Laser Eye Safety in Digital Fabrication: Protecting Your Vision

Disclaimer: This article is not an official training or certification for laser safety. You are responsible for the safety of yourself and others while you are operating a laser cutter or engraver.

Digital fabrication tools, such as laser cutters and laser etchers, have revolutionized industries ranging from manufacturing to arts and crafts. The accuracy and precision achieved with such tooling allows intricate designs as well as rapid cuts across a multitude of materials. The same powerful laser beams that enable this capability can pose significant risks to the eyesight of any living creature in the vicinity of the tool if proper safety precautions are not employed. Laser radiation, even in small doses, can cause severe and permanent eye damage. Laser use in makerspaces or home workshops tend to lack the appropriate controls for both the laser operator as well as bystanders. Even worse, high wattage laser pointers and laser diodes have entered the market at shockingly low prices from vendors like Amazon, Ebay, and Aliexpress. Industrial and military laser use is strictly controlled, and these regulations will be cited as proposed best practices for the home hobbyist. This article explores the importance of laser eye safety, potential hazards from improper use, and best practices for safeguarding your vision while working with laser tooling so you can unleash your creative potential. Pew, pew, pew!

Understanding the Threat

What is a Laser?

L.A.S.E.R is an acronym which stands for Light Amplification by Stimulated Emission of Radiation. As compared to light originating from a tungsten filament light bulb or a Light Emitting Diode (LED), laser light exhibits some unique properties. Laser light is:

• Monochromatic: single color/wavelength
• Coherent: light waves travel in phase
• Collimated: light beam remains parallel (without diverging) over great distances
• Polarized: electric field oscillates in the same direction
• Intense: concentrated power density

Depending on the type of laser, radiation may be emitted in the visible, ultraviolet, or infrared portion of the electromagnetic spectrum, each posing unique dangers. Regardless of visibility, all laser beams carry the potential for severe and potentially irreversible eye damage.

Lasers in Digital Fabrication

Digital fabrication lasers include CO2, diode, and fiber. Figure 1 illustrates the laser wavelengths used in these laser devices. Invisible CO2 lasers are used for cutting/etching materials like wood and acrylic while such tools can only etch materials like glass, metal, or slate. Many hobbyists utilize these tools for the removal of paints or top coating layers for items spanning homemade printed circuit boards to custom drink containers or coasters. Visible diode lasers can process a subset of materials than that of CO2 lasers where the difference largely falls to the inability to process transparent plastics (acrylic and PETG) and glass. Invisible fiber lasers offer versatility across various materials with an emphasis on marking and engraving metal.

Diode lasers have also been touted as “upgrades” for existing 3D printers or CNC machines to breathe new life into existing hardware. For example, Creality offers blue laser diode (450nm) upgrade kits for the Ender 3 product line as high as 10W for less than $200! [1]. With great (laser) power comes great responsibility, and for many average hobbyists, a general understanding of safely using these high-power lasers is often lacking.

Biological Hazards of Laser Beams

Thus far we have discussed laser light as waves; however, light may also be described as particles which is a better example when discussing laser safety. Ultimately, we want to limit the number of these light particles that enter our eyes or touch our skin. Just as these light particles etch away the surface of your slate coaster, they can also do the same to your skin, cornea, or retina.

There are 3 mechanisms for biological tissue damage from laser radiation: thermal, chemical, and acoustic (or mechanical). Photothermal is the major cause of tissue damage whereby the laser heats up subdermal tissue and denatures proteins or kills biological cells. The effects may range from reddening of tissue to burns. Photochemical is a process where the absorbed laser light directly modifies the chemical structure of the tissue. Photoacoustic (or photomechanical) damage involves the vaporization of tissue due to rapid changes in localized pressure which can create a mechanical shockwave that leads to tissue tearing [2]. Example eye and skin hazard based on the type of laser platform is summarized in Figure 2.

With respect to eye hazards, laser light may enter the eye via 3 possible routes: direct exposure, specular reflectance, or diffuse reflectance as shown in Figure 3. Direct or intra-beam exposure occurs when the laser light travels directly from the laser to the eye and is by far the most hazardous. One should never point a laser directly at a person’s eye as the cornea or retina will receive a blast of trillions of light particles before the 0.25 second blink reflex of the human body intervenes. Specular reflectance occurs when the laser light reflects off a mirror-like surface before entering the eye. This reflected laser light has the potential to cause harm over long distances as more than 80% of the original power (and particles) may be reflected. Diffuse reflectance occurs when the laser light is scattered from a roughened or matte-like surface. Diffusely reflected laser light is hazardous over very short distances; however, as the laser power increases so does the hazard distance. Ultimately, the intensity and wavelength (or color) of the laser determine the severity of the hazard which will be discussed later.

Standards Organizations and Laser Classification Levels

Laser Standards Organizations

In the United States, organizations like OSHA (Occupational Safety and Health Administration), FDA (Food & Drug Administration), and ANSI (American National Standards Institute) set stringent safety standards for laser usage in the industrial sector. Many of the standards in ANSI have been incorporated from international standards groups like the IEC (International Electrotechnical Commission). These standards classify lasers based on their power output and potential for biological harm, outlining permissible exposure limits, and recommending appropriate safety measures. Compliance with these regulations is not just a matter of best practice – it is often legally mandated.

“ANSI Z136.1-2022: American National Standard for Safe Use of Lasers” sets recommended guidelines for the safe use of lasers that operate at wavelengths between 180nm and 1000μm. It also specifies both the environment in which the laser is being used and any environment around the path of the beam; however, this document is only available for sale from the ANSI webstore for $250 [3] which is possibly more expensive than some hobbyist diode laser systems. OSHA technical manuals are freely available online. Specifically, the “OSHA Technical Manual Section III: Chapter 6” thoroughly describe laser hazards and reference ANSI and FDA documentation as appendices [4].

Laser Classification Levels

The classification of a laser or laser-based product is a detailed process. The governing standards include a measurement of the laser emission, a calculation of the exposure level, and an evaluation of protective housings or interlocks. A numerical scale of Class I (lowest) to Class IV (highest) based on biological hazard level to both the skin and eyes has been established.

Class I lasers are considered safe under all conditions of normal use, including direct viewing. Class I lasers either emit very low power levels, confine laser emission within an enclosure combined with safety interlocks, or prevent any accessible exposure above the permissible exposure limits. These lasers also do not require any label or marking and include laser printers, Bluray players, and CO2 laser cutters with an enclosure and interlocks.

Class II lasers consider visible (400nm–700nm), continuous-wave emission at laser powers <1mW. These lasers require a label marking the laser class and output power; however, they are considered safe because the blink reflex will limit the exposure in the eye to 0.25 seconds. Example Class II lasers include laser bar code scanners and certain laser pointers.

Class III lasers are split into 2 subcategories and require appropriate labeling of laser class and output power. Class IIIA lasers are considered intermediate power at 1mW–5mW of continuous-wave emission, and Class IIIB lasers are considered moderate power at 5mW–500mW of continuous-wave emission. Direct viewing and specular reflectance of the laser beam is hazardous. Example Class III lasers include certain laser pointers, laser scanners, and certain laser light show equipment.

Class IV lasers include >500mW continuous-wave emission device. Direct viewing, specular reflectance, and diffuse reflectance of the laser beam is hazardous. These lasers are also a fire risk because they may ignite combustible material. In addition to proper labeling of laser class and output power, these lasers must be equipped with a key switch and a safety interlock. Example Class IV laser products include non-enclosed diode laser engravers/cutters, non-enclosed fiber lasers, surgical laser equipment, and industrial laser cutters.

Figure 4 summarizes laser classifications according to OSHA & the FDA.

The laser product manufacturer is required to define the appropriate laser classification, and the FDA requires 2 key pieces of information to be included on the label: laser classification and output power. The addition of the laser output wavelength is critical for assessing the appropriate laser safety equipment which will be discussed below. Figure 5 shows two examples of proper and improper laser labeling.

The label on the left is from a scientific-grade laser intended for research and properly includes the laser class, max output power, and wavelength. The label on the right is a 20W blue (450nm) diode laser intended to be used for a DIY laser engraver. It is irresponsible of the laser vendor to not include both the output power (FDA required) and wavelength (helpful for defining safety measures) on this label. At such a high laser power, this Class IV laser has the potential to cause retinal burning leading to permanent vision loss. Understanding these classifications is key to assessing both risks and implementing appropriate controls.

Laser Hazard Risks

Always know the classification of the laser you are operating. At the heart of laser digital fabrication tooling is a Class IV laser even though the manufacturer may have provided appropriate controls to classify it as a Class I laser. Do not purposefully bypass any safety measures or interlocks while operating a laser tool. For the sake of quantifying the level of potential hazard with inappropriate laser use, we will assume that all lasers used from this point forward are Class IV. Never stare into a laser beam or specular reflected laser beam and keep your head above beam height. Do not wear jewelry especially when servicing or working near the laser beam as this provides additional sources of potential specular reflection.

At this point you might be wondering how far away from the laser source is the potential danger. When considering laser eye damage, three considerations impact this answer:

• Power and density of laser
• Exposure duration, dose, and distance from source of exposure
• Type of exposure: direct, specular reflectance, or diffuse reflectance

We start with defining the Maximum Permissible Exposure (MPE) which is the single most useful number in laser safety calculations. The MPE is the minimum exposure that may be incident upon the eye or skin without causing biological damage. As stated previously, the biological blink reflex of 0.25 seconds is important as this defines the timeframe for which quantities like MPE are calculated. The Nominal Optical Hazard Distance (NOHD) is the distance along the axis of the emitted beam at which the MPE is achieved and is dependent on beam characteristics such as the power, diameter, and divergence. The Nominal Hazard Zone (NHZ) is the distance within which exposure to a direct, reflected, or scattered beam is greater than the MPE. Mirrors, optics, and reflective materials in the beam path may result in diffuse or specular reflections in unintended directions. Specular reflections are hazardous over a greater range than diffuse reflections. If any biological creature is in the NHZ, it is at risk of an exposure above the MPE.

The University of Chicago has created a Laser Safety Calculation Guide [5]. Although the mathematical calculations are beyond the scope of this article, the calculations for MPE, NOHD, and NHZ have been compiled for varying laser powers as shown in Figure 6. An assumption of 2.55mW/cm2 is used to define the MPE, and the laser beam is assumed to have a very low divergence. A specular reflectance is assumed to be 80% of the original laser intensity (which may be considered low), and the diffuse reflectance is assumed to be 20% (which may be considered high). Such assumptions were made to provide a conservative estimate of the resulting hazard distances based on the laser power being considered.

Consider an open frame diode laser operating in a home garage in the suburbs. If pointed directly outside the garage, the 1W laser would yield a NOHD of approximately 732 feet (223m)! This means any neighbors within that distance from the laser would be in a situation where the MPE could be surpassed and potential eye damage could occur. If the laser underwent a specular reflection and reflected outside the garage, the NHZ would be 655 feet (200m). The diffusely reflected beam would yield a NHZ at approximately 2 inches (5cm). Those distances should come as a shock considering the types of laser powers in the marketplace are reaching levels like 20W like the inappropriately labeled laser illustrated previously.

Laser Control Measures: Minimizing Hazards

Engineering and Administrative Controls

To ensure the safety of the both the laser tooling operator and bystanders, layers of safety control measures may be employed. Engineering controls may include features developed by both the laser tooling manufacturer as well as aftermarket solutions incorporated by the end user. Enclosures and shielding may contain laser beams to reduce exposure risks. Safety interlocks prevent laser operation when such enclosures are open.

Home workshops and makerspaces should consider utilizing designated areas or even rooms for laser tooling to confine the laser beam even further. Prominent placement of Illuminated signage to show when laser beams are active can limit family members or other bystanders from accidental hazards. Administrative controls involve training, procedures, and policies to promote safety.

Laser workspaces should be well lit. Dark environments trigger a biological response where the pupils of the eyes dilate (or the iris of the eye opens fully) to capture more ambient light. Ensuring a bright workspace allows ones’ natural defense to intense light to function normally. The last line of defense for minimizing laser hazards is Personal Protective Equipment (PPE), and the most important to consider is laser safety glasses.

Certified Laser Safety Glasses

To provide sufficient blocking of laser radiation, laser safety glasses need to attenuate (or decrease) light transmission at specific wavelengths while still maintaining enough visible light to safely see what the wearer is doing. Sunglasses are not suitable laser safety glasses and offer virtually no protection against laser beams. Optical Density (OD) is a measure of how much a material or substance can attenuate the intensity of light that passes through it. The OD value is expressed as the logarithm of the transmitted light intensity through the material. Higher OD values indicate greater light attenuation while lower OD values indicate more light Transmission (T). T may range from 0.0 (0 %) to 1.0 (100%). The following equations define the relationship between OD and T.

Figure 7 illustrates the relationship among OD, attenuation factor, and transmission applied to a hypothetical instance of 10,000,000 photons passing through laser safety glasses. Once again, we are treating light as a particle (or a photon) in this example. As the OD (and attenuation factor) increases, the transmission decreases long with the total number of photons that pass through the material. With no eye protection (OD=0), all 10 million photons would reach the eye in this hypothetical example compared to only a single photon if laser glasses rated at an OD=7 were worn.

The ANSI Z136 standard provides specific guidelines for laser eye protection, and OSHA Labeling [1926.102(c)(2)(ii)] [6] specifies three critical pieces of information for inclusion on laser eye protection and are illustrated on a pair of Thorlabs Certified Laser Safety Glasses (LG10) in Figure 8:

1. Defined laser wavelengths for intended use
2. Optical Density (OD) at defined laser wavelengths
3. Visible light transmission (VLT)

A graph of OD and transmission for an example pair of certified laser safety glasses is illustrated in Figure 9.

Laser safety glasses are manufactured with 2 different technologies for creating the necessary OD for the desired wavelengths. Polycarbonate lenses with absorptive dyes absorb the laser light directly based on the type and amount of the selected dye. These glasses provide a broad wavelength usage with a good level of visible light transmission. Thin film interference filters utilize an engineered stack of optical thin films designed to attenuate the laser wavelength of interest via destructive interference. We can think of this destructive interference like noise canceling headphones. While noise cancelling headphones produce audio waves out of phase with the incident noise to provide a destructive interference condition, these thin film stacks creates a situation where specific wavelengths (or colors) shift out of phase of each other and thus cancel out. These thin films may be coated onto polycarbonate or glass. Such glasses can provide narrow wavelength attenuation and have a higher visible light transmission with better color balance. Figure 10 illustrates both laser safety glass technologies where the incident laser beam shown in blue is attenuated as it passes through the respective material.

Always purchase certified laser safety glasses for your Class II or greater laser tooling for as many people potentially in the NOHD. Do not trust inexpensive or included laser safety glasses! I purchased a 2.5W blue (450nm) laser diode from Aliexpress in November 2018 for $68.11 which included free laser safety glasses. As of December 2024, this laser diode/glasses combo is still available and in even greater laser power options. The glasses were not certified and did not include any markings of intended wavelength, OD, or visible light transmission. So, I decided to measure it myself. Figure 11 illustrate the 3 items included in the purchase (laser, glasses, and cable) as well as a photo of the laser pointed directly at the laser safety glasses.

A tremendous amount of light was passing through the glasses. Figure 12 shows a spectroscopic analysis of the laser safety glasses transmission and calculated OD. The glasses offered a dismal protection of less than OD=2 for the intended laser wavelength of 450nm which leads to a false sense of security for the end user.

Final Thoughts Regarding Laser Safety

You are responsible for both operating a laser digital fabrication tool as well as the safety of those around you:

• Make informed laser cutter/etcher purchases from reputable vendors as well as know the classification of your laser cutter/engraver.
• Follow all engineering and administrative controls for your laser cutter/engraver.
• Protect your eyes by purchasing certified laser safety glasses for any Class II or greater laser for as many people potentially in the NOHD. Do not trust inexpensive or included laser safety glasses
• Keep rooms brightly lit to ensure that pupils are not dilated
• Do not wear jewelry while using or servicing the laser
• Never look into a laser beam or specular reflected laser beam
• Keep your head above beam height

Laser cutting and engraving offer incredible possibilities, but safety must always be paramount. By understanding the risks, implementing appropriate safety practices, and investing in proper eye protection that meets ANSI standards, you can enjoy the benefits of laser technology while safeguarding your precious eyesight. Responsible laser use ensures a brighter future for both your creations and your vision.

References

1. Creality Laser Module [https://store.creality.com/products/creality-laser-module]
2. Thomsen S. Pathologic analysis of photothermal and photomechanical effects of laser-tissue interactions. Photochem Photobiol. 1991 Jun;53(6):825-35.
3. ANSI Z136.1-2022: American National Standard for Safe Use of Lasers [https://webstore.ansi.org/standards/lia/ansiz1362022]
4. OSHA Technical Manual (OTM) Section III: Section 6 [https://www.osha.gov/otm/section-3-health-hazards/chapter-6]
5. University of Chicago Laser Safety Calculation Guide [https://researchsafety.uchicago.edu/programs/laser-safety/mpe-and-nhz-calculation-guide/]
6. OSHA Regulations [https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.102]