Light is a type of radiation hazard that includes visible light and invisible light such as UV and infrared light. Because some of these hazards are invisible to the human eye, it is important to understand the technical ratings of safety glasses to know if a specific lens and frame is suitable for the desired application.
In the case of lampworking (also called flameworking), the use of didymium glasses are historically popular because these lenses are capable of filtering out the bright yellow light caused by ignition of sodium gas emitted by glass materials exposed to a torch flame. However, many people are not aware that these glasses and frames actually do not pass minimum safety requirements for industrial eye protection.
The ANSI Z87.1 Standard for Safety Glasses
The "gold standard" for rating of safety glasses is provided by a document titled, "American National Standard Occupational and Educational Personal Eye and Face Protection Devices" also known as the ANSI Z87.1 standard. This document is written and maintained by the American National Standards Institute and the International Safety Equipment Association. ANSI Z87.1 defines the ratings for safety glasses, how ratings are marked on the lenses, and recommended safety ratings for specific types of eye hazards such as radiation (light), blunt-force impact, high-velocity impact, chemical splashes and dust.
Physical Requirements for Safety Glasses
According to the NIOSH, the majority of eye injuries are striking and scratching injuries to the eyeball and cornea caused by small particles or objects striking the eye, such as dust, chips and slivers. The objects may be ejected by tools, blown by air, or may result from dropping or breaking objects. Each day up to 2000 people in the US experience an eye injury on the job that requires medical treatment. In severe cases, penetration of the eye can occur resulting in total loss of vision. Injuries can also be caused by chemical burns, a risk of working with liquids such as acids.
To prevent these types of physical contact injuries, safety glasses must be made from materials that can withstand high-impact forces, and must provide full-coverage protection meaning they guard against flying objects from both the front and side of the eyes.
Traditional didymium lenses are made from glass, which is susceptible to breaking and shattering under impact. Today nearly all safety glasses are actually not made with actual glass lenses, but rather with polycarbonate lenses, which is a type of clear plastic that is capable of withstanding extremely high intensity impact without shattering.
The strength of glass can be enhanced with chemical tempering, but is still considered a low-impact material and is not recommended by optometrists for use in safety glasses.
Optical Radiation Protection for Lampworking
The ANSI Z87.1 standard does not specifically address the needs of lampworking, but does discuss the rating requirements for torch use with metals such as torch soldering, torch brazing and oxyfuel torch cutting. We can look to these recommendations for guidance as they involve similar levels of intensity of infrared and UV light that are encountered in lampworking.
According to the ANSI/ISEA Z87.1 Eye and Face Protector Selection Guide, optical radiation hazards may be addressed with a spectacle frame providing side protection, or using goggles with suitable filtering lenses.
Soft glass lampworking uses a low intensity torch flame which is most similar torch soldering. In the guide linked above, it is recommended to use a Shade #2 lens for torch solderin. A Shade #2 lens is also a good starting point for low intensity lampworking. To pass the Shade #2 requirements, lens must block at least 85% of infrared light in the range of 780nm to 2000nm.
Lampworking or flameworking with hard glass (such as borosilicate glass or "boro") requires a high intensity torch and oxygen-enriched flame. For use of oxyfuel torches, ANSI Z87.1 recommends a minimum Shade #3 lens. Shade #3 lenses block a minimum of 91% of infrared light.
A further requirement, which is often overlooked in lampworking practice, is that safety glasses must also provide the same or better filtering of optical radiation in the frame components and side protectors. Put simply, safety glasses made from clear plastic, or with clear side protectors, are considered inadequate for torch work due to the potential for hazardous light to enter the peripheral vision. For the solo lampworking practitioner where there is only one workstation, side shield protection may not be a primary concern, however in the context of a glassworking studio where multiple people are working, it is important to understand that side protectors must also provide filteration and cannot be made from clear plastic.
How to Check the Rating of Safety Glasses
To comply with ANSI Z87.1 standards, the ratings for safety glasses are required to be printed on the lenses using a permanent, non-removable marking. Usually this is done by laser engraving on the lens. These markings follow a standard system of codes that can be easily understood, once you know what you are looking for.
First, the lens must be marked "Z87.1" to indicate that the product complies with the ANSI Z87.1 standard for safety glasses.
If the lens and frame are impact-rated, meaning they provide protection from both high velocity and high mass impacts, the lenses are also marked with a plus-sign, e.g. "Z87.1+".
Special purpose lenses are marked with an "S". Lampworking is a type of special purpose lens, as it involves the sodium flare filtering which is not a standard feature of welding shade protection.
Welding shades are marked with "W" followed by the shade number. For example "W2" is a welding Shade #2. "W3" is a welding shade #3, and so on.
Alternatively, lenses may be marked with a shade number for each component of optical radiation: "U" for ultraviolet, "L" for visible light and "R" for infrared light.
For example, a welding Shade #3 or "W3" marking is the same as "U3L3R3". Look for these letters and numbers printed in small text somewhere on the lens of the safety glasses.
If the lenses are not marked, then the glasses are not compliant with the ANSI Z87.1 standard.
Rating of Didymium Glass Lenses
As discussed above, didymium lenses are made from glass which is a material with poor impact-resistance. Unless the lenses are chemically strengthened and have a thickness of 3.0mm it is unlikely they will pass the basic impact requirements of ANSI Z87.1. In addition, these lenses are often paired with spectacle frames that are not impact rated and do not have side protectors, or have clear side protectors that do not protect the eyes from optical radiation hazards such as infrared light.
Standard didymium glass provides minimal filtering of infrared light. Nonetheless, use of didymium glass is still common practice in the lampworking community. We recommend that, at a minimum, didymium glass lenses are combined with welding shade lens of at least Shade #2 or greater and preferably a Shade #3. The welding shade could be in the form of a ANSI Z87.1 compliant "fit-over" goggle, or full face shield, to achieve adequate protection from both impact hazards and optical radiation hazards. However, a downside to this approach is the resulting combined lenses will be significantly darker and less comfortable than a single pair of glasses.
Rating of "Polycarbonate Sodium Flare" Lenses
To address the poor impact resistance of didymium glass lenses, some manufacturers offer "polycarbonate sodium flare" lenses, which can be identified by their blue-purple color and plastic composition. In some cases these lenses may be combined with additional welding shade filters to provide a Shade #3 or Shade #5 lens, in which case you can check the lens for markings indicating compliance with that shade. However, in other cases the lenses are sold for lampworking without the addition of any infrared-filtering materials. While these lenses do provide improved shatter resistance and excellent UV protection thanks to the inherent properties of polycarbonate plastics, polycarbonate sodium flare lenses unfortunately provide minimal to no protection from infrared light and are not compliant with ANSI Z87.1.
Rating of VetroSafe Lenses and Frames
VetroSafe is a unique eyewear product that is designed from the ground-up specifically for lampworking and flameworking. Our lenses are made from polycarbonate, which is the preferred material for safety glasses thanks to its excellent impact resistance. Due to its special purpose construction, the Vetrosafe Vetrosafe lenses are marked with specific indications for shade-level in each category of optical radiation: For ultra-violet light, Vetrosafe has a "U6" rating or 99.9999% filtering. In visible light, the lens is a Shade #3 or "L3" lens with an average visible light transmission of 15%. With respect to infrared light in the 780nm to 2000nm range, Vetrosafe is rated with a Shade #4 or "R4" having 95% infrared light filtering.
In addition to UV, visible and infrared hazards, Vetrosafe lenses incorporate a blue-light filter that blocks 99% of optical radiation in the high-energy visible band or "HEV" band between 400nm to 420nm. While not yet addressed by ANSI Z87.1 standards, HEV light has been shown to cause retinal damage from long term exposure and is HEV light is present in the blue-colored torch flame used in lampworking.
Regulation of Safety Glasses
Safety glasses are a type of PPE or Personal Protective Equipment. The use of safety glasses in the workplace is regulated by OSHA. According to OSHA, if PPE is required in the workplace, then the employer must implement a PPE program that includes selection, maintenance and use of protective equipment, training of employees, and monitoring to ensure its effectiveness.
While many lampworkers are independent artisans and hobbyists, the activity of lampworking does come with significant safety hazards that should not be underestimated. Looking to OSHA standards and ANSI standards that apply to similar industrial activities involving torch use, such as torch soldering, torch brazing and torch cutting, is a good starting point for gaining an understanding of the optical radiation hazards of lampworking and the best lampworking safety glasses to use for a project.
Summary of Key Points
- Use a minimum Shade #2 lens for soft-glass lampworking (85% infrared light blocking - marked "W2" or "R2")
- Use a minimum Shade #3 lens for hard-glass lampworking (91% infrared light blocking - marked "W3" or "R3")
- The frame should also provide protection on the sides, either with side protectors, goggle design or a "wrap-around" lens.
- Check that your eyewear is compliant with ANSI Z87.1 standard by looking for an engraving "Z87.1" on the lens
- If using non-rated didymimum glass lenses, adequate protection can be achieved by combining the glasses with a welding shade goggle such as a "fit-over" style frame.
- For those doing lampworking professionally or as an employee, look to OSHA guidance for recommendations on implementing a PPE program.