Lasers are becoming increasingly important research tools in the fields of medicine, physics, chemistry, geology, biology and technology. If used improperly, they can blind and injure (including burns and electrical injuries) operators and other personnel, including casual visitors to the laboratory, as well as cause significant damage to property. Users of these devices must fully understand and apply the necessary safety measures when handling them.
What is a laser?
The word "laser" (English LASER, Light Amplification by Stimulated Emission of Radiation) is an abbreviation that stands for "amplification of light by induced radiation." The frequency of the radiation generated by the laser is within or near the visible part of the electromagnetic spectrum. Energy is amplified to a state of extremely high intensity using a process called “laser-induced radiation”.
The term "radiation" is often misunderstood because it is also used in the description of radioactive materials. In this context, it means energy transfer. Energy is transferred from one place to another through conduction, convection, and radiation.
There are many different types of lasers operating in different environments. Gases (for example, argon or a mixture of helium with neon), solid crystals (for example, ruby), or liquid dyes are used as the working medium. When energy is supplied to the working medium, it goes into an excited state and releases energy in the form of particles of light (photons).
A pair of mirrors at both ends of the sealed tube either reflects or transmits light in the form of a concentrated stream, called a laser beam. Each working medium produces a beam of unique wavelength and color.
The color of the laser light is usually expressed in wavelength. It is non-ionizing and includes the ultraviolet (100-400 nm), visible (400-700 nm) and infrared (700 nm - 1 mm) parts of the spectrum.
Electromagnetic spectrum
Each electromagnetic wave has a unique frequency and length associated with this parameter. Just as red light has its own frequency and wavelength, all other colors - orange, yellow, green and blue - have unique frequencies and wavelengths. People are able to perceive these electromagnetic waves, but are not able to see the rest of the spectrum.
The highest frequencies are gamma rays, x-rays and ultraviolet. Infrared, microwave and radio waves occupy the lower frequencies of the spectrum. Visible light is in a very narrow range between them.
Laser radiation: human exposure
The laser produces an intense directional beam of light. If it is directed, reflected, or focused on an object, the beam will be partially absorbed, increasing the temperature of the surface and the inside of the object, which can cause a change or deformation of the material. These qualities, which have found application in laser surgery and material processing, can be dangerous for human tissues.
In addition to radiation, which has a thermal effect on tissues, laser radiation producing a photochemical effect is also dangerous. Its condition is a sufficiently short wavelength, i.e., the ultraviolet or blue parts of the spectrum. Modern devices produce laser radiation, the impact on humans of which is minimized. The energy of low-power lasers is not enough to cause harm, and they do not pose a danger.
Human tissues are sensitive to the effects of energy, and under certain circumstances, electromagnetic radiation, laser including, can cause damage to the eyes and skin. Studies of threshold levels of traumatic radiation have been conducted.
Eye hazard
The human eye is more prone to injury than skin. The cornea (the transparent outer front surface of the eye), unlike the dermis, does not have an outer layer of dead cells that protect against environmental influences. Laser and ultraviolet radiation is absorbed by the cornea of the eye, which can harm it. Injury is accompanied by edema of the epithelium and erosion, and with severe damage - clouding of the anterior chamber.
The lens of the eye can also be prone to injury when it is exposed to various laser radiation - infrared and ultraviolet.
The greatest danger, however, is the effect of the laser on the retina of the eye in the visible part of the optical spectrum - from 400 nm (violet) to 1400 nm (near infrared). Within this region of the spectrum, collimated beams focus on very small areas of the retina. The most unfavorable effect occurs when the eye looks into the distance and a direct or reflected beam enters it. In this case, its concentration on the retina reaches 100,000 times.
Thus, a visible beam with a power of 10 mW / cm 2 affects the retina with a power of 1000 W / cm 2 . This is more than enough to cause damage. If the eye does not look into the distance, or if the beam is reflected from a diffuse, non-mirrored surface, significantly more powerful radiation leads to injuries. The laser effect on the skin lacks the focusing effect, so it is much less prone to injury at these wavelengths.
X-rays
Some high-voltage systems with a voltage of more than 15 kV can generate X-rays of significant power: laser radiation, the sources of which are high-power electron-pumped excimer lasers , as well as plasma systems and ion sources. These devices must be tested for radiation safety, including to ensure proper shielding.
Classification
Depending on the power or energy of the beam and the radiation wavelength, lasers are divided into several classes. The classification is based on the potential ability of the device to cause immediate injury to the eyes, skin, fire when directly exposed to the beam or when reflected from diffuse reflective surfaces. All commercial lasers are identifiable using the markings applied to them. If the device was manufactured at home or otherwise not labeled, you should get advice on its appropriate classification and labeling. Lasers are distinguished by power, wavelength and exposure time.
Secure devices
First-class devices generate low-intensity laser radiation. It cannot reach a dangerous level, so the sources are exempted from most control measures or other forms of surveillance. Example: laser printers and CD players.
Conditionally Safe Devices
Second class lasers emit in the visible part of the spectrum. This is laser radiation, the sources of which cause a person’s normal reaction of rejection of too bright light (flashing reflex). When exposed to the beam, the human eye blinks after 0.25 s, which provides sufficient protection. However, laser radiation in the visible range can damage the eye with constant exposure. Examples: laser pointers, geodetic lasers.
Class 2a lasers are special-purpose devices with an output power of less than 1 mW. These devices cause damage only when exposed directly for more than 1000 s in an 8-hour working day. Example: barcode readers.
Dangerous Lasers
Class 3a includes devices that do not injure during short-term exposure to an unprotected eye. May be hazardous when using focusing optics, such as telescopes, microscopes or binoculars. Examples: 1–5 mW helium-neon laser, some laser pointers, and building levels.
A class 3b laser beam can cause personal injury or direct exposure. Example: 5-500 mW helium-neon laser, many research and therapeutic lasers.
Class 4 includes devices with power levels greater than 500 mW. They are dangerous to the eyes, skin, and also fire hazard. Exposure to the beam, its specular or diffuse reflections can cause eye and skin injuries. All safety precautions should be taken. Example: Nd: YAG lasers, displays, surgery, metal cutting.
Laser radiation: protection
Each laboratory should provide appropriate protection for persons working with lasers. The windows of the rooms through which radiation from class 2, 3 or 4 class devices can be harmful in uncontrolled areas must be covered or otherwise protected during operation of such a device. To ensure maximum eye protection, the following is recommended.
- The bundle must be enclosed in a non-reflective, non-combustible protective sheath in order to minimize the risk of accidental exposure or fire. To align the beam use luminescent screens or secondary sighting devices; Avoid direct eye exposure.
- Use the least power for the beam alignment procedure. Whenever possible, use low-end devices for preliminary alignment procedures. Avoid the presence of excess reflective objects in the laser area.
- Limit the passage of the beam in the danger zone after hours, using dampers and other obstacles. Do not use room walls to align the beam of class 3b and 4 lasers.
- Use non-reflective tools. Some inventory that does not reflect visible light becomes mirrored in the invisible region of the spectrum.
- Do not wear reflective jewelry. Metal jewelry also increases the risk of electric shock.
Protective glasses
When working with Class 4 lasers with an open hazardous area or when there is a risk of reflection, goggles should be worn. Their type depends on the type of radiation. Glasses must be selected to protect against reflections, especially diffuse ones, and to provide protection to a level where the natural protective reflex can prevent eye injuries. Such optical devices will retain some visibility of the beam, prevent skin burns, and reduce the possibility of other accidents.
Factors to consider when choosing safety glasses:
- wavelength or region of the emission spectrum;
- optical density at a specific wavelength;
- maximum illumination (W / cm 2 ) or beam power (W);
- type of laser system;
- power mode - pulsed laser radiation or continuous mode;
- reflection possibilities - mirror and diffuse;
- line of sight;
- the presence of corrective lenses or a sufficient size that allows wearing glasses for vision correction;
- comfort;
- the presence of ventilation holes to prevent fogging;
- effect on color vision;
- impact resistance;
- the ability to perform the necessary tasks.
Since safety glasses are susceptible to damage and wear, the laboratory safety program should include periodic checks of these safety elements.