Laser safety

Laser safety:

Introduction:

The Laser Safety Manual describe laser safety program and provides guidance for the safe use of lasers and laser systems. This has adopted the elements of this program to assist researchers in conducting work with lasers as safely as possible while also meeting reasonable and legally defensible standards of precaution in the use of lasers. The program is intended to minimise record keeping, follow accepted good practices, and provide useful resource materials for laser users. Comments on the program and manual content are always welcome and may be addressed to either the Laser Safety Officer or the Laser Safety Committee.

The information contained in this manual is based on the American National Standard for the Safe Use of Lasers, ANSI Z136.1-2000. Although the Z136.1 standard is frequently cited in this manual, for more thorough guidance the complete standard should be reviewed.

Manual Organisation:

This Manual is divided into three sections

(1) Laser Safety Program,

(2) Classification and Control,

(3) Non-Beam Hazards and

  • Section One, Laser Safety Program, describes the program roles and responsibilities of the individual laser users, principal investigators, Laser Safety Committee, and campus Administration.
  • Section Two, Classification and Control, addresses laser safety based on the classification scheme and required control measures of the Z136.1 standard.
  • Section Three, Non-Beam Hazards, identifies the typical non-beam or ancillary hazards of laser systems.

Section 1 : LASER SAFETY PROGRAM

Individual Laser Users:

Individual laser users must be aware of and responsible for:

  • Attending laser safety training sessions as determined by the hazard classification of the laser they intend to operate.
  • Reviewing, understanding and complying with the laser safety procedures prior to operating their laser system.
  • Wearing required protective equipment, such as approved eye wear and protective clothing.
  • Maintaining engineering controls (e.g., interlocks not defeated) on the laser system as designed, specified and approved by the laser manufacturer, or the principal investigator, in consultation with the LSO. Assuring that safety features which are not functioning properly are reported to the principal investigator.
  • Promptly reporting the details of any accident involving a laser to the principal investigator.

Principal Investigators:

Principal investigators are responsible for assuring that the use of lasers under their supervision complies with Laser Safety Committee policy, as described in this manual.

Specific responsibilities include:

  • Notifying the Laser Safety Officer whenever the principal investigator acquires, fabricates, transfers a laser to a different laboratory, or changes the hazard classification of a laser system. Notification can be accomplished by submitting a completed laser inventory form to EH&S.
  • Developing written laser safety procedures for Class 4 lasers and ensuring that laser operations are carried out in accordance with those procedures. Laser safety procedures must be posted near the laser system or made readily available for review.
  • Ensuring that laser operators, prior to actually using lasers, are properly instructed and trained in laser safety and are familiar with the laser safety procedure for their laser system. Training must be documented for all employees. Visitors to areas or laboratories in which lasers are used must also be informed of the hazards and control measures associated with these systems.
  • Ensuring that laser maintenance and repair work are performed by qualified, trained individuals and conducted in a safe manner.
  • Promptly notifying the Laser Safety Officer and discontinuing operation of a laser when an accident related to laser use has occurred.

Laser Safety Committee (LSC):

The Laser Safety Committee (LSC) consists of faculty, staff and student members who function as a peer review committee and are selected from departments where lasers are used. The LSC is appointed by the Vice Chancellor, Administrative Services, and is responsible for establishing and enforcing campus policies relating to laser safety. The Laser Safety Committee serves as an adviser to the campus Administration on matters relevant to laser safety and is the ultimate reviewing and authorising agent for the use of lasers on campus.

Laser Safety Officer (LSO)

The Laser Safety Officer is a member of the Laser Safety Committee, carries out the directives of the Committee and advises on the overall status of the laser safety program. Major responsibilities and duties of the Laser Safety Officer are:

Providing knowledgeable consultation and evaluation of laser hazards, reviewing and approving the written laser safety plan for a particular laser system.

  • Ensuring that the campus use of lasers is in conformance with Laser Safety Committee policy.
  • Maintaining records related to the campus laser safety program. Typical records include the laser inventory, accident investigations, hazard analysis and laser safety training.
  • Inspecting and auditing laser systems and operations.
  • Classifying or verifying the classification of laser systems.
  • Suspending, restricting or terminating the operation of a laser system if the LSO
  • considers the laser's hazard controls inadequate.
  • Investigating any real or suspected accident resulting from a laser operation, and initiating appropriate corrective action.

Environmental Health and Safety (EH&S)

Environmental Health and Safety is responsible for: surveillance of laser operations through the staffing of a campus Laser Safety Officer (LSO); providing consultation and laser safety services in conformance with the policies set forth in this manual, governmental regulations, and national laser safety standards. EH&S is authorised to inspect all areas of campus operations and activities.

Medical Surveillance

Medical surveillance needs of personnel working in a laser environment are the same as for other potential health hazards. Medical surveillance examinations may include assessment of physical fitness to safely perform assigned duties, biological monitoring of exposure to a specific agent, and early detection of biologic damage or effect.
Medical surveillance is strongly recommended for laser operators of Class 3b, and Class 4 laser systems. Laser operators should have, at a minimum, a baseline examination of the following, as specified in ANSI Z1361:

  • Ocular history
  • Visual acuity
  • Macular function
  • Color Vision
  • Ocular Fundus with an Ophthalmologist
  • Skin

CLASSIFICATION AND CONTROL

Hazard Classification:

The four laser hazard classes, along with their subdivisions, are:

Class 1

Class 1 lasers are considered safe based on current medical knowledge. This class includes lasers which cannot emit levels of optical radiation in excess of the exposure limit for the eye (i.e. Maximum Permissible Exposure) under any exposure condition inherent in the design and intended use of the laser. A Class 1 laser system may contain a more hazardous laser embedded in the enclosure, but no harmful levels of the laser radiation can escape the system enclosure. For Class 1 lasers containing an embedded higher class of laser, the enclosure must be interlocked.

Class 2

All Class 2 lasers operate in the visible wavelength region (400-700 nm), are sub-divided into
Classes 2a and 2, and are considered low-power lasers operating at less than 1 milliWatt. Class 2a lasers are not intended for prolonged viewing of the beam, but under normal operating conditions would not be hazardous if viewed directly (i.e. intrabeam viewing) for periods not exceeding 1,000 seconds. Class 2 lasers are not considered hazardous for momentary viewing of the direct beam for up to 0.25 seconds (i.e., aversion response time). The aversion response, blinking of eye and turning away, will afford ample protection from the beam of all Class 2 lasers. However, a Class 2 laser beam could be hazardous if one were to intentionally overcome the aversion response and stare directly into the beam for longer than 0.25 seconds. As a comparison, conventional bright light sources are also considered hazardous if one were to overcome the natural aversion response and directly stare into the light for an extended period.

Class 3

A Class 3 laser system can emit any wavelength, but cannot produce a hazardous diffuse reflection unless viewed for extended periods at close range or with collecting optics. Class 3 is subdivided into Class 3a and Class 3b. Class 3a lasers would normally not present a hazard if viewed directly for momentary periods with the unaided eye (i.e., without collecting optics) and operate at 1 to 5 milliWatts for those emitting a continuous wave beam. Class 3b lasers operate at 5 to 500 MW for continuous wave. The beam from all Class 3 lasers are not considered a fire, skin, or a diffuse reflection hazard.

Class 4

Class 4 laser systems can emit any wavelength, exceed 500 milliWatts, and are considered a fire, skin, and a diffuse reflection hazard. The most stringent control measures have been established for these lasers.

Laser Hazard Classes:

Various ranges, in nano meters, are:

  • Ultraviolet (100-400)
  • Visible (400-700)
  • Near Infrared (700-1400)
  • Far Infrared (1400-106).

Maximum Permissible Exposure:

Maximum Permissible Exposure (MPE) levels have been established by ANSI Z136.1 for various laser wavelengths and exposure durations. The MPE is the level of laser radiation to which a person may be exposed without hazardous effect or adverse biological changes in the eye or skin. In most cases it is unnecessary to make use of the MPE directly, if the laser hazard class is known and appropriate controls for that hazard class are implemented. Since the determination of the MPE for various wavelengths and exposure situations can be quite complicated, the complete ANSI Z136.1 standard or the Laser Safety Officer should be consulted for further information.

It is good practice to maintain exposure levels as far below the MPE values as possible. One
reason is that exposure to levels at the MPE values may be uncomfortable to view or feel upon the skin. MPEs for the eye and skin, along with correction factors for certain wavelengths, are listed on Tables 5 (a,b), 6 and 7 of this manual.

0.25 second: The human aversion time (i.e., blinking, turning away) for a bright light stimulus, which only applies to visible wavelengths (400-700 nm). The aversion response becomes the first line of defence for unexpected exposure to Class 2 lasers.

10 seconds: The time period chosen by the ANSI Z136.1 committees that represents the “worst
case” time period for ocular exposure to an infrared (principally near infrared) laser beam. Eye movements provide a natural exposure limitation, eliminating the need for calculations
greater than 10 seconds, except for unusual viewing conditions.

600 seconds: The time period chosen by the ANSI Z136.1 committees that represents the typical "worst case" time period for viewing visible diffuse reflections during tasks such as
alignment.

30,000 seconds: The time period that represents a full one-day (8 hour) occupational exposure. This results from computing the number of seconds in 8 hours (28,800 seconds) and rounding it off to 30,000.

Nominal Hazard Zone (NHZ):

The nominal hazard zone (NHZ) is a term used in ANSI Z136.1 to describe the space within which the level of direct, scattered or reflected laser light emitted during laser operation exceeds the MPE. Outside of the nominal hazard zone, the level of laser radiation is less than the applicable MPE.

The NHZ allows one to eliminate more restrictive Class 4 laser control measures if an area falls outside the NHZ. For instance, if the NHZ does not extend to the doorway in a laser laboratory, the door need not be safety interlocked or have a safety latch. This would eliminate the inconvenience of disrupting laser operation when frequent passage through the doorway is required. The NHZ boundary would, however, need to be visibly identified with tape or other suitable means. At the entryway to the NHZ, a warning sign is required which indicates the laser hazard, with special precautions and instructions written on the sign.


Laser Hazard Control Measures:

Control measures are established in the Z136.1 standard as a means of reducing the possibility
of skin and eye exposure to laser radiation, during normal operation and maintenance,above their respective MPE values. Hazard control measures can be grouped into three general categories:

  • Engineering (e.g., enclosures, interlocks, beam stops)
  • Administrative (e.g., policies, laser safety procedures, training)
  • Personnel Protective Equipment (e.g., eye wear, clothing)

Maximum emphasis should be placed on engineering control measures. However, if engineering controls are impractical or inadequate, warning devices, personnel protective equipment or administrative controls must be used. During the development of written laser safety procedures, one must consider the limitations of control measures (e.g., failure modes of enclosure, eye protection damage thresholds, inability of some personnel to understand written warnings). For all uses of lasers and laser systems, it is recommended that the minimum laser beam energy or power be used for the application and the beam location maintained at a height other than eye level for one seated or standing. If it is not feasible to locate the beam at a height other than eye level, the beam should be enclosed.

Engineering Controls:

Protective Housing:

Required on all classes of lasers. In certain instances, operation of a laser or laser system without a protective housing may be necessary. In these instances, the Laser Safety Officer will conduct a hazard analysis and assure that alternative controls are used. Alternate controls may include, but are not limited to:

  • access restrictions
  • eye protection
  • area controls
  • barriers, shrouds, beams stops, or other suitable measures.
  • additional training and administrative controls.

Interlocks on Protective Housing

Class 3b and Class 4 lasers require an interlocked protective housing, which is activated when
the protective housing is opened during operation and maintenance. The interlock is designed to prevent access to the beam above the applicable MPE. The interlock can be, for instance, mechanically or electrically interfaced with a shutter.

Service Access Panel

Panels of the protective housing which are intended to be removed only by service personnel, thereby permitting access to a Class 3b or Class 4 beam, must either be interlocked or require
a special tool for removal. A label must be affixed to the panel which reads: “Caution-Laser Radiation Inside. Avoid Exposure.”

Key Control

A master switch operated by a key, or by coded access (e.g., computer code). The appropriate
supervisor is vested with the authority to enable the master switch. The master switch is disabled when the laser is not intended to be used.

Viewing Portals

Viewing portals and display screens shall incorporate a suitable method (e.g., interlocks, filters, attenuates) to assure that personnel are not exposed to laser radiation greater than the applicable MPE during conditions of operation and maintenance.

Collecting Optics

Suitable methods shall be used (e.g., interlocks, filters, attenuates) to ensure that personnel
using collecting optics (e.g., lenses, telescopes, microscopes, endoscopes, etc.) are not exposed
to laser radiation levels greater than the applicable MPE.