laser safety at fermilab. blast from the past! – 10/17/2007

Laser Safetyat 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 nitrogenlaser enclosure

(2 lasers)

A0 photoinjectoraccessory table

Laser applications at Fermilab

IB1 GammeVexperiment 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 – 1964-2001

• DOE– 34 laser incidents– 1983-2004

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 103 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– 10-9 to 10-5 sec– VIS @ high intensity

• Plasmagenic– High E-field destroys

tissue– Below 10-9 sec– VIS

Damage threshold (approximate)

EFFECT IR VIS UV

WARMTH 0.2 0.3 N/A

PAIN 2 3 N/A

ERYTHEMA (1st DEGREE BURN)

5 6 0.01

BLISTER (2nd DEGREE BURN)

10 12 <1

LENS EFFECT 10,000 N/A 0.2

RETINAL DAMAGE >0.3 0.03 >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

• Low @ Class 1, 2 & 3a => few requirements• High @ Class 3b & 4 => many requirements

• BTW - Consumer products are usually “safe”– Read and obey warning labels– Don’t take things apart

Some lasers @ 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 inventoryWavelength nm Medium

266 Nd:YAG(4X)337 N2 Many397 Diode532 Nd:YAG(2X)532 Ar ion633 HeNe Many656 InGaAlP669 GaAs780 GaAlAs808 Diode850 GaAlAs

1054 Nd:YLF1064 Nd:YAG1064 GaAs1310 Diode1550 Diode

What standard do we follow?

• ANSI Z136.1-2000– 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/cm2 or W/cm2)

– 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 103 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 mW @ 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/cm2

• 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

IsolationGoal: 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 density @ wavelength

• Hp = potential eye exposure

• MPE = Maximum Permissible Exposure

D = log10(Hp/MPE)

Get help from LSO, online applications, and eyewear distributors.

Estimated exposure duration

Wavelength(m)

Intrabeam viewing

(seconds)

Diffuse viewing

(seconds)

0.2 to 0.4 30,000 30,0000.4 to 0.7 0.25 6000.7 to 1.4 10 6001.4 to 1,000 10 10

Values are taken from ANSI Z136.1-2000

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