ANSI Class IIIB Laser Safety

Direct eye exposure to a Class IIIB laser beam can cause retinal damage.

The American National Standards Institute (ANSI) collates U.S. and international data to form standards for various industries and applications. ANSI publishes and sells standards for laser safety based on laser wavelength, power, and likelihood of direct or indirect exposure.

History

ANSI was founded in 1918 and is the U.S. representative to the International Organization for Standardization (ISO). ANSI provides voluntary guidelines for laser safety. ANSI Z136 standards were written in 1973 and revised in 1976, 1980, 1986 and 1993. Z 136.1 assesses laser hazard by defining the nominal hazard zone (NHZ) and establishes maximum permissible exposure (MPE) limits. It also establishes a general classification scheme for lasers and outlines recommended control measures, medical surveillance, and training requirements. ANSI Z 136.2 defines service groups for optical fiber communications systems using laser diodes or LED sources for lasers powered less than 500 mW and defines MPE based on a 5mm limiting aperture (136.1 was based on a 7mm aperture).

Class IIIB

Class IIIB lasers are moderate-power lasers, continuous beam between 5 and 500 milliwatts (mW) or pulsed beam of 10 joules per square centimeter. Class IIIB lasers do not pose a risk of skin burns or retinal damage from diffuse reflections except toward the upper power limit of 500 mW, but pose a hazard for retinal damage for intrabeam exposure. Class IIIB lasers do not pose a fire hazard from the beam. Class IIIB lasers are available in wavelengths from ultraviolet through infrared. Class IIIB lasers are labeled with a starburst warning sign in black and yellow "CAUTION" signs. Black red and white "DANGER" signs should be displayed in areas where IIIB lasers are used according to ANSI Z535.1 Safety Color Code.

Dangers

All class IIIB lasers are hazardous if the beam is viewed directly or otherwise comes in direct contact with the retina of the eye. Higher-powered class IIIB lasers are also dangerous if direct reflections are viewed directly. Viewing a class IIIB laser through optics can amplify danger and retinal damage. Proper eye protection should be worn when working around class IIIB lasers. Specular reflections (from shiny surfaces) can be as damaging as viewing the beam directly. UV and IR lasers pose damage to the cornea, not the retina. Exposure to UV or IR beams does not trigger a blink response, making these lasers potentially more hazardous than visible light lasers.

Uses and Standard Precautions

Class IIIB lasers are commonly used in stereolithography, spectrometry and entertainment light shows. Basic safety includes isolating the work space with curtains and closed doors. Background illumination in the workspace should be as bright as possible to constrict the pupils of users. Laser beam path should be waist high or lower. The beam should be entirely enclosed when possible. Beam terminators are required for all lasers that have the potential to exceed the MPE.

Embedded Lasers

High-powered lasers that are embedded in devices and are not normally visible when operating are given a lower class rating. However, when the equipment is opened for servicing or modification, the higher class rating and precautions apply. Embedded lasers must have housing interlocks that shut the beam off if the housing is opened.

References

• ANSI: Overview
• OSHA: Laser Hazards
• Hyochum: Sweet Briar College Laser Safety Manual