Risk Management Services

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Laser Hazard Evaluation

Laser Safety and Program Development

Laser Hazard Evaluation

Laser hazard evaluation factors include:

• Hazard Analysis Calculations

• Environment in which the laser is used

• Personnel training and awareness

Hazard Analysis Calculations

Any time there is a potential exposure to a class 3b or 4 laser beam the user must perform a hazard analysis. The first part of this hazard analysis consists of a series of calculations that yield a numerical description of the magnitude of the hazard. This is the laser’s capability of causing an injury. It includes calculations of the following values:

• Maximum Permissible Exposure • Optical Density of Eyewear • Nominal Hazard Zone

(Each of these are explained in later slides.)

Hazard Analysis

The second factor in hazard analysis is the environment in which the laser is used. The hazards present and the controls required in an industrial setting may be quite different from those found in a research laboratory. The third factor to be considered is the nature of the personnel who operate the laser. Laser hazards are best controlled by well-trained laser personnel taking responsibility for managing hazards in the workplace. Personnel with little or no training in laser safety, such as many student workers, are much more likely to have laser accidents.

Laser Exposure Limits - Terms

MPE (Maximum Permissible Exposure): • The level of laser light to which a person may be exposed

without risk of injury. NHZ (Nominal Hazard Zone):

• The space within which the potential exposure exceeds the MPE.

NOHD (Nominal Ocular Hazard Distance):

• The distance within which potential intrabeam exposure exceeds the MPE. Can sometimes be referred to as NHZ (intrabeam) vs NHZ (diffuse reflective).

Law of Reflection

Specular Surface

Angle of Incidence = Angle of Reflection

Diffuse Reflection – Smooth or Rough?

It is in these situations that a NHZ (diffuse reflective) calculation is required to be performed.

The times chosen were:

1. 0.25 second: The human aversion time for bright-light stimuli (the blink reflex). Thus, this becomes the "first line of defense" for unexpected exposure to some lasers and is the basis of the Class II concept. 2. 10 seconds: The time period chosen by the ANSI Z 136.1 committees represents the optimum "worst-case" time period for ocular exposures to infrared (principally near-infrared) laser sources. It was argued that natural eye motions dominate for periods longer than 10 seconds. 3. 600 seconds: The time period chosen by the ANSI Z 136.1 committees represents a typical worst-case period for viewing visible diffuse reflections during tasks such as alignment. 4. 30,000 seconds: The time period that represents a full 1-day (8-hour) occupational exposure. This results from computing the number of seconds in 8 hours.

MPEs are expressed in irradiance terms (W/cm2) that would be measured at the cornea. Note that they vary by wavelength and exposure time.

MPE values change for different lasers operating for different overall exposure times

LASER TYPE NHZ (m) NHZ (m)DIFFUSE & EXPOSURE INTRABEAM REFLECTION

CW Nd:YAG 100 W, 10 s 1130 0.80

CW CO2

1000 W, 10 s 1060 0.56

Typical NHZ Values

• The intrabeam NHZ of a class 4 laser is usually hundreds or thousands of meters.

• The diffuse reflection NHZ is usually a few meters or less.

Protective Eyewear

PPE and Lasers

Protective Eyewear

Laser protective eyewear is intended to protect from accidental exposure only! It does not protect from intended viewing of the direct laser beam! It is intended to reduce the potential ocular exposure to a level below the applicable maximum permissible exposure (MPE).

Selecting Eye Protection

Determine the maximum irradiance exposure, either through specular reflections or diffuse radiation, and perform the optical density calculations based on the worst-case hazard.

Take into consideration the damage threshold of the filter material.

Choose the eyewear based on wavelength and optical density and be sure that the damage threshold of the filter material matches the laser environment.

Optical Density of Laser Safety Eyewear

Optical Density is a mathematical method of describing the ability of a filter to reduce the intensity of light transmitted. Optical density numbers represent “orders of magnitude” or “powers of 10.” This means that increasing the OD number by 1 increases the attenuation of the filter by a factor of 10. The area used to determine the irradiance of the beam in the optical density calculation is the area of the limiting aperture. This provides a worst case OD based on the assumption that the entire beam enters the eye. If the beam diameter is smaller than the pupil of the eye, the hazard does not increase. The worst situation is when the largest beam possible enters the eye. This produces the smallest spot on the retina. If the laser beam is significantly larger than the pupil, the actual area of the beam may be used. This will result in a OD that will protect the eye from the larger beam but will not provide adequate protection if a smaller beam of the same power enters the eye.

OD % Transmission

0 100%

1 10%

2 1%

3 0.1%

4 0.01%

5 0.001%

6 0.0001% OD = log

E0

MPE

Given: l = .488 mm

F = 5 W

d = 7 mm

A = 0.4 cm2

E0 = (5W)/(0.4 cm2) = 12.5 W/cm2

MPE = 2.5 x 10-3 W/cm2 (for 0.25 sec.)

OD = log10

12.5 W/cm2

2.5x10-3 W/cm2

OD = 3.7

Laser E0 MPE

Eyewear

Optical Density of Laser Safety Eyewear

Eyewear Labels

All eyewear must be labeled with the optical density and wavelength for which it provides protection. In many cases the same eyewear will provide a different optical density at different wavelengths. Optical Density curves for all eyewear is available from the manufacturers. In research situations it is sometimes necessary to use eyewear that is not labeled for the specific wavelengths in use. In these cases, eyewear data must be available in the laboratory.

Eyewear Labels

Selecting Eye Protection

• High Visual Transmittance

• Appropriate for wavelength

• Resistance to Fogging

• Good Peripheral Vision

• Side Shield and Vent Ports

• Optical Correction

• Resistance to UV Degradation

• Comfort

• Geek Factor

Laser Hazard Analysis #1: Class 3b Frequency Doubled CW Nd:YAG

Exposure parameters

• Wavelength: 532 nm

• Power: 200 mW

• Beam diameter*: 1 mm

• Beam divergence*: 1 mrad

• Exposure time: 0.25 s

* Note: All hazard analysis examples use 1/e2 beam diameter and divergence

Calculated values

• MPE: 2.55 mW/cm2

• Eyewear OD: 2.31

• Intrabeam NOHD: 141 m

• Diffuse Reflection NHZ: 5 cm

Laser Hazard Analysis #2: CW Argon Ion Laser

Exposure parameters

• Wavelength: 488 nm

• Power: 120 W

• Beam diameter*: 1.1 mm

• Beam divergence*: 0.6 mrad

• Exposure time: 0.25 s

Calculated values

• MPE: 2.55 mW/cm2

• Eyewear OD: 4.01

• Intrabeam NOHD: 1670 m

• Diffuse Reflection NHZ: 0.354 m

* Note: All hazard analysis examples use 1/e2 beam diameter and divergence

Laser Hazard Analysis #3: Q-Switched, Pulsed Nd:YAG Laser

Exposure parameters

• Wavelength: 1064 nm

• PRF: 10 Hz

• Pulse Duration: 10 ns

• Energy per Pulse: 1 J

• Beam Diameter: 6.4 mm

• Beam Divergence: 0.23 mrad

• Exposure Time: 10 s

Calculated values

• MPE: 1.58 X 10-5 W/cm2

• Eyewear OD: 6.22

• Intrabeam NOHD: 5520 m

• Worst Case Diffuse Reflection NHZ: 4.49 m

• (Peak Power: 10 MW; Average Power: 10 W)

* Note: All hazard analysis examples use 1/e2 beam diameter and divergence

Free Laser Hazard Analysis Software

Easy Haz hazard analysis software is available for use free on our web site. This laser hazard analysis tool has been designed to be easy to use and to provide basic laser hazard information. The values it will calculate are:

• MPE (small source ocular)

• OD of eyewear (worst case)

• Intrabeam NOHD

• Diffuse Reflection NHZ (worst case)

Hazard Evaluation by Laser Users

All users of lasers with exposed beams should:

• Understand the hazards associated with the laser they use

• Evaluate the control of hazards every time they operate the lasers

• Use their best judgment in controlling all laser hazards (be conservative; don’t take chances)

• Consult their Laser Safety Officer whenever they have safety concerns or questions

Calculations are only the beginning of a laser hazard evaluation. They allow you to quantify the hazard so you can more easily understand how it effects the workplace. To complete the hazard evaluation, the Laser Safety Officer (LSO) must go where the laser is and examine it in the real work environment. Then, the LSO must talk to the laser users and make sure they understand the hazards and the control measures they are to use. The LSO must also evaluate the written SOP for any procedures requiring access to the laser beam and determine if all laser users understand it. Finally, the LSO must use his/her best judgment to assess the risks and determine if additional or different control measures are needed. The effective daily control of laser hazards depends on the laser user’s understanding of the hazards, following procedures, and making good decisions in controlling laser hazards.

Hazard Evaluation by Laser Users

There are additional hazards from lasers that do not involve the laser beam itself, they are:

• Electrical • Chemical • Optical • Explosion • Fire

Non-Beam Hazards

Electricity is the most common non-beam hazard. Watch out for high voltage from power supplies and capacitor banks. Use standard electrical safety techniques to prevent injury: • Use one hand when working around power supplies,

capacitors or other electrical equipment • Avoid wearing metallic items • Never handle electrical equipment when hands are wet or

when standing on wet ground • Personnel should be trained in CPR • Liquid cooling equipment should be in secondary

containment

Non-Beam Hazards - Electrical

• Organic dyes are a major source of chemical hazard

• Mutagenic, carcinogenic, toxic and/or highly reactive chemicals

• Gases from laser or interaction of laser with target Use standard laboratory safety techniques to prevent injury: • Personal Protective Equipment • Proper chemical storage • Fume hoods • Etc.

Non-Beam Hazards - Chemical

• UV from laser welding

• UV from discharge tubes and pumping lamps

• Visible light and IR-A from pumping systems

Use shielding to prevent injury!

Non-Beam Hazards - Optical

• Lamps

• Capacitor banks

• Static electricity buildup in circulating dye tanks (non-polar solvents; eg: dioxane)

Use explosion “proof” housings to prevent injury

Ground wire in tubing for circulating dye

Non-Beam Hazards - Explosion

• Electrical circuits

• Improper beam enclosures

• Ignition of gases/fumes from laser

• Flammable dyes

Use flame-resistant beam enclosures and check electrical circuits for safety to prevent injury

Non-Beam Hazards - Fire