Generated by stimulating radiation emissions, laser beams differ from ordinary light because they’re coherent.
The spatial coherence keeps the laser beam narrow even over long distances. The temporal coherence keeps the beam in a narrow spectrum.
Laser beams vary by the amount of energy they contain, and this determines what the laser can accomplish. Lasers of moderate and high intensities damage eyes and skin. Even low-powered lasers, such as those teachers and speakers use as pointers, are dangerous under certain circumstances. One little girl damaged her eyes temporarily by sharing directly at a laser pointer.
To protect workers, scientists and medical patients from laser damage, the government regulates their use. In the United States, 21 Code of Federal Regulations (CFR) Part 1040 is the authority. In the EU it’s IEC 60825. They set out a structure for defining “classes” of laser based on power and wavelength.
How Laser Beams Damage Eyes
Laser beams are primarily dangerous because of the heat they generate. This is what burns skin and retinas, and can cause flammable materials to catch fire. However, some specific wavelengths cause photo-chemical effects.
For most people who work with lasers, their eyes are most at risk. Because they are so coherent, laser beams narrow to an extremely small spot on the retina, destroying photoreceptor cells. If the light is powerful enough, it causes permanent damage almost immediately, creating a permanent blind spot in the retina.
Beams of infrared lasers are not visible to the human eye, and therefore do not cause eyes to blink. That means an infrared laser beam can enter the pupil of someone’s eye and burn their retina without their knowledge. It’s not immediately painful. The person may just hear a click or pop. The beam can generate a temperature above the boiling point of water.
Laser beams in the spectrum 400-1400 nm or nanometers penetrate eye balls and heat retinas. The eye’s lens absorbs beams shorter than 400 nm, where it causes photochemical damage. The cornea absorbs beams shorter than 300 nm, which leads to increased risk of cataracts.
Lasers require the use of certain safety precautions and equipment, as determined by the American National Standards Institute (ANSI) Z136. The Occupational Safety and Health Administration details the hazards and regulations about using lasers.
Class 4 Lasers are the Most Dangerous
For visible laser beams, they have output power of 500 milliwats or over, pulsed. Most lasers used for medical, scientific, industrial and military applications are Class 4.
Class 4 (or IV) lasers damage eyes, burn skin and start fires. This kind of light is dangerous even when it’s reflected. That is, the facility must closely control the path of the beam. When something reflects a laser beam, even glass or a matte surface, its light still damages the eye. While dealing with Class 4 lasers, users must remain conscious of the beam’s location so they can avoid it.
Even diffuse laser light damages eyes. Do not stare at a laser dot.
Keep the beam away from skin and flammable materials such as papers and cloth, and dark materials that absorb heat.
Class 4 beams distract or blind airplane pilots or automobile drivers, so never aim a laser into anyone’s eyes. It’s illegal.
These are not toys for children. Adults must supervise use of Class 4 lasers by teenagers.
Class 4 lasers are too powerful to serve as safe pointers.
The law requires a key switch and a safety interlock to come with all Class 4 lasers. An interlock is a circuit that remains broken if a safety condition is not met. For example, an interlock might prevent shut down the laser if the room’s door or the casing are open instead of safely closed.
Some of the Most Important Other Safety Requirements for Class 4 Laser Use
* A controlled area
* Outdoor controls
* Area posting
* Education and Training
* Spectator control
* Standard operating procedures
Laser Safety Glasses and Goggles are Most Important
Everybody exposed to a Class 4 laser beam must wear appropriate safety glasses. These glasses must meet two variables:
* Laser beam wavelength
* Optical density
Every laser beam has a certain wavelength or color. Therefore, manufacturers make glasses of glass and polycarbonate to protect against different wavelength ranges.
The other variable is Optical Density. This is how to measure the amount of radiation the glasses permit to pass through the lenses. OD is the base-0 logarithm of the factor by which the glasses or other filter reduces the power of the laser beam. For example, an OD of 4 reduces the laser beam’s power by 10,000, a factor of 4, because 1,000 is 10 to the power of 4.
Find out your laser beam’s wavelength and OD. If there is no permanent label or user guide, contact the manufacturer. Have your Certified Laser Safety Officer make certain you are using glasses and goggles with the correct wavelength and OD.
Laser curtains and barriers block and control laser beams, protecting workers from reflected exposure to Class 4 lasers. Curtains work especially well in medical and laboratory settings. Barriers can come in many sizes, and must meet fire-retardant standards.
Laser windows and domes come as glass or acrylic sheeting, a standard 3 millimeters thick. Like laser glasses, the windows block only specified ranges of laser wavelengths. And you must make certain their OD is high enough.
Phillips Safety is a leading manufacturer of occupational safety products, including the safety goggles, glasses, windows and barriers required to work safely with Class 4 lasers. Contact us today for help determining your laser’s wavelength, and what optical density your safety equipment requires.