ANSI Z136.4-2021: Laser Safety Measurements

Red laser on optical table in physics laboratory, adhering to ANSI Z136.4-2021.

The beam of light emitted from a laser is so intense that it can cut straight through the densest materials—metal, leather, marble, diamonds, and ceramics. Laser safety requirements for optical measurements (those that use light) are specified in ANSI Z136.4-2021: Recommended Practice For Laser Safety Measurements For Classification And Hazard Evaluation.

The Light Emitted by a Laser

“Laser” is an acronym for Light Amplification by Stimulated Emission of Radiation. It is created when electrons in the atoms in optical materials like glass, crystal, or gas absorb the energy from an electrical current or a light. The heat of the laser beam is therefore a result of the laser beam hitting the material’s surface, transferring from light energy into thermal energy (heat).

What Is the Difference Between a Laser and a Light Bulb?

The major difference between laser light and light generated by white light sources, such as a light bulb, is that laser light is monochromatic, directional, and coherent.

Monochromatic: The light emitted from a laser is monochromatic, that is, it is of one wavelength (color). Whereas, ordinary white light is a combination of many all visible wavelengths (colors).
Directional: The beam of light has very low divergence. Light from a conventional sources, such as a light bulb, candle, or the sun diverges, spreading in all directions. The intensity may be large at the source, but it decreases rapidly as an observer moves away from the source.
Coherent: the waves of light are in phase with each other in space and time. A light bulb produces many wavelengths, making it incoherent.

These three properties of laser light are what makes it more of a safety hazard than ordinary light. Laser light can emit an immense amount of energy within a very small area as James Bond nearly found out in Goldfinger and Agent 86 (Steve Carell) discovered in Get Smart.

What is ANSI Z136.4-2021?

This American National Standard, published by the Laser Institute of America (LIA), provides guidance for optical measurements associated with laser safety requirements. Optical measurements refers to the study of the intensity, spectral distribution, polarization, or other characteristics of light that is emitted by or reflected from an object or passes through some medium. ANSI Z136.4-2021 maintains that to conduct successful optical measurement, the beam must be correctly aligned with each element in its path, and these elements include apertures, lenses, wedges, filters, mirrors, beam dumps, and detectors.

Moreover, this standard specifically addresses only the measurement of those parameters associated with the laser output beam required to obtain values for quantities used in calculations of classification and/or hazard evaluation. Evaluation consists of comparing measured exposures with the maximum permissible exposure (MPE) values found in ANSI Z136.1 that are based on the ability of the direct, reflected, or scattered laser beam to cause biological damage to the eye or skin. ANSI Z136.1 and Z136.4 Combination Set contains information from both ANSI Z136.1 and ANSI Z136.4, making the information more easily accessible for manufacturers, laser safety officers, technicians, and other trained laser users.

What Are the Laser Measurements in ANSI Z136.4-2021?

The quantities measured in ANSI Z136.4-2021 can be categorized by the characteristics of the laser beam. For example, the spectral, temporal, radiometric, and spatial characteristics of the laser beam determine the accessible exposure for classification and hazard calculations.

Spectral Characteristics: Wavelength (pulse interval, amplitude, and width).
Temporal characteristics: Pulse duration and pulse repetition frequency.
Radiometric Characteristics: power or irradiance for continuous-wave (CW) lasers, and energy or radiant exposure for pulsed lasers.
Spatial Characteristics: Divergence, beam quality, direct viewing, angular subtense, waist location and size, and beam profile (size and shape).

The ANSI Z136 Series

The present scope of Z136 includes nine standards that aim to protect against hazards associated with the use of lasers and optically radiating diodes being used in the following industries: manufacturing, research and testing (labs), health care, and higher education (universities). Check out how lasers are being used in those fields here: Applications Of Lasers.

ANSI Z136.1 is the parent document of the Z136 series of laser safety standards, laying out the Z1 foundation of laser safety programs, and more information about this standard can be found here: ANSI Z136.1-2022: Safe Use of Lasers.

The Nine Z136 Standards Currently Issued

ANSI Z136.1-2022: American National Standard for Safe Use of Lasers provides guidance for the safe application of lasers and lasers systems by defining control measures for each of the seven hazard classifications.
ANSI Z136.2-2012: American National Standard for Safe Use of Optical Fiber Communication Systems Utilizing Laser Diode and LED Sources addresses hazards and provides guidance for the safe use, maintenance, service, and installation (manufacturer) of optical communications systems (OCS) utilizing laser diodes or light emitting diodes (LED) operating at wavelengths between 0.6 mm and 1 mm.
ANSI Z136.3-2018: American National Standard for Safe Use of Lasers in Health Care provides guidance for the safe use of lasers in health care. Laser radiation here refers to the ultraviolet, visible, and infrared regions of the electromagnetic spectrum.
ANSI Z136.4-2021: American National Standard Recommended Practice for Laser Safety Measurements for Classification and Hazard Evaluation provides guidance for optical measurements associated with laser safety requirements.
ANSI Z136.5-2020: American National Standard for Safe Use of Lasers in Educational Institutions addresses laser safety concerns and situations that may occur in educational environments, such as teaching laboratories, classrooms, lecture halls, science fairs, museums, and student projects on-and-off campus.
ANSI Z136.6-2015: American National Standard for Safe Use of Lasers Outdoors provides guidance for the safe use of potentially hazardous lasers and laser systems (180 nm to 1 mm), in outdoor environments.
ANSI Z136.7-2020: American National Standard for Testing and Labeling of Laser Protective Equipment provides recommendations for testing and labeling laser protective materials and protective equipment, such as eye protection, barriers, and windows.
ANSI Z136.8-2021: American National Standard for Safe Use of Lasers in Research, Development, or Testing includes policies and procedures to ensure laser safety in any area where research, development, or testing is performed, including universities, product development labs, private and government research labs (e.g., National Laboratories) and product testing settings.
ANSI Z136.9-2013: American National Standard for Safe Use of Lasers in Manufacturing Environments provides recommendations for the safe use of lasers and laser in the manufacturing environment, which includes material processing, fabrication, laser alignment, leveling, inventory, metrology, and machine vision.