1. Harm caused by laser radiation in laser welding and laser cutting
On the one hand, laser welding has the danger and harmfulness of conventional welding (such as mechanical injury, electric shock, burning, etc.);
On the other hand, its unique harm is laser radiation.
With high laser intensity, it can produce extremely violent interaction with body tissue, such as photochemical, photothermal, photodynamic, light dissociation, light wave electromagnetic field and so on, causing serious damage to the operator.
The surrounding equipment, especially combustible and explosive materials, will also cause disasters.
(1) Harm to eyes and skin
The cornea and conjunctiva of human eyes are not protected by the general skin stratum corneum and are most vulnerable to light beams and other environmental factors.
The intensity of the laser is so high that it causes injury before the reflex action of the eyelid produces a protective effect.
Therefore, it is generally recommended not to look directly at the laser with your eyes during laser welding.
When welding, you must wear professional protective glasses for laser welding.
When the eyes are irradiated, the retina will be burned, causing vision loss, and even burning the pigment epithelium and adjacent light sensing rod cells and cone cells, resulting in vision loss. Special attention should be paid to the protection of the eyes, as shown in figure 1.
The wavelength of Nd: YAG laser is 1064m, which can penetrate the cornea, eyeball and vitreous to focus on the fundus
Will cause permanent damage
Figure 1 Damage to eyes caused by laser welding
When the energy density of the pulsed laser is close to joules per square centimeter, the skin may be seriously damaged.
The radiation excited by the visible light band (400 ~ 700nm) and infrared band will cause erythema on the skin and then develop into blisters;
Extremely short pulse and high peak power laser radiation will carbonize the skin surface;
Although the harm and cumulative effect of ultraviolet laser are not fully studied, it can not be taken lightly.
When the laser radiation reaches the eyes or skin, it will cause tissue damage if it exceeds the maximum allowable exposure of the human body.
The maximum allowable exposure is related to wavelength, wave width, exposure time, etc.
When the irradiation time is nanosecond and sub nanosecond, it is mainly the light pressure effect;
When the irradiation time is 100ms, it is mainly photochemical effect.
(2) Hazard of additional radiation
The non-amplified electromagnetic radiation generated by the laser device will overflow from the laser outlet of the laser device or the gap of the shell.
Because there may be free radiation, such as ultraviolet or X-ray, it may cause injury, especially after long-term exposure.
(3) Other hazards
1) High voltage electric shock.
The laser is connected with high-voltage electricity (the excitation device of flash lamp) and large electric energy storage device, so there is the possibility of fatal electric shock.
2) The circuit is on fire.
When the wire is short-circuited, overloaded or the equipment next to the circuit is not resistant to high temperature or hits the circuit part, it is easy to cause fire.
3) Circuit assembly burst.
The capacitor and transformer in the laser are most likely to burst, resulting in injury, fire, short circuit, etc.
4) Other bursts.
A strong flash lamp used to excite a laser, a gas tube or an ion tube filled with a medium, may burst due to accidental collision.
5) Danger of cryogenic refrigerant or compressed gas.
Cryogenic refrigerants or compressed gases used in lasers may be dangerous due to unsafe containers (such as steel cylinders) or improper placement.
6) Toxic gas or dust.
The interaction between laser beam and weldment will produce substances harmful to human body;
Some metal fumes produced during laser deep penetration welding are harmful substances;
The formation of intense plasma will produce ozone and so on.
2. Prevention of hazards in laser welding and laser cutting
1) The surface of equipment and room shall be matte, the absorber shall be coated to prevent reflection, and the room shall be properly shielded.
2) The laser equipment and operation site shall be set in a special room with safety warning signs.
3) Laser safety signs shall be set on the laser processing equipment.
The signs must be permanently fixed during the use, maintenance or overhaul of the laser.
The warning signs of laser radiation shall be regular triangles, which are in the middle.
In the center are 24 long and short alternating sunlight radiation lines, including 1 long line, 11 medium and long lines and 12 short lines, as shown in figure 2.
Figure 2 Warning signs
4) The laser shall be equipped with a protective cover to prevent the exposure of personnel from exceeding the standard, or a protective enclosure to prevent personnel from being exposed to the laser.
The most effective measure is to place the whole laser system in an opaque cover.
5) All light paths in the workplace (including areas that may cause material combustion or secondary radiation) shall be sealed to make the laser light path significantly higher than the human body as far as possible.
6) The working energy of the laser is high-voltage equipment, and guardrails and safety signs shall be set to prevent electric shock or burns.
7) Maintenance personnel must regularly check the capacitor, transformer and other circuit components in the laser and make necessary updates to avoid bursting due to excessive use, resulting in injury, fire, short circuit and other accidents.
8) The equipment must have a reliable grounding or neutral connection device, with good insulation and can not be overloaded.
9) Containers of low-temperature refrigerant or compressed gas shall be tested regularly and placed according to safety regulations.
10) The workplace shall have fully functional local air extraction and smoke exhaust equipment, and the smoke shall be properly filtered before being discharged.
11) Strong flash lamps, gas tubes or plasma tubes filled with media for laser excitation shall be provided with solid protective covers to prevent bursting due to impact and falling.
3. Personal protection and safety technology
1) Display the indicator light before operation and inform the operator to do well in protection.
2) During operation, two persons must work, one for operation and one for supervision.
3) Do not look directly at the main beam at any time during the operation of the laser.
4) In case of abnormal vision during operation, immediately go to the medical department for visual examination and treatment.
5) Strengthen personal protection.
Even if the laser processing system is safely closed, workers may be exposed to accidentally reflected or scattered laser, so personal protection cannot be ignored.
Personal protection mainly uses the following equipment and protective articles:
① Laser protective glasses.
The most important part is the filter (sometimes the filter assembly), which can selectively attenuate the laser of a specific wavelength and transmit the visible radiation in the non-protective band as much as possible.
Laser protective glasses include ordinary type, side light-proof type and semi side light-proof type.
② Laser protective mask.
In fact, it is a helmet with laser protective glasses, which is mainly used to prevent ultraviolet and laser.
③ Laser protective gloves.
Workers’ hands are most vulnerable to excessive laser radiation, especially accidental exposure of high-power and high-energy laser, which poses a great threat to their hands.
④ Laser protective clothing.
Protective clothing is made of refractory and heat-resistant materials, which is a kind of white protective clothing with strong reflection.
6) Conduct safety training for operators.