5062.1
Revised 05/2005
LASERS
INTRODUCTION
There are many kinds of lasers and numerous applications.
In addition, the relationships between emitted radiations and harmful effects can
be complicated. In order to simplify the implementation of control measures,
laser radiation hazards are rated on a scale from class 1 (safe) to class 4
(dangerous). It is unlikely that a hazard class 1, 2, or 3a laser would cause
an inadvertent injury. On the other hand, hazard class 3b and 4 lasers have a
significant potential for causing accidental injuries. Not surprisingly, most
control measures are associated with these higher class systems.
At Fermilab, class 3b and class 4 laser systems are
primarily utilized in scientific applications. For example, class 3b nitrogen
lasers are used as a source of pulsed ultraviolet radiation for calibrating
scintillation detectors. Class 4 Nd:YAG (and similar) lasers are also used in
material applications and for direct photon-particle interactions. Lasers used
in commonly-encountered commercial applications such as bar code scanners,
pointers, alignment systems, CD/DVD systems, and fiber optic communication
systems tend to be class 2 or class 3a diode lasers.
APPLICABLE STANDARDS
ANSI Z136.1 – American National Standard for the Safe
Use of Lasers
DEFINITIONS
Failsafe interlock – An interlock where the failure
of a single interlock component will cause the system to go into, or remain in,
a safe mode.
Interlocked – With regard to a laser radiation
enclosure, “interlocked” means that laser radiation levels are automatically
reduced to harmless levels when a protective enclosure is opened. If the
interlock is not failsafe, an appropriate warning label must also be attached
to the enclosure.
Laser Safety Officer (LSO) – The individual who
assures that laser hazards are adequately monitored, evaluated, and controlled.
Locked – With regard to a laser radiation enclosure,
“locked” means that a tool is required to gain access to the laser beam and an
appropriate warning label has been attached to the enclosure.
Maximum Permissible Exposure (MPE) – The level of
laser radiation to which a person may be exposed without hazardous effect or
adverse biological changes in the eye or skin. The MPE is a complex function
of wavelength, modulation and exposure duration.
Nominal Hazard Zone (NHZ) – The space within which
the level of direct, reflected, or scattered radiation exceeds the applicable
MPE. Exposure levels beyond the boundary of the NHZ are below the appropriate
MPE level.
Public – For the purposes of laser safety,
individuals whose access to laser radiation is not explicitly controlled by the
laser operator. For public displays, there must be a lateral distance of at
least 2.5 m between hazardous levels of laser radiation and locations where
members of the public are permitted. The minimum vertical distance between
hazardous levels of laser radiation and surfaces upon which members of the
public may stand is 6.0 m. The vertical distance can be reduced to 3.0 m if
the laser system is continuously controlled by an experienced trained operator
who maintains constant surveillance of the laser display and can terminate the
laser emission in the event of a problem.
Spectator – For the purposes of laser safety, an
individual whose access to laser radiation is explicitly controlled by the
laser operator.
Tool - With regard to a laser radiation enclosure, the
requirement for a “tool,” when used in conjunction with a warning label,
greatly reduces the likelihood of inadvertent access to hazardous laser
radiation levels. A key to a lock is considered a tool for the purposes of
this chapter.
SPECIAL RESPONSIBILITIES
The LSO plays a Labwide consultative and oversite
role in the evaluation and control of laser hazards including system
classification, procedures, protective equipment, warning systems, facilities,
training, and medical surveillance.
Division/Section ES&H personnel play a
consultative and oversite role for laser hazards pertaining to their
division/section. They are also responsible for maintaining an inventory of
hazard class 3b and class 4 lasers within their organization.
PROCEDURES
Below is a summary of Fermilab’s laser safety requirements.
Precautions for beam hazards are presented according to hazard class and are
based on the latest version of the applicable standard, ANSI Z136.1. Though general
in nature, this information provides a solid basis for understanding the
required actions. Exhaustive guidance is available in the applicable standard,
some of which is presented in subsequent pages of this chapter.
1. HAZARD
CLASS 1
a.
Description
Any laser that requires more than
eight hours of direct eye exposure to produce an injury. Considered harmless.
The maximum output of a class 1 visible wavelength CW laser ranges from 40 to
400 mW, depending on wavelength.
b.
Precautions
Usually none. However problems may
arise if the laser is modified in a way that may increase its output or there
is an embedded laser that has a higher hazard class. If these are encountered,
follow the precautions for the appropriate hazard class.
2. HAZARD
CLASS 2
a.
Description
A laser that emits radiation in the
visible portion of the spectrum and requires more than 0.25 seconds of direct
eye exposure to produce a retinal lesion. Since the bright light emitted from
such a device triggers a “blink reflex”, and most people can blink within 0.15
seconds, an injury can only occur by forcibly staring into the beam.
Considered low hazard. The body has a mechanism to protect itself and
significant retinal damage requires prolonged staring. The maximum output of a
class 2 CW laser is 1 mW. The wavelength of the radiation must be within the
visible portion of the spectrum (0.4 to 0.7 mm).
b.
Precautions
Do not stare into the beam. Do not
point the laser in the direction of other people or shiny objects. Precautions
for public displays apply (see definitions). As with hazard class 1 lasers,
problems may arise if the laser is modified in a way that may increase its
output or there is an embedded laser that has a higher hazard class. If these
are encountered, follow the precautions for the appropriate hazard class.
3. HAZARD
CLASS 3a
a.
Description
A laser that has 1 to 5 times the
output of a class 1 laser in the invisible portions of the spectrum (<0.4 mm or >0.7 mm),
or 1 to 5 times the output of a class 2 laser at visible wavelengths (0.4 to
0.7 mm). In addition, the applicable
exposure limit must not be exceeded, e.g., due to large beam diameter. For
example, a class 3a visible wavelength CW laser can have an output of 1-5 mW,
as long as the irradiance does not exceed 2.5 mW/cm2. Considered a modest hazard.
b.
Precautions
Do not stare at the beam or view
directly with optical instruments. Do not point the laser in the direction of
other people or shiny objects. Precautions for public displays apply (see
definitions). As with hazard class 1 lasers, problems may arise if the laser
is modified in a way that may increase its output or there is an embedded laser
that has a higher hazard class. If these are encountered, follow the
precautions for the appropriate hazard class.
4. HAZARD
CLASS 3b
a.
Description
Any laser that exceeds hazard class
3a, but less than class 4. At visible and infrared wavelengths (>0.4 mm), a 3b laser can cause eye injury within
the time it takes to blink. This applies to the direct beam or a beam that is
reflected from a specular surface. A class 3b visible wavelength laser has an
output of 5 to 500 mW. UV lasers (<0.4 mm)
have a relatively lower threshold for hazard class 3b - 0.1 to 10 mW. Consequently, much longer exposures are
required to produce an injury near this threshold. A class 3b laser is
considered hazardous.
b.
Precautions
·
Avoid eye exposure to the direct or reflected beam.
·
The Laser Safety Officer and any personnel deemed appropriate by
the division/section responsible for the operation of the laser should be
notified prior to operation.
·
Laser training is required for persons who may be exposed to the
beam while operating, maintaining, or servicing the laser. Training requests,
schedules, and sign-ups are accessible in electronic form via TRAIN at the
Fermilab ES&H Section website.
·
A special laser eye exam is required for all persons who will
operate, maintain, or service the laser. This exam is conducted at an offsite
eye clinic. Contact Fermilab’s Medical Department at X3232 to schedule an
appointment. An exam is required (1) prior to initial participation, (2)
following a suspected laser eye injury, and (3) upon termination from work at
Fermilab.
·
Try to reduce the hazard class by enclosing the beam path,
especially for extended/repeated operations in a single location. Enclosure is
typically in the best interest of the laser operator since it simplifies safety
requirements and reduces the likelihood of damage to the laser set up.
Enclosures must be interlocked or locked to prevent inadvertent exposure.
·
Establish a controlled area during periods of unenclosed
operation. Spectators should not be permitted within the controlled area
unless (1) approval has been obtained from the laser operator, (2) the degree
of hazard and avoidance procedures have been explained to them, and (3)
appropriate protection measures have been taken. Precautions for public
displays apply (see definitions).
·
Wearing of appropriate laser eye protection is recommended, but
not required.
·
Post signs during periods of unenclosed operation.
·
Exercise special care (1) during alignment, (2) when using
invisible beams, and (3) where people who are not involved with the operation
can be exposed to the beam.
·
Initial laser system installation or subsequent modification,
including changes in usage or location must be brought to the attention of your
division/section ES&H organization.
5. HAZARD
CLASS 4
a.
Description
Any laser where diffusely scattered
radiation can cause eye injury within 0.25 seconds. In other words, radiation
scattered from a rough surface can cause eye damage within the time it takes to
blink. Additionally, depending on output characteristics, class 4 lasers can
damage skin, ignite fires, and thermally decompose irradiated materials. A
class 4 laser presents a significant hazard that must always be treated with
great care. A continuous wave laser of any wavelength with an output exceeding
0.5 W is considered to be class 4.
b.
Precautions
·
Avoid eye and skin exposure to the direct or scattered beam.
·
Operation requires the prior signature approval of the Laser
Safety Officer and any other personnel deemed appropriate by the
division/section responsible for the operation of the laser. This is typically
accomplished via review and approval of written safety operating procedures
that are required in any case.
·
Laser training is required for persons who may be exposed to the
beam while operating, maintaining, or servicing the laser. Training requests,
schedules, and sign-ups are accessible in electronic form via TRAIN at the
Fermilab ES&H Section website.
·
A special laser eye exam is required for all persons who will
operate, maintain, or service the laser. This exam is conducted at an offsite
eye clinic. Contact Fermilab’s Medical Department at X3232 to schedule an
appointment. An exam is required (1) prior to initial participation, (2)
following a suspected laser eye injury, and (3) upon termination from work at
Fermilab.
·
Make every effort to reduce the hazard class by enclosing the
beam path, especially for extended/repeated operations in a single location.
Enclosure is typically in the best interest of the laser operator since it
simplifies safety requirements and reduces the likelihood of damage to the
laser set up. Enclosures must be interlocked or locked to prevent inadvertent
exposure.
·
Establish a controlled area during periods of unenclosed
operation. Spectators must not be permitted within the controlled area unless
(1) approval has been obtained from the laser operator, (2) the degree of
hazard and avoidance procedures have been explained to them, and (3)
appropriate protection measures have been taken. Precautions for public
displays apply (see definitions).
·
Use an audible or visual start up warning to alert others that
the laser will be activated.
·
ALWAYS wear appropriate laser eye protection within the
controlled area during periods of unenclosed operation. This is a critical
precaution. Scattering of the beam from any surface may be able to produce an
eye injury within the time you can blink.
·
Post signs during periods of unenclosed operation.
·
Exercise special care (1) during alignment, (2) when using
invisible beams, and (3) where people who are not involved with the operation
can be exposed to the beam.
·
Initial laser system installation or subsequent modification,
including changes in usage or location must be brought to the attention of your
division/section ES&H organization.
6. NON-BEAM
HAZARDS
Non-beam
hazards are those that do not result from exposure to a laser beam. These
include the following:
·
Laser components (power supplies)
·
Materials used to generate the laser beam (gases, dyes, solvents)
·
Materials exposed to the beam (fires, thermal decomposition
products)
·
Laser environment (mechanical hazards, confined spaces)
Non-beam hazards must be considered
in the use of lasers. Guidance on these hazards can be found elsewhere in this
manual, in the applicable standard, from your division/section ES&H
organization, or the LSO.
5062.1TA
Revised 04/2005
TECHNICAL APPENDIX
1. LASER SAFETY EYEWEAR
Laser protective eyewear is required for unenclosed
operation of hazard class 4 systems and recommended for unenclosed operation of
hazard class 3b systems. The eyewear must match the characteristics of the
laser radiation: the optical density must be sufficient at the correct wavelength.
This information must be marked on the eyewear. The optical density is
calculated as follows.
Dl =
optical density @ wavelength l
Hp = potential eye exposure
MPE = Maximum Permissible Exposure
Hp and MPE have the same units.
Actual/Expected exposure durations should be used whenever
possible. In the absence of time estimates the values shown below can be used
in calculating a minimum optical density.
Suggested exposure times for eyewear design
|
Wavelength
(mm)
|
Intrabeam viewing
(seconds)
|
Diffuse
viewing (seconds)
|
|
0.2 to 0.4
|
30,000
|
30,000
|
|
0.4 to 0.7
|
0.25
|
600
|
|
0.7 to 1.4
|
10
|
600
|
|
1.4 to 1,000
|
10
|
10
|
Values are taken from ANSI Z136.1-2000.
“Intrabeam viewing” refers to direct or specularly-reflected
eye exposure as might occur in an accident. “Diffuse viewing” refers to
looking at scattered radiation such as occurs during many alignment activities.
Determination of Hp and MPE is often a complex
matter. Assistance in the determination of the optical density can be provided
by the Laser Safety Officer and/or the manufacturers of the laser protective
eyewear.
2. LASER SIGNS AND LABELS
|
Sign
Hazard class 3a
Visible ≤ MPE
|
CAUTION
LASER RADIATION
DO NOT STARE INTO BEAM OR
VIEW DIRECTLY WITH
OPTICAL INSTRUMENTS
(Other precautionary
instructions which may apply)
(Laser specifications)
CLASS 3A
|
|
|
|
|
Sign
Hazard class 3a
Visible > MPE
|
DANGER
LASER RADIATION
AVOID DIRECT EYE EXPOSURE
(Other precautionary
instructions which may apply)
(Laser specifications)
CLASS 3A
|
|
|
|
|
Sign
Hazard class 3a
UV/IR ≤ MPE
|
CAUTION
INVISIBLE LASER RADIATION
AVOID DIRECT EYE EXPOSURE
(Other precautionary
instructions which may apply)
(Laser specifications)
CLASS 3A
|
|
|
|
|
Sign
Hazard class 3a
UV/IR > MPE
|
DANGER
INVISIBLE LASER RADIATION
AVOID DIRECT EYE EXPOSURE
(Other precautionary
instructions which may apply)
(Laser specifications)
CLASS 3A
|
Acceptable content for laser warning signs and labels is
shown below. In most cases, commercial lasers will be labeled by the
manufacturer. Signs are required for Class 3b and Class 4 lasers and laser
systems and are recommended for Class 3a lasers and laser systems. All listed
labels are required regardless of the operational hazard class. Laser
radiation hazard warning signs and labels are available from the ES&H
Section.
|
Sign
Hazard class 3b
(The word INVISIBLE
precedes the word LASER for UV or IR radiations.)
|
DANGER
LASER RADIATION
AVOID DIRECT EXPOSURE
LASER TRAINING AND EYE EXAM
REQUIRED
(Other precautionary
instructions which may apply)
(Laser specifications)
CLASS 3B
|
|
|
|
|
Sign
Hazard class 4
(The word INVISIBLE
precedes the word LASER for UV or IR radiations.)
|
DANGER
LASER RADIATION
AVOID EYE OR SKIN EXPOSURE
TO DIRECT OR SCATTERED
RADIATION
LASER TRAINING AND EYE EXAM
REQUIRED
(Other precautionary
instructions which may apply)
(Laser specifications)
CLASS 4
|
|
|
|
|
Label
Classification/Inventory
|
NOTICE
THIS DEVICE HAS A LASER
RADIATION HAZARD CLASS
OF (System class as
used)
ASSESSED ON (Date)
BY (Name)
X4646 ES&H SECTION
(Laser sequence number)
|
|
|
|
|
Label
Laser enclosure
|
CAUTION
THIS DEVICE CONTAINS
A CLASS (3B OR 4)
LASER
DO NOT OPEN WITHOUT
AUTHORIZATION FROM
(Name of designated
person)
|
|
|
|
|
Label
Laser fiber optic
|
CAUTION
HAZARDOUS LASER RADIATION
WHEN DISCONNECTED
DO NOT DISCONNECT WITHOUT
AUTHORIZATION FROM
(Name of designated
person)
|
3. LASER ENCLOSURES
It is a good idea to reduce the hazard class of a laser
system by enclosing the beam path, especially for extended/repeated operations
in a single location. Enclosure is in the best interest of the laser operator
since it simplifies safety requirements and reduces the likelihood of damage to
the laser set up.
Enclosures must be locked or interlocked in order to minimize
the risk of inadvertent exposure. Labeling is also required, unless failsafe
interlocks are used. The enclosure must be “tight” enough such that any
escaping laser radiation is not at harmful levels. For class 4 systems, the
enclosure should be near-perfect since even non-specular reflections can be very
hazardous. Enclosures for class 3b systems may be constructed with less
conservatism. Openings can often be allowed where the beam path requires
multiple non-specular reflections.
Radiations are often transported from lasers to their use
locations via systems of optical fibers or piping with reflective surfaces. If
the transported radiation levels are hazardous, then the rules for enclosure must
also be applied to the transport system.
Where ready access to an operating laser or laser radiation
is needed, the room in which the activity is taking place typically becomes the
enclosure. When stable operation has been established, the laser is often put
into a box so it is isolated from people. These boxes are most often
constructed of aluminum. One side of the box is equipped with a piano hinge
and threaded closures to serve as an access panel. The closures require a tool
to open the panel. This qualifies as a “lock” for making up the enclosure.
The access panel is labeled with a cautionary statement that the box contains
hazardous levels of laser radiation and must only be opened upon authorization
of the primary laser operator for the system. If hazardous levels of laser
radiation are transmitted from the interior of the box to another location via
fiber optics, they too are considered part of the enclosure.
Maximum continuous
wave laser power
as a function of
wavelength and hazard class
(Interpreted from
ANSI Z136.1-2000 values for MPE)
Power to reach ocular
MPE
as a function of
wavelength and exposure time
(Interpreted from
ANSI Z136.1-2000 values for MPE)
