The Advanced Photon Source
a U.S. Department of Energy Office of Science User Facility

Experiment Hazard Class 4.4 – Use of Class 4 Lasers


This hazard classification applies to all experiments involving Class 4 lasers.  Other hazard classifications and their associated hazard controls may also apply to experiments in this hazard class.

Class 4 lasers are a pulsed or CW, visible or invisible beam laser that produces sufficient power or energy to cause retinal or other injury to the eye from the briefest of exposures to the direct or specularly reflected beam and diffuse reflections of which can be hazardous.  Class 4 lasers are also skin burn hazards and fire hazards.  Class 4 laser output exceeds 0.5 watts for periods >0.25 seconds and 0.125 joule for periods <0.25 seconds.

Experiment Category

Experiments involving previously reviewed hazard controls qualify for medium risk.

Experiments involving new equipment or modified hazard control schemes are categorized as high risk.

Experiment Hazard Control Verification Statements

Before a Class 4 laser is used at the APS for the first time, appropriate engineered controls and procedural controls must be developed and implemented.  A Laser Control Area (LCA) must be established.  A summary of laser operation requirements and a model SOP can be found at summary of laser operation requirements and model SOP.

Engineered Controls – The engineered controls for an existing reviewed and approved laser installation should already be in place and described in necessary detail in the applicable standard operating procedure.  Guidance for new installations is available through the link in this section's introductory paragraph.

Procedural Controls – All work with Class 4 lasers must be performed in accordance with a standard operating procedure (SOP).  The procedure must be reviewed and approved by the APS and the Argonne Laser Safety Officer (LSO).  Experimenters can obtain copies of the SOPs for existing laser facilities from the appropriate LCA Supervisor.  Guidance for new installations and a model SOP are available at the link in this section's introductory paragraph.

Design Reviews and Equipment Inspections – All Class 4 lasers at Argonne must be registered with and reviewed by the APS Laser Safety Officer (LSO) and an ANL Laser Operating Permit, ANL-609A must be obtained.  Please contact the APS Laser Safety Officer (630-252-6714, to obtain an ANL-609A form.  All SOPs must be reviewed and approved by APS management.


  • ESH120, Laser Safety Training
  • Orientation to the standard operating procedure for the laser facility
  • Note: If the ANL LSO approved SOP for the laser system includes a "User Mode" of operation that utilizes engineered controls to reclassify the system as a Class 1 or Class 2 equivalent, then the requirement for training is waived for "User Mode" only operation.  Any mode of operation other than "User Mode" of the laser would reinstate the training requirements.

Signs and Labeling – Required signs and labeling should already be in place for previously reviewed laser facilities.  The requirements specific to an installation should be listed in the associated standard operating procedure.  The LCA must be posted with the most recently approved laser operating permit.  Lasers brought to the APS must have a label that clearly identifies the class of the laser.  The Argonne LSO or the APS will provide signs needs for new installations.

Personal Protective Equipment – PPE requirements for laser usage are specified in the associated standard operating procedure.

Dosimetry and Monitoring – As of March 1, 2018, Argonne has incorporated the latest laser safety ANSI standard (ANSI Z136.1 (2014) Safe User of Lasers).  Adoption of this standard eliminates the baseline eye and termination examination requirements for Class 3B and 4 laser users, which had been previously referred to as "Laser Worker Medical Certification". However, workers who have a suspected accidental laser eye or skin exposure must report this incident immediately in accordance with LMS PROC-157: Incident Notification.

Experiment Authorization

Unless otherwise noted in the approved experiment safety plan, the PSC Deputy Associate Laboratory Director of Operations delegates the authority to authorize an experiment in this hazard class to the ESH Division Coordinator or their delegate, a member of the APS Experiment Safety Review Board, and resident beamline personnel having the authority to authorize experiments as listed in the ESAF system.  Approval by both the host beamline and APS Experiment Safety Review Board are mandatory prerequisites for experiment authorization.

Hazard Control Verification

The PSC Associate Deputy Laboratory Director of Operations delegates responsibility for verifying that required controls are in place to the experiment On-Site Spokesperson and the local beamline Laser Safety Officer.


ANL LMS-PROC-285:Laser Safety, 05/21/2018 (Internal link)

Contact the APS User Safety Program with any questions or if the internal links are not working properly.

Reviewed: July 24, 2020