Design Specifications for Class IV Laser Laboratories

Summary

Signage

• Printed Door Sign (Danger)
• Illuminated "Laser On" Sign

Controlled Entry

• Self-closing Door
• Standard Keyed Lock
• Cipher Lock

Laser Beam Containment Curtain

• Fabric
• Overlap
• Pull-apart Interlock

Control Circuit

• Start/Stop/EPO
• Interlocks
• Sign Control
• Control Voltage/ Contactor Action

• Curtain w.r.t. Door
• Secondary entry/exits
• Windows

This summary of NC State design guidelines for Class IV laser laboratories provides additional detail for design and construction to meet the basic requirements set forth in the latest edition of ANSI Z136.1, American National Standard for Safe Use of Lasers.

The final design for Class IV laser laboratories at NC State University will be determined through a review of proposed laser usage involving the responsible principal investigator (PI) and the NC State Laser Safety Officer (LSO), who resides in the NC State Environmental Health and Safety Center. The LSO will need to approve final design.

In some cases, laser lab design determined by the LSO and PI will deviate from this specification to achieve the best mix of safety and flexibility / efficiency for the principal investigator. For this reason, it is strongly recommended that laser design discussions be held early in the design process with participation from both the principal investigator and NC State laser safety officer (LSO).

Please contact the NC State LSO for any questions regarding this specification.

Signage

Entryways into the laser usage area shall have signs that alert personnel to the type(s) of laser(s), wavelength(s) in use, and maximum power level(s) that may be encountered within that particular lab. A list of authorized users and emergency contact numbers should also be provided on this sign. This is typically a laminated sheet attached to the door. A person entering the lab will use the posted information in selecting appropriate laser eye wear (goggles) before passing into the laser usage area. See "goggle station" in section V, Laboratory Layout

In addition, an ANSI compliant illuminated laser warning sign shall be mounted above the entryway to the lab and shall be illuminated whenever the laser is energized and capable of producing a beam. This sign contains the following warning:

DANGER
Visible and/or Invisible Laser Radiation
Avoid Eye or Skin Exposure
To Direct or Scattered Radiation
Eye Protection Required
Class 4

See example.

Controlled Entry

The door to the laboratory shall be equipped with a self-closing device and be secured at all times. The door may be locked with a standard keyed lock, but a cipher lock with key override is preferred so that the code may be easily changed as necessary. Key override is provided for custodial services or emergency access. See photo example.

Laser Beam Containment Curtain

If the curtain is parted wide enough, however, (e.g. for equipment access) an interlock sewn into the curtain shall activate and the laser(s) will be de-energized.

Please contact the NC State Laser Safety Officer for preferred equipment. Refer to the next section for a description of the interlock and shut-down circuit.

Control Circuit

An electrical control circuit shall be installed in the laboratory for the primary purpose of shutting down laser operation in the event that one or more of the following occurs:

• Curtain interlock opened
• Door interlock opened
• An "emergency laser off" switch activated
• "Stop" switch activated
• Power lost to control circuit

Refer to the schematic. The control circuit is typically housed in an electrical panel labeled “Laser Control Panel”.  A 24VAC control transformer feeds an interlock loop comprising of various elements required for the laboratory: curtain and door interlocks, laser kill switch, and other interlocks deemed necessary for laser safety can be added to this loop.
When all the interlocks are satisfied, the START switch may be activated, thereby closing contacts for the laser’s own external interlock inputs and illuminating the “Laser In Use” sign at the lab entrance.

When one of the elements in the control loop listed above causes a loss of continuity, relays K1 – K3 lose power and the maintained contacts across the laser external interlocks open and beam operation ceases. The shut down condition holds even if the interlock is once again satisfied.  A manual reset at the panel is required before resuming beam operation.
Some labs will have a single EPO, emergency power off button, which will drop power to the entire lab as well as the control circuit and thus serve as the emergency laser off button.

Laboratory Layout

An emergency laser beam off switch is located just inside the door, as shown, and is available to emergency responders to cease laser beam operation before entry. A second laser stop switch may be located in the laser usage area and be available to lab occupants.

The curtain is parted and the user may enter the laser usage area via the curtain overlap without breaking the pull-apart interlock. A secondary exit may be equipped with a "hard interlock" as shown. This switch action will cease laser operation when the door is opened and can not be defeated. Within the lab are located the start / stop controls for the laser power supply which are wired similar to the supplied schematic. Refer to the circuit description in the previous section. Window panels in doors should be covered or replaced with an opaque material. In general, windows in the laboratory are covered both for light level control and to contain stray beams so that they are not reflected outside. All class IV laser labs should be equipped with smoke detectors, sprinkler heads, and fire alarm annunciators. Gases required for excimer lasers require gas cabinets with adequate exhaust and an exhaust monitoring device, additional sprinkler heads, and a gas detection system wired for fail-safe shutdown.