Laser safety instruction – 2009 Eric R. Eliel Leiden University Laser safety instruction
Why instruction? Awareness is all-important! Applying safety rules is essential for the safety of you and others! Not caring for your own safety is one thing, being reckless with someone else’s is criminal. Laser safety instruction April 26, 2017
Optical What are the dangers? Thermal Electrical Chemical Associated with optical beam Optical Thermal Associated with apparatus Electrical Chemical Laser safety instruction April 26, 2017
Laser accident summary Laser safety instruction April 26, 2017
Optical damage Prime victim: the eye Laser safety instruction April 26, 2017
Laser safety instruction April 26, 2017
Eye: optical properties Transmission of the vitreous gel + lens Absorption (red line) by the retina Laser safety instruction April 26, 2017
Eye sensitivity vs. wavelength Laser safety instruction April 26, 2017
Looking into the sun Irradiance at earth surface: 140 mW/cm2. When you are looking directly at the Sun, the eye collects around 4 mW. Diameter of sun’s image on retina: 0.16 mm. Irradiance on retina: 20 W/cm2 Damaged spot on retina from direct viewing of sun Laser safety instruction April 26, 2017
A laser can do much more damage! Fluorescein angiograph of rabbit retina after laser irradiation Laser safety instruction April 26, 2017
Why is laser more dangerous? Better beam quality (better spatial coherence) yields smaller spots! Retinal spot diameter: 10-20 μm. Irradiance at retina: 0.5x106 that at cornea. Laser safety instruction April 26, 2017
Different wavelengths 315 - 400 nm Laser safety instruction April 26, 2017
Laser biological hazards - Eyes Near Ultraviolet Wavelengths (UV-A) 315 - 400 nm Absorbed in the lens of the eye. Slow buildup of damage (e.g.; cataracts). Far Ultraviolet (UVB) 280 - 315 nm and (UVC) 100 - 280 nm Radiation is absorbed in the cornea. Snow blindness/welder's flash) will result with high doses. Visible (400 -760 nm) and Near Infrared (760 - 1400 nm) Radiation is transmitted to the retina. Overexposure may cause flash blindness or retinal burns and lesions. Far Infrared (1400 nm - 1 mm) Most of the radiation is absorbed by the cornea. Overexposure to these wavelengths will cause corneal burns. Laser safety instruction April 26, 2017
Materials processing Laser safety instruction April 26, 2017
Laser biological hazards - Skin Laser safety instruction April 26, 2017
Laser safety standard IEC 60825-1 Edition 1.2 (2001-08) Safety of Laser Products - Part 1: Equipment classification, requirements and user’s guide Objectives of standard: To indicate safe working levels To introduce classification system according to hazard To lay down user and manufacturer requirements proper precautions. To ensure adequate warning is given of potential hazard To reduce possibility/risk of injury To specify user control measures. To protect against other hazards. Applies to LED’s and lasers in wavelength range 180 nm to 1 mm Laser safety instruction April 26, 2017
IEC 60825-1 -- Laser classes NCDH IEC Range Hazard I 1 n.a 1M II 2 < 1 µW No hazard n.a 1M < 1 µW entering the pupil, Total power < 0.5 W No skin hazard; hazardous for eye if viewed through optical instruments; no optics II 2 < 1 mW; 0.25 s, 400-700 nm No hazard for skin or eye: protection by the eye reflex n.a 2M < 1 mW/Pupil 0.25s, 400-700 nm; Total power < 0.5 W IIIa 3R < 5 x Class 2; 0.25 s, 400-700 nm < 5 x Class 1; 100s, invisible light Hazardous for the eye, but nor for the skin IIIb 3B > 3R, max 0.5 W Hazardous for both, eye and skin IV 4 > 3B Hazardous to eye and skin, fire hazard Note: M-classes apply to (strongly) expanded beamdiameters Laser safety instruction April 26, 2017
Definitions - 1 About 10% of dose that has P=0.5 to yield damage Max Permissible Exposure (MPE)* Maximum limit to which person may be exposed without suffering adverse effects Accessible Emission Level (AEL) Actual exposure that person can access. AEL is the limit allowed within a laser class Nominal Occular Hazard Distance (NOHD) Distance at which beam irradiance (or exposure) equals MPE Nominal Occular Hazard Area (NOHA) Area within which beam irradiance (or exposure) equals MPE About 10% of dose that has P=0.5 to yield damage Calculated for fully open pupil (0.39 cm2). Laser safety instruction April 26, 2017
MPE- Continuous Wave Laser safety instruction April 26, 2017
MPE-Pulsed Laser safety instruction April 26, 2017
MPE-collimated Laser safety instruction April 26, 2017
Exposure limits Numerical example: A 4% reflection (glass surface!) from a 2.5 mJ laser in a 2 mm beam, gives an exposure of (10-4 J)/( π/4 (0.2)2 cm2) = 3.2 10-3 J /cm2 , exceeding the threshold value on the cornea of appr. 10-7 J/cm2 by a factor 3.2 104. To be adequately protected against this exposure, protection with an optical density (OD) of log(3.2 104) = 4.5 is required Laser safety instruction April 26, 2017
Common unsafe practices • Not wearing/using appropriate protective eyewear • Misaligned optics and upwardly directed beams • Equipment malfunction • Improper methods of handling high voltage • Intentional exposure of unprotected personnel • Lack of protection from nonbeam hazards • Bypassing of interlocks, door and laser housing • Insertion of reflective materials into beam paths • Lack of pre-planning, training • Turning on power supply accidentally Laser safety instruction April 26, 2017
Control- Class 3B & 4 lasers 1 Controlled access areas. 2 Warning signs, visible lights when in operation. 3 Protective housing and interlock systems (laser shuts off when housing is opened). 4 Removable master key switch. 5 Area interlock system and remote shut-off device. 6 Internal shutter blocking the beam when it is not required. 7 Plane of laser beam above or below seated or standing (eye)level. 8 Avoid beams out of the horizontal plane. If do, they must be clearly marked. The lowest possible/practical power must be used during alignments. Use a HeNe alignment laser if possible. Use beam stops, screens and covers to terminate beams! All optical holders should be rigidly mounted, Don’t leave unnecessary components and tools in the laser control area. Laser safety instruction April 26, 2017
Class 3B & 4: protection 1 No unauthorized personnel in the room or area. 2 All personnel need appropriate training program. Only authorized personnel may operate the laser. Establish communication and mutual supervision in the lab. 4 Wear protective eyewear, with proper OD and other specs,. 5 Access by spectators or visitors must be limited and controlled by the laser user. 6 Never lower your eyes to the level of the laser beams. 7 Identify and terminating each and every stray beam. 8 Watches and reflective jewelry should be taken off. 9 Use infrared viewers or CCD camera to view the beam. Do not align or modify the laser set up after regular working hours. NEVER work alone in the evening, and only with explicit permission of your supervisor. Laser safety instruction April 26, 2017
Protective equipment Laser safety instruction April 26, 2017
Protective equipment Laser safety instruction April 26, 2017
Goggle specification Example: D652 L7 CE95 ZZ Symbol Laser type Pulse duration (s) No. of pulses D CW 10 1 I Pulsed 104 - 101 100 R Giant pulsed 109 - 107 M Mode locked < 109 Example: D652 L7 CE95 ZZ Means: D indicates that they are intended for CW laser 652 indicates for 652 nm only L7 indicates OD (transmission at 652 nm) is 107 CE95 is the European test mark ZZ indentification of Approved Inspection Body Laser safety instruction April 26, 2017