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Chapter 3
Laser Hazard Classification
ANSI Z136.1, Safe Use of Lasers, provides comprehensive information for evaluating
potential hazards from a laser system. Three aspects of a laser’s use will influence
total hazard evaluation and the application of control measures. These are:
1. The laser device’s capability of injuring workers. This ability is measured in
terms of the Maximum Permissible Exposures or MPE which is measured
by the radiant exposure, H (J/cm2) or the irradiance (power density), E
(W/cm2) for point sources.
2. The physical environment in which the laser is used (e.g enclosed laser system
versus open lab bench). Laser beam exposure conditions are usually broken
into three areas.
• In intrabeam viewing the target organ is directly exposed to a primary
laser beam. This is the traditional worst case exposure condition and
suggests the first rule of laser safety: Never look directly in to any laser
beam for any reason.
• In a specular reflection, the target organ is exposed to a mirror-like
reflection of a primary laser beam from a smooth surface. In this type
of reflection, the power being delivered to the target organ can approach
that of an intrabeam exposure. Consequently exposure to specular reflections
is usually as hazardous as intrabeam exposure.
• With diffuse reflections, the target organ is exposed to a laser beam
being reflected from an uneven surface (i.e., surface has irregularities
larger than the wavelength of the laser beam). As the beam is spread
by the uneven surface, it rapidly increases in diameter and decreases the
beam irradiance, reducing or eliminating the hazard for all but class 4
lasers.

3. The persons or populations who may be exposed (e.g., general public versus
laser worker).

A practical means for both evaluation and control of laser radiation hazards is
to first classify laser devices according to their relative hazards and then to specify
approximate controls for each classification. The benefit from using a hazard classification
system is that it usually precludes the need for laser measurements and
reduces the need for calculations. Classification of lasers is usually the manufacturer’s
responsibility, but becomes the user’s responsibility if any modifications are
made. The laser hazard classification system (Table 3.1) has four classes. While the
hazard depends upon a laser’s output parameters and potential to cause injury, the
classification system is based upon the amount of radiation accessible during normal
use, not during service or maintenance. Each laser system class has associated
safeguards which must be implemented to protect the worker from injury

A practical means for both evaluation and control of laser radiation hazards is
to first classify laser devices according to their relative hazards and then to specify
approximate controls for each classification. The benefit from using a hazard classification
system is that it usually precludes the need for laser measurements and
reduces the need for calculations. Classification of lasers is usually the manufacturer’s
responsibility, but becomes the user’s responsibility if any modifications are
made. The laser hazard classification system (Table 3.1) has four classes. While the
hazard depends upon a laser’s output parameters and potential to cause injury, the
classification system is based upon the amount of radiation accessible during normal
use, not during service or maintenance. Each laser system class has associated
safeguards which must be implemented to protect the worker from injury.

Table 3.1: Laser Classification

Class Type Hazard Parameter (P/A = Laser Power / Pupil Area)
Class I No Hazard P/A < 3 hr MPE
Class II Visible Laser P/A <.25 sec MPE
Class IIIa Eye Hazard P/A ≤ 5× Class I MPE
P/A ≤ 5× Class II MPE
Class IIIb Eye/ Skin Hazard

≤ 0.5 W for t > 0.25 sec
≤ 10 J/cm2 for t < 0.25 sec

Class IV

Diffuse reflection Eye Hazard
Fire Hazard

≥ 0.5 W for t > 0.25 Sec
≥ 10 J/cm2 for t < 0.25 sec

     

Class I - Exempt Laser, No Hazard
Class I lasers are termed ”No-Risk” or ”Exempt” lasers because they are not capable of emitting hazardous laser radiation levels under any operating or viewing conditions. Continuous output power levels are < 0.39 μW. The exemption from hazard controls strictly applies to emitted laser radiation hazards and not to other potential hazards. Most lasers by themselves do not fall into the Class I category but when the laser is incorporated or imbedded into a consumer or office machine equipment (e.g., laser printers and CD players may have class IIIb or IV lasers) the resulting system may be Class I. If a Class I system contains a more dangerous laser, the access panel to the embedded laser must contain a warning to alert the user of the potentially hazardous laser radiation which will be encountered if the panel is removed.

Class II - Low Power, Low-Risk

Class II lasers, often termed “Low-Power” or “Low-Risk” laser systems, are visible lasers operating at power levels < 1 mW and are only hazardous if the viewer overcomes his or her blink reflex response to bright light and continuously stares into the source. The possibility of such an event is remote since it could just as readily occur as blinding oneself by forcing oneself to stare at the sun for more than 10 to 20 seconds. Because this hazard, although rare, is as real as eclipse blindness, Class II lasers must have a CAUTION label affixed to indicate that an individual should not purposefully stare into the laser. Precautions are required to prevent continuous staring into the direct beam. Momentary (< 0.25 sec) exposure occurring in an unintentional viewing situation is not considered hazardous. Examples of Class II lasers are code readers in food stores, laser tag guns, pointers and positioning lasers in medical applications. This class is further refined depending whether a laser is continuous-wave or pulsed:

• Visible, CW laser devices that can emit a power exceeding the limit for Class I for the maximum possible duration inherent to the design of the laser or laser system, but not exceeding 1 mW.
• Visible repetitively pulsed laser devices that can emit a power execeeding the appropriate limit for the Class I for the maximum possible duration inherent to the design of the laser device but not exceeding the limit for a 0.25 second exposure. Additionally, there is a Class IIa defined as a visible (400 nm to 700 nm) laser or laser system used exclusively in bar code scanning systems where the laser is not intended to be viewed and does not exceed the exposure limit for 1000 seconds of viewing time. These lasers are exempt from any control measures.

Class III - Moderate Power, Moderate-Risk

Class III, “Moderate-Risk” or “Medium Power” laser systems are those which are potentially hazardous for intrabeam viewing and even specular reflection (i.e., mirrorlike
image) can cause injury within the natural aversion response time, i.e., faster
than the blink reflex (0.25 sec). They are not capable of causing serious skin injury or hazardous diffuse reflections under normal use but they must have DANGER
labels and safety precautions are required to prevent intrabeam viewing and to control
specular reflections. Class III lasers are divided into two subclasses, Class IIIa
and IIIb. Class IIIa is a visible laser or laser system with an output between 1 mW
and 5 mW which is normally not hazardous for momentary viewing but which may
cause eye injury if viewed with magnifying optics from within the beam. Class IIIb
is a laser or laser system with an output between 5 mW and 500 mW. Class IIIb is
further broken into four different frequency and energy regions:

• Infrared and ultraviolet laser devices. These emit a radiant power in excess of
the Class I limit for the maximum possible duration inherent to the design to
the laser device. Cannot emit an average radiant power of 0.5 W or greater
for viewing times greater than 0.25 seconds, or a radiant exposure of 10 J/cm2
with an exposure time of less than 0.25 seconds.
• Visible CW or repetitive pulsed laser devices. These produce a radiant power
in excess of the Class I assessable exposure limit for a 0.25 second exposure
(1 mW for a CW laser). Cannot emit an average radianct power of 0.5 W or
greater for viewing time limits greater than 0.25 seconds.
• Visible and near-infrared pulsed laser devices. These emit a radiance energy
in excess of the Class I limit but cannot emit a radiant exposure that exceeds
that required to produce a hazardous diffuse reaction.
• Near-infrared CW laser devices or repetitively pulsed laser devices. These emit a power in excess of the exposure limit for Class I for the maximum duration inherent in the design of the laser device. Cannot emit an average power of 0.5 W or greater for periods is excess of 0.25 seconds.



Class IV - high power, high-risk

Class IV, “High-Power” laser systems have average outputs of greater than 500 mW
for CW or greater than 10 J/cm2 for a 0.25 second or less pulsed laser and pose a
“high-risk” of injury and can cause combustion in flammable materials. This class
includes pulsed visible and near IR lasers capable of producing hazardous diffuse
reflections, fire, and skin hazards. Also, systems whose diffuse reflections may be
eye hazards and direct exposure may cause serious skin burns. Class IV lasers
usually require the most restrictive warning label and even more restrictive control
measures (i.e. safety goggles, interlocks, warning signs, etc.). Class IV is broken
into two frequency (i.e., wavelength) based subclasses:

  • Ultraviolet (200 nm to 400 nm) and infrared (1.4 μm to 1000 μm) laser devices
    that emit an average power of 0.5 W or greater for periods greater than 0.25
    seconds, or a radiant exposure of 10 J/cm2 within an exposure duration of
    0.25 seconds or less.
  • Visible (400 nm to 700 nm) and near-infrared (700 nm to 1400 nm) laser devices that emit an average power of 0.5 W or greater for periods greater than 0.25 seconds, or a radiant exposure in excess of that required to produce a hazardous diffuse reaction.

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