Paperback Laser Safety for the Laser Worker by University of Twente

Laser safety for the laser worker

INTRODUCTION

This syllabus is part of the course 'Laser safety for laser the laser worker’ and was developed by Sentix Stralingszorg, an advice organization for radiation protection and laser safety. Both the course and the associated e-learning have been drawn to the "Guide to levels of competence required in laser safety," NPR-CLC / TR 50448: 2005. The course, along with the e-learning and related test lead to the level of the laser worker in the research environment. The purpose of the e-learning is to examine the knowledge and understanding of the risks in working with lasers in a research environment, identifying risks in practice and stating appropriate measures to limit the risks. Author: René Heerlien, MSc Sappemeer, June 2014 Revised: August 2016 Sentix Stralingszorg Noorderstraat 388a 9611 AW Sappemeer T: 0598 851848 F: 0598 851848 I: www.sentix.nl E: info@sentix.nl KvK nr. 51702959 Translated into English by Connect International, www.connect-int.org. © All rights reserved. No part of this publication may be reproduced, made public or saved in an automated database, in any form or in any manner, whether electronic, mechanical, through photocopying, recording or in any other manner, without the author’s or holder’s prior written permission.

CONTENTS

Introduction .................................................................................................................................... 1 Chapter 1. The ubiquitous laser ....................................................................................................... 4 Chapter 2. Laser beam characteristics ............................................................................................ 10 Chapter 3. The laser classification system ...................................................................................... 15 Chapter 4. Laser beam hazards ...................................................................................................... 21 Chapter 5. Laws and regulations .................................................................................................... 29 Chapter 6. Protective eyewear ...................................................................................................... 31 Chapter 7. Laser safety measures .................................................................................................. 34

CHAPTER 1. THE UBIQUITOUS LASER

INTRODUCTION Theodore Maiman demonstrated in 1960 for the first time how a laser works. With a ruby crystal and a flash light he showed that the existing laser theory could be put into practice. This very important discovery was not valued at the time because Maiman used the term “maser” (precursor to the laser) in the publication title. In a time when many papers were being published over masers, his paper was rejected for publication. This gave the chance for others, including Bell Laboratories Ltd., to appropriate the discovery of the laser. The actual discoverer is therefore difficult to prove, but it is clear that Maiman demonstrated the first successful working laser. The laser came into being in a world full of public suspicion. The image of the laser had been shaped by the media since the 1930s, when the concept of ray weapons was first introduced in the movies. For example, in the 1964 James Bond movie “Goldfinger”, Bond was nearly cut in half by a high power heliumneon laser. In the 1960s, substances other than ruby crystals were discovered that could be used to create laser beams. In the beginning of the 1970s, the first commercial products came on the market, including laser light shows, checkout scanners, and laser printers. After the discovery of the laser diode in the 1980s, the CD player was launched. In the same decade, laser spectroscopy and laser games came into being and the first trans-Atlantic fiber connection was laid. In addition, the LASIK eye laser treatment was applied for the first time. This was immediately an “eye-opener” in the field of laser safety. People had not realized that when a high-power laser beam was aimed at a ball filled with water, a significant portion of the beam would be reflected, with a consequence being that, in the first laser eye treatment, both the eyes of the patient as well as those of the surgeon were lasered. For obvious reasons, since then a laser filter has been used in the oculairs of the surgeon. A further refining of the laser diode technology appeared in the 1990s when the DVD player was introduced to the market and hair removal lasers were launched, first in beauty salons and later for the home market. From 2000 to the present time, the DVD player is slowly being overtaken by the Blue-ray player, it has been demonstrated that with the help of lasers material can be launched, and the energy required for nuclear fusion can be gathered by laser beams.

For the near future, interesting applications of lasers await in the wings. For example, people are working on the development of the X-ray Free Electron Laser, lasers are being used to realize holographic 3-D television and NASA is starting a program in which three laser-coupled satellites will be used to demonstrate the existence of gravitational waves for the first time. THE LASER Lasers can be fully accommodated in a single housing unit, including power supply, such as in a laser pointer. Other lasers consist of several loose components, including: - Laser head - Power supply - Cooling - Accessories: - control panel - gas supply - connections (pipes / wires) The laser head contains the active medium that produces the beam. It is this medium that gives the laser its name. For example, a helium neon laser contains a mixture of helium and neon gases. The laser head houses the component that supplies the energy to activate the medium. This excitation of the medium can stem from electrical, optical or chemical energy. In addition, the head can contain a number of optical elements. Laser beams exit the medium on one side. There are also lasers in which the beam exits the medium on two sides! WORKING OF THE LASER Laser is an acronym for â&#x20AC;&#x153;Light Amplification by the Stimulated Emission of Radiationâ&#x20AC;?. The laser contains an active medium. This medium can be a gas, liquid or solid. A laser also contains an energy source to excite the active medium and a set of mirrors. A laser can be best represented as a variant of the fluorescent light bulb, in which gas is excited by an electrical current and results in the emission of light. A simple model of an atom can be described as a heavy core with surrounding electrons circling in strictly defined orbits around the nucleus. When energy is added Figure 1. Excitation and emission to these atoms, electrons can transfer from one orbit to another orbit farther away from the nucleus. This principle is called excitation. The energy state of the atom is now unstable and the electron falls back to its original position and emits the difference in energy. This energy comes free in the form of light (Figure 1). When we describe this process for the laser model in Figure 2, then is the ruby crystal activated by the flash lamp. The atoms in the ruby crystal become excited (E1) then fall back to their ground state (E0) and emit a red light.

Figure 2. Model of a laser Because a semi-transparent mirror sits on only one side of the laser, the emitted light particle (photon) is bounced between the two mirrors until the photon can exit the laser parallel to the opening in the semitransparent mirror. During this bouncing back and forth, the photon causes a cascade of relapse of other excited atoms, through which new photons are produced on a large scale, each of which can generate new cascades until they also can exit the laser parallel to the opening in the semi-transparent mirror. When sufficient energy is added to the active medium, the majority of atoms will be in the excited state. This situation is called “population inversion” and leads to an enormous production of emitted photons, which is necessary to create a laser beam. Through the cascade of decaying particles, which have first bounced back and forth between the mirrors for a while, a high energy beam is produced that eventually exits the laser. As long as sufficient energy is added to the active medium and the population inversion is maintained, the beam is maintained. The beam has three properties that are characteristic of laser radiation: › the beam is collimated (the particles move substantially parallel with each other) › the beam is monochromatic (one color) › the beam is coherent (temporal and spatial alignment of photons) The above described principle is schematically displayed in Figure 3.

Figure 3. Laser principle DIFFERENT TYPES OF LASERS

The explanation of how a laser works in the previous paragraph describes the excitation of a ruby crystal and the subsequent emission of photons. In this case, the ruby rod constituted the active medium to

achieve the light amplification. Other types of lasers possess different active media to generate with other characteristic properties. GAS LASERS These possess a gas as an active medium and are mostly excited by means of an electric current. Examples of gas lasers include: EXCIMER Excimer lasers contain an active medium consisting of a combination of noble gas, halogen gas and buffer gas, and emits laser light in the UV region. Excimer stands for 'excited dimer', wherein in the excited state, a dimer is formed between noble gas atoms, and atoms of the halogen. The medium is activated via electrical gas discharge. example: KrCl excimer laser which emits laser light at a wavelength of 222 nm. GAS-ION LASERS This type of lasers includes a pure gas (e.g., argon or krypton) as the active medium that is activated comparable to excimer lasers, by means of electrical gas discharge. This gas discharge is achieved by a high DC voltage across the gaseous medium. This produces a plasma consisting of ions and electrons. Examples are the argon laser and the krypton laser. This type of lasers emits multiple colors, originating from the different transition states possible in the excited ions. There are several emitted colors, but the main emission lines are at, for example, an argon-ion laser 514.5 nm (green) and 488 nm (blue). The main emission line of a krypton-ion laser is located at 647.1 nm. CO 2 LASERS A carbon dioxide-laser contains an active medium, consisting of a mixture of carbon dioxide (CO2), nitrogen (N2) and helium (He) as the active medium. The laser operates in the infrared wavelength range. The nitrogen molecules are activated via electricity and gas discharge and they transfer, by collisions, their energy to the CO2 molecules. At the emission step of the excited CO2 molecules to a lower energy state, the laser light is generated. Helium gas serves as a cooling gas in order to dissipate the buildup heat. DYE LASERS The active medium is a liquid that can be excited by intense flash, normal light or another laser (a pump laser). The use of different liquids makes it possible to produce beams of different wavelengths, depending on the settings of the laser optics. The liquids are generally very toxic or carcinogenic and their use brings several additional risks with it. Example: Rhodamine-6G dissolved in Dimethyl Sulphoxide (DMSO)

SOLID-STATE LASERS The active medium consists of a rod-shaped solid or transparent material such as ruby or emerald. Excitation is generated by bright light flashes or a strobe light. Other types of solid-state lasers are Neodymium-YAG (Nd:YAG) and Holmium-YAG (Ho:YAG). Excitation is generated by bright flashes of light or a strobe light, but also often realized through the use of a diode laser (see details below). A laser, wherein the solid substance as the active medium is pumped by a diode laser, is called a diode-pumped solid state (DPSS) laser. SEMICONDUCTOR LASERS (DIODE LASERS) These are miniature lasers made from semiconductor material. The diode lasers work according to the same principle as a transistor. An electrical current is placed directly on the material. The wavelength and power are dependent on the chosen semiconductor material. Diode lasers are applied on a large scale in the telecommunication field but also gaining ground in other applications, partly due to its small size. Thus, diode lasers are used in laser pointers and apparatus for geodesy. High-powered diode lasers are also suitable for pumping in solid-state lasers such as Nd:YAG (so-called Diode Pumped Solid State lasers (DPSS). Examples › GaAIAs-diode 785 nm (CD-player), 808 nm (pump laser for Nd:YAG in DPSS-laser) › InGaAsP-diode 1310 -1654 (gas detection and optical fiber communication) LASER WAVELENGTHS Depending on the active medium, settings of the laser optics, size of the pulse energy or the use of frequency multipliers, it is possible to generate a range of different wavelengths. Below is a list of examples of wavelengths from characteristic laser radiation from the active media, frequency doubled wavelengths for the Nd:YAG laser, and e.g. wavelengths for different excitation parameters for the He-Ne laser. Ultraviolet (not visible) › KrCL excimer 222 nm › He-Cd 325 nm › XeF excimer 351 nm Visible light › Argon ion 488/514 nm › Nd:YAG (fx2) 532 nm › Copper vapor 578 nm › He-Ne 633 nm › Ruby 694 nm Infrarood (not visible)

› › › ›

GaAIAs diode Nd:YAG He-Ne CO2

750 - 900 nm 1064 nm 1150 nm 10600 nm

LASER APPLICATIONS There is a wide variety of applications for lasers. Often the laser application is focused on the field in which they are used. Applications in industry are substantially different than those in scientific research, and yet again different than those in the medical sector. In addition, there are many consumer products on the market that use lasers and many examples can be found in the entertainment industry. The following is a number of laser applications that are commonly used in research, but this is still not a complete list: › Open laser setup › Laser diffraction › Confocal microscopes › Cell sorters (FACS) › DNA sequencers › IR-laser microscopes › Optical tweezers

CHAPTER 2. LASER BEAM CHARACTERISTICS INTRODUCTION In this chapter, we assume that we are dealing with an available (open) laser beam. The characteristics of the laser beam and the potential health hazards people face should they come in direct contact with the beam will be discussed. RADIATION OR BEAM The term radiation is used scientifically to describe the process where something is emitted from a source. In general usage, the term radiation is associated with nuclear explosions, nuclear energy, etc. However, the laser also emits laser radiation. To prevent the association of laser radiation with Xradiation, gamma radiation, etc, we will use the term laser beam as much as possible. The terms laser radiation and laser beam are interchangeable and will, where appropriate, be used interchangeably. THE LASER BEAM Different types of lasers produce laser beams of different wavelengths with different capacity or energy. They can also emit different types of beams. They can emit a stable, continuous, sustained beam (continuous wave, or CW laser). The laser can also emit a beam in the form of a series of extremely short pulses, which is called a pulsed laser. In general, it is not possible to use a pulsed laser in a continuous mode. It is often possible to use a continuous laser in a pulsed mode, such as the CO2-laser, for example. This is done to increase the capacity (the same amount of energy is emitted in a shorter time). The light emitted from a laser has characteristic properties. These properties are: › The emitted light is monochromatic – one or more distinct colors or wavelengths, depending on the active medium that is being used, › The beam has a low divergence – the light exits the laser as an almost parallel beam, › The radiation is coherent – the photons align in phase with each other WHAT MAKES LASER LIGHT SPECIAL To understand why light from a laser deviates from normal light, it is necessary to explain about the behavior of light and other light sources. THE ELECTROMAGNETIC SPECTRUM “Light”, for most people, means daylight or light from a lamp. To be more precise, light is a type of radiation energy or radiation that is discernable by the human eye. We call daylight as white light, because there is no dominant color visible. Daylight is, in fact, a mix of colors: the colors of the rainbow. Sir Isaac Newton proved this fact of white light by using a prism to split the various individual color bands, with red on one end and violet on the other end of the color range. This color range is called a spectrum. White light is but a small portion of a much larger spectrum, which is called electromagnetic spectrum. If

it would be possible for us to look further than our own visible light spectrum, we would perceive infrared, ultraviolet, x-radiation, microwaves and radio waves, all different types of radiation. Although these types of radiation are not visible to the human eye, there are ways to detect their presence or display them. For example, infrared light produces warmth and can be measured with a thermometer. All electromagnetic radiation propagates in space with a constant speed: 299,792,900 meter per second (rounded off to 3.0 x 108 m/s). Although the aforementioned appearance is diverse, this involves various forms of radiant energy with the same basic characteristics.

The optical portion of the electromagnetic spectrum consists of ultraviolet, visible light and infrared radiation. This region consists of a wavelength between 100 nm and 1 mm, where 1 nm amounts to one billionth of a meter and 1 mm is a thousandth of a meter.

DEFINITIONS OF OPTICAL RADIATION A number of characteristics of optical radiation are described below: wavelength The position of the radiation within the electromagnetic spectrum is specified by the wavelength of the radiation. The radiation can be seen as something that moves away from the source (such as a lamp) in the form of a wave, in a manner that is comparable with the formation of ripples after a stone is thrown in water. The distance between the peaks (or valleys) of the wave is a wavelength, represented by l (lambda) and measured in nanometers (nm). velocity As described earlier, waves move out from a source with a constant velocity in the material. When there is no interaction with the material (as in a vacuum), the velocity is equal to approximately 300,000,000 meters per second (the speed of light), written as 3 x 108 m/s.

frequency When waves move away from a source and one counts the number of waves from a fixed point from the source, then the frequency is the number of waves that in one second pass this point, displayed in Hertz (Hz). It is possible to calculate the frequency of radiation if the wavelength and the wave velocity is known: frequency = velocity / wavelength The frequency of optical radiation is very high; for example, red light with a wavelength of 694 nm has a frequency of: = 3 x 108 mÂˇs-1 / 694 nm = 300,000,000 / (694 / 1,000,000,000) = 432,000,000,000,000 Hz = 432 THz Radio waves are usually given on the basis on their frequency, e.g. Radio 1 uses approximately 99,000,000 Hz of 99 MHz. ELECTROMAGNETIC RADIATION As mentioned earlier, the radiation from a source, such as a lamp, can be regarded as a wave phenomenon. A wave is composed of two components: an electric field and a magnetic field, thus the term electromagnetic radiation. These two components are perpendicular to each other, but oscillate in a similar manner. That is, a peak in the electric field falls together with a peak in the magnetic field. These components are said to be in phase with each other. One of the properties of electromagnetic radiation is that it can also manifest properties of a particle as well as a wave. This particle is called a photon. A detailed understanding of quantum mechanics is required to understand the reason why, but for the purposes of this course only one property is important: the quantity of energy that a photon carries. The quantity of energy is directly related to the wavelength of the radiation and is given in the following equation: Energy = Planckâ&#x20AC;&#x2122;s constant x wave velocity / wavelength Therefore, the shorter the wavelength, the larger the energy of the corresponding photon is. The unit that is used to assess the level of energy to be displayed is the joule (J). One joule is a relatively large unit and represents the kinetic energy that a small glass with water gains when it falls from a height of 50 cm.

Planck’s constant is a physical constant and amounts to 6.63 x 10-34 J/s. For example: for a “red” radiation with a wavelength of 694 nm, the maximum energy equals Energie = (6.63x10-34 x 3x108) / 694x10-9 = 2.87 x 10-19 J This is a very small number, given in joules. Another unit, mostly used in atomic and nuclear physics is the electron-volt (eV). One electron-volt is equivalent to 1.602 x 10-19 J. The calculated value of 2.87 x 10-19 J is then also equivalent to 1.79 eV. When the wavelength is given in nm than the energy amounts to about 1240/l: for example, 1240/694 = 1.79 eV. On the basis of this, it is apparent why laser radiation belongs to the non-ionizing radiation. Approximately 10 eV is necessary to ionize biological materials. WAVELENGTH BANDS The visible portion of the spectrum forms only a small part of the total optical spectrum and is an even smaller portion of the total electromagnetic spectrum. The optical portion is subdivided on the basis of when the radiation interacts with people. De subdivision is not fixed and different texts may describe them differently. The visible region derives its name from the manner in which the radiation interacts with the eye and gives us the sensation of seeing. The eye can, however, also focus on radiation in the IR-A region, but this goes unnoticed because the photo receptors in the eye cannot detect this radiation. This is addressed below. Band Subdivision Wavelengths Ultraviolet UV-C 100 nm – 280 nm (UV) UV-B 280 nm – 315 nm UV-A 315 nm – 400 nm Visible Thermal hazards 400 nm – 700 nm Photochemical 400 nm – 600 nm hazards Infrared (IR) IR-A 700 nm – 1400 nm IR-B 1400 nm – 3000 nm IR-C 3000 nm – 1 mm PROPERTIES OF LASER BEAMS As stated previously, there are several characteristics of a laser beam that makes it different from optical radiation, such as light produced from a lamp. These include: › Low beam divergence › Monochromatic light › Coherent beam

Low beam divergence The optical radiation from a normal house, garden or kitchen light radiates in all directions. When a lamp is placed in a glass sphere and the intensity is measured with a photometer, the values over the surface of the sphere will vary only very little. Radiation from a laser is emitted through an opening (aperture) as a beam with a small diameter. When the beam is visible and projected on a piece of paper, the diameter of the beam does not change when the paper is held farther away from the laser apparatus. This is called low divergence. Divergence is described as the dispersion angle of the beam, given in radians (rad). There are exceptions to lasers with a low divergence. Laser diodes usually have a relatively large divergence and therefore one uses lenses to correct for this. There are also laser applications where the beam, after it has been strongly focused on a certain point, it may diverge beyond this point. This applies to beams used in laser cutting, material handling or surgical laser applications. Monochromatic light The radiation from a lamp can be split into the separate colors of the visible portion of the electromagnetic spectrum. In addition, a significant portion of the infrared part of the spectrum is present herein. Laser radiation generally consists of one, or a few, well-defined wavelengths. A laser can be designed to generate only a particular color, or optical components can offer the opportunity to select the desired wavelength. An example of this type of laser is the Helium-Neon-laser. The most He-Ne lasers give a wavelength of 633 nm (to be precise, 632.8 nm) and has a red color, although it is also possible to generate radiation with a wavelength of 543.5 nm (green), 1152.6 nm (infrared) and 3392.0 nm (infrared). Coherence Coherence is a unique property of a laser beam and is related to the definition that the photons have a mutual relationship with each other. Photons from a normal lamp do not have this relationship and this light is then called non-coherent. Laser radiation is coherent over a certain distance from the laser. This is called the coherence length. This property is important when the laser beam carries information or must interfere with another laser beam. A characteristic of laser light, which can be observed when the beam is scattered, is "laser speckle", and is seen as a speckled phenomenon. This is caused by reflections interfering with the incident laser beam. The observed image has light and dark elements, depending on whether reinforcement or extinction in interfering radiation occurs.

CHAPTER 3. THE LASER CLASSIFICATION SYSTEM INTRODUCTION From a safety perspective, there are unique risks from the beam of a laser. The accessibility of the transmitted beam is the basis of the classification system. Hazards of the beam are related to the power, wavelength and the exposure time. The most important standard that refer to the safety of laser products is: NEN-EN-IEC 60825-1:2014 “Safety of Laser Products, Part 1, Equipment classification and requirements. This standard contains many of the details that are necessary for manufacturers and users to classify the risks of a laser. The main standard languages are English, French and German, and we use the English version throughout the course material. LASER CLASSIFICATION Lasers are subdivided in groups based on their injurious potential. The risk is related to the wavelength, the energy and the pulse characteristic of the laser beam. The classification system assists in the determination of the necessary operating steps. This classification system is described in NEN-EN-IEC 60825-1:2007. The standard lists tables for manufacturers or their representatives to support the allocation of the appropriate class. The following information is necessary to appropriately classify lasers: wavelength, exposure time and observation circumstance. For each class of laser, there are established security measures and requirements. The maximal emission of laser radiation is compare to the Accessible Emission Limit (AEL) for a given class. This is the maximum level of laser radiation that the laser can emit during use at maximal capacity, at any time after the production of the radiation. The AEL takes into account the wavelength, the exposure time (for both continuous and pulsed lasers) and the observation conditions for the laser beam. NEN-EN-IEC 60825-1 gives tables with AEL-values for every laser class. These specify the maximal power and the exposure time within each class. NEN-EN-IEC 60825-1 specifies eight laser classes. The classification scheme also applies to “laser products”, which are defined as: “any product or assembly of components in which a laser or laser system is used or is housed within or is intended to do so” A laser product can thus possess a laser system from a higher class! For example, a CD player is described as a laser product, because it contains a laser system, i.e. a laser and a suitable energy source. The classification of a laser product may differ from that of the laser system. CLASS 1 (CONSIDERED SAFE)

For the intended use applications, Class 1 lasers are safe for both the eyes as well as the skin. The maximal power in Class 1 is equivalent to <0.5 ÂľW. This Class is applicable to both visible and invisible lasers. Class 1 laser products can contain a high power laser system (for example, the Class 3b laser in a confocal laser microscope), where the technical design ensures that the power during usage will never go over the value of one AEL. Note: Class 1 lasers are not inherently safe. An example of this class is a DVD recorder. CLASS 1M (UNDER NORMAL CIRCUMSTANCES CONSIDERED SAFE) Only applicable for wavelengths between 302.5 and 4000 nm. Class 1M lasers may not exceed the AEL for Class 1 lasers, but the power of the beam can be fairly high. The concept is based on the amount of the beam that falls into the eye. Laser beams in Class 1M are therefore very divergent (are rapidly increasing in diameter with increasing distance) or have a large diameter and are collimated. Therefore, lasers in this class are not safe for the skin and eye when using optical devices such as lenses. An example in this class is testing equipment for optical fibers. CLASS 1C (UNDER FORESEEN USE CONSIDERED SAFE) This laser class was introduced with EN 60825-1: 2014 in August 2014. Class 1C can be assigned to appliances with a direct-contact application to the skin or non-eye tissue. Although the output of these lasers may be of class 3R, 3B or 4, they are protected technically such that, during use, no eye exposure can take place above a maximum permissible exposure limits. For example, opto-acoustic imaging. CLASS 2 (LOW POWER) Class 2 is only applicable for lasers in the visible region (400 â&#x20AC;&#x201C; 700 nm). They can be either continuous or pulsed. Protection of the eye is mediated by the natural defense reactions, including the blink reflex. It is believed that the maximal exposure for the eye is 0.25 seconds (the time necessary to avert the head or blink the eyes). The maximum power in Class 2 is set at <1 mW. An example of this class is: guided lasers and leveling tools. CLASS 2M (LOW RISK, UNDER NORMAL CIRCUMSTANCES) Class 2M lasers may not exceed the AEL for Class 2 lasers, but the power of the beam can be fairly high. The concept is based on the amount of beam that falls into the eye. Laser beams in Class 2M are therefore very divergent (are rapidly increasing in diameter with increasing distance) or have a large diameter and are collimated. Therefore, lasers in this class are not safe for skin and eyes when using optical devices such as lenses. An example of this class is: laser torch. CLASS 3R (MEDIUM POWER)

Class 3R lasers cover the wavelength region from 302.5 nm – 1 mm. Direct exposure to the beam is hazardous, but less than a Class 3B laser product. The AEL is within 5x the AEL-value for Class 1 or Class 2 (400 – 700 nm). The maximum power amounts to <5 mW. An example of this class is: terrestrial scanning equipment. CLASS 3B (MEDIUM / HIGH POWER) Class 3B applies to both visible and invisible laser radiation. Looking directly at the beam is always dangerous. Diffuse reflections are normally safe to look at, if the eye is located more than 13 cm from the reflecting surface and the exposure time is less than 10 seconds. The maximum power in Class 3B is < 500 mW. An example of this class is: Research HeNe-laser. CLASS 4 (HIGH POWER) Class 4 lasers are dangerous. Looking directly into the beam or at the reflected beam is always hazardous and the chance of injuries is high. Also, damage to the environment (fire) is a serious possibility. Diffuse reflections can still be dangerous and contribute to eye and skin injury or can ignite other materials. Class 4 lasers should always be used with the utmost caution. Note: The power limit applies only for point sources and not for the so-called “extended sources”. Additionally, the limits are only applicable for the given spectral bandwidth. More information about the classification of apparatus that function in other bandwidths can be found in NEN-EN-IEC 60825-1:2014. PRODUCTION REQUIREMENTS IN NEN-EN-IEC 60825-1:2014 The most important chapters of NEN-EN-IEC 60825-1:2014 discuss the requirements for the manufacturer. These requirements include, among others, the classification and labeling of laser products. This part of the standard is called the “normative” part. In essence, this means that anyone who states that he conforms to these norms must show that his conduct conforms to the contents of these chapters. Normally, when one buys a laser, the manufacturer must ensure that the laser has the appropriate labels. The meaning of these labels must be described in the literature accompanying the appliance. In addition to the labels for the user, labels should be applied for the purpose of maintenance personnel. The labels must be permanently applied, legible and clearly visible during normal use and maintenance. They must be applied such that they can be easily read without running the risk of exposure to the beam. The text, edges and symbols must be marked in black on a yellow background, except for Class 1, for which this requirement does not apply. When labeling is impractical due to size or design of the laser, for example with small laser diodes, then the labels must be added to the user documentation or placed on the package.

Some examples of explanatory labels are given below: Class 1 labels can be any color and the manufacturer can choose to place the label on the device or include it in the user information.

Class 1M products can be labeled in a similar manner as a Class 1 laser product label and therefore do not necessarily have to be installed on the device. However, a risk inventory shows that it is useful to place a label on the device.

For Class 3B and 4 lasers, the aperture (where the beam exits the laser) must be fixed with a label.

APERTURE FOR LASER RADIATION

Access panels must be provided with labels when, if removed, potential exposure to laser radiation in excess of the AEL-value for Class 1 exists. The same applies for connections, protected areas of the housing or protected parts of the container, where, after removal, access to a beam exists in which the AEL-value exceeds the Class 1 value. The exact working is dependent on the accessible radiation. For example, for a Class 1 product with a Class 3B laser system, the panels must be labeled as follows:

Panels may be provided with an interlock such that the beam cuts off at the time that the enclosure is opened. Under some circumstances, for example during maintenance, it may be necessary to intentionally override the interlock. A label must be visible before and during the disabling of the interlock and must be placed in the vicinity of the opening created by the removal of the interlocked panel:

When there is a laser beam outside of the visible wavelength region (400 nm to 700 nm), then the words “Laser Radiation” should be replaced by “Invisible Laser Radiation”. If both visible and invisible laser radiation is present, then the wording should become “Visible and Invisible Laser Radiation”. Except for Class 1 laser products, all lasers must be provided with an explanatory label with information about the power and information that must be reported in accordance with the standards. This includes maximum power, pulse time (if applicable) and emitted wavelength. The name and publication date of the used standard should be included on the explanatory label or in the vicinity of the label. For example: MAXIMUM OUTPUT < 1 MW WAVELENGTH 630 – 680 NM

CLASSIFIED TO NEN EN 60825-1:2007

On all lasers from Class 2 and higher, the yellow triangular sticker with a black edge and star burst logo should be used, together with an explanatory label as described previously.

Separate from the classification and the labeling requirements for the manufacturer, safety information must also be included, with additional details about the built in laser system. This information should contain: › Product manual › Power specifications › Setting adjustments › List of necessary precautions In addition, manufacturers must have subjected their products to specified test procedures.

CHAPTER 4. LASER BEAM HAZARDS When laser radiation falls on the body, a portion of the radiation will be absorbed. When the radiation strength or dosage is high enough, the absorbed radiation can cause injury. The two parts of the body that are most vulnerable for injury following exposure to laser radiation are the eyes and the skin. The amount of absorbed radiation through the eye and skin varies due to: › Wavelength › Tissue type › Energy and power of the incident beam › Surface area of the radiated area › Length of the exposure time The risks from laser radiation are directly proportional to the generated power of the beam. INTERACTION WITH EYES AND SKIN The relevant properties of the laser beam were already introduced. The following points are of particular importance when exposed to the eye or skin: › A good collimated, low divergent laser beam. A potential hazard is thereby virtually independent of the distance to the laser. › The coherent beam, which propagates in phase (coherent in time) is observed by the eye as if it leaves from a source (coherent in place). The significance of coherence in place when considering potential hazards is that a visible (400 nm – 700 nm) and even an invisible (< 1400 nm) source can be focused through the eye to a very small spot size. This results in an enormous increase of the irradiance on the back side of the eye, in comparison with the irradiance to the incident surface. TISSUE DAMAGE Optical radiation is damaging for two types of tissues: the eye and the skin. The collimated beam and the high radiant intensity provides for the transfer of large amounts of energy in small volumes of tissue. The absorption of energy in the tissue is the primary process that leads to damage. Excessive exposure leads to damage via multiple processes: warmth, thermo-acoustic or photochemical processes. The precise mechanism depends on physical and biological factors, including tissue type, wavelength of the radiation, exposure time, spot size and irradiance. Thermal effects The primary process is extreme temperature increase in the absorbing tissue (also called burning). Photochemical effects Absorbed laser energy can lead to destructive chemical processes. Acoustic Transitions

Absorption of laser energy can cause a shockwave in the absorbing tissue. This shockwave can cause physical damage in the surrounding tissue. Chronic exposure Long-term or chronic exposure to laser radiation might have a damaging effect but there is still insufficient scientific evidence to support this. For a better understanding of the damaging effects of laser radiation, a basic understanding of anatomy and physiology of the eye and skin is required. THE EYE The eye is most vulnerable to laser radiation. Injuries occur at much lower energy levels than the skin and injuries to the eye are in general more severe. The human eye can be seen as an optical system for the pass through, focusing and detection of light. Light passes through the first portion of the eye and then is focused to form an inverted image on the back of the eyeball. These images are sent to the brain to interpret. The spot size of the image on the back of the eye amounts to about 10 Âľm in diameter, for parallel beams such as those from the laser. When an incident laser beam falls on the fully dilated pupil (7 mm), the increase in energy on the surface of the retina is a factor of 500,000 greater in comparison with the front of the eye. This increase is called the optical gain of the eye. The general anatomical properties are illustrated in the following images:

The eyeball is protected by a bony armor, the orbit, in the skull. The protection is further formed by an underlying layer of fatty tissue. The inner eye mainly consists of two water-filled cavities, which are slightly under pressure and gives firmness to the eye. The outer white layer of the eye is called the whites of the eye. The whites help to give the eye its shape, together with the internal fluids.

The cornea is the outer, transparent layer that covers the front side of the eye. The cornea is partially resistant to the effects of sand, dust and coarser particles because it renews itself every 48 hours. The cornea is, however, provided with a large number of nerve endings. Exposure to dust and sand is coupled with severe eye pain. The rounding of the cornea is necessary to focus on the lens. This is brought about by the large difference between the refractive indices of the cornea-air interface. The first chamber of the eye consists of a lightly viscous, transparent fluid (mostly water) and is called vitreous or aqueous fluid. The lens is a flexible tissue that can change its shape and together with the cornea helps to focus the light on the back side of the eye. The lens does not have any blood vessels, because these would affect the view. Any excessive heating of the lens leads to a reduced transparency, because no blood vessels are present to help dissipate the heat. On top of the surface of the lens is the pigmented iris (this gives the eye its color). The iris controls how much light can enter the eye. It is a muscle-like structure that can contract or relax to change the diaphragm opening of the eye. The circle-shaped diaphragm opening, which is formed by the iris, is called the pupil and appears black colored. Pupil size can vary from 2 mm to 7 mm, depending of the intensity of the incident light. The fully dilated pupil of an adult human is taken to be 7 mm. The vitreous humor is a colorless gel that fills the larger back chamber of the eye and it contributes to the maintenance of the eye shape. The retina contains the crucial light-sensitive cells. Light must first pass through a number of layers of nerve and support cells in the retina before it comes in contact with the photo receptors. There are two types of photo receptors: rods and cones. The rods are responsible for seeing in dim light and the cones are responsible for color vision. The back side of the cornea consists of pigmented epithelium that absorbs all the light, extinguishes reflections and physically supports the retina. The fovea, or the focal point, is the most sensitive part of the retina. It is a small depression in the surface of the retina about 350 Âľm in diameter and consists mostly of closely packed cones. This area provides the greatest visual acuity. Surrounding it is the macula (yellow spot) which consists of both rods and cones. The optical disk, the place where the eye nerves leave the back of the eye, is also called the blind spot. There are no light sensitive cells here. LASER DAMAGE TO THE EYE Tissue damage occurs when energy is absorbed through the respective tissue. Different wavelengths influence different parts of the eye. This is due to the specific absorption characteristics of the respective tissue (Figure 1).

Figure 1. Penetration of optical radiation in the eye (source: Health Protection Agency) Ultraviolet radiation (UV 180 – 400 nm) and the eye Shorter wavelengths (< 315 nm) are mostly absorbed through the retina. This results in the inflammation of the cornea and is known as keratitis, also popularly called “snow blind”, or actinic conjunctivitis. The condition is very painful and is accompanied by copious amounts of tears, and a high sensitivity to bright light. The eye recovers within 48 hours. When UV-C (180-280 nm) and UV-B (280-315 nm) wavelengths are absorbed in deeper layers of the cornea, a photochemical reaction occurs that turns the cornea milky white. This reaction occurs six to twelve hours after exposure. As a primary absorption source of UV-A (315-400 nm), the lens is vulnerable to photochemical reactions. Elevated, chronic exposure can lead to yellowing of the lens or the formation of cataracts. Normally, the retina is not significantly exposed to UVradiation, because UV-rays are absorbed in the cornea and the lens. However, personal hypersensitivity, or the use of antibiotics and other drugs can lead to increased sensitivity to light. Radiation in the visible and IR-A (780 - 1400 nm) region This radiation is guided through the optical system of the eye and is focused on the retina. The largest part of the radiation is absorbed in the pigmented epithelium and the choroid. This wavelength region is thus associated with the danger zone for retinal damage. Permanent tissue damage can occur when the radiant intensity or radiation exposure is intense enough. Two important factors play a role in laser-induced retinal damage: radiant intensity on the retina and the exposure time. With pulsed lasers, the repetition frequency is also an important factor. This makes the exact nature and extent of the damage difficult to predict. The location of the damage also plays a role; damage in the area of the fovea leads to a strong reduction in eyesight, while injuries outside the fovea may only cause small blind spots or damage detectable only after medical investigation. Infrared radiation (IR 780 nm – 1mm) and the eye The most important biological effects of IR-radiation are infrared cataracts and burn wounds on the

cornea. Infrared absorption is mostly a thermal process and the injuries arise through elevated temperatures in the absorbing tissue. When the wavelength increases to the IR-B en IR-C regions (> 1400 nm), the radiation is no longer guided through the retina, but is absorbed in the cornea. Above 2000 nm, the radiation causes burn wounds on the cornea as a result of short, intense, heat exposure. When the IR-radiation is strong enough to inflict damage to the cornea, the pain that the damage causes stimulates the immune system to respond, thus minimizing tissue damage. THE SKIN The skin can be considered as a separate organ, just like the liver and the lungs, with the main difference being that it is spread out over the entire body instead of being located in one defined location. Because of the large surface area, the risk of exposure is greater. The risk of injury to the skin is considered secondary to the risk of eye damage, because skin damage is often not as threatening or has a lower impact on the quality of life than eye damage. Cutaneous lesions generally recover, even after deep injury and the occurrence of infections. Skin damage usually leads to a local loss of function (e.g. reduced sensation) or scarring. Damage to the skin can be thermal or photo-chemical in nature, in which the intensity and length of exposure that leads to damage to the skin is in accordance with the values which are considered dangerous for the cornea (with the exception of the danger zone for the retina). The skin consists of two important layers: the epidermis (outer layer) and the dermis (middle layer with underlying connective tissue). The epidermis consists of multiple layers of cells. The bottom basal cell layer is rapidly dividing and moves the cells toward the top. The top layer of the epidermis is called the stratum corneum and is a protective layer of dead cornified cells. This layer forms the barrier with the outside world and protects against the loss of fluid, abrasion, dust, air and radiation. In the cell layer directly under the epidermis are special cells that produce melanin (pigment granules). This pigment can spread over the whole epidermis and protect the skin against the influence of damaging UV-radiation. The precise thickness of the epidermis differs very little over the entire body and is about 0,1 mm. In places where extra durability is required (heels, palms), the thickness is about 1,5 mm. The dermis has a thickness between 1 and 3 mm. There are many specialized cells and glands in the dermis and is consists mostly of connective tissue. The connective tissue provides elasticity and support for the skin and consists of hair follicles, sweat and fat glands, and nerve endings for pain perception, warmth, pressure, etc. LASER DAMAGE TO THE SKIN The effect of laser radiation on the skin depends on the power and the wavelength of the beam, the exposure time, the spot size and the blood circulation and the thermal conductivity of the exposed skin. Successive layers of the skin can be considered as different filters for optical radiation. The penetrating

ability of radiation in the skin layers will be indicated in the table at the end of this section, and in Figure 2. Figure 2. Penetration of optical radiation in the skin Ultraviolet radiation and the skin Exposure to UV-radiation leads to redness of the skin (erythema) and can result in browning of the skin (change in pigmentation through production of melanin granules). Forming a tanned skin protects the skin from further exposure to UV radiation. Chronic exposure to UV rays age the skin and increases the risk of skin cancer. Absorption characteristics of the skin will be determined in part by the amount of melanin in the skin and the skin thickness. This reaction varies from person to person. Visible light and the skin Wavelengths in the visible region penetrate about 1 to 2 mm in the basal layers of the epidermis. Thermal damage is possible after exposure to high irradiance or radiant energy. Long-term effects such as changes in skin pigmentation can also follow high levels of exposure. Infrared radiation and the skin Laser induced thermal skin injury occurs most frequently in the near IR wavelength range (IR-A), such as those produced by an Nd: YAG laser (1064 nm). This radiation penetrates the deepest into the dermis. Energy absorption increases the tissue temperature and ensures dilation of the blood vessels, making the skin turn pink. When this cooling method is insufficient, burning arises from the basal layer. The pain that is associated with thermal injury is generally sufficient to alert the user and to motivate one to move outside the range of the beam. Visible and IR-lasers are, however, able to cause burning of the skin in a fraction of a second. Because of this, the user has insufficient time to avoid the laser beam before injury occurs. Chronic exposure There are also known cumulative or latent effects of low chronic exposure to laser radiation. It takes years or decades before they become visible. Examples of this are aberrant pigment coloring, accelerated skin aging, loss of elasticity of the skin and the formation of skin cancer. These chronic effects are negligible

compared to the acute exposure risks. However, research has suggested that, with repeated exposure to a particular place, sensitization of the skin may occur, which leads to a stronger reaction than expected under the circumstances. Some people can, due to their genetic background, be naturally more susceptible to certain (laser) radiation than others, and still others can develop this form of hypersensitivity due to the use of cosmetics, medications or exposure to chemicals. LIMITING EXPOSURE VALUES FOR EYE AND SKIN Maximum permissible exposure levels (MPE-values) are given for the exposure of eye and skin to laser radiation. These MPE-values are represented in Watts per square meter (W/m2), called radiation strength, or in Joules per square meter (J/m2), called radiation dose. MPE-values depend on wavelength and exposure duration. At class 3B- and class 4-lasers, one must be careful that the laser beam does not directly, or via specular reflection, exposes the eye and / or the skin. For class 4 lasers is also the diffuse scattered light hwhich can be harmful to eyes and skin. It is therefore of great importance that laser operators, during alignment and during the execution of operations in the beampath, wear safety glasses for the protection of the eyes. The filter in the glasses must prevent against the emission wavelength (s) of the laser, and must reduce the intensity of the incoming laser beam sufficiently to prevent damage to the eyes. "Sufficient" here means that the resulting exposure of the eyes are below the MPE-value. Furthermore, it is important to avoided reflecting materials (e.g., jewelry, watches, and the like), in which one should be anticipated to the fact that the reflection properties of materials for non-visible light (UV and IR) could be different than to visible light. Windows and openings must be blinded so that the laser light cannot leave the room. During alignment work and when performing actions in the beam path one must also prevent people from accessing the laser room without glasses. This can be achieved by warning signs, e.g. â&#x20AC;&#x2DC;LASER ONâ&#x20AC;&#x2122; or a remote interlock that shuts down the laser at unforeseen door opening. The latter is not always desirable. OTHER RISKS In addition to the above-described risks, which are related to the laser beam itself, there are a number of risks which are related to the equipment. Examples are: - Chemical risks: Some lasers contain an active medium of toxic substances, such as dyes in a liquid dye laser, - Exposure to toxic gases in excimer lasers, e.g. Fluorine gas; - Inhalation of toxic or noxious products / gases / microorganisms as a result of materials processing; - Electrical hazards: many laser systems use high voltages; - Electric supply voltages greater than 5 kV (Tyratron) may generate X-rays; - Explosion of bulbs (used for optical pumping of the medium); - Fire.

Particularly in the case of (periodic) maintenance such risks play an important role e.g. because of the (partial) removal of the casing of the laser device. The advice here is to work with a maintenance protocol from the manufacturer or that is drawn by the organisation itself.

CHAPTER 5. LAWS AND REGULATIONS INTRODUCTION The obligation related to fulfilling laser safety lies in legislation. These obligations are set out in the Working Conditions Decree and the standards of e.g. the International Electro-technical Commission with respect to laser radiation, supplemented by Ministerial Order designated standard sheets with a scientific basis. REGULATORY FRAMEWORK The legal framework on laser safety is part of the Working Conditions Decree. Chapter 6 of this decree was expanded on 27 April 2010 with Section 4a â&#x20AC;&#x153;Artificial Optical Radiationâ&#x20AC;?. This section describes the requirements that must be met in the field of artificial optical radiation with regards to lasers. In addition, this section also includes the use of LEDs and UV radiation, among others, in the work situation. The legislation is derived from the implementation of the European Directive No. 2006/25/EC of the European Parliament and the Council of the European Union on 5 April 2006. The act includes several references to "the Directive" which refers to this European guideline. Scope Section 4a applies to employment in which the employee is or may be exposed to artificial optical radiation to the extent that this could be a danger to health and safety, specifically by having adverse effects on the eyes or skin. In the case of laser radiation, this concerns lasers in Classes 3R, 3B and 4; 1M and 2M when they are viewed with optical aids; and laser set-ups of the lower classes, which in certain applications or circumstance, form a significant risk. LEGAL REQUIREMENTS The legislation in the field of laser safety leads to the following obligations for employers in terms of working with lasers belonging to the aforementioned categories: - Registration of at least all lasers in class 3B and 4 and those with a significant risk; - A written risk analysis, assessable by a representative body; - Establish and implement measures to prevent and reduce exposure; - Ensure adequate training and information; - The availability of occupational health research. MEDICAL SURVEILLANCE When an employee is exposed, or if there is an alleged exposure of the eyes or skin to laser radiation above the limit value, he or she should be given the opportunity for an occupational health medical examination. This examination should also be offered when the employee has experienced an identifiable

disease or adverse health effect as a result of exposure to laser radiation at work. There is no requirement for a periodic eye exam. According to the generally accepted views, an exposure leads to direct damage and a periodic eye exam has no predictive value for eye damage in the future. In these situations, it could be useful to have the information available about laser wavelength and laser power, for effective communication with the ophthalmologist.

CHAPTER 6. PROTECTIVE EYEWEAR For protective eyewear intended to protect the eyes from laser radiation, two harmonized standards are important: EN 207 (protective glasses) and EN 208 (alignment glasses). These standards also provide the calculation methods for the determination of the so-called scale numbers required for adequate protection. Eye protection against laser radiation which does not meet the requirements of one of the two EN 207 or EN 208 standards, must be regarded as not suitable. Satisfying glasses are at least CE marked to subscribe the requirements of the harmonized standards and are provided with a scale number in the form respectively L or LB for EN 207 and R or RB to EN 208. Protective eyewear is designed to provide protection against inadvertent, incidental exposure and should never be used for deliberately looking into the beam (also not in order to determine the optical density by means of measurement). An exposed pair of glasses need to be replaced, since it has become unsuitable due to photo bleaching effects, which makes it future protective skills unpredictable. Wearing the wrong glasses is equivalent to not wearing glasses! All eye protection filters in combination with the frame must be marked with the following: 1. The symbol of the test condition (D, I, R of M in Table 1) 2. The wavelength or wavelength region (in nanometer - nm) in which protection is given 3. The scale numbers or the lowest scale number that gives protection against a specific bandwidth 4. If the product has not been tested with low repetition frequencies (â&#x2030;¤ 25 Hz), the suffix â&#x20AC;&#x153;Yâ&#x20AC;? should be added to the scale number: e.g. LB5Y 5. The CE mark Glasses and filters that fulfill the requirements of EN 207 are tested for stability to laser radiation for 5 seconds for continuous waves and for 50 pulses for pulsed lasers. Markings are used to differentiate between continuous wave and pulsed lasers, and a further subdivision for pulsed lasers based on the pulse time. These markings are given in the following table: Table 1. Test conditions Symbol Laser type Pulse time (s) Minimum number pulses D Continuous wave 5 1 -6 I Pulsed 10 to 0.25 50 R Q switch >10-9 to 10-6 50 -9 M Mode coupled pulsed < 10 50

Marking example Laser glasses can be marked as follows: D 652 LB7 CE10 ZZ D indicates that the glasses give protection against continuous laser radiation 652 indicates that the glasses only gives protection against laser radiation with a wavelength of 652 nm (in other words, it is only tested and approved for this wavelength) LB7 is the scale number that the optical density (OD) of the filter yields at 652 nm. An OD of 7 gives a spectral transmission at 652 nm of 10-7 CE10 is the European quality seal; the number 10 indicates the year that the article was tested by an official European testing authority ZZ This is the optional mark or number of the official testing authority that tested the eyewear Marking example (2) Protective eyewear may be marked with the inscription: DR 630-720 LB5 CE10 ZZ S This protective eyewear protects against continuous wave (D) and Giant pulsed (R) laser radiation in the wavelength region from 630 to 720 nm. They have an optical density of 5, which means they offer a weakening of the laser radiation by a factor of 10-5 and were approved by the testing authority in 2010. The symbol S indicates that the eye protection fulfills the requirements for an extra mechanical strength test described in EN 166. A pair of glasses may provide protection against several wavelengths or bandwidths, with its own level of protection for each of these wavelengths. In practice, a pair of glasses can bear several markings, as shown in the following picture of a laser glasses:

PROTECTION AGAINST OTHER HAZARDS Besides eye and skin exposure to the direct beam, with laser use there are associated non-optical hazards that must be considered. In the preparation of liquid dye solutions for use in lasers, there is a risk of contact with the dye powder and the solvent. Dyes may be carcinogenic, and the solvents are, in most cases, irritants. Gloves and eye protection against splashing is recommended. It is also advisable to check for any special precautions associated with the solvent and the dye during storage or use, and to dispose of the materials in a suitable manner. Some laser detectors, in particular those used for measurements in the infrared region, require cryogenic cooling to temperatures of 77 K (-196 Â° C) using liquid nitrogen. The use of liquid nitrogen requires special precautions; it is strongly recommended to wear a lab coat to protect the skin against burns that can occur if there is contact with the skin. Face protection, for example in the form of a plastic visor, must be worn to protect the eyes from splashes. The choice of appropriate personal protective equipment (PPE) is crucial in ensuring safety and often belongs to the tasks of the Laser Safety Officer. A laser worker should always be informed about changes in the standards or the design of PPE and must be able to choose the most suitable protection equipment necessary for the safe performance of his or her work. Summary of the protective equipment: Personal protective equipment Function Eye protection Laser eyewear makes it possible to see everything in the work area, but reduces the laser radiation or reflections to a safe, acceptable level. The utility of eye protection depends on many factors, including: wavelength, laser power, energy, optical density, comfort, etc. Protective clothing and gloves Class 4 lasers harbor a fire risk. Protective clothing can be necessary. Lasers that produce UV-radiation carry a risk to the skin and the skin should be protected by suitable protective clothing. Gloves should be worn when preparing chemicals for liquid lasers, using cleaning solutions for optical components, handling cryogenic liquids, and handling metal plate materials. Gloves should also be worn when replacing filters from extraction systems used in material processing. Breathing equipment Toxic and damaging gases can be formed when treating materials. Breathing protection can be necessary in case of emergency situations, such as the escape of toxic gases during the use of excimer lasers. Hearing protection Noise from industrial applications and lasers can form a hazard. Condensers from pulsed lasers can form a danger when one is exposed to a noise level for a long time.

CHAPTER 7. LASER SAFETY MEASURES Measures for the safe handling of lasers are always described in general and specific work instructions. The general work instructions are for general work with any laser application. The specific work instructions handle the risks that must be observed with specific laser setup. These are based on the results of the laser safety risk analysis. EXPOSURE PREVENTION SIGNALING The outside of all access doors to the laser room that houses a class 3R laser or higher, clearly state that a laser can be in use, by means of a standardized warning sign with starburst logo. In areas where a laser is permanently installed these signs should be present. At momentary arrangements, the warning signs are applied at the moment that a laser is present in the actual room. This applies even when from a Class 1 laser product under normal conditions, the body is removed and a higher class laser becomes available in the room. For laser areas where class 4 lasers are in use, an additional warning light is provided with the text 'laser on', which is illuminated when the laser is in operation. ACCESS In the use of a class 3R laser or higher a second access barrier needs to be present, for example formed by half moon-shaped laser curtains or a second physical entrance door. This, to prevent unwanted exposure of people down the aisle. Preferably only people directly involved with the laser setup should have room access. WINDOWS In the use of a laser that has a NOHD which is greater than the distance to a window, this window must have blinded with a, for the wavelength of the laser, impervious material. The choice of protecting material must be based on the fire resistance capability and fire risk (calculated energy deposition in accordance with EN 207 and material validation according to EN 60825-4). WALLS AND FLOORS Walls and floors in the room should be non-reflecting. Reflective surfaces should be avoided whenever possible. CONTROLS The laser device must be protected by a key switch to prevent unauthorized start of the laser. Key control is limited to people involved with the setup and these people are appointed by the laser contact person.

EYE PROTECTION Exceeding the Maximum Permissible Exposure Limits for the eyes, need all those present in the laser room to protect their eyes appropriately using laser safety glasses according to EN 207. At the glasses the scale number (L or LB) and the appropriate wavelength are stated. In order to reduce the risk of wrong glasses, lasers and laser safety eyewear can be provided with a unique and corresponding color-code. The color coding on the glasses will correspond to the color coding on the laser against which the glasses provide protection. SKIN PROTECTION At incidental irradiation, the natural reflex to retract is sufficient to prevent serious injury. Skin protection against scattered or diffusely reflected laser radiation is not necessary. LASER SAFETY OFFICER Each laser system of class 3B or 4 has a risk assessment in writing. This risk analysis is indicative of the method laid down in protocols and to use personal protective equipment when carrying out work. The prescribed measures are binding. The employer is obliged to communicate the risks to the employee. This is done through risk assessment and work instructions towards the employee. The employee is obliged to use the prescribed method and to wear the provided personal protective equipment at the prescribed times. Performing the risk analysis, the translation of the results into action in the workplace and to supervise and enforce compliance of these, are tasks that are assigned to the Laser Safety Officer (LSO). This person serves as a contact for all questions in the field of laser safety. Contact should also be recorded with the LSO if a setup changes drastically in design, at the built of new facilities or when buying of new lasers is concerned.