The Occupational Health and Safety Administration sets the requirements for workers who use lasers as part of their jobs, whether in industry, a scientific laboratory or a medical institution.
OSHA describes in requirements in great detail in its technical manual.
Lasers pose other health and safety threats to workers, but laser beams are most dangerous to eyes.
Laser Beams Transmit Heat Energy in Ways that Easily Put Eyes in Danger
Laser beams by their directional nature consist of highly collimated light. That means it is highly concentrated into a narrow beam. When laser light raises eye temperature it denaturates the protein in the eye’s tissue, resulting in burns. Because of laser light’s nature, it’s orders of magnitude more damaging than ordinary light, which is not narrowed into a single beam. In some cases it’s greater than that of looking directly into the sun.
Lasers can also burn skin, but eyes are more vulnerable.
Just like ordinary light, lasers vary by their wavelength, and can range from ultraviolet to infrared. Just as with ordinary light, the human eye can see only the regular spectrum. This makes infrared lasers especially dangerous. Because they are effectively invisible to the human eye, it’s easier for people who work around them to become complacent. They are therefore more likely to forget or ignore the path of the laser beam, and as a result expose themselves. If the beam does reflect off a smooth surface, they cannot see it. And because infrared beams are invisible, they do not trigger the human eye’s blink reflex. They can go right through somebody’s cornea, lens and pupil and land on the retina. The intense heat burns the photoreceptors there, causing temporary or permanent blind spots.
The heat of the laser induces acoustic waves which also damage eye tissues. Near ultraviolet and visible spectrum laser beams damage the cornea and conjunctiva, causing photokeratis. Photokeratis is basically sunburn of the cornea, and it’s painful. It’s usually caused by overexposure of the eyes to sunlight, especially reflected glare of snow, when it’s called snow blindness. It’s also a problem for welders if they don’t use the proper protective goggles.
Laser Beams Damage Eyes in Other Ways
The lens absorbs some ultraviolet and infrared wavelengths, increasing someone’s risk of developing cataracts. A cataract is when the lens of the eye clouds up, worsening vision. They are normally by caused by old age and by prolonged exposure to the ultraviolet rays of the sun, which is why the United States government requires sunglasses manufacturers to sell only lenses that block the sun’s ultraviolet radiation. But laser light exposure increases the risk of getting them at a younger age.
Some ultraviolet and the visible spectrum laser beams cause additional photochemical damage to your eye. Some infrared beams cause aqueous flares in your eyes. That’s inflammation of the aqueous humour in the anterior chamber of the eye. The laser beam increases protein content and inflames the cells. This reduces vision depending on how large the aqueous flare is.
Legal Laser Classifications
Federal Law, 21 CFR Part 1000 requires laser manufacturers to label them with the appropriate classification. They must certify it meets all requirements of the Federal Laser Product Performance Standard to the Food and Drug Administration’s Center for Devices and Radiological Health.
FLPPS establishes the standard classes lasers based on their Accessible Emission Limits. The American National Standard Institute technical document on lasers, Z 136.1, defines AEL as the Maximum Permissible Exposure multiplied by the area of the limiting aperture. That is, by pupil of your eye, and it assumes the worst possible case, a 7 millimeter circular opening.
The two most important facets of the laser itself are its power and its pulse’s duration. The more power behind it, the more heat it transmits and, therefore, the more damage it can do to your eyes. Every time the laser light pulses, that is another exposure of your eye. Therefore, the more often the beam pulses, the more it damages your eye. That makes it more dangerous than beams that pulse less often or lasers that do not pulse at all.
The most damaging laser categories are Class 3A, 3B and 4. Class 4 lasers are the most powerful, and, so, are the most dangerous.
Glasses, Goggles and Windows are Required for Eye Safety
Manufacturers make glasses and goggles of glass and polycarbonate material capable of absorbing the heat and energy of a laser beam, reducing its intensity so it does not damage the wearer’s eyes. Made of glass or acrylic, windows are large plates that also shield the eyes of people standing behind them.
Workers exposed to laser beams must always protect their eyes. Glasses, goggles and windows work basically the same. All of them must fit the laser beam itself or they are not effective.
Lasers come in a wide variety of wavelengths ranging from ultraviolet, through the visible spectrum, to infrared. The eye protection you wear must match the laser you are operating. If they do not, your eyes are not protected. Glasses made to filter infrared light will not block purple lasers, and vice versa.
Laser manufacturers include this information on the machines and manufacturers stamp it on the frames of glasses and goggles. If you’re in doubt, consult your Certified Laser Safety Officer.
This specifies and measures how strong the glasses are. The higher the OD, the more laser light and energy they block. Therefore, you must make sure you wear glasses or goggles with an OD high enough to weaken the laser you’ll be exposed to. If you wear glasses with an OD that’s too weak, that puts your eyes at risk.
Two factors especially affect OD. The first is the strength of the laser. The stronger the laser, the higher the OD glasses you need to wear. The speed or duration of the pulse also affect it. The more the beam pulses, the more laser light lands on your retina, causing more retina.
The OSHA manual has a table of Optical Densities. The Laser Institute of America’s website has an online OD calculator. However, you should not rely on doing it yourself.
Manufacturers of laser safety glasses and goggles also stamp their ODs in the frames, so make sure you wear safety lenses strong enough to keep your eyes safe from the laser you use.
The industry experts at Phillips Safety Products make all types of goggles, glasses and windows for laser eye protection requirements. They’ll help you determine what optical density your laser requires. They also make barriers to guard against laser beams. Contact them today to learn more.