Laser Safety for Arecibo

Laser Safety for Arecibo
Jeff Leavey Laser Safety Officer Env Health & Safety Cornell University Ithaca, NY

Questions? Contact Info Jeff Leavey or

Purpose of this Program
To increase awareness in laser safety Low hazard lasers Class 1 to 3a High hazard lasers Class 3b and 4

Program Outline Some Definitions Laser Classification
Laser Safety Regulations Laser Hazards Eyes and Skin Other Hazards Safety Guidelines & Control Measures

Some Definitions LASER – Light Amplification by Stimulated Emission of Radiation MPE – Maximum Permissible Exposure – used for exposure limits to people (typically mW/cm2) Limiting Aperture – max diameter of a circle over which an exposure is measured, taken as 7 mm for the eye pupil (0.38 cm2)

Some Definitions Aversion Response – natural reflex response
to look away or close your eyes to bright light, 0.25 sec for humans (blink reflex) Controlled Area – any area where access or occupancy is controlled for radiation protection purposes Embedded Laser – a laser incorporated into or inside other equipment Fail-Safe Interlock – An interlock where the failure of a single component will cause the equipment to go into or remain in a safe state

Some Definitions NHZ - Nominal Hazard Zone – an area where levels of direct, scattered or reflected laser radiation are above the MPE OD - Optical Density – power of 10 reduction of light transmitted through a material – e.g. OD3 = fraction of light transmitted thru laser eye protection or other absorber UV Light – wavelength shorter than 400 nm Visible Light – wavelength 400 – 700 nm IR Light – wavelength longer than 700 nm

Some Definitions HeNe Nd:YAG Doubled AlGaAs Ruby HeCd Ar GaN BluRay
1064nm CO2 10,600nm ArF 193nm KrF 248nm XeCl 308nm XeF Ti:Sapphire nm Cu Vapor Red Pointers AlGaInP

Laser Classifications
Laser Classes – 1, 2, 2a, 3a, 3b, 4 Class number groups lasers with similar hazards Based on power, wavelength and pulse duration Class 1 = no hazard Class 4 = most hazardous New Class Designations for the Future Users of Class 1 laser products are generally exempt from radiation hazard controls during operation and maintenance (but not necessary during service). Since lasers are not classified on beam access during service, most Class 1 industrial lasers will consist of a higher class (high power) laser enclosed in a properly interlocked and labeled protective enclosure. In some cases, the enclosure may be a room (walk-in protective housing) which requires a means to prevent operation when operators are inside the room.

Class 1 - Exempt lasers or laser systems that cannot, under normal operation conditions, produce a hazard – below MPE Visible beams <0.4 mW, UV and IR much lower limit Usually higher class lasers inside Requires protective housing, interlocks, labeling Example - Compact disk or DVD player Users of Class 1 laser products are generally exempt from radiation hazard controls during operation and maintenance (but not necessary during service). Since lasers are not classified on beam access during service, most Class 1 industrial lasers will consist of a higher class (high power) laser enclosed in a properly interlocked and labeled protective enclosure. In some cases, the enclosure may be a room (walk-in protective housing) which requires a means to prevent operation when operators are inside the room.

Class 2 - Do not normally present a hazard, but may if viewed directly for extended periods of time. Visible wavelengths only, > MPE but < 1 mW Hazardous for direct beam eye exposure longer than 0.25 sec (aversion or blink reflex protects the eye) Example - Most alignment lasers are Class 2 Class 2a is special case of Class 2 Hazardous for viewing > 1000 sec Class 2: low-power visible lasers that emit above Class 1 levels but at a radiant power not above 1 mW. The concept is that the human aversion reaction to bright light will protect a person. Only limited controls are specified. Low output in the nm range

Class 3a – Visible wavelengths > 1 mW but < 5 mW Invisible wavelengths > Class 1 but < 5 * Class 1 AEL Hazardous for direct beam eye exposure with optics for less than 0.25 sec (aversion or blink reflex does NOT protect the eye) DANGER label Example - Some laboratory lasers (including normal HeNe up to 5 mW total power), laser pointers, laser levels Class 3A: intermediate power lasers (cw: 1-5 mW). Only hazardous for intrabeam viewing. Some limited controls are usually recommended. NOTE: There are different logotype labeling requirements for Class 3A lasers with a beam irradiance that does not exceed 2.5 mW/cm2 (Caution logotype) and those where the beam irradiance does exceed 2.5 mW/cm2 (Danger logotype).

Class 3b - Visible wavelengths > 5 mW (Class 2) but < 500 mW Invisible wavelengths > Class 1 but < 500 mW Hazardous for direct beam eye exposure less than 0.25 sec Hazardous to skin in upper region of limit Not a diffuse reflection or fire hazard Lasers or laser systems that can produce a hazard if viewed directly.

Class 4 - Visible and invisible wavelengths > 500 mW (Class 3b AEL) Hazardous for direct beam eye exposure less than 0.25 sec Hazardous to skin Is a diffuse reflection and/or fire hazard Class 4: High power lasers (cw: 500 mW, pulsed: 10 J/cm2 or the diffuse reflection limit) are hazardous to view under any condition (directly or diffusely scattered) and are a potential fire hazard and a skin hazard. Significant controls are required of Class 4 laser facilities.

International Laser Classifications
ANSI uses international classes Class 1 – eye safe with optical aids Class 1M – eye safe except with optical aids Class 2 – safe for momentary viewing Class 2M - safe for momentary viewing except with optical aids Class 3R – replaces Class 3a, marginally unsafe intrabeam viewing Class 3b – same as current US requirements Class 4 – no changes

Laser Standards and Regulations
OSHA General duty clause for protecting workers References ANSI Z136 standard STD Guidelines for Laser Safety and Hazard Assessment supports the use of ANSI

Laser Standards and Regulations
American National Standards Institute ANSI are consensus standards, regular updates ANSI Z For Safe Use of Lasers Recommends laser MPEs and AELs Often used as basis for regulations Other ANSI Z136.x apply to specific uses Z136.5 for educational institutions Z136.6 for laser use outdoors

Laser Hazard - Eye Eye Structures
Cornea – Interface to the environment, protected by thin tear film, high metabolism, cells replaced every 24 – 48 hours Lens – Focuses images on retina, flexible crystalline structure, slow metabolism, not repairable so damage causes cataracts and discoloration The diagram shows a laser beam entering the eye and being focused on the fovea. If the beam power is sufficient this situation could cause blindness. The three parts of the eye of concern in laser injuries are the cornea, lens, and retina. Damage to the retina can result from visible and near-infrared radiation, (400 to 1400 nm). Light directly from the laser or reflection from a mirror-like surface entering the eye can be focused to an extremely small image on the retina due to the focusing effects of the cornea and lens. Laser radiation in the middle-ultraviolet, (200 to 315 nm), and far-infrared, (3 micrometer to 1 mm), produce damage principally at the cornea. Radiation in the near-ultraviolet, ( nm), and middle-infrared, ( micrometer), passes through the cornea with little damage but effects the lens behind the cornea. Therefore you can see that the tissues of the eye are susceptible to various forms of laser radiation and should be protected by appropriate eye protection depending on the wavelength of the laser emission.

Laser Hazard - Eye Eye Structures
Retina - rods for night and peripheral vision, cones for color and resolution Macula and Fovea – Macula provides central vision while fovea (~0.15 mm wide) has highest concentration of cones for detailed vision e.g. reading or looking directly at an object The diagram shows a laser beam entering the eye and being focused on the fovea. If the beam power is sufficient this situation could cause blindness. The three parts of the eye of concern in laser injuries are the cornea, lens, and retina. Damage to the retina can result from visible and near-infrared radiation, (400 to 1400 nm). Light directly from the laser or reflection from a mirror-like surface entering the eye can be focused to an extremely small image on the retina due to the focusing effects of the cornea and lens. Laser radiation in the middle-ultraviolet, (200 to 315 nm), and far-infrared, (3 micrometer to 1 mm), produce damage principally at the cornea. Radiation in the near-ultraviolet, ( nm), and middle-infrared, ( micrometer), passes through the cornea with little damage but effects the lens behind the cornea. Therefore you can see that the tissues of the eye are susceptible to various forms of laser radiation and should be protected by appropriate eye protection depending on the wavelength of the laser emission. Acuity

Laser Hazard - Eye Eye Structure
The diagram shows a laser beam entering the eye and being focused on the fovea. If the beam power is sufficient this situation could cause blindness. The three parts of the eye of concern in laser injuries are the cornea, lens, and retina. Damage to the retina can result from visible and near-infrared radiation, (400 to 1400 nm). Light directly from the laser or reflection from a mirror-like surface entering the eye can be focused to an extremely small image on the retina due to the focusing effects of the cornea and lens. Laser radiation in the middle-ultraviolet, (200 to 315 nm), and far-infrared, (3 micrometer to 1 mm), produce damage principally at the cornea. Radiation in the near-ultraviolet, ( nm), and middle-infrared, ( micrometer), passes through the cornea with little damage but effects the lens behind the cornea. Therefore you can see that the tissues of the eye are susceptible to various forms of laser radiation and should be protected by appropriate eye protection depending on the wavelength of the laser emission.

Laser Hazard - Eye The diagram shows a laser beam entering the eye and being focused on the fovea. If the beam power is sufficient this situation could cause blindness. The three parts of the eye of concern in laser injuries are the cornea, lens, and retina. Damage to the retina can result from visible and near-infrared radiation, (400 to 1400 nm). Light directly from the laser or reflection from a mirror-like surface entering the eye can be focused to an extremely small image on the retina due to the focusing effects of the cornea and lens. Laser radiation in the middle-ultraviolet, (200 to 315 nm), and far-infrared, (3 micrometer to 1 mm), produce damage principally at the cornea. Radiation in the near-ultraviolet, ( nm), and middle-infrared, ( micrometer), passes through the cornea with little damage but effects the lens behind the cornea. Therefore you can see that the tissues of the eye are susceptible to various forms of laser radiation and should be protected by appropriate eye protection depending on the wavelength of the laser emission.

Laser Hazard - Eye Visible and NIR – thermal damage
Lens focusing concentrates light by ~100,000 times, 1 mW/cm2 into eye becomes 100 W/cm2 at retina Damage occurs when retinal blood flow can’t absorb the extra heat load < 1 mW/cm2 with blink reflex not likely to cause damage (Class 1 and 2) Damage can occur from both acute and chronic exposure to laser radiation depending on the wavelength and exposure levels. Corneal and/or retinal burns can result from acute overexposure. Cataracts and/or retinal injury may be possible from chronic exposure to excessive levels. The cornea is the transparent layer of tissue covering the surface of the eye. The cells on the surface of the cornea have a lifetime of only about 48 hours, therefore cell turnover is quite fast. Injury to cells on the surface of the cornea is generally repaired quickly, but injury to deeper layers of the cornea can result in permanent change to the cornea. The lens of the eye focuses light to form images in the eye. Damage to the lens can cause the destructive interference of light within the lens, resulting in a “milky” area or cataract. The retina is made up of layers of nerve cells and is used for reception of the light in the eye. Damage to cells in the retina can result in loss of vision.

Laser Hazard - Eye UV – photochemical damage
UVA (315 – 400 nm) lens absorption leading to cataracts UVB (280 – 315 nm) and UVC (< 280 nm) most absorption in cornea and sclera leading to photokeratitis (painful, irritated itchy eyes usually lasts few days) Damage can occur from both acute and chronic exposure to laser radiation depending on the wavelength and exposure levels. Corneal and/or retinal burns can result from acute overexposure. Cataracts and/or retinal injury may be possible from chronic exposure to excessive levels. The cornea is the transparent layer of tissue covering the surface of the eye. The cells on the surface of the cornea have a lifetime of only about 48 hours, therefore cell turnover is quite fast. Injury to cells on the surface of the cornea is generally repaired quickly, but injury to deeper layers of the cornea can result in permanent change to the cornea. The lens of the eye focuses light to form images in the eye. Damage to the lens can cause the destructive interference of light within the lens, resulting in a “milky” area or cataract. The retina is made up of layers of nerve cells and is used for reception of the light in the eye. Damage to cells in the retina can result in loss of vision.

Laser Hazard - Eye Pulsed lasers
Pulses < ~10 msec can have acoustic shock effects with severe damage Damage can occur from both acute and chronic exposure to laser radiation depending on the wavelength and exposure levels. Corneal and/or retinal burns can result from acute overexposure. Cataracts and/or retinal injury may be possible from chronic exposure to excessive levels. The cornea is the transparent layer of tissue covering the surface of the eye. The cells on the surface of the cornea have a lifetime of only about 48 hours, therefore cell turnover is quite fast. Injury to cells on the surface of the cornea is generally repaired quickly, but injury to deeper layers of the cornea can result in permanent change to the cornea. The lens of the eye focuses light to form images in the eye. Damage to the lens can cause the destructive interference of light within the lens, resulting in a “milky” area or cataract. The retina is made up of layers of nerve cells and is used for reception of the light in the eye. Damage to cells in the retina can result in loss of vision.

Laser Hazard - Skin Skin Structure
Stratum Corneum – Outer most layer of dead cells, ~ 8 – 20 mm Epidermis – Outer most layer of living cells, ~ 50 – 150 mm, tanning layer Dermis – Mostly connective tissue, gives elasticity and strength, blood supply and nerves, 1 – 4 mm Subcutaneous – Mostly fatty tissue for insulation and shock absorption over muscle Burns can result from acute exposures to high levels of optical radiation. Some specific ultraviolet wavelengths can cause cancer of the skin. Erythema, (sunburn), skin cancer and acceleration skin aging are possible from exposure of laser radiation in the range of 0.2 to 0.28 micrometer. Chronic exposure of 0.28 to 0.4 micrometer wavelength radiation can cause increase pigmentation. Photosensitive reactions are possible from wavelengths from 0.31 to 4 micrometer. And skin burns and excessive dry skin effects are possible from radiation in the range of 0.7 to 1 micrometer. Even though skin effects have been considered of secondary importance from a safety standpoint, cases of skin damage has been increasing due to the increase use of lasers emitting ultraviolet light and high-power lasers.

Laser Hazard - Skin Visible and IR
Thermal effects predominate through out skin depth Thermal damage strongly dependant on exposure duration and area exposed Repairable tissue will heal just like any thermal burn Burns can result from acute exposures to high levels of optical radiation. Some specific ultraviolet wavelengths can cause cancer of the skin. Erythema, (sunburn), skin cancer and acceleration skin aging are possible from exposure of laser radiation in the range of 0.2 to 0.28 micrometer. Chronic exposure of 0.28 to 0.4 micrometer wavelength radiation can cause increase pigmentation. Photosensitive reactions are possible from wavelengths from 0.31 to 4 micrometer. And skin burns and excessive dry skin effects are possible from radiation in the range of 0.7 to 1 micrometer. Even though skin effects have been considered of secondary importance from a safety standpoint, cases of skin damage has been increasing due to the increase use of lasers emitting ultraviolet light and high-power lasers.

Laser Hazard - Skin UV Range
Near UV (UVA 315 – 400 nm) Erythema (sunburn), pigmentation darkening (tanning) UV (UVB 280 – 315 nm) Erythema, possible carcinogenic effects Deep UV (UVC <280 nm) Limited data but possible carcinogenic effects UVB most hazardous, surface to epidermis effects Effects of erythema (like sunburn) are delayed Certain chemicals and prescription drugs can increase skin sensitivity Burns can result from acute exposures to high levels of optical radiation. Some specific ultraviolet wavelengths can cause cancer of the skin. Erythema, (sunburn), skin cancer and acceleration skin aging are possible from exposure of laser radiation in the range of 0.2 to 0.28 micrometer. Chronic exposure of 0.28 to 0.4 micrometer wavelength radiation can cause increase pigmentation. Photosensitive reactions are possible from wavelengths from 0.31 to 4 micrometer. And skin burns and excessive dry skin effects are possible from radiation in the range of 0.7 to 1 micrometer. Even though skin effects have been considered of secondary importance from a safety standpoint, cases of skin damage has been increasing due to the increase use of lasers emitting ultraviolet light and high-power lasers.

Laser Hazard - Skin Burns can result from acute exposures to high levels of optical radiation. Some specific ultraviolet wavelengths can cause cancer of the skin. Erythema, (sunburn), skin cancer and acceleration skin aging are possible from exposure of laser radiation in the range of 0.2 to 0.28 micrometer. Chronic exposure of 0.28 to 0.4 micrometer wavelength radiation can cause increase pigmentation. Photosensitive reactions are possible from wavelengths from 0.31 to 4 micrometer. And skin burns and excessive dry skin effects are possible from radiation in the range of 0.7 to 1 micrometer. Even though skin effects have been considered of secondary importance from a safety standpoint, cases of skin damage has been increasing due to the increase use of lasers emitting ultraviolet light and high-power lasers.

Other Laser Hazards Chemical Safety Electrical Dyes Solvents
High voltage 5 kV to 35+ kV Follow standard electrical safety precautions Learn CPR rescue procedures Avoid wearing rings, metallic watchbands and other metallic objects When possible, use only one hand in working on a circuit or control device Never handle electrical equipment when hands, feet or body are wet, perspiring, or when standing on wet floor. Another example is ozone emitted by laser printers Reactions induced by lasers can release hazardous particulate and gaseous products. An example of this occurs in material processing such as laser welding, cutting, and drilling which can create potentially hazardous fumes and vapors. General ventilation safety procedures should be used when lasers are used in this manner.

Good Housekeeping

Poor Housekeeping

Safe Beam Alignment Cornell follows ANSI Z136
Most beam injuries occur during alignment Only trained personnel may align class 3b or class 4 lasers (NO EXCEPTIONS!) Laser safety eyewear is required for class 3b and class 4 beam alignment ANSI requires approved, written alignment procedures for all Class 3b and Class 4 alignment activities Class 4 lasers are required to have written operating procedures – recommended for Class 3b

Safe Beam Alignment Exclude unnecessary personnel from the laser area during alignment Where possible, use low-power visible lasers coaxially with high power beam path Perform alignment tasks using high-power lasers at the lowest possible power level Use beam attenuator filter to reduce intensity as much as possible

Safe Beam Alignment For invisible beams Beam display devices
Image converter viewers e.g. IR cameras Phosphor cards Examples – next slide

Safe Beam Alignment

Laser Lab Design and Layout
Safety goal Protect uncontrolled areas – doors, windows, safe area to put on eye protection Items to consider Orientation of optical table – point away from doors Beam tubes, fiber optics, etc. Full table enclosures or perimeter shields, interlocked or not Fixed vs. movable curtain tracks Interlocked curtains – ensures protection is in place before laser operates Curtain material – rarely has to be bulky heavy weight

Required: Lighted sign Class 4 lasers Laser In Use

Required: Emergency OFF Switch Located As Needed Class 4 lasers Laser In Use

Medical Monitoring ANSI suggested, limited medical-legal value
Document prior injury/conditions Baseline for real accident Required at Cornell prior to laser use Completed prior to using lasers or laser system Complete CU health history form and consultation/referral form. Schedule an appointment with physician that is listed on the consultation/referral form and advise the Doctor’s office that this appointment is for a laser baseline eye exam. The consultation/referral form should be given to the Doctor when you have the exam. After you have completed the exam, advise the Doctor to send the bill to your department’s Business Office.

Controls – Personal Protective Equipment (PPE)
Appropriate eyewear Eyewear must be for the appropriate laser wavelength, attenuate the beam to safe levels, yet be comfortable enough to wear Gloves – UV Lab coats and skin covering – UV Of particular importance in prevention of laser hazards is eyewear. Laser protective eyewear is usually made of filters which absorb and/or reflect specific wavelengths of laser light An important factor to look for in choosing laser protective eyewear is the optical density (OD) of the lenses. The OD of the eyewear is a measure of its capacity to filter light; OD is the opposite of transmission. The higher the OD, the less the light that is transmitted to the eye. The OD must be chosen so as not to impair vision significantly, yet at the same time, must be chosen so as to be capable of reducing the laser light to the MPE. When choosing laser protective eyewear it is also important to select eyewear that is designed to filter shorter wavelengths of the laser light that will be used. Eyewear designed to filter shorter wavelengths of light are not appropriate for use with lasers that emit linger wavelengths of light. Finally, it is also important that some attention be paid to the style of the laser protection so that comfort to the wearer is maximized. Laser protection eyewear cannot protect personnel if not worn!

How Do I Pick the Right Eye Protection? For the laser find Wavelength (nm) Energy (J/cm2) and pulse rep rate for pulsed lasers or Power (mW/cm2) for continuous wave lasers Look up MPE based on wavelength and maximum expected exposure time (i.e. ANSI Z136.1) Time depends on working conditions e.g. brief “flash” exposure to long term observation of diffuse reflection – be conservative OD = log10 (laser output / MPE) Of particular importance in prevention of laser hazards is eyewear. Laser protective eyewear is usually made of filters which absorb and/or reflect specific wavelengths of laser light An important factor to look for in choosing laser protective eyewear is the optical density (OD) of the lenses. The OD of the eyewear is a measure of its capacity to filter light; OD is the opposite of transmission. The higher the OD, the less the light that is transmitted to the eye. The OD must be chosen so as not to impair vision significantly, yet at the same time, must be chosen so as to be capable of reducing the laser light to the MPE. When choosing laser protective eyewear it is also important to select eyewear that is designed to filter shorter wavelengths of the laser light that will be used. Eyewear designed to filter shorter wavelengths of light are not appropriate for use with lasers that emit linger wavelengths of light. Finally, it is also important that some attention be paid to the style of the laser protection so that comfort to the wearer is maximized. Laser protection eyewear cannot protect personnel if not worn!

Example for Calculating OD Assume HeNe laser at 638 nm, 20 mW output, maximum of 3 sec exposure and 2 mm beam diameter ANSI Z136.1 gives MPE = 1.8 t 0.75 x 10-3 J/cm2 MPE = 4 mJ/cm2 Laser = 60 mJ (using J = W x sec) Beam smaller than eye pupil so use beam area = 0.03 cm2 Laser = 60 / 0.03 = 2000 mJ/cm2 OD = log10 (2000 / 4) = 2.7 round up to 3 Use eye protection with an OD of 3 or more Of particular importance in prevention of laser hazards is eyewear. Laser protective eyewear is usually made of filters which absorb and/or reflect specific wavelengths of laser light An important factor to look for in choosing laser protective eyewear is the optical density (OD) of the lenses. The OD of the eyewear is a measure of its capacity to filter light; OD is the opposite of transmission. The higher the OD, the less the light that is transmitted to the eye. The OD must be chosen so as not to impair vision significantly, yet at the same time, must be chosen so as to be capable of reducing the laser light to the MPE. When choosing laser protective eyewear it is also important to select eyewear that is designed to filter shorter wavelengths of the laser light that will be used. Eyewear designed to filter shorter wavelengths of light are not appropriate for use with lasers that emit linger wavelengths of light. Finally, it is also important that some attention be paid to the style of the laser protection so that comfort to the wearer is maximized. Laser protection eyewear cannot protect personnel if not worn!

Resources and Information
Cornell Laser Safety Manual Work in progress – ETA 4Q08 Laser Institute of America LIA guide for the selection of laser eye protection and copies of ANSI Z136 FDA CDRH Federal regulations Laser Tutorials - technical tutorial, lots of links to other pages too Google LASER SAFETY ACGIH OSHA

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