Laser Safety Tutorial - ISSC 2016 OrlandoTutorial Outline Laser Overview ... Example of Laser Safety Calculations ... – A Class 2M laser is safe because of the blink reflex of the

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Laser Safety Tutorial

34th International System

Safety Conference

Anish Donda, Micah Koons

August 11, 2016

This document does not contain technology or Technical Data controlled under either the U.S.

International Traffic in Arms Regulations or the U.S. Export Administration Regulations.

Tutorial Outline

Laser Overview/Operation

Laser Safety Terminology

Laser Classification

Laser Parameters

Laser Hazards

Laser Standards

Hazard Controls

Laser Safety Attributes

Laser Safety Tools

Example of Laser Safety Calculations

Summary

2016-09-12 2



Tutorial Outline




Laser Parameters

Laser Hazards

Laser Standards

Hazard Controls


Laser Safety Tools


Summary

2016-09-12 3



Laser Uses

Laser is an acronym for Light Amplification by the Stimulated Emission of Radiation

Lasers have many real-world applications– Commercial

DVD/Blu-ray Player

Laser Pointers

Scanners

Cutting

Welding

– Medical

Hair Removal

Cancer Diagnosis

Imaging

– Military

Communication

Ranging

Targeting

2016-09-12 4



Optical Spectrum

The optical spectrum is a subset of the electromagnetic

spectrum– Consists of the ultraviolet (UV) , visible, and infrared (IR) radiation

2016-09-12 5



Stimulated Emission

Conventional light sources (i.e. a light bulb) emits photons ‘spontaneously’

via a process known as spontaneous emission

In contrast, lasers emit photons via a process known as stimulated

emission

– Individual atoms or molecules are ‘stimulated’ to release energy before going through the

spontaneous emission process

– Stimulation is achieved by a causing a photon to collide with the atom or molecule

– Both photons now travel in phase and in the same direction

2016-09-12 6

Reproduced from

Henderson and

Schulmeister,

Laser Safety,

2004.

Reproduced from

Henderson and

Schulmeister,

Laser Safety,

2004.



Fundamentals of Lasers

A typical laser is comprised of three fundamental elements– Lasing medium

Can be a solid, liquid or gas that emits radiation when excited

Major factor that determines the wavelength of the laser system

– Excitation mechanism

The energy source used to excite the lasing medium

– Typical excitation mechanisms include electricity from a power supply, a flash lamp, or the energy from another laser

– Optical cavity

Consists of mirrors to act as the feedback mechanism for light amplification

2016-09-12 7

REFLECTIVEMIRROR

PARTIALLY REFLECTIVE

MIRROR

OPTICAL CAVITY

EXCITATION MECHANISM

LASING MEDIUM

LASEROUTPUT



Properties of Lasers

Lasers are different from regular light in that they are– Monochromatic

Laser light consists of essentially one wavelength

A typical light bulb, for example, emits light that contains various wavelengths

– Coherent

The waves of the laser radiation are in phase with each other

Light waves from a light bulb are a mixture of frequencies and wavelengths and are not in phase with one another

– Directional

Light output from a laser is highly directional

Unlike a typical light bulb which radiates in an omni-directional manner, laser energy diverges very slowly and is concentrated in a narrow cone that propagates in a single direction

Laser operating modes– Single pulse

– Repetitive pulse: multiple pulses emitted

– Continuous wave: continuous output for a period ≥ 0.25 sec

2016-09-12 8



Tutorial Outline




Laser Parameters

Laser Hazards

Laser Standards

Hazard Controls


Laser Safety Tools


Summary

2016-09-12 9



Some Laser Safety Terminology

Accessible Emission Limit (AEL)– The maximum accessible emission level permitted within a particular laser hazard class

Continuous Wave (CW)– A laser having a continuous output for a period > 0.25 seconds

Eye-Safe Laser– Class 1 laser product

– This term is frequently misused and is discouraged

Irradiance– Radiant power incident per unit area upon a surface, expressed in W/cm2

Maximum Permissible Exposure (MPE)– The level of laser radiation to which an unprotected person may be exposed without

adverse biological changes in the eye or skin

Pulsed Laser– A laser that delivers its energy in the form of a single pulse or a train of pulses that are

<0.25 seconds

Radiant Exposure– Surface density of the radiant energy received, expressed in units of J/cm2

2016-09-12 10



Tutorial Outline




Laser Parameters

Laser Hazards

Laser Standards

Hazard Controls


Laser Safety Tools


Summary

2016-09-12 11




The most accepted standard for workplace safety of lasers, in

the U.S., is ANSI Z136.1– Most of the international community uses IEC 60825-1

Laser classification is based on the potential for a laser to

exceed the Accessible Emission Limit for unaided viewing and

optically aided viewing

The standard defines the following classes of lasers– Class 1, 1M

– Class 2, 2M

– Class 3R, 3B

– Class 4

2016-09-12 12



Class 1 Lasers

Class 1– A Class 1 laser is considered to be incapable of producing damaging radiation

levels during operation and is safe under all conditions of normal use

The MPE cannot be exceeded when viewing a laser with the naked eye or with

the aid of typical magnifying optics

Class 1M– Considered to be incapable of producing hazardous exposure conditions during

normal operation unless the beam is viewed with collecting optics

– The power when viewed by the naked eye is less than the Accessible Emission

Limit (AEL) for Class 1, but the power that can be collected into the eye by

magnifying optics is higher than the AEL for Class 1 and lower than the AEL for

Class 3B

2016-09-12 13



Class 2 Lasers

Class 2– A Class 2 laser is considered to be safe because the blink reflex of the eye will

limit the exposure to no more than 0.25 seconds

– Emits in the visible portion of the spectrum (400 nm to 700 nm)

– Class-2 lasers are limited to 1 mW continuous wave

Power can be higher if the emission time is less than 0.25 seconds

Class 2M– A Class 2M laser is safe because of the blink reflex of the eye if not viewed

through optical instruments

– Similar to Class 1M, Class 2M lasers are potentially hazardous if viewed with

collecting optics

2016-09-12 14



Class 3 Lasers

Class 3R– A Class 3R laser is considered safe if handled carefully, with restricted beam viewing

– Potentially hazardous under some direct and specular reflection viewing conditions if the

eye is appropriately focused and stable, but the probability of an actual injury is small

– Visible continuous lasers in Class 3R are limited to 5 mW.

– This laser will not pose either a fire hazard or diffuse reflection hazard

Class 3B– Class 3B lasers are hazardous under direct and specular reflection viewing, but diffuse

reflections are not harmful

– Typically not a fire hazard

– The AEL for continuous lasers in the wavelength range from 315 nm to far infrared is 0.5 W

– For pulsed lasers between 400 and 700 nm, the limit is 30 mJ

– Protective eyewear is typically required where direct viewing of a class 3B laser beam may

occur

2016-09-12 15



Class 4 Lasers

Class 4 is the highest and most dangerous class of lasers

These lasers can burn skin, or cause permanent eye damage

as a result of direct, diffuse or indirect beam viewing

Class 4 lasers may ignite combustible materials, and thus may

represent a fire risk

Most industrial, scientific, military, and medical lasers are in

this category

2016-09-12 16



Comparison of Laser Classes

ANSI Z136.1 IEC-60825-1 CDRH Examples

Class 1 Class 1 Class I Laser printers, CD/DVD

playersClass 1M Class 1M

Class 1C Laser hair removal

Class 2 Class 2 Class II Barcode scanners

Class 2M Class 2M Class IIa

Class 3R Class 3R Class IIIa Laser pointers

Class 3B Class 3B Class IIIb Laser light show

projectors, industrial

lasers, research lasers,

medical lasers

Class 4 Class 4 Class IV

2016-09-12 17



Tutorial Outline




Laser Parameters

Laser Hazards

Laser Standards

Hazard Controls


Laser Safety Tools


Summary

2016-09-12 18



Laser Parameters

Wavelength– the distance (typically expressed in nm or µm) between successive crests of the

wave of light from the laser

Beam Diameter– The distance between diametrically opposed points in that cross-section of a

beam where the power/energy is 1/e (0.368) times that of the peak power/energy

Beam diameter is typically expressed in millimeters, centimeters, or inches.

2016-09-12 19



Significance of 1/e

In laser safety calculations, beam diameter and beam

divergence are measured at the 1/e point– This is the position at which the beam irradiance has dropped to 1/e, or ~37% of

the on-axis value

– By joining the two points on each side of the curve, the corresponding circular

aperture centered on the axis of a Gaussian beam will enclose 63% of the total

beam power

The use of the 1/e criterion is not arbitrary– If the total power in the beam is divided by the area

defined by the 1/e diameter, the resulting value

(having units of power per unit area) is equal to the

peak (on-axis) value of the beam irradiance

Therefore, it defines the maximum or (from the safety

perspective) the worst-case value

2016-09-12 20

Reproduced from

Henderson and

Schulmeister,

Laser Safety,

2004.



Laser Parameters cont.

Divergence– the increase in the diameter of the laser beam with distance from the beam

waist, where the irradiance (or radiant exposure for pulsed lasers) is 1/e times

the maximum value

– Beam divergence is expressed in radians or degrees

Power/Energy– CW Lasers

The output power of the laser expressed in watts (W)

Irradiance (power density in Watts/cm2)

– Pulsed Lasers

Total energy in a single pulse expressed in joules (J)

Radiant Exposure (energy density in Joules/cm2)

2016-09-12 21



Laser Parameters cont.

Beam Distribution– the energy distribution of the laser beam

– Typical distributions include Gaussian and Top Hat (also known as Flat Top).

Beam Profile– Circular

– Elliptical

– Rectangular

Pulse Repetition Frequency (PRF)– The number of pulses occurring per second expressed in hertz (Hz)

2016-09-12 22



Tutorial Outline




Laser Parameters

Laser Hazards

Laser Standards

Hazard Controls


Laser Safety Tools


Summary

2016-09-12 23



Effects of Laser Radiation Laser radiation poses two concerns for the human body

– Damage to the eye

– Skin burns

The exact effect on the human body is dependent on various parameters including wavelength, power, and exposure duration

While hazards related to direct beam viewing are generally appreciated, the exposure to specular and diffuse reflections can also pose a hazard to skin and eyes and must be considered

2016-09-12 24

Intrabeam Viewing

Specular Reflection

Diffuse Reflection



Effect of Laser Radiation cont.

Three principal mechanisms of laser damage to human tissue– Photothermal effect

Process in which laser radiation incident at the tissue surface is absorbed in

the underlying tissue, increasing the temperature of the tissue

– Photochemical effect

Process in which absorbed laser radiation directly modifies the chemical

structure of tissue components

– Photoacoustic effect

Acoustical effects result from a mechanical shockwave, propagated through

tissue, ultimately damaging the tissue

2016-09-12 25



Laser Hazards

Majority of injuries involve the eye

26

Summary of reported laser accidents in the United States and their causes from 1964 to 1992



Laser Hazards cont.

There are several contributing factors to laser related injury– Majority of accidents are due to lack of eye protection, incorrect eyewear, and

alignment procedures

27

Summary of reported laser accidents in the United States and their causes from 1964 to 1992



Eye Hazards

The major hazard of laser radiation is from beams entering the eye– The eye is the organ most sensitive to light

– The eye can focus a beam of light to a spot 20 µm in diameter on the retina

The major parts of the eye that are susceptible to damage are– Cornea

Damaging wavelengths: 100 nm to 315 nm & 1400 nm to 1 mm

– Lens

Damaging wavelengths: 315 nm to 400 mm

– Retina (Fovea)

Damaging wavelengths: 400 nm to 1400 mm

2016-09-12 28

Cornea

Damage

Retina

Damage



Skin Hazards

The skin is the largest organ of the body and, as such, is at

the greatest risk for coming in contact with the laser beam– The most likely skin surfaces to be exposed are the hands, head, or arms

Depending on the wavelength of the laser, different layers of

the skin can be damaged

2016-09-12 29

Sliney D H and

Wolbarsht M 1980

Safety with Lasers and

Other Optical Sources

(New York: Plenum)

Wavelength Skin Effects

Ultraviolet C (0.200-0.280

μm)

Erythema (sunburn)

Skin cancer

Ultraviolet B (0.280-315 μm) Accelerated skin aging

Increased pigmentation

Ultraviolet A (0.315-0.400

μm)

Pigment darkening

Skin burn

Visible (0.400-0.780 μm) Photosensitive

reactions

Skin burn

Infrared A (0.780-1.400 μm) Skin burn

Infrared B (1.400-3.00 μm) Skin burn

Infrared C (3.00-1000 μm) Skin burn



Other Laser Hazards

Fire/Explosion Hazards– The high amount of radiant power within the beam of a Class 4 laser (and

sometimes focused beams of lower classes), can be enough to ignite materials including flammable liquids, plastics, wood, and fabrics

– Laser beams can also cause explosions in combustible gases or in high concentrations of airborne dust

Thermal Hazards– Objects in the path of a laser beam (i.e. mirrors, beam stops, etc.) may get

extremely hot and could pose a burn hazard

Industrial Hygiene– Potential hazards associated with compressed gases, cryogenic materials, toxic

and carcinogenic materials and noise

– Adequate ventilation shall be installed to reduce noxious or potentially hazardous fumes and vapors, produced by laser welding, cutting and other target interactions

2016-09-12 30



Other Laser Hazards cont.

Collateral Radiation– Certain lasers may emit other forms of radiation in addition to the laser beam

UV radiation from gas laser discharge tubes

RF energy associated with some plasma tubes

X-rays may be generated from electrical equipment (>15kV)

Hazardous Material– The materials used as the laser medium or excitation mechanism may be

hazardous

– Any compresses gases used

Electrical Hazards– Laser can use high voltage and contain large capacitors

– Electrical components should be enclosed to prevent accidental contact

– Interlocks should be used as appropriate

2016-09-12 31



Tutorial Outline




Laser Parameters

Laser Hazards

Laser Standards

Hazard Controls


Laser Safety Tools


Summary

2016-09-12 32



Laser Regulations and Standards

U.S. Commerce– Laser products sold in or imported into the United States must comply with the

Federal Performance Standard for Laser Products issued by the Food and Drug

Administration (FDA), Center for Devices and Radiological Health (CDRH), in

Title 21, Code of Federal Regulations, Subchapter J, Parts 1040.10 and 1040.11

The Federal Laser Standards require laser products to incorporate certain

safety features

– In order for a laser to comply, manufacturers must (note, not an exhaustive list):

Meet the performance standards in the CFR

– Protective housing, key switches, interlocks, attenuators, labelling, etc.

Generate user manuals

Generate a Product Report and file it with the CDRH

Generate a certification test procedures

Record keeping and annual reports

2016-09-12 33



DoD Laser Requirements

U.S. Department of Defense (DoD)– In 1976, the FDA Commissioner allowed the DoD, or its components, to exempt certain

military laser products from the provisions of the Federal Laser Standard

This exemption applies to DoD lasers used for actual combat or combat training or those classified in the interest of national security

The exemption was granted with the following provisions:

– Laser product specifications must include, to the extent practicable, the safety features required by the FDA standard

– Laser product specifications will be supplemented with safety controls specified by DoD

– DoD exempted laser products will be clearly identified through labeling

– MIL-STD-1425A

A provides uniform requirements for safe design of military equipment containing lasers

– U.S. Army

Technical Bulletin Med 524 – Control of Hazards to Health from Laser Radiation

– U.S. Navy

OPNAVINST 5100.27B – Navy Laser Hazards Control Program

– U.S. Air Force

AFOSH 48-139 – Air Force Laser Radiation Protection Program

– Mil-Std-1425A and each of the military laser safety programs use ANSI Z136.1 for laser classification and hazard evaluation

2016-09-12 34



Standard for Safe Use of Lasers

ANSI Z136.1-2014 is the most widely used standard for classifying lasers and ensuring they are used safely by specifying the appropriate controls– Provides a means for calculating the laser class

– Provides control measures to ensure no exposure above the applicable MPE

– Facilitates the calculation of the MPE, OD and NOHD

– Provides labeling requirements

– Discusses non-beam hazards and mitigation techniques

The standard prescribes a 2-step process– Determine the appropriate class of the

laser or laser system

– Comply with the requirements specified for that class

IEC 60825-1 is an equivalent international standard

2016-09-12 35



Laser Regulations/Specifications

Use of laser may also be controlled by State and Local

regulations

Example– The Department of Safety and Health Services in the state of Texas requires that

all Class 3B and 4 laser be registered

Registration also includes the identification of a qualified Laser Safety Officer

All Class 3B and 4 lasers need to be inventoried annually

– Title 25, Texas Administrative Code, Section 289.301

Mandates that Class 3B and 4 lasers be registered

Provides regulations for controlling laser radiation hazards

It is recommended to check with your State and Local

regulations for laser registration and operation requirements

2016-09-12 36



Tutorial Outline




Laser Parameters

Laser Hazards

Laser Standards

Hazard Controls


Laser Safety Tools


Summary

2016-09-12 37



Control Measures

Purpose– Reduce the likelihood of exposure to beam and non-beam hazards

Types of controls– Engineering (1st priority)

Inherent/inbuilt safety features

– Procedural/Administrative

Signs and notices

Operational activities including policies and procedures

Appointment of LSO, Training, Audits

– Personal protective Equipment (PPE) (Last priority)

Goggles

Gloves

Respirators

2016-09-12 38

Order of Precedence

Engineering, Procedural/Administrative, then PPE



Hazard Controls

Engineering controls– First Line of Defense!

– More reliable than other controls

Examples– Protective Housing

– Safety Interlocks

– Beam Stop or Attenuator

– Beam Enclosures

– Laser Emission Indicators

– Key Control

– Protective Barriers and Curtains

2016-09-12 39



Hazard Controls

Procedural/Administrative Controls– Standard Operating Procedures

– Alignment Procedures

– Limitations on Spectators

– Personnel Training

– Danger/Warning/Caution Signs

2016-09-12 40

CAUTION!

VISIBLE DIODELASER RADIATION

ANSI CLASS 2LASER PRODUCT

LASER RADIATIONDO NOT STARE

INTO BEAM

= 650 nm

Power < 200 W

DANGER!!LASER RADIATION

AVOID EYE OR SKINEXPOSURE TO DIRECT OR SCATTERED RADIATION

INVISIBLE CARBON-DIOXIDELASER RADIATION

W AVELENGTH: 10.6 mPOWER: 10 Watts

ANSI CLASS 4LASER PRODUCT



Military Exemption & Labeling

Prior to the implementation of the federal standard, it was

recognized that military lasers have unique functional

requirements which sometimes preclude the incorporation of

some safety features

FDA issued Exemption Number 76EL-01DOD to the

Department of Defense on July 29, 1976. See 21CFR1010.5

2016-09-12 41

Exemption stipulations– FDA stipulated that the DoD must

establish alternative control measures

– Mil-Std-1425 (Safety Design

Requirements for Military Lasers and

Associated Support Equipment) was

developed

– Exemption label has to be “affixed or

inscribed” on the product



Personal Protective Equipment (PPE)

– Protective Eyewear and Clothing

Eye-protection devices (Goggles)

– Eyewear has to be marked with OD

(Optical Density) and wavelengths

– Multi-band eyeware eliminates the need

to change for various wavelengths

– Visible transmittance can become

problematic

– Goggles can fog and be uncomfortable

2016-09-12 42

In general, other controls should serve as primary protection rather

than depending on employees to use protective eye wear

Skin protection can best be achieved through engineering controls

– For UV (0.200-0.400 m), skin covers and/or sun-screen creams

– For the hands, gloves will provide some protection

– Laboratory jacket or coat can provide protection for the arms

– For Class IV lasers, flame-resistant materials may be needed



Facility

Entryway Interlocks– Use switches, motion detectors, etc. to deactivate the laser if unexpected entry occurs

Procedural Entryway Controls– Blocking barrier, screen, or curtain may be used inside the controlled area to prevent the

laser light from exiting the area

– Warning light or sound is required outside the entryway that operates when the laser is

energized and operating

2016-09-12 43

Reproduced

from ANSI

Z136.1-2014,

pg. 97

Entryway Warning Systems– Laser activation warning light installed

outside the entrance to each laser room

– Light to be conspicuously different from

general lighting

– Laser warning sign shall be posted both

inside and outside the laser-controlled

area



Class 4 Laser Controls--General Requirements

Supervision by individual knowledgeable in laser safety

Entry of any noninvolved personnel requires approval

Appropriate laser protective eye wear must be provided all

personnel within the laser controlled area

Beam path located and secured above or below eye level for

any standing or seated position in the facility

Windows, doorways, open portals, etc., of an enclosed facility

should be covered or restricted to reduce any escaping laser

beams below appropriate ocular MPE level

Require storage or disabling of lasers when not in use

2016-09-12 44



Tutorial Outline




Laser Parameters

Laser Hazards

Laser Standards

Hazard Controls


Laser Safety Tools


Summary

2016-09-12 45



Typical Exposure Durations

0.25 seconds: blink reflex and aversion response– Time for typical head movement, eye movement, eyelid closure when exposed

to bright light.

– Can be used for visible laser only.

10 seconds: Worst case time used for exposure to near IR

(700 nm to 1400 nm) laser sources.– Natural eye motions dominate for periods longer than 10 seconds.

600 seconds: Worst case time for viewing diffuse reflections– Typical time personnel could be exposed during alignment tasks

30,000 seconds: The time that represents one typical day of

occupational exposure.– 8 hrs = 28,800 s rounded up to 30,000 s

– Time that is used to determine the MPE for OD calculations when long term

exposure is possible

2016-09-12 46



Accessible Exposure Limit (AEL)

Definition: The maximum accessible emission level permitted

within a particular laser hazard class

2016-09-12 47


Dependencies– MPE (with all of its dependencies)

– Limiting aperture

Class 1 AEL = MPE x area of limiting aperture

Exposure

Concern

Limiting Apertures (mm)

Retina 7

Cornea 1.0, 1.5 t 0.375 , 11.0

Skin 3.5 for 180 nm to 100 um

11.0 for 100 um to 1,000 um



Optical Density (OD)

Definition: Logarithm to the base ten of the reciprocal of the transmittance (). Transmittance is defined as the ratio of the total transmitted radiant power to the total incident radiant power.

Where:– Hp is the potential eye exposure expressed in the same units as the appropriate

MPE

– MPE is calculated based on Tables 5 through 5f in ANSI Z136.1-2014.

The higher the OD value the greater the attenuation provided

2016-09-12 48


Rating Transmittance reduce by

OD 1 Reduced by a factor of 10

OD 6 Reduced by a factor of 1,000,000

𝑂𝐷 = log10𝐻𝑝

𝑀𝑃𝐸𝑂𝐷 = − log101



Nominal Ocular Hazard Distance (NOHD)

Definition: The distance along the axis of the unobstructed

beam from a laser, fiber end, or connector to the human eye

beyond which the irradiance or radiant exposure does not

exceed the applicable MPE

Where:– Where ϕ is the divergence of the laser beam as measured at the 1/e point in

radians and Φ is the radiant power

– Assuming no atmospheric loss

2016-09-12 49

Primary driver for the NOHD is the divergence of the laser beam.

The tighter the divergence of the laser beam, the larger the NOHD.


𝑁𝑂𝐻𝐷 =1

∅1/𝑒

1.27Φ

MPEcm



Nominal Skin Hazard Distance (NSHD)

Definition: The distance along the axis of the unobstructed

beam from the laser beyond which the irradiance or radiant

exposure is not expected to exceed the skin MPE

Where:– Where ϕ is the divergence of the laser beam as measured at the 1/e point in

radians and Φ is the radiant power

– The Skin MPE is taken from ANSI Tables 7a-7c

– Above equation assumes no atmospheric loss

2016-09-12 50


𝑁S𝐻𝐷 =1

∅1/𝑒

1.27Φ

MPEcm



Definition: Aided viewing is viewing that takes place using a

telescopic (binocular) or magnifying optic

For typical magnifying optics– Transmissivity

70% for 700 nm to 2800 nm

90% for 400 nm to 700 nm

NOHD impact– NOHD will be larger compared to unaided viewing

OD impact– OD may increase depending on the beam size

2016-09-12 51

Aided viewing can have a significant impact on OD and NOHD

Aided Vs. Unaided Viewing



Atmospheric Attenuation

Definition: The decrease in the radiant flux as it passes

through the atmosphere (i.e. any absorbing and/or scattering

medium)

Example values for 1030 nm wavelength

2016-09-12 52




Tutorial Outline




Laser Parameters

Laser Hazards

Laser Standards

Hazard Controls


Laser Safety Tools


Summary

2016-09-12 53



Laser Hazard Analysis Software (LHAZ), v6.0

https://gumbo2.wpafb.af.mil/portal USAFSAM ESOH Service Center

[email protected]

LHAZ 6.0 is a laser hazard assessment program that combines a maximum

permissible exposure (MPE) calculator with the American National Standards

Institute (ANSI) classification routine. The program also includes a hazard

assessment and range equation worksheets to aid trained laser safety officers

during laser safety and hazard control assessments.

2016-09-12 54

Tools

https://gumbo2.wpafb.af.mil/portal

mailto:[email protected]



LIA Laser Evaluator https://www.lia.org/evaluator/ This innovative System provides a reliable way to easily double-check laser

safety calculations. It is based on the ANSI Z136.1 American National

Standard for Safe Use of Lasers and will perform repeated calculations of

maximum permissible exposure (MPE), optical density (OD), nominal ocular

hazard distance (NOHD), nominal hazard zone (NHZ), and laser hazard

classification.

Easy Haz https://lasersafetyu.kentek.com/product/ EASY HAZ™ LSO Edition is software designed to provide comprehensive

laser hazard analysis information for Laser Safety Officers. It includes all the

most useful hazard calculations and additional calculations of laser parameters

and hazard values found nowhere else. EASY HAZ™ LSO is the best choice

for LSOs in any environment, LSOs with multiple lasers using different beam

profiles, and LSOs performing comprehensive diffuse reflection calculations

2016-09-12 55

Tools

Tools are not meant to be a replacement for a knowledgeable laser safety officer (LSO)

https://www.lia.org/evaluator/

https://lasersafetyu.kentek.com/product/software/easy-haz-laser-hazard-analysis-advanced-lso/



Tutorial Outline




Laser Parameters

Laser Hazards

Laser Standards

Hazard Controls


Laser Safety Tools


Summary

2016-09-12 56



Laser Calculation Example

The following examples will assume that we have an off-the-

shelf “purple” laser with the following parameters from the

manufacturer

2016-09-12 57

Parameter Value

Wavelength 405 nm

Power 15 mW

Mode CW

Beam Profile Circular

Beam Distribution Gaussian

Beam Diameter at 1/e 1.25 mm

Beam Divergence at 1/e 0.41 mrad

Class 3B

405 nm




AEL is the parameter that is used to establish the

classification of the laser AEL is computed by taking the given MPE multiplied by the appropriate area of

the limiting aperture

Looking at Table 5b we get an MPE = CB x 10-4 where CB is

taken from Table 6a. CB = 1 for 400-450 nm

Therefore the Class 1 MPE = 1 x 10-4 W/cm2

2016-09-12 58

Reproduced from ANSI Z136.1-2014



Laser Classification (cont’d)

Multiplying the MPE by the area of a dilated pupil we get

AEL = 10-4 W/cm2 x (π x (0.7cm/2)2 = 38.5x10-6 W

AEL = 38.5μW for a Class 1 laser at 405 nm

Since 15 mW > 38.5 μW our laser is not a Class 1

For Class 2 and 2M the AEL is 1.0 mW (ANSI 3.2.4.3)– Our laser exceeds 1.0 mW so we are not a Class 2 laser

2016-09-12 59




Laser Classification (cont’d)

For Class 3R the laser has to be less than 5 times the Class 2

AEL or 5mW.– Our laser is greater than 5 mW so we are not a Class 3R

2016-09-12 60

Our laser is a Class 3B

because we are over the

3R limit but less than the

3B limit of 0.5 W


paragraph 3.3.3.1

Reproduced from LHAZ 6.0.0.17



MPE for Hazard Assessment

From a hazard assessment standpoint we look at the MPE at a 0.25s exposure time (aversion response time)

MPE for hazard assessment can be calculated as follows:– 1st we determine the MPE from Table 5b

We then convert the energy density to power density by dividing the MPE by the exposure duration (1 J = 1 W·sec)

2016-09-12 61


MPE = 1.8 x t0.75 mJ/cm2 = 1.8 x 0.250.75 = 0.636 mJ/cm2

MPE = 0.636 mJ/cm2 / 0.25 s = 2.55 mW/cm2



MPE for Hazard Assessment

(cont’d)

To remain safe we need to make sure that we keep personnel

exposed to an irradiance < 2.55 mW/cm2

Note that, with no attenuation, our laser irradiance is:

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Exposure mitigations– Provide suitable protective covers to prevent emissions

– If emissions are necessary, use engineering controls, administrative/procedures,

and/or laser goggles with an appropriate optical density

Eo = 15 mW / (π x (0.125/2)2 = 1.22 W/cm2



OD Calculation

As discussed earlier, OD can be

calculated using this equation:

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𝑂𝐷 = log1038.9 𝑚𝑊/𝑐𝑚2

2.55 𝑚𝑊/𝑐𝑚2 = 1.2

which we round up to 2.0 to

specify a goggle OD

𝑂𝐷 = log10𝐻𝑝

𝑀𝑃𝐸

Hp= 15 mW / (π x (0.7cm/2)2 = 38.9 mW/cm2 and

MPE = 2.55 mW/cm2



OD Calculation (cont’d)

OD can be calculated using power

density or energy density

Hp is the potential eye exposure

(15 mW) expressed in the same units

as the appropriate MPE

Note that, in our specific example, where the beam is smaller than the

limiting aperture we average the beam over the area of the limiting

aperture to compute the MPE for the OD calculation

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Reproduced from ANSI Z136.1-2014, paragraph 4.4.4.2.3.1



NOHD Calculation

From our prior slides we

know that:

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Therefore:

As shown in the paper a more exact

formula is:

𝑁𝑂𝐻𝐷 =1

∅1/𝑒

1.27Φ

MPEcm

𝑁𝑂𝐻𝐷 =1

0.41 𝑥 10−3 𝑟𝑎𝑑

1.27(15 mW)

2.55 mW/𝑐𝑚2= 6666 cm = 66.7 m

𝑁𝑂𝐻𝐷 =1

∅ 1 𝑒

−𝐷𝑓2

𝑙𝑛 1 −𝐴𝐸𝐿𝑃

− 𝐷 1 𝑒2

𝑁𝑂𝐻𝐷 =1

0.41−3−0.72

𝑙𝑛 1−1.001

15

− 0.1252 = 64.9 m

MPE = 2.55 mW/cm2

AEL = 2.55 mW/cm2 (π x (0.7 cm/2)2 = 1.001 mW



NSHD

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Looking at Table 7b we get the MPE = 0.2 x CA where CA is taken from

Table 6a and is equal to 1.0

Since the available power, 15 mW is less than the 19.24 mW AEL

there is no skin hazard therefore the NSHD = 0 m.


MPE = 0.2 x 1.0 = 0.2 W/cm2

AEL = 0.2 W/cm2 (π x (0.35 cm/2)2 = 19.24 mW



NSHD (cont’d)

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If we increase the power to 20 mW we get:

𝑁𝑆𝐻𝐷 =1

0.41−3−0.352

𝑙𝑛 1−19.24

15.0

− 0.1252

𝑁𝑆𝐻𝐷 =1

0.41−3−0.352

𝑙𝑛 −0.28− 0.1252 = 0 m

Must be a positive number

𝑁𝑆𝐻𝐷 =1

0.41−3−0.352

𝑙𝑛 1−19.24

20.0

− 0.1252 = 3.6 m



Tutorial Outline




Laser Parameters

Laser Hazards

Laser Standards

Hazard Controls


Laser Safety Tools


Summary

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Summary Lasers have many practical uses

– Personnel safety must be managed

A typical laser consists of three fundamental elements– Excitation mechanism

– Lasing medium

– Optical cavity

Lasers can be classified into 4 basic laser classes

Lasers can be harmful to humans and can lead to eye and skin damage

Basic properties of laser beams for performing safety calculations include– Wavelength

– Output power/energy

– Pulse Repetition Frequency

– Beam diameter, beam divergence, beam profile, and beam distribution

Protecting personnel includes– Engineering controls

– Administrative/procedural controls

– Personal protective equipment

Three calculated parameters to ensure safe operation include– Optical Density

– Nominal Ocular Hazard Distance

– Nominal Skin Hazard Distance

Laser safety calculations can be performed using available software

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Biography

Anish Donda, Raytheon Space and Airborne Systems, 2501

West University Drive, McKinney, Texas 75071, USA,– Telephone: 972-344-4060, Email: [email protected].

– Anish Donda is a Principal Systems Engineer for Raytheon Space and Airborne

Systems in McKinney, Texas. He received his BS in Computer Engineering from

the University of Arizona in 2000, his MS in Computer Engineering from the

University of Arizona in 2003, and his MBA from the University of Arizona in

2005. He has worked for 17 years in the System Safety group at Raytheon with

the last 5 years as a system safety engineer in the advanced electro-optical

systems group specializing in laser safety.

Micah Koons, P.E., Raytheon Space and Airborne Systems,

2501 West University Drive, McKinney, Texas 75071, USA,– Telephone: 972-952-6665, Email: [email protected]

– Micah Koons is a Section Manager for Raytheon Space and Airborne Systems in

McKinney, Texas. He received his BS in Electrical Engineering from Texas A&M

University in 1982. He has worked for 32 years providing reliability and system

safety support for advanced radar and electro-optical programs.

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mailto:[email protected]

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