a minimum thickness of 3 mm, making them significantly thicker and heavier than regular eyeglass lenses.)
Safety lenses now have two classifications of performance: basic impact and high impact.
The “drop ball” test determines the basic impact safety classification for lenses. In this test, a one-inch diameter steel ball is dropped onto the lens from a height of 50 inches. To pass, the lens must not crack, chip or break.
All glass safety lenses must undergo this test. For plastic safety lenses, however, only a statistical sample of a large batch of lenses needs to be tested.
In high impact testing, a high velocity test is performed by shooting a quarter-inch diameter steel ball at the lens at a speed of 150 feet per second. To pass, the lens must not crack, chip or break, and it must not become dislodged from the lens holder.