Lasers are becoming increasingly important research tools in medicine, physics, chemistry, geology, biology and engineering. If misused, they can cause dazzle and injury (including burns and electrical shock) to operators and other personnel, including casual laboratory visitors, and cause significant property damage. Users of these devices must fully understand and apply the necessary safety precautions when handling them.
What is a laser?
The word "laser" (eng. 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 a laser is within or near the visible part of the electromagnetic spectrum. The energy is amplified to a state of extremely high intensity through a process called "laser induced radiation".
The term "radiation" is often misunderstoodwrong, because it is also used to describe radioactive materials. In this context, it means the transfer of energy. Energy is transported 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 and neon), solid crystals (for example, ruby) or liquid dyes are used as the working medium. When energy is supplied to the working environment, 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 a concentrated stream called a laser beam. Each work environment produces a beam of unique wavelength and color.
The color of laser light is usually expressed in terms of wavelength. It is non-ionizing and includes ultraviolet (100-400 nm), visible (400-700 nm) and infrared (700 nm - 1 mm) part 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. Humans are able to perceive these electromagnetic waves, but are unable to see the rest of the spectrum.
Gamma rays, X-rays and ultraviolet have the highest frequency. infrared,microwave radiation and radio waves occupy the lower frequencies of the spectrum. Visible light lies in a very narrow range in between.
Laser radiation: human exposure
The laser produces an intense directed beam of light. If directed, reflected, or focused on an object, the beam will be partially absorbed, raising the surface and interior temperatures of the object, which may cause the material to change or deform. These qualities, which have found use in laser surgery and material processing, can be dangerous to human tissue.
In addition to radiation, which has a thermal effect on tissues, laser radiation is dangerous, producing a photochemical effect. Its condition is a sufficiently short wavelength, i.e. the ultraviolet or blue part of the spectrum. Modern devices produce laser radiation, the impact on a person of which is minimized. Low power lasers do not have enough energy to cause harm, and they do not pose a danger.
Human tissues are sensitive to energy, and under certain circumstances, electromagnetic radiation, including laser radiation, can damage the eyes and skin. Studies have been conducted on threshold levels of traumatic radiation.
Eye hazard
The human eye is more susceptible to injury than the 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 ultravioletthe radiation is absorbed by the cornea of the eye, which can harm it. The injury is accompanied by edema of the epithelium and erosion, and in severe injuries - 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 impact of the laser on the retina 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 variant of exposure 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/cm2 acts on the retina with a power of 1000 W/cm2. 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-specular surface, much more powerful radiation leads to injury. The laser effect on the skin is devoid of the focusing effect, so it is much less prone to injury at these wavelengths.
X-rays
Some high-voltage systems with voltages above 15 kV can generate X-rays of significant power: laser radiation, which sources are high-power electron-pumped excimer lasers, as well asplasma 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 wavelength of the radiation, lasers are divided into several classes. The classification is based on the potential for the device to cause immediate injury to the eyes, skin, or fire when exposed directly to the beam or when reflected from diffuse reflective surfaces. All commercial lasers are subject to identification by markings applied to them. If the device was homemade or not otherwise marked, advice should be sought on appropriate classification and labeling. Lasers are distinguished by power, wavelength and exposure time.
Safe Devices
First-class devices generate low-intensity laser radiation. It cannot reach dangerous levels, so sources are exempt from most controls or other forms of surveillance. Example: laser printers and CD players.
Conditionally safe devices
Lasers of the second class emit in the visible part of the spectrum. This is laser radiation, the sources of which cause a person to have a normal reaction of rejection of too bright light (blink 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 1mW. These devices only cause damage when exposed directly for more than 1000 s in an 8-hour workday. Example: Barcode readers.
Dangerous lasers
Class 3a refers to devices that do not injure with short-term exposure to the unprotected eye. May be hazardous when using focusing optics such as telescopes, microscopes or binoculars. Examples: 1-5 mW He-Ne laser, some laser pointers and building levels.
Class 3b laser beam may cause injury if applied directly or reflected back. Example: 5-500mW HeNe 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 are also a fire hazard. Exposure to the beam, its specular or diffuse reflections can cause eye and skin injuries. All security measures must be taken. Example: Nd:YAG lasers, displays, surgery, metal cutting.
Laser radiation: protection
Each laboratory must provide adequate protection for persons working with lasers. Windows of rooms through which radiation from devices of class 2, 3 or 4 can pass, causing harm touncontrolled areas must be covered or otherwise protected during operation of such an apparatus. For maximum eye protection, the following is recommended.
- The beam must be enclosed in a non-reflective, non-flammable protective sheath to minimize the risk of accidental exposure or fire. To align the beam, use fluorescent screens or secondary sights; Avoid direct eye contact.
- Use the lowest power for the beam alignment procedure. If possible, use low-end devices for preliminary alignment procedures. Avoid the presence of unnecessary reflective objects in the laser area.
- Restrict the passage of the beam in the danger zone during non-working hours, using shutters and other obstacles. Do not use the walls of the room to align the beam of class 3b and 4 lasers.
- Use non-reflective tools. Some inventory that does not reflect visible light becomes specular in the invisible region of the spectrum.
- Do not wear reflective jewelry. Metal jewelry also increases the risk of electric shock.
Goggles
When working with Class 4 lasers with an open hazard area or where there is a risk of reflection, safety goggles should be worn. Their type depends on the type of radiation. Spectacles must be chosen to protect against reflections, especially diffuse reflections, and to provide protection to a level where the natural protective reflex can prevent eye injury. Such optical devicesmaintain some visibility of the beam, prevent skin burns, reduce the possibility of other accidents.
Factors to consider when choosing goggles:
- wavelength or region of the radiation spectrum;
- optical density at a specific wavelength;
- maximum illuminance (W/cm2) or beam power (W);
- laser system type;
- power mode - pulsed laser light or continuous mode;
- reflection capabilities - specular and diffuse;
- field of view;
- presence of corrective lenses or of sufficient size to allow the wearing of corrective glasses;
- comfort;
- presence of ventilation holes to prevent fogging;
- effect on color vision;
- impact resistance;
- ability to perform necessary tasks.
Because safety goggles are susceptible to damage and wear, the laboratory's safety program should include periodic checks of these protective features.
