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Laser Radiation

Viimati uuendatud: 25.02.2017

Laser Radiation

Laser radiation is an optical radiation that can either be visible or invisible. If the wavelength of a laser beam is 400-780nm (nanometres), the beam is visible to the human eye. But when the environment air is clean from flying dust and other particles, the beam itself may not be visible, except for the mirror point on the targeted object. Invisible laser radiation is mostly infrared radiation, but UV-lasers also exist. Laser with an invisible beam is dangerous because when a person cannot see it, they cannot sense danger. In the case of an accident, when the infrared laser beam strikes the eye, a person does not sense it as light – meaning that no defence reaction (closing eyes, squinting, or iris contraction) follows, and this can result in irreversible damage to the eye retina. Therefore, work zones of laser instruments must be clearly marked and care taken that the beam would not hit bystanders.

Laser radiation is a special case of optic radiations, as the beam makes the laser dangerous also very far from its’ source; whereas some other optical or invisible light energy (from lamps, for example) disperses notably when the distance increases.

Health Effects

Laser radiation is characterized by the following physical attributes:

• radiates on one certain wavelength (differently from other lights      which usually have a wide spectrum);
• electromagnetic wave created by a laser is coherent – meaning that      all waves are in the same phase;
• the radiation source point is very small and beam brightness very      great.

Emanating from these aspects, the laser is dangerous because it enables to direct a very huge amount of radiation energy onto a very small area (such as the skin surface) during a very short time. As a result, skin and other biological tissues may be damaged.

Laser radiation is artificial light and cannot penetrate very deep into the organism, therefore, the organs at risk the most are skin and eyes. Also weak lasers may be dangerous as the laser beam might damage the eye retina.

Eyes

Watching a laser beam from aside can be uncomfortable for the eyes already on levels much lower from the marginal rate and cause blurred vision. Special attention must be paid to using lasers near vehicles as momentary blinding could cause a traffic accident.

Lasers on wavelengths 400-1,400 nm pose the greatest danger to humans. This includes visible light (400-780nm) and proximate infrared lasers (780-1,400nm). As the eye lense system functions in the range of visible light, the front part of eyes does not shield the corresponding wavelengths. Therefore, laser beam can reach the eye retina and damage it.

If and to what extent damage is caused, depends on:

• the amount of absorbed energy and whether the laser was pulsating,
• what focus-setting the eye was in, and
• which place in the eye the laser beam hit.

Health damage caused by a laser beam means loss of eyesight, accompanied by a momentary bright flash. Sometimes the person may hear a cracking noise and feel pain. Whether the damage is persistent depends on which point in the eye the laser beam hits. For example, damage hitting the edge of the retina may remain unnoticed.

In accidents involving powerful lasers, the eye damage may not only be limited to the area that the laser beam hit. Eyesight nerve connections and retina may be injured or an eye-internal bleeding can occur.

Mid-range infrared laser mostly causes thermal or heat radiation damage. As the mid-range infrared radiation is absorbed in water, then most of the laser radiation has usually already been absorbed when it reaches the eye back.

Skin Damage

Laser-induced skin damage is mostly limited to small burns. In milder cases, skin only blushes and heals fast. Longer exposure may cause blisters, 3^rd degree burns and even the charring of skin tissues.

Sub-cutaneous tissues are mostly well protected against laser radiation. However, constant laser beam with great power (exceeding several kilo-Watts) may penetrate the skin and damage sub-cutaneous tissues. But when safety requirements are properly adhered to, such accidents are unlikely.

Prevention

Most laser-related occupational accidents have occurred during experiments in research laboratories. These have mostly been caused by neglect of safety requirements.

Also military distance measure lasers have caused accidents. These are very powerful and dangerous both to handling personnel and civilians many kilometres away.

When handling laser radiation, most attention must be paid to the safety of eyes. Employees handling laser radiation must wear protective glasses. Even when wearing protective glasses, laser beam must never be directed into eyes.

General industrial safety requirements are as follows:

• properly train employees about hazards and safe handling techniques;
• if the work process enables, screen the laser beam completely from      people,
• not to direct the laser beam towards people,
• use the laser under supervision,
• verify that the storage and transport conditions do not harm the      laser,
• follow safety requirements applicant for the specific laser class,
• monitor the observance of safety requirements.

Protective glasses is the most common safeguard against laser radiation. It must certainly be checked that chosen glasses are able to block out these wavelengths on which the laser works. It must also be checked if the glasses protect against all wavelengths that the laser generates. Cheaper glasses have proven to be non-compliant with accompanying specification (actually shielded range of wavelengths).

Strong UV-radiation is a side-effect in the CO2-laser welding process. Therefore, the entire process must be completely separated, if possible. If screening is not possible, all present parties must use personal protective gear (protective clothing, mask).

Measuring

Regarding laser safety, it is important:

• how big amount of energy is absorbed into the biological tissues, and
• what is the wavelength (which type of laser).

When dealing with laser radiation, most attention is paid to the energy density (J/m²) and power density (W/m²) of the laser beam falling into the eye or onto the skin.

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