September 1, 2007
Impact resistance has been regulated by agencies like FDA since the early 1970s for products furnished through medical and retail channels, such as sunglasses and prescription eyewear. It is determined by a simple drop-ball test where a 5/8-inch steel ball is dropped free-fall through a tube from a height of 50 inches onto the lens surface.
For protective eyewear meant for industrial or occupational use, the governing document is ANSI Z87.1, which has been in existence, through several iterations, for almost 40 years. OSHA in its regulations (see CFR 1910.133) specifically cites Z87.1 as the minimum performance requirement for protective eyewear, effectively giving it the weight of law.
Originally, Z87.1 also specified a drop-ball test, with the difference being an increase in the ball diameter to 1 inch for most lens types. Glass lenses at least 3 mm (1/8 inch) thick and properly treated could meet this test. Plastic lenses also were required to pass a penetration test wherein a weighted needle is dropped 50 inches onto the product. The lens cannot fracture or be pierced.
In 1989, the standard was upgraded to add elevated impact and lens retention tests. Technology â€” particularly the advent of polycarbonate plastic as a high-performance lens material â€” drove this change. More robust products could be designed that would benefit those needing to wear protective eyewear where significant impact hazards existed.
ANSI Z87.1 tests
The current edition of the standard is Z87.1-2003. Lenses in all protectors must at a minimum meet a basic impact requirement: the 1-inch drop-ball test. Models can achieve “high” impact levels indicating elevated performance. The following “high” impact tests apply to lenses, as well as to the frames or product housing:
• A lens retention test is conducted via a “high mass” impact. A pointed 500 gm (1.1 lb.) projectile is dropped 50 inches onto the complete protector mounted on a headform. No pieces can break free from the inside of the protector, the lens cannot fracture, and the lens must remain in the frame or product housing. This test simulates a blow such as from a tool that slips from the work surface or when the lens collides with stationary objects.
• A high velocity test is conducted, at 20 specified impact points, where the projectile is a 1/4-inch steel ball traveling at specific speeds depending upon the type of protector. For spectacles, the velocity is 150 ft/sec or 102 mph. The pass/fail criteria are the same as for the high mass test, plus no contact with the eye of the headform is permitted through deflection of the lens. This is meant to simulate particles that would be encountered in grinding, chipping, machining or other such operations.
In the U.S., compliance with the standard is self-certified, based on test results generated by the manufacturer as part of its initial design and ongoing quality control procedures. No independent certification is required. Products meeting the basic impact standard are marked “Z87” on all major components. Products that pass the “high” impact tests listed above can carry a “Z87+” marking on the lens(es).
Other impact standards
Other standards exist for assessing the performance of protective eye and face products, including requirements for impact resistance. While test procedures may differ somewhat from region to region, the intent is to measure impact strength of the entire protector, and to set criteria for minimum levels of performance. However, one test that has been harmonized across many key regional standards is the high-velocity test conducted with a 1/4-inch steel ball.
In Canada, the pertinent standard is Z94.3-2002 developed by the Canadian Standards Association (CSA). Impact performance is assessed with the 1/4-inch steel ball traveling at 46.5 m/sec or 152 ft/sec. Impact points that must be evaluated include the midpoint of the protector, as well as multiple frontal and lateral locations, some of which duplicate those assessed for Z87.1. Other points are selected to test areas of the protector that could be vulnerable to impact, such as where the lens attaches to the frame, where the temple pieces attach to the frame or where thin material sections are present. These sites will vary with the design of the product, providing a thorough evaluation of its ability to provide protection. Failure criteria are equivalent to those in ANSI Z87.1.
A manufacturer can test products on its own or submit products to CSA International to have them tested and thus “third-party” certified as being in compliance. In the latter case, a product in conformance can be marked with the CSA logo, a recognized Quality Mark in Canada. It can be compared to marks such as Underwriter’s Laboratory (UL). Certain manufacturers are authorized by CSA International to test products on its behalf because their laboratories have been audited to a strict set of guidelines. This allows the CSA logo to be marked on the product after review and acceptance of the test results by CSA.
Military ballistic performance
The U.S. Army specifies that protective eyewear comply with Military Standard 662, which outlines a number of ballistic fragmentation tests for different classes of products. A special shrapnel-simulating projectile is fired at a specified velocity. The cylindrical fragment has an angled face that will burrow into the product. For ballistic spectacles, the fragment is 0.15 caliber and the velocity of the projectile is 650 +/- 10 ft/sec (440 mph). In this case, the test protocol specified is as “V0” (V-Zero), which means no (zero) impact failures are allowed at the velocity specified. The spectacle is impacted once, at a point coinciding with the center of either the left or right eye. The lens cannot fracture, nor can the projectile penetrate to the eye. Impact energy for this test is about seven times that of a 1/4-inch steel ball traveling at 150 ft/sec.
Is this test is too extreme for eyewear meant primarily for industrial use? Consider the added level of protection and security afforded by products offering V0 impact performance. For example, an obvious impact hazard may be particulate generated by an operation such as grinding. A less obvious threat is the explosion of the grinding wheel, which can send shards of material flying at speeds considerably higher than ANSI standard tests. Higher performing products offer better protection in case of unforeseen accidents.
The proper combination of design, materials and controlled manufacturing processes will yield superior impact protection in products that are stylish, comfortable and a great value given the level of protection delivered.