Safety

Dr. David Youssian, Physicist Laser Safety Officer Tel.: 2810 [email protected] Laser Safety in research labs contents laser beam properties compared to other optical . Interaction between laser beam & tissue, biological damages. Basic terms in laser safety: MPE, NOHD, DL etc.. Laser classification by level of risk. Safety measures and work procedures. Laser accidents Prevalence percentages Eyes 70 Skin 10 Electricity 8 fire 4 others 8 The most common cause of laser accidents is the lack of use of laser safety glasses or use of inappropriate safety glasses.

LASER – Acronyms of: Amplification by Stimulated Emission of The Laser beam properties Monochromatic: Uniform Wavelength Laser beam properties

Directionality and small beam size: High power & energy densities even at high distances. Coherent: Uniform Phase for all waves. Optical properties of laser beam The interaction between the laser beam and matter is identical to that of the "regular", optical beam including: Reflection Diffraction Focusing Absorption in mater including biological medium Laser beam properties

Monochromatic Parallel beam

Laser source Eye structure

. Conjunctiva – inside of the eyelids and covers the white of the eye – sclera. . – The transparent front part of the eye that covers the iris, and anterior chamber. . Pupil . Vitreous liquid. . Eye structure . The iris is a thin circular structure responsible for controlling the diameter and size of the pupil and thus the amount of light reaching the retina. Eye color is defined by that of the iris. In optical terms, the pupil is the eye's aperture, while the iris is the diaphragm that serves as the aperture stop. Eye structure

. Pupil – a hole in the center of the Iris that allows passage of light through the lens towards the retina. Eye structure

Lens - along with the cornea, helps to refract light to be focused on the retina Eye structure Vitreous liquid – Gives the eyeball its globular structure. The eye structure Focusing system : Cornea & Lens Focal Distance of 2 cm; strength : 50 Diopter. Pupil Cornea, lens and Vitreous liquid the Vitreous liquid must be with a high level of transparency. Retina Retina is a light-sensitive surface where the observed object image is constructed. The optical image being transformed into electrical signals transmitted to the brain for image processing. Retina is the focal plane of the optical imaging system and must be stick to the inner wall of the eyeball. Its area: 2-3 cm2. The sensors in the Retina 1. Rods – responsible for a. peripheral vision b. poor lighting – night c. black and white vision 2. Cones responsible for 1. Color vision 2. high resolution Macula The central vision: Macula - ~ 5 mm of diameter. The acute vision is created in this area needed for everyday functioning as reading and color vision.

Macula & Fovia

In the center of Macula: Fovia ~ 0.35 mm ‘Diameter – higher ‘pixel resolution. The High power & energy density of laser beam on Fovia Assuming a 7 mm diameter laser beam enters the eye, the beam diameter on the retina is 350 times smaller. Power density on the retina is 122,500 times greater than the original at the Cornea. The Laser power density on the Fovia

Light Power [W] On the Retina Source Image Diameter Power Density [W/cm²] The Sun 3.86 x 1026 1 mm 250 Lamp * 100 ~ 0.35 mm 0.015 Laser 0.001 2 mm 30,000 Pointer

* At a distance of 5 m from the eye. Biological effects of laser radiation on tissue Photothermal effect: the optical energy of the laser absorbed in tissue is converted into heat. The increase in the tissue temperature may cause burns, coagulation, evaporation, and so on. Photothermal effect

Photo Thermal effect: the optical energy of the laser absorbed in tissue is converted into heat. The increase in the tissue temperature may cause burns, coagulation, evaporation, and so on. The Photothermal damage depends on: Beam intensity – Power or pulse energy

Absorption coefficient – depending on beam wavelength and the tissue Exposure Duration – usually the longer heat transfer time – the lower damage. The temperature dependence of Photothermal damage

1. No real damages for temperatures below 60 °C for short periods of time. 2. Starting from 60 °C begins death of tissue cells.

The temperature dependence of Photothermal damage

3. At about 70 °C starts denaturation of proteins and burning (coagulation) of the tissue. 4. Starting from 70 °C burn occurs, its severity increases with increase in temperature The temperature dependence of Photothermal damage

5. Starting from 100 °C the water in tissue evaporates and leaks to cold areas. 6. At about 250 °C begins the process of carbonization of the tissue 7. At about 350 °C begins the evaporation process of the tissue. Laser Radiation Interactions with tissue The Photochemical Damage Chemical reactions caused/disturbed in the tissue due to the absorption of light

Occurs mainly in the Visible Light & UV range. Over pigmentation Acceleration of the aging process. Laser Radiation Interactions with tissue The Photochemical Damage

Chemical reactions caused/disturbed in the tissue due to the absorption of light Photo-activation of Nucleic Acids & DNA. The formation of free radicals that damage the immune system and lead to the development of carcinogens (UV B & UV C). Photons energy capable of breaking molecular bonds and break down the tissue (UV C). The Photochemical Damage

The Photochemical damage depends on: Beam intensity – Power or pulse energy

Absorption coefficient – depending on beam wavelength and the tissue No time exposure dependent נזק פוטו אקוסטי (מכאני)

תנאי הסף לייצור גלי הלם אקוסטיים בעלי יכולת לגרימת נזק ממשי: 1. טמפרטורת הרקמה עוברת את הסף של .150°C 2. משך פעימת הלייזר קצר מ- µs 10. גלי ההלם האקוסטיים המונעים ע"י לחצים בשיעור של מאות אטמוספרות גרומים לקרע הרקמות. The penetration of Optical radiation in the eye The penetration of Optical radiation in the eye The interaction between UV radiation and Eye & Skin Biological Damage Wavelength range [nm] Radiation absorbed in the upper cell 100 – UV-C layers of the eye and skin. High 280 efficiency in causing . Higher penetration in tissue than 280 – UV-B UV-C . 315 High efficiency in causing ‘sun burns’ and . Higher penetration in tissue. 315 – UV-A Potential Damage to the lens. 400 Biological damage of UV laser radiation Injuries resulting from the Photochemical interaction Eye injuries Damage to the cornea Partial tearing of the cornea Redness haze Photophobia - eye sensitivity to light. Biological damage of UV laser radiation Injuries resulting from the Photochemical interaction Skin injuries Redness Aging processes Hyperpigmentation Carcinogen Activity Radiation Wavelength Effect range [nm] Visible 400 - 700 Laser with power above 5 mW causes light retinal damage. The damage increases with the increase in the intensity of the laser. IR-A 700 – Is focused on the retina. High skin 1400 penetration. IR-B 1.4 – 3 The penetration in the tissue decreases µm with the increase in the wavelength. IR-C 3 µm – 1 The radiation absorbed outer cell layer of mm the skin and eye. Visible light Laser beam damages

Skin Injuries Eye Injuries Redness Retinal burns External & Internal Retinal Detachment burns Fatal damage to Ulcers and scars the macula כיבים וצלקות Examples of Retina injuries

Hit

Macula Optical Nerve Laser Beam Biological Damages in near IR range 700-1400 nm

Skin Injuries Eye Injuries Redness Lens Cataract External & Internal Lack of burns transparency of Ulcers and scars the cornea Retinal damage

Laser Damage in the IRB & IRC range1.4 - 100 µm

Skin Injuries Skin Injuries Redness Damage to the Cornea External Burns What can be done in the case of laser injury Eye injury – Eye damage can be temporary or permanent damage to vision may be accompanied by hysteria. – Reassure the victim and take him to the emergency room as soon as possible Skin injury – Since the damaged area is small there is no danger of death. – Burns and the treatments are the same for burns resulting from other heat sources. Treatment Effects Burn degree Wetting with Pain, redness and minimal 1 cold water, dry swelling bandage The destruction of cells in 2 covering the epidermis

Cover the burn Destruction of all layers of 3 area with sterile the skin bandage and referral for As 3 degree burns, in 4 medical care addition carbonized skin Examples for the penetration of visible an IR in skin & water

Laser Wavelength typical penetration (nm) depth (mm) Skin Water Ar 488, 514 0.6 100 Nd:YAG 1060 5 10 Er:YAG 2940 0.004 0.004

CO2 10600 0.017 0.017 MPE – Maximum Permissible Exposure MPE –The highest power or energy density of a light source that is considered ‘safe’. It is usually about 10% of the dose that has a 50% chance of creating damage under worst-case conditions. The MPE is measured at the cornea of the human eye or at the skin.

MPE=[ED50]/10 MPE – Maximum Permissible Exposure

MPE Values are given in units of W/cm2 or J/cm2 Depend on radiation wavelength, divergence angle and exposure time. For CW visible light lasers the value of MPE is 10 W/m2, which corresponds to the power of 0.4 mW. NOHD – Nominal Optical Hazard Distance Due to the beam divergence, the beam power or energy density decreases with the distance from the source. At a certain distance the beam power/energy density equals the MPE. Laser Classification Class 1 A Class 1 laser is safe under all conditions of normal use. This means the maximum permissible exposure (MPE) cannot be exceeded when viewing a laser with the naked eye or with the aid of typical magnifying optics (e.g. telescope or microscope). Max Power of 0.4 mW for CW visible lasers Laser Classification Class 1M

A Class 1M laser is safe for all conditions of use except when passed through magnifying optics such as microscopes and telescopes. Class 1M lasers produce large- diameter beams, or beams that are divergent. Laser Classification - Class 2

A Class 2 laser is considered to be safe because the blink reflex (glare aversion response to bright ) will limit the exposure to no more than 0.25 seconds. It only applies to visible-light lasers (400– 700 nm). Class-2 lasers are limited to 1 mW continuous wave, or more if the emission time is less than 0.25 seconds or if the light is not spatially coherent. Intentional suppression of the blink reflex could lead to eye injury. Some laser pointers and measuring instruments are class 2. Laser Classification - Class 2M

A Class 2M laser is safe because of the blink reflex if not viewed through optical instruments. As with class 1M, this applies to laser beams with a large diameter or large divergence, for which the amount of light passing through the pupil cannot exceed the limits for class 2. Laser Classification - Class 3R

A Class 3R laser is considered safe if handled carefully, with restricted beam viewing. With a class 3R laser, the MPE can be exceeded, but with a low risk of injury. Visible continuous lasers in Class 3R are limited to 5 mW. Laser Classification - Class 3B

A Class 3B laser is hazardous if the eye is exposed directly, but diffuse reflections such as those from paper or other matte surfaces are not harmful. The AEL for continuous lasers in the wavelength range from 315 nm to far is 0.5 W. For pulsed lasers between 400 and 700 nm, the limit is 30 mJ. Laser Classification - Class 3B Protective eyewear is typically required where direct viewing of a class 3B laser beam may occur. Class-3B lasers must be equipped with a key switch and a safety interlock. Class 3B lasers are used inside CD and DVD writers, although the writer unit itself is class 1 because the laser light cannot leave the unit. Laser Classification - Class 4 Class 4 is the highest and most dangerous class of laser, including all lasers that exceed the Class 3B AEL. By definition, a class 4 laser can burn the skin, or cause devastating and permanent eye damage as a result of direct, diffuse or indirect beam viewing. Laser Classification - Class 4 Class 4 lasers may ignite combustible materials, and thus may represent a fire risk. These hazards may also apply to indirect or non-specular reflections of the beam, even from apparently matte surfaces—meaning that great care must be taken to control the beam path. Most industrial, scientific, military, and medical lasers are in this category. Laser eyewears

The beam intensity should be reduced to MPE or below. The protection provided by the eyewear are specific for the wavelengths. Goggles features Israeli Standard 4141, identical to the European standard EN-207, states the eye protection requirements regarding resistance to laser radiation D continuous wave I ms & ms pulses R ns pulses M shorter than ns pulses As the laser power is higher, a higher value of DL, IL ,RL or ML is needed. laser Goggles

The values of DL, IL ,RL or ML needed for laser goggles are given in tables as a function of laser intensity and duration of exposure. For CW laser in the visible range and power density of 104 W/m2 , DL3 is needed. Safety glasses features

Other examples For visible laser with power density of 106 W/m2 DL5 is needed. For 10 ms pulse duration

of 10600 nm (CO2) laser IL4 is needed. Laser Safety Regulations The Israeli regulations adopt the international standard, IEC 60825 standard, regarding laser classifications and eyeglasses The regulations include Employer obligations – Prepare laser safety program – Getting initial and annual permission of use – Internal and external reviews. Laser Safety Regulations

Employer obligations – Training, signage, personal and environmental protective measures, work procedures, equipment maintenances etc. – Laser Accidents - investigation and conclusions. Laser Safety Regulations ‘Laser worker’ obligations

To follow the safety instructions when working with lasers Do not use new laser or laser system or change Laser devices without permission from laser safety officer authorized entity. Participate in trainings. Other laser risks

Fire Toxic substances High Voltage – Shock hazard , RF, non laser UV Mechanical hazards Smoke & fume Contact the Safety Unit for assistance and expert advice Other laser risks • Fire – Do not use flammable materials in the laser lab. – Should be able to put out the fire using a fire extinguisher /fighting equipment • Mechanical hazards – moving parts in vacuum and pressure pumps; implosion or explosion of flashlamps, mechanical obstacles Common accident causes Some common unsafe practices that are causes of preventable laser accidents are Lack of use of protective eyewear, including during alignment procedures, or Wearing the wrong eyewear. Misaligned optics and upwardly directed beams - pay particular attention to periscopes, and reflections from windows and beam splitters/combiners. Common accident causes Bypassing of door interlocks and laser housing interlocks. Insertion of reflective materials into beam paths. Lack of pre-planning. Operating unfamiliar equipment. Lack of protection from non-beam hazards for example, Improper methods of handling high voltage. Failure to follow safety protocols. Laser safety procedures The work with laser is allowed only for trained personnel certified by the from the Principal Investigator. The entry of workers or visitors such as maintenance personnel and cleaning the room only with the approval of the Laboratory Director. Laser safety procedures Before turning on the laser make sure: Warning lights above the entrance doors to the rooms are ON. Room entrance doors are locked. Laser goggles are proper and appropriate for the laser beam. Everyone in the room wears suitable goggles. Laser safety procedures

Approval from Laser Safety Officer is a must in the following cases Applying a new laser or new laser system. Work in a new laser lab. Changes in the laser device including beam power and optical directional of the beam. -נהלי עבודה משקפי מגן The lab staff have to know the specifications of the eyewear needed for the lasers – DIRM L, and wear them when the HV is supplied to laser.

The Laser Safety specifications must be written on the eyewear. Laser safety procedures

‘Laser workers’ should know the location of the fire extinguishers and know how to operate it

Never look at the direct or reflected laser beam. Laser safety procedures

The openings in the laser room /work area must be blocked during work.

People whose presence in the room is not essential, should leave the room before beginning the work with lasers. Laser safety procedures

אין בשום אופן להביט ישירות לקרן הלייזר או לכוון אותו לעיניים של עובד אחר. Do not use a laser when there are flammable or explosive materials in the room. Do not look directly into the laser beam. Do not align the beam towards your eyes or any other person's eye. Laser safety procedures The microSwitches must be tested periodically. At the end of the work remove the operating key and make sure the warning lamp is off. Maintenance and service of the laser will be carried out only by authorized representatives of the manufacturer and after approval by the Laser Safety Officer. Laser safety procedure for Beam Alignments

Many laser accidents occur during laser alignments.

Rabbit Cornea burn Beam Alignments Before beginning the work make sure – Warning lights ON – Doors locked – A warning sign announcing the performance or beam Your vision alignment should be hanged on the outsider sides of the lab doors. – System Emergency switch proper 0.1 sec after laser strike Beam Alignments

Use beam blocks at all stages of the work. Before beginning the work remove all reflecting objects such as watches, rings, chains and jewelry. Beam Alignments Use non-reflecting tools. Remove any reflecting or needless equipment from the table. Beam Alignments Prepare the required materials and equipment before beginning the work: tools, targets, beam blockers, power meter, instruments for determining the beam profile, goggles etc. Beam Alignments Make sure appropriate laser eyewear for the beam is available. All persons present in the laboratory will wear appropriate glasses. Before beginning the work, the optic table will be surrounded by beam blocks at all possible area. Beam Alignments When working with invisible lasers use a visible light beam for path simulation when possible. Ensure all elements are tightened to the table. Beam Alignments Alignment will be performed using minimum beam intensity possible. The beam will be viewed only using viewing aids such as fluorescent devices and detectors. Never look at the direct or reflected beam. Beam Alignments

When viewing invisible radiation using IR card, one should be aware of the potentially reflections and returns from these measures. Beam Alignments Do not work with beam intensities that can ignite combustible materials. Any unused or reflected beam will be blocked. The work will be performed on standard horizontal optic table. Beam Alignments

Enter optic elements only when the beam is blocked. One should be aware of the possible reflections from the optical elements and add blocks as needed.