Laser Safety at Fermilab

Blast from the past! – 10/17/2007

Laser beam safety: a complex problem? Lasers are everywhere They vary in every respect How do we know that people are safe?

Laser applications at Fermilab CDF nitrogen laser enclosure (2 lasers) A0 photoinjector accessory table

Laser applications at Fermilab IB1 GammeV experiment laser enclosure

Laser hazard factors - radiation Intensity / Duration Wavelength – Kind of effect – Threshold exposure Modulation – CW – rPW – Other

Laser hazard factors - people Part of body exposed – Eye most important Body covers – Laser protective eyewear – Other Pre-existing conditions

Laser accidents RLI – Rockwell Laser Institute – Examined 417 laser accidents – DOE – 34 laser incidents –

RLI – overall analysis Unanticipated eye exposure during alignment. Available eye protection is not often used. Equipment malfunction causes many unwanted exposures. Improper methods of handling high voltage lead to severe shock and even death.

RLI – overall analysis Protection for non-beam hazards is often lacking. Improper restoration of equipment following service frequently causes undesired hazards. Incorrect eyewear selection and/or eyewear failure are frequent causes of unwanted exposure.

DOE – overall analysis Eye exposure – 67% of all incidents Alignment – 47% of all incidents – 63% of eye incidents Immediate causes – Failure to verify beam off – Fully qualified person absent

Spectral distribution UV Ultraviolet radiation – Less than 0.4  m Standard starts at 0.18  m VIS Visible radiation – 0.4 to 0.7  m IR Infrared radiation – Greater than 0.7  m Retinal hazard region 0.7 to 1.4  m Far IR 1.4 to 10 3  m

Eye damage = fcn( ) UV - Cornea + lens VIS - Retina IR - Cornea

Effect of on damage threshold

Damage mechanisms Thermal – Increased temperature destroys tissue – VIS + IR Photochemical – Photon promotes chemical reaction – UV + far blue VIS Photoacoustic – Thermal expansion creates shock wave – to sec – high intensity Plasmagenic – High E-field destroys tissue – Below sec – VIS

Damage threshold (approximate) EFFECTIRVISUV WARMTH N/A PAIN 23N/A ERYTHEMA (1 st DEGREE BURN) BLISTER (2 nd DEGREE BURN) 1012<1 LENS EFFECT 10,000N/A0.2 RETINAL DAMAGE > >3 Units of J/cm2 in exposures of ~ 1 sec

Making things easier Classification scheme to simplify controls – Class 1 (safe) to Class 4 (dangerous) – Likelihood of inadvertent injury Class 1, 2 & 3a => few requirements Class 3b & 4 => many requirements BTW - Consumer products are usually “safe” – Read and obey warning labels – Don’t take things apart

Some Fermilab Class 3b and 4 systems – mostly physics apps – Class 3b nitrogen lasers to calibrate scintillation detectors – Class 4 Nd:YAG lasers for photon-particle interactions or material applications Class 2 and 3a systems – often diode lasers – Pointers, scanners & alignment systems – CD/DVD & fiber optic communication systems (usually enclosed)

Lasers in Fermilab’s inventory Wavelength nmMedium 266Nd:YAG(4X) 337N2Many 397Diode 532Nd:YAG(2X) 532Ar ion 633HeNeMany 656InGaAlP 669GaAs 780GaAlAs 808Diode 850GaAlAs 1054Nd:YLF 1064Nd:YAG 1064GaAs 1310Diode 1550Diode

What standard do we follow? ANSI Z – American National Standard for the Safe Use of Lasers – Guidance is exhaustive (and exhausting) Required by 10 CFR 851 – DOE Worker Safety & Health Rule – Locked into “2000” version of ANSI standard

Some acronyms LSO Laser Safety Officer MPE Maximum Permissible Exposure – The max amount of laser radiation that doesn’t cause a harmful effect (units are J/cm 2 or W/cm 2 ) – BTW – The MPE is a complex function of wavelength, modulation & exposure duration NHZ Nominal Hazard Zone – The space within which the MPE is exceeded – Includes direct, reflected & scattered radiations

Reflections Specular – Mirror-like – Irregularities <<  “Smooth” – Angle incidence = Angle reflection Diffuse – Fuzzy – Irregularities >>  “Rough” – Max reflected normal to surface

Different kinds of “laser people” Laser operators – People who operate laser systems that emit harmful levels of laser radiation. Spectators – People whose access to potentially harmful levels of laser radiation is controlled by the laser operator.

More roles The Public – People who must be isolated from potentially harmful levels of laser radiation because the laser operator cannot control their access.

Lasers by hazard class

Class 1 Description – Any wavelength (meaning 0.18 to 10 3  m) – Over 8 hrs of direct eye exposure to cause injury – 40 to 400  W for visible CW lasers Precautions – Usually none – But watch out for the following Disassembly if enclosed laser has higher hazard class Modifications that may increase the hazard class

Class 2 - description Visible wavelength beam (0.4 to 0.7  m) Over 0.25 sec to cause eye injury Up to 1 CW Depends on aversion response

Class 2 - precautions Do not stare into the beam Do not point the beam at people or shiny objects Maintain separations for public displays Precautions for Class 1 lasers apply

Class 3a - description 1X to 5X Class 2 limits for visible radiations – 0.4 to 0.7  m – Up to 5 mW as long as <2.5 mW/cm 2 1X to 5X Class 1 limits for invisible radiations – UV (<0.4  m) – IR (>0.7  m)

Class 3a - precautions Do not view the beam directly with optical instruments Precautions for Class 1 and 2 lasers apply

Class 3b - description More than Class 3a but less than 0.5 W “Immediate” eye hazard – UV: less than 1.6 hours – VIS: less than 0.25 sec – IR: less than 0.1 to 0.9 sec

Class 3b - precautions Avoid eye exposure to direct or reflected beam Review & approval by LSO & D/S/C Qualify laser operators Isolate people from the beam Post signs during unenclosed operation Consider laser eye protection (optional) Other

Qualify laser operators Laser operator Qualification – Laser safety training – Laser eye exam – Laser system manager authorization

Training General Fermilab laser safety training (this course) On-the-job equipment-specific training

Eye exam Special laser eye exam When – Prior to initial participation – Following suspected harmful exposure – Termination of work at Fermilab Coordinate through Fermilab Medical – Wilson Hall Ground Floor NW / X3232 – Exam actually done offsite at eye clinic

Isolation Goal: Keep people away from harmful levels of laser radiation Best – An enclosed light-tight laser system “box” that qualifies for Class 1 status Good – Open laser beam(s) in a light-tight room with only qualified allowed inside Weak – Unqualified people kept away from open laser beam(s) in a way that relies heavily on common sense and trust (e.g., safety tape)

Isolation: box or room Goal: Reduce hazard class Usually aim to drop Class 3b/4 to Class 1 Enclose as much of beam path as possible Fiber optics can be part of enclosure “Good enough” radiation tightness - OK Enclosure must be locked or interlocked Added benefit: protects your laser set-up

To lock or interlock? Locked enclosure (typical for box) – “Tool” required to open enclosure (can be a key) – Warning message also required Label(s) on box Sign(s) on room door(s) – Objective: opening enclosure must be deliberate act Interlocked enclosure (typical for room) – Opening enclosure turns off beam

CDF laser box - locked

CDF laser box - open

Signs Recommended designs Post where they will best warn potentially- exposed people (e.g., doors) Avoid long-term posting – People will learn to ignore warning – Magnets, velcro, illumination

Signs & labels

A0 laser room entrance

Laser eye protection D = optical wavelength H p = potential eye exposure MPE = Maximum Permissible Exposure D = log 10 (H p /MPE) Get help from LSO, online applications, and eyewear distributors.

Estimated exposure duration Wavelength (  m) Intrabeam viewing (seconds) Diffuse viewing (seconds) 0.2 to 0.430, to to to 1,00010 Values are taken from ANSI Z Suggested exposure times for eyewear design. Use actual times when known.

Other Exercise special care – During alignment – With invisible beams – Where people not involved in the operation can be exposed to the beam Precautions for public displays apply