Collage

Laser Safety Information

Personal Protective Equipment

A. Laser Protective Eyewear

The exclusive use of laser protective eyewear has, in the past, often been stressed as the best method of eye safety in the laser laboratory. Laser protective eyewear is only one of many required laser safety control measures. In general, it is better to control laser hazards through the use of engineering controls (enclosures, beam blocks, etc.) and administrative controls (posting, procedures, etc.) rather than to rely solely on laser protective eyewear.

Laser protective eyewear is essential during the beam alignment process. Most laser accidents occur during beam alignments and these can be prevented by wearing the appropriate laser protective eyewear. The laser protective eyewear selected must allow proper viewing of the beam at or just below the MPE. Laser users commonly suffer eye injury when they remove their eyewear because they cannot properly view the beam. NOTE: The intensity of a visible beam at the MPE is, by definition, sufficient to trigger the human aversion response. This means a diffuse reflection off a card is more than bright enough to view in a lighted room. The visible light transmission (VLT) of the laser protective eyewear must be sufficient (35% or more) to eliminate the need to remove the eyewear while working in the lighted laser facility. ORS recommends that the lights be kept on in the laser facility. Working in a darkened room will increase the potential hazard of eye injury by increasing the pupil size while increasing the need to remove the laser protective eyewear to be able to see.

All laser protective eyewear must be marked with the absorption wavelength and the optical density (OD) at that wavelength. It is recommended that laser protective eyewear be color-coded to the laser of concern with colored tape. This can prevent mishaps when several lasers of different wavelengths are being used.

Selection of appropriate laser protective eyewear is very important. Several different laser protective eyewear styles are available depending on the needs of the user (see Appendix H). The laser protective eyewear selected must have the appropriate OD at the wavelength(s) of concern and must be comfortable enough to wear as required. Contact the Radiation Safety Officer (RSO) if you need additional information on laser protective eyewear.

B. Skin Protection

UV laser systems or UV excitation sources can present severe hazards to exposed skin surfaces. If the UV source cannot be enclosed to prevent scattered radiation exposure, it may be necessary to wear appropriate coverings to protect the skin. These coverings may include gloves, UV face shield, lab coat, etc.

Ancillary Hazards and Control Methods

A. Toxic Dye Hazards

The fluorescent dyes (used with dye lasers) can present substantial hazards due to their toxicity. Some of these dyes are suspected of being carcinogenic or mutagenic. The solvents used for mixing the dyes may be flammable, toxic, or present other health hazards. Material Safety Data Sheets (MSDS) on dyes or solvents are available from your department or by contacting the RSO.

Because the dyes normally come in a dry power form, they are readily dispersible and should be handled and mixed with great care. A lab coat, disposable gloves, safety glasses or goggles, and a properly functioning chemical fume hood must be used when handling or mixing the dyes. Good housekeeping should be maintained before, during, and after the mixing. Use double containment adequate to contain the entire volume of the dye solution when they are being mixed, stored, and used. Clean up any spills immediately using the appropriate protective equipment. Contact the RSO if you need additional information.

B. Hazards from Laser Generated Air Contaminants (LGAC)

The interaction of the laser beam with target materials may produce toxic dusts, vapors or gases called LGAC. This is particularly true during material processing (welding, cutting, vapor deposition, etc.). Toxic products resulting from laser processing must be properly controlled through the use of adequate ventilation and filtration. The RSO should be consulted whenever LGAC may result from the laser use.

C. Cryogen Hazards

Some lasers and laser systems may require the use of cryogenic liquids (liquid nitrogen, oxygen, hydrogen, etc.). These liquids present skin and eye hazards from their extremely low temperatures and should not be handled without insulated gloves, goggles and a face shield. The dewars used for transport and storage of cryogens may present implosion hazards if they are made of glass. Glass dewars should be carefully wrapped with strong tape to contain glass fragments should they implode.

If the cryogenic liquid is allowed to warm to room temperature, the resulting gas will expand to more than 600 times the volume in the liquid state. Once it expands to become a gas, the gas may present an additional hazard (toxic, asphixiant, etc.). The specific hazards of the cryogen can be found in the MSDS. Your department safety contact should be consulted whenever cryogenic liquids are being used.

D. Compressed Gas Hazards

The use of compressed gases is common in the laser laboratory. Some lasers use both pure gases and gas mixtures as the lasing media. The high pressure of the gas translates into substantial potential energy stored in the cylinder. If this pressure is released in an uncontrolled manner (such as broken nozzle) the cylinder can become an unguided missile. Compressed gas cylinders must be properly restrained to prevent damage to the nozzle or regulator.

The gases themselves may present a variety of hazards if they leak from the cylinder. Depending on the gas, it may be toxic, corrosive, flammable, etc. Again, refer to the MSDS for detailed information on the gas in question. If the hazards are sufficient, it may be necessary to provide a gas cabinet under negative pressure to control the hazard in the case of a leak. Inform your department safety contact if compressed gases are to be used in the laser facility.

E. High Voltage Power Hazards

The high voltage power supplies associated with laser systems have been responsible for serious injuries and electrocutions. For this reason, it is important to know the hazards associated with your laser and the laser's power supply. Capacitor systems are of particular concern because they can remain hazardous long after the main power is disconnected. Capacitor systems should be safely discharged several times with the main power off to reduce the hazard before beginning work.

Only qualified persons should perform high voltage laser or power supply maintenance or repair. As a precaution, a second person (knowledgeable in high voltage safety and CPR) should always be in attendance when high voltage work is being performed.

F. Collateral Radiation Hazards

Laser excitation systems and power supplies may produce hazardous collateral radiation of various types. These hazards are normally controlled by the equipment housings, and are usually a problem only if the protective housings are removed.

The laser excitation device may produce very intense UV/Visible/IR radiation that can be hazardous. Collateral ultraviolet radiation may injure both the eye and the skin if the exposure duration is long enough. Blue light presents a special hazard because of it's ease of absorption in the retina. This "Blue Light Hazard" is thought to create photochemical injury in the retina. Exposure to any very intense visible light source can seriously degrade color vision and night vision capabilities. Exposure to these intense light sources should be carefully controlled or eliminated by leaving the housings in place.

Laser power supplies capable of creating energies greater than 15 kVp may be a source of x-rays if they contain high voltage vacuum tubes. Electric discharge excitation sources in lasers may also be a source of x-rays. Generally, these x-rays are low energy and are shielded by the equipment housings.

G. Fire and Explosion Hazards

As mentioned before, Class 4 lasers can present fire hazards. Lasers being operated in a CW mode with a beam power that exceeds 0.5 Watt can ignite or cause off-gassing in combustible materials left in the beam path. Beam stops, barriers, and curtains used with Class 4 lasers must be made of non-combustible materials. All Class 4 laser labs should have an ABC Type extinguisher readily available as a fire precaution. Laser users should receive fire prevention training. Contact the EH&IS Fire Prevention Group at Ext. 7233 for information on fire prevention training.

Explosion hazards in the laser lab include: the storage and use of flammable solvents and gases (both compressed and cryogenic) and the implosion potential from dewars and excitation flashlamps. Proper storage and control of these sources should reduce the potential hazard.

H. Noise Hazards

Some laser systems create significant levels of noise in the laser laboratory. If the noise level seems unpleasant or painful, contact EH&IS (Ext. 7233) to have a noise survey done.

All of the above information is from Dewey Sprague, Laser Safety Officer, at the University of California, Berkeley. He is a highly respected authority in laser safety and we are grateful for the information that he provides to laser users around the country and worldwide.

Revised: 7/2001