What makes a safety eyewear lens stronger than a regular lens – What are the options?March 1, 2023
By Glyn Jones
Modern Safety Eyewear Lenses
Eyeglasses have been used to correct vision problems for hundreds of years. Their use as safety eyewear dates back to 1880 when P. Johnson’s patented “eye protector” was used to reduce eye exposure to the bright light associated with the work of firemen and furnacemen. This safety eyewear was effective in reducing the light intensity but the semi-opaque cloth lenses did little to offer impact protection.
In the early part of the twentieth century the first safety eyewear worn to offer impact protection had a glass lens. Although bulky and heavy, these lenses provided protection against a variety of hazards such as dust, dirt, and flying debris.
By 1980, standards were in place requiring safety eyewear to pass specific high speed, high impact tests. The modern era of safety eyewear had arrived. Today, safety eyewear is worn by millions of employees working in the manufacturing, construction, medical industries and other workplaces to shield the eyes from flying debris, and other hazardous projectiles created at work.
Canadian Standards Association (CSA) & Safety
One of the things that makes safety eyewear safe is that it must be CSA approved. All CSA approved equipment is subject to rigorous testing to confirm that it performs to the intended standard. CSA Z94.3 Eye and Face Protectors applies to eye and face protectors used in all occupational settings where hazards to the eyes or face may exist. This standard sets the minimum performance requirements for this range of performance tests including the “drop ball” and “high impact” test of the lens and frames. CSA-certified eye and face protectors must meet the criteria for impact resistance as outlined in the standard. Protective eyewear that has been certified by CSA as meeting its requirements will bear the CSA mark on the frame or temple of the eyewear.
Let’s Talk Lenses
Safety eyewear is made with one of a number of shatter-resistant lens materials including glass, plastic, polycarbonate, and polyurethane.
Glass lenses were the first lens type and are still available today. They provide excellent optics and have good scratch resistance properties. The lens material naturally blocks UV light. Glass lenses suffer the disadvantage of being heavy and thick, and if broken create a new danger to the eye.
Plastic lenses, also known as CR-39, are made of a conventional plastic material widely used since the mid-1940s. CR-39 is the trademarked name of the plastic polymer allyl diglycol carbonate. The abbreviation CR-39 stands for “Columbia Resin #39” which was the 39th formula tested during resin development back in 1940. These plastic lenses are made from a cast molding process where a liquid plastic material is baked for long periods in a lens form, solidifying the liquid plastic to create a lens. One of the biggest advantages of this lens is its affordability and it provides good optical clarity. Plastic lenses are softer and so are prone to scratching and they tend not to be as impact resistant even though they are heavier and thicker. It is less common to find plastic lenses in use today.
Polycarbonate lenses are the most common lens type used today. Polycarbonate is a synthetic polymer resin first developed in the 1970s for aerospace applications. It is used for the helmet visors of astronauts and for space craft windows and windshields. Eyeglass lenses made of polycarbonate were introduced in the early 1980s. These lenses are light-weight, fog-resistant, and have a higher impact resistance, however they are subject to scratching so they need a scratch resistant coating. Polycarbonate lenses are thin, lightweight and much more impact-resistant than regular plastic or glass lenses. They have become the standard for safety eyewear.
Polyurethane lenses are available under the brand names Trivex and Hi Vex. Developed in the early part of the twenty-first century, polyurethane lenses are made from a cast molding process similar to how regular plastic lenses are made. Polyurethane lenses have a very high level of light transmittance resulting in brightness, clarity, and crispness. They also have a higher tensile strength than polycarbonate lenses allowing for a lighter lens while ensuring impact protection. Polyurethane lenses tend to be somewhat more expensive. Trivex is a brand name for urethane lens material. The name is in reference to the three main properties: superior optics, ultralight weight, and extreme strength. Hi-Vex refers to its high refractive index.
In the Know
There are advantages and disadvantages of every lens type, but with a better understanding of lens choices, safety professionals are able to select safety eyewear that achieves the hazard control necessary for their workplace while balancing cost, comfort, and price.
A key to eye protection is that only CSA approved safety eyewear is worn and that the glasses are always worn on the job. Consult your eye care professional to make sure your selection of safety eyewear is consistent with best practices. Always follow the manufacturer’s instructions and recommendations for cleaning, maintenance, and storage of the glasses. Safety eyewear should be inspected before every use to ensure the highest safety standards are being met. Attention to care and maintenance is key to a long life for safety eyewear regardless of lens type.