Laser safety for laser workers
Lasers and laser mediated risks
When working with lasers there are four main hazard categories to be aware of: 1. Laser radiation 2. High voltages 3. Process emissions
4. Moving parts/ manipulators
Laser radiation Laser radiation differs in several characteristics from ‘normal’ light. Mainly these characteristics make lasers a source of special interest regarding eye and skin damaging potential.
Lasers: radiation with special characteristics
Laser light has specific characteristics: The emitted laser radiation is monochromatic: The emission wavelength (color) of the laser is determined by the atomic structure of the laser medium. Laser beams have low divergence: The beam emits the medium in one direction. The beam diameter increases only very little over increasing distance to the laser source. Laser radiation is coherent radiation: The radiation particles (photons) show a spatial and temporal relationship. Due to the oscillating process in the laser medium groups of photons show a group-related dependency in time and place.
Lasers are characterised by the phase and composition of the laser medium. Often used types of lasers in research and industry are: • • • •
Solid state lasers (Nd:YAG, Ruby) Liquid dye lasers (>100 dyes) Gas lasers (CO2 ,He-Ne) Semiconductor lasers (diode)
Laser wavelengths are: • Primarily given by the laser medium They can be influenced by: • Laser optics • Pump energy
• Use of frequency doubling
Ultraviolet radiation (non-visible) Laser medium wavelength KrCl excimer 222 nm He-Cd 325 nm XeF excimer 351 nm Visible light Laser medium Argon ion Nd:YAG (fx2) Copper vapour He-Ne Roby
wavelength 488/514 nm 532 nm 578 nm 633 nm 694 nm
Infrared radiation (non-visible) Laser medium wavelength GaAIAs diode 750 – 900 nm Nd:YAG 1064 nm He-Ne 1150 nm CO2 10600 nm
Risk profile based laser classification Lasers are devided in classes 1 to 4 ,based on their human eye and skin damaging potential and according to the standard EN 60825-1 (www.nen.nl). A laser product can house a laser system of higher class.
E.g. a DVD-recorder contains an eye hazardous class 3B laser. Because this laser is housed in a lightproof enclosure the laserproduct is of an eyesafe class 1. Be aware of this fact during maintenance conditions. When the enclosure is opened there is a risk of exposure to the now accessible eye unsafe class 3B laser.
Risk profile based laser classification (2) Lasers in class 1 and 2 produce low power output and can be considered as safe under normal conditions. Class 1M en 2M lasers become dangerous when viewed with optical aids. The safety of class 2 laser depend on the blink and aversion reflex to bright light. These blink and aversion reflexes limit the exposure duration to 0,25 second for visible laser light. In this way the actual exposure remains below the maximum permissible exposure level and therefore a class 2 laser is considered to be eye safe.
The laser class is always stated at the laser product. Besides stating the laser class, there are several additional warning signs that must be put on the laser product, depending on the actual laser classification. These labels are the first source of risk information regarding the determination of the lasers risk in use. For example a class 2 laserpointer needs to be provided with the following labels:
Laserpointer: 0,98 mW
Eye damaging potential
The spot size of a collimated (low divergent) visible beam at the retina is 10 µm The diameter of a fully dilated adult pupil is 7 mm Focusing of a visible laser beam from 7 mm down to 10 µm at the retina leads to an optical gain of a factor 500.000 (1 mW of entrance power → 500 W in a 10 µm spot at the retina)
Effect of laser radiation at different wavelengths.
Eye damaging potential (2) The maximum permissible exposure (MPE) of the human eye for a visible laser beam (400 – 700 nm) is 25,4 W/m2. MPE values vary depending on the wavelength of the laser and on exposure times and can be calculated from NEN-EN 60825-1:2014. Exposure can be caused by direct and indirect beam looking and so can also be caused by direct and indirect reflections from components and e.g. jewelry. All laser beams of class 3B and 4 operate above eye MPE-level for the given wavelength(s). Therefore, eye protection by laser safety goggles is always needed at open beam handling (e.g positioning of samples in a laser beam) or under alignment conditions!
Skin damaging potential Also skin MPE values are wavelength dependent and can be calculated from NEN EN 60825-1:2014 Depending on the outcome of the risk calculations regarding skin MPE, additional skin protection against laser beam exposure may be needed.
Skin absorption profile of different wavelengths
High voltage equipment • Using of high voltage power supplies, there’s a risk of X-ray generation (> 5 kV Thyratron supplies). Under foreseen conditions these are contained within the housing. • Risk of electrocution when in contact with conducting elements. At high voltages in the kV ranges each material must be treated as a potential conductor. Hazard
Source
Electrocution High voltage and high power Water cooling
Measures: • Maintenance is restricted to qualified people only!
Remarks A 2 kW CO2-laser needs a 100A, 3-phase power supply of 40kW. Working and mainenace in contact with the conducting elements is restricted to qualified people only.
Process emissions
Hazard
Source
Remarks
Due to:
Exposure to harmfull chemicals
Laser gases Laser generated fumes and particles Cleaners
Local extraction of hazardous particles and fumes is favourable under all conditions.
• Material processing • Laser generated particles and fumes • Use of organic solvents and cleaners
Examples Material PVC Stainless steel ZnSe – mirrors
Laser generated particles (s) and fumes (g) Benzene (g) and HCl (g) Chrome-6 (s) and Vanadium-6 (s) SeO2 (s) deposition at mirror surface
Breathing of milling and / or cutting products (size between 0,5µm and 7µm) can lead to health complaints. The MSDS of each laser exposed material must be studied prior to start with the experiment to determine the direct emissions or metabolic products due to material processing!
Process emissions – incidents and intervention • Leakage of laser gases; if there’s a chance for leakage of toxic gases like fluorine, gas detection must be placed. Rooms need to be evacuated after detection of these gases in the room air. Conduct clearance measurements by wearing personal protective equipment (gas suit and mask) before re-entering the room. • Release of organic solvents, cleaners and / or laser dyes; depending on the type of solvent or dye, a protocol must prescribe how to deal with spills (when necessary, protect skin, lungs and mucous membranes). • Breakage of a ZnSe mirror → release of SeO2; cleaning of a spill only under breathing protection and by protocol! At suspected or actual exposure to toxic compounds, call for medical surveillance!
Manipulators and machines
In the use of machines and manipulators, it is important to ensure that the operator can not come into contact with the moving parts of the machine. This is a requirement from both the Machine Directive and the Working Conditions Decree. Moving parts must therefore be inaccessible from the position of human control to prevent unwanted interaction between person and machine.
Laser processing machine
Risk assessment and safety measures
Risk assessment In a risk assessment, the risks to the people in the room, the room itself and the surrounding areas are assessed. Based on the outcome, measures are taken to mitigate the present risks. Measures need to be taken, according to the occupational health strategy, in the following order: 1. Technical measures 2. Administrative controls 3. Personal protective equipment.
Examples of technical measures: • • • • • • • • • • •
Access control to the laser room Emergency stop buttons Interlock systems Key switches Beam dump Beam pipes Beam path above or below eye-level Use of non-reflective components Use of beam attenuators / color filters Use of black-out material Use of shutters
Emergency stop button
Beam attenuators (OD-filters)
Beam dump
Black-out material
Color filters Shutter
Examples of administrative controls: • • • • •
Warning signs General working instructions Specific working instructions Availability of maintenance documentation Use of incident procedures
Personal protective equipment
If, after application of technical measures and administrative controls, residual risks are left, one should proceed to the use of personal protective equipment. The employer states within the specific work instructions when it should be worn. The employer is obliged to provide personal protective equipment to the employees. The employee is then obliged to wear them according to the work instructions.
Personal protective equipment When working with lasers, various types of personal protective equipment (PPE) may be required:
•
Eye protection, if exposed to a laser beam above eye MPE
•
Protective clothing / gloves to protect the skin when exposed to a laser beam above skin MPE, in possible contact with hot or cold surfaces, when handling sheet metal and when exposed to chemicals of e.g. a liquid laser.
•
Breathing apparatus , if exposed to escapd toxic gases from e.g. excimer lasers or at replacing extraction filters.
•
Hearing protection in industrial environments or when using capacitor banks of high power pulsed lasers.
In the next slides the selection criteria for laser safety goggles are explained in more detail. Specific use of other PPE is explained in the workplace, in the context of the specific working instructions.
Laser safety glasses Laser safety glasses are wavelength and beam character specific. It is therefore important to verify that the proper glasses are used. The necessary shielding is calculated by the Laser Safety Officer in the preparation of the risk assessment. The implementation of these calculations falls beyond the scope of this laser operator course.
Only glasses with a CE mark or scale number represented in L or LB are authorized for use as personal protection equipment. Glasses which lack the CE-mark, an L or LB scale number or only display a scale number in OD should be considered unsuitable for the task according to the Personal Protective Equipment Decree.
Marking In order to check the suitablility of the glasses for your application, all glasses are marked with: - The symbol of the beam characteristics to which the glassses provide protection (D, I, R or M), - The wavelenghth or bandwith in nanometer (nm), against which protection is provided, - The scale numbers or the lowest scale number in case of protection against a spectral bandwith. - A suffix “Y” is added to the scale number if the product is not tested at low repetition frequencies of exposure (≤ 25 Hz), e.g.. R LB5 Y, - The CE mark, eventually followed by a year of type aproval (e.g.. CE 10), - Optional marking by a notified body (TüV, DEKRA etc.).
Question: You want to use the underneath described glasses for application with a pulsed Nd:YAG laser at a wavelength of 1064 nm. The protection needed is LB6 Are these glasses suitable for the application?
Yes: These glasses are marked with both OD and LB specifications. The LB specification makes them suitable in accordance with EN 207. The glasses comply to the demands for CE approval and are suitable as Personal Protective Equipment. The glasses needed for the application with the pulsed laser must be suitable for at least I,R, and/or M characteristics. It must be protective at 1064 nm and the scale number must be minimal LB6. The line “>950 to 1080 nm (IRM LB7)� meets these demands. These glasses are therefore suitable for the application.
Remarks: Laser safety glasses are designed to prevent against accidental exposure and may never be used for looking deliberately into a laser beam (not even to evaluate the optical density by measurements). Exposed glasses need to be replaced because, due to photobleaching effect on the material, the quality is no longer guaranteed. Also glasses with clear scratches or other demonstrable damage need to be replaced.
Variety of laser safety goggles
Work instructions
Work instructions Lasers fall into the class of potential hazardous tools in the workspace. These kind of tools may only be used if the risks are assessed and the outcome is translated into work instructions for safe use. We distinguish general and specific work instructions.
General work instructions General work instructions do apply for work that is done with no matter what type of laser. The general work instructions form the uniform rules of laser safe work in a laser safety facility and, not seldom, they are part of a laser safety policy. Part of the general work instructions are the 10 demands on laser safety.
Ten demands on laser safety: 1. 2. 3. 4. 5.
Always wear laser safety goggles when working with lasers powers above eye MPE Never look deliberately into a laser beam, also not when wearing safety goggles Never look into the laser set-up through any kind of optical element Never use reflecting components in the beam path Always work according to the safety instructions as they were communicated and as they are part of your room authorisation. These are mandatory
6. Remove rings, bracelets, watches and other kinds of jewelry with a reflecting potential prior to start working with the laser 7. Make sure that fibers are firmly attached to their driver. If there is no fiber coupled, make sure that the output-coupler is closed 8. Never look or work above a harmful laser set-up without wearing laser safety glasses 9. Visitors and unauthorised people may only access the laser room in company of authorised personnel or after authorisation by the responsible person 10. Wearing the wrong goggles is the same as wearing no goggles! Make sure you wear the appropriate ones for the application
Specific work instructions Besides the general work instructions for every laser application, there are work instructions regarding the safe use of each specific application. These consider the specific handlings with the application of the laser and the specific risks that were recognised herein together with the suggested measures to work safe with the equipment and set-up. For specific steps in the protocol the need for the use of Personal Protective Equipment is given for safe handling.
Case studies
Despite technical measures and administrative controls, residual risks often remain when working with accessible laser beams.
It’s important to realise these residual risks and minimise them intrinsically by the design of the laser set-up. The next pages will go into a couple of practical aspects of laser safe design and awareness regarding unwanted, unsafe situations;
Laser set-up Laser beams in the set-up may not be directed towards windows and doors. Beams may also never be aimed at individuals. So make sure that the beam always radiates away from you. In this way, cross-eye exposure to the primary beam is limited to a minimum. All laser beams from Class 3B and 4 must follow an as short as possible optical path. Each beam has to end in a suitable beam dump. If the periscope is misaligned, the 10W laser beam is aimed directly at the laser operator!
Entrance barriers The 'laser on' signaling at the entrance of a laser room is often already lit when the laser is just turned on. This gives no information on the actual situation in the room (whether or not a beam is present, or alignment is undertaken). By making good use of a second barrier behind the entrance door, one can make the distinction in the actual status in the room.
The second barrier is mandatory for roomsize exceeding NOHD in Class 3R, 3B and 4 lasers, to prevent exposure to the corridor. It can thus play an important role in the communication regarding the actual situation in the laser room and indicate the risk at entry.
Entrance barriers - sequel A stationary laser set-up has an aligned beam parallel to the optical table and is provided with blacked-out sides. A laser beam is therefore locked in by definition at the optical table and the room can be entered without laser safety glasses in that situation. The secondary barrier can remain open in this situation, because exposure to the beam is not possible. In the case of beam alignment, a laser beam may be located anywhere in the room and it may only be accessed with laser safety glasses. The secondary barrier is closed to indicate the alignment work. The barrier may then only be passed through under the wearing of suitable laser safety eyewear, which must be present in the space between the entrance door and the second barrier.
Electrical hook-up Lasers and accessory devices must be connected directly, as far as possible, to the electrical sockets available in the wall. The use of extension cords and junction boxes in particular should be kept to a minimum.
If a cable reel is used as an extension, it should be ensured that the permitted power in both coiled and uncoiled state is not exceeded. 24 (!) connections via one coiled cable reel. A power overload causes a direct fire hazard!
Cables Connection of cables and optical fibers must be positioned in such a way that, when one walks through the laser room, there’s no possible entanglement in cabling. Entanglement can shift the position of laser beams, but also components or equipment and they can end up in the beam path, with all the consequences that entails. The images on the right depict undesirable cable arrangements which give a high probability of entanglement.
Through the maze‌
Labeling of apertures and enclosures In the use of secondary enclosures, it is of importance that the housing of a higher class laser inside is indicated. All removable panels, with or without interlock, must be provided with appropriate warning labels. All openings where laser light exits from a housing must be provided with aperture indication.
Warning labels
Laser safety glasses Laser safety glasses must be intact for reliable operation. It is therefore important to treat laser safety eyewear carefully and store it preferably in the supplied case after use. Glasses with visible damage or those that are exposed by a laser beam should be replaced.
Unauthorised repair of laser safety eyewear.
Neat and tidy A tidy laser laser room is essential for a safe work environment. A possible fall or trip hazards by pipes, cables, etc. should be avoided at all times. A fall in the laser room breaches all the taken safety measures. The beam path may be relocated, causing unpredictable beams in the room, with the risk of eye and skin exposure as a result. One can also end up on the optical table itself and end up in the beam path, by which reflection of the beam, direct eye exposure or ignition of clothing or materials can occur.
Also, eating and drinking are not allowed in a laser room!
Neat and tidy (2)
Disordered (left) versus orderly (right) structure in the above figures.
Dye lasers There are over one hundred known laser dyes. The used solvents for these dyes are mostly organic solvents with their own risk profiles. Rhodamine-6G dissolved in DMSO is an often used combination. Rhodamine-6G is known carcinogenic and DMSO sensitises the skin, making it more permeable for Rhodamine. Positioning the dye pump above a spill tray is of importance, so that the liquid does not spread in the room in case of leakage. In addition, the appropriate personal protective equipment should be used to clean up any spill. Therefore a dye handling protocol is needed.
Dye lasers (2) Waste of dye lasers is collected separately. Make sure that the waste container is labelled, so the content is clear to anyone. The difference by methyl orange dissolved in ethanol and Rhodamine-6G dissolved in DMSO is hard to determine by eye, they’re both orange colored solutions. However, the risk profile is completely different. In the event of an accident or undesired spill it is essential to know which substance has been spread or someone has been exposed to.
? Proper labeling of waste containers can prevent from a lot of misery.
Welding, cutting and milling products When processing materials with high power lasers, toxic fumes and components may be emitted. It is important to know these metabolites well. E.g. laser cutting of PVC emits carcinogenic benzene and airway-irritating HCl gas. Laser cutting of stainless steel releases chrome-6 and vanadium-6, which builds up quickly to toxic levels in the human body. The most important measure is the use of local extraction, so that exposure to toxic fumes and substances is prevented.
Excimer lasers Excimer lasers can make use of corrosive gases (e.g. fluorine) and produce severe amounts of ozone. These gases are harmful to the health and the environment. When using this type of lasers, additional measures relating to the properties of materials exposed to the corrosive gases, gas detection and local extraction is necessary. Excimer laser
Lab tour
Lab tour The next slides will introduce you to, and provide a “lab tour� of, a typical laser controlled area. The tour will show you what you are likely to see in a typical laser laboratory, the associated potential hazards, as well as the control measures in place to protect yourself and others.
Lab tour Before entering the laser laboratory, pay attention to notices and signs at the entrance. These will inform you on the type of laser source(s) that are inside and what safety protocols are in place to ensure your safety when you are in the laboratory.
Lab tour Next to the door are documents that provide more details about the laser source(s), and other equipment inside. These may include Risk Assesments and Local Laboratory Rules, as well as other relevant Safety and Emergency Information. For example instructions on which actions to undertake in case of an emergency. Before undertaking any work in the laboratory, users are required to read and understand these documents.
Lab tour Laboratories containing hazardous laser source(s) and/or other hazardous equipment or substances, are always of restricted access. You would usually need a swipe card, key or a numerical key code to enter.
Access should only be made available to authorized personnel. All other persons must be accompanied by an authorized member of staff, whatever their reason is for entering the lab.
Lab tour Immediately after entering the laboratory, you will often see a wall portion, a screen, or a curtain, between the access door and the laser source(s). This is to protect you from any direct exposure to possible (stray) laser beams as you enter. In this laboratory, you enter to a locker or changing room.
Lab tour Also, in this locker room, you find an emergency phone, an emergency button, a safety light and (again) safety instructions.
Lab tour In the locker room, you will also find storage boxes containing personal protective equipment. This nearly always includes, at least one pair, of protective goggles.
Some labs my require that you have your own set of goggles.
Lab tour Laser goggles can provide protection from single or multiple laser sources. But generally, the more laser wavelengths the goggles protects against, the less usable they are. This is because, in that case, less light is transmitted through the goggles. And certain colours are obscured, making it difficult to see clearly. The correct goggles specified for the laser source in use must be worn to prevent eye injury when laser sources are operating.
Lab tour You should also remember to remove all reflective clothing, jewelry (watch, rings, bracelets, etc.) and objects that may be on your person before entering the main laboratory area.
Lab tour In some laboratories you may be required to wear additional protective clothing. For example, gloves, face masks, coveralls, protective footware or head wear.
Lab tour In this locker room, a sign indicates that you are about to enter a laboratory that hosts one or more laser sources. When a laser source is in operation, this sign will light up.
Lab tour The laser laboratory may host several work stations, including several laser sources with different wavelengths. This may be indicated by different lights above the door providing access to the laboratory. This laser laboratory hosts 3 workstations (numbered as WS1, WS2 and WS3). Lights indicate when a work station is in a so-called Processing Mode (SAFE), or Maintenance Mode (MAINT) and whether goggles are required (GOGGLES) when entering the laboratory.
Lab tour Before entering the laser laboratory it is important to know whether there are already users inside. That is beacuse, the warning signs will only inform you if a laser source is active. So you should check if anyone is inside, everytime. If the laboratory is currently in use, you should alert the persons who are inside, that you are about to enter the laboratory. You may be able to use an intercom or doorbel. If not, simply knock on the door and wait for a repsonse before entering.
Lab tour When entering the actual laboratory you will notice that the general environment is designed with user safety in mind. The room is well lit. And there are no windows that could allow laser beam(s) to escape from the laboratory. The walls have a mat surface, which is able to diffuse laser light and prevent reflections.
Lab tour In this lab, one of the work stations hosts an optical table with laser source(s) The work station is shielded with sliding and roller doors, to avoid that laser beam(s) escape from the work station when in operation. When the doors are closed, the work station is in the Processing Mode. In this mode, opening a door would activate the interlock circuit, resulting in the closure of the (mechanical) shutter of the laser source. In this situation the laser beam can not escape from the source.
Lab tour In this laboratory, to override the interlock of the work station, a button must be activated to avoid closure of the shutter of the laser source(s). Then, the mode of the work station changes to the so-called Maintenance Mode. You might be exposed to a laser beam in this mode. Output “window� of a laser source
Lab tour After opening the door(s) of the work station, you will see the optical table, on which • the laser source (here the blue/white device in the back), • other optical equipment, • stages or manipulators, • etc.
are installed.
MIRROR
LENS
GAVANOSCANNER
Lab tour Z-STAGE Typical components which might be part of a work station are shown here.
LASER SOURCE
FUME EXHAUST PIPE
SAMPLE HARMONIC CONVERTER MIRROR
BEAM BLOCKER OPTICAL TABLE
Y-STAGE
X-STAGE
Lab tour Typically the laser source, or its supply box, is key operated, to avoid unauthorized use.
Lab tour Here, the beam path is shown in green. To avoid injury or damage to the eyes, skin or other body parts, no body part may be placed in the beam’s path.
Lab tour There are many types of laser sources. Their wavelengths span the extreme UV, the visual spectrum and far beyond in the far infrared.
Several tools, such as infraredcameras or detector cards may be used to visualize the (path of the) laser beam, which is invisible to the human eye.
Lab tour Other useful devices might include power and/or energy meters. These typically consist of a sensor/detector and a read-out unit.
Lab tour Be also aware of other potential hazards associated with lasers, such as: • fumes emitted from the laser-material interaction zone, during laser processing, • fire, • high voltage power supplies, • water leakage for the cooling system of the laser source, • noise, which might cause communication problems in the laboratory. Consult the Risk Assessment of the lab for more details on the hazards and associated control measures.
Lab tour Upon leaving the lab it is good practice to ensure that the laser source(s) and work station are switched off. And ensure that all other equipment, instruments, apparatus, devices and tools are returned to their orginal position, ready for the next user.
Lab tour If laser source(s) are to be left on, e.g. for longterm experiments, close the doors of the work station, changing its mode to Processing Mode. It is then also good practice to put up a sign on the work station, as well as on the door provinding access to the laboratory, indicating: • your name & contact details, and • details about the experiment being performed.
The latter is to inform other users and/or emergency personnel about the experiments running in the laboratory.
Lab tour This ends the lab tour through a typical laser laboratory. Besides an overview of what you are likely to see in a typical laser laboratory, it has provided you with basic measures of laser safety.
You have gone through all the pages of the elearning. Along with having studied the syllabus "Laser safety for laser workers" you are now ready for taking the test. Good luck!
77