Laser Eye Safety
by Glyn Jones
Lasers beams and laser devices are in use in thousands of workplaces every day in Canada. Are you working with lasers?
The term “laser” conjures up images of science fiction weapons used to vaporize the enemy or high-tech applications used to manufacture silicon chips for computers. The reality is that lasers are everyday tools used in millions of everyday workplaces around the country. Laser light has hundreds of applications ranging from laser pointers, used as a leveling light in construction, medical uses such as cosmetic and surgical procedures, and industrial applications such metal cutting. Many everyday items you encounter use lasers, including CD and DVD players; hair and tattoo removal treatments, bar code scanners; telephone and internet transmission, and even a dentist’s drills.
Lasers, like any workplace tool, can be very useful to us but has associated with it hazards that need to be recognized and controlled. According to the Canadian Standards Association Z94.3 – Guideline for Selection, Use and Care of Eye and Face Protectors there are special considerations regarding the safety of your eyes and laser light. Used improperly laser devices are potentially dangerous with effects ranging from mild skin burns to irreversible injuries, including injuries to the eyes. Some lasers can result in permanent retinal damage and blindness.
The term “laser” is an acronym that stands for “Light Amplification by Stimulated Emission of Radiation.” Laser light is a form of non-ionizing radiation. Laser light differs from ordinary light in three ways:
1) It consists of just one wave length or colour;
2) it is non-diffuse; and
3) highly directional, and it can be generated in any part of the spectrum, ultraviolet, visible, and infrared. The specific wavelength ranges of lasers operation fits within what is called the “retinal hazard region.” Eye exposure within this region can result in permanent retinal damage.
Lasers are classified as one of four classes according to their power:
– Class 1 are low power and are generally safe for normal use as intended. The most common uses are in CD-ROM players and drives.
– Class 2/2a create an eye hazard if you were to stare into the beam. Fortunately, the normal blink reflex provides protection from over-exposure. A supermarket barcode scanner is an example of this class of laser.
– Class 3a/b and Class 4 lasers are a concern. These lasers pose an eye hazard that requires control, and are typically found in research, medical and manufacturing applications. Use of these higher power lasers are regulated and require hazard control by way of a laser safety program.
If you work with or around regulated lasers, there should be a person in charge of laser safety that is responsible for making sure everyone is adequately protected. This person will likely be a Certified Laser Safety Officer (LSO) or a Registered Occupational Hygienist (ROH).
The design of the laser safety program and any necessary controls requires you know the wavelength and the power of the laser. This can be determined by looking at the laser. It will have an information panel that lists the wavelength in nanometers (nm) or micrometers (um), and power in Watts (W) or milliwatts (mW). The laser safety program will include engineering and administrative controls and personal protective equipment typically required – including safety eyewear. Selecting safety eyewear requires you adhere to appropriate standards such as CSA Standard Z94.3. You should also consult with the operator’s manual of the laser equipment.
Safety eyewear is selected based on the laser wavelength and it operating density (OD). The OD is a measure of how much of a particular wavelength of energy can pass through a lens. In general, if you can see the beam of the laser or you can tell that the beam is exposed by how it is acting on materials laser safety eyewear should be worn. Your lens provider can provide consultation regarding of optical density.
If the laser light source is a pulsed laser selection of the safety eyewear will require information about the specific laser energy level (joules), pulse duration (seconds) and pulse rate (hertz). Laser safety eyewear works by both absorption and reflection. Some of the laser light is absorbed in the lens or in the pigments in the lens. Some of the laser light will also be reflected. The key to choosing laser safety eyewear is to carefully match what the laser is emitting to what the safety eyewear can protect. As with all safety eyewear, comfort is critical to ensure maximum benefit.
According to the CSA, users of laser safety eyewear need to be aware that the filters will gradually reduce their efficacy. Laser safety eyewear requires careful inspection to ensure it remains in good condition over time and as exposed to laser light. Carbon dioxide (CO2) lasers create a special laser hazard and require special CO2 eyewear.
Lasers as a workplace tool are here to stay. The hazards of laser use need to be recognized and controlled for the protection of workers. The risks are real and improper use or incomplete control can result in serious eye injury and blindness. Safety eyewear is an essential element of any laser safety program. Controlling exposure is manageable with proper planning, selection, and use of safety eyewear.
This article was published in eyesafe.ca on January 28, 2019. Glyn Jones is a partner at EHS Partnerships Ltd. in Calgary. He is a consulting occupational health and safety professional with 30 years of experience. He is a regular safety conference speaker in Canada and he provides program design and instructional support to the University of New Brunswick’s OHS certificate and diploma programs.