Protective Equipment

Overview

Protective equipment for laser safety generally means eye protection in the form of goggles or spectacles; this includes special prescription eyewear using high optical density filter materials or reflective coatings (or a combination of both) to reduce the potential ocular exposure below MPE limits. Some applications, such as use of high power excimer lasers operating in the ultraviolet, may also dictate the use of a skin cover if chronic (repeated) exposures are anticipated at exposure levels at or near the MPE limits for skin.

The main threat lies to your hands and eyes. Typically, you will be continuously adjusting optical components, and so necessarily placing your hands close to a beam. Invariably, you will be hit once and awhile. Usually this will just sting a little. There are a few beams in the lab, however, that can give a nasty bruise or burn. Before you modify or work on any system, you must know exactly where all the beams are and how powerful they are. Every intense infrared or ultraviolet beam must have its path clearly marked, or it must be shielded. When you are planning a new beam path, at any wavelength, try to place the optics so they may be easily reached without your hand crossing any beams.

Your eyes are your greatest concern - they are the most easily damaged. We have laser goggles, which provide some protection from the lasers in our lab. The degree of protection will vary depending on the wavelength and pulse energy involved.

Eyeglasses offer extra protection against ultra-violet light without degrading overall vision. There is often diffuse UV scatter present in the lab and the hazards from long term exposure to such radiation have already been noted. The amount of protection offered varies with wavelength and lens type, but is easy to measure. Eye glasses also present a hazard. No beam should ever be at eye level, but if one were, a user's eye glasses could direct light into his or her eyes that would otherwise miss. The principle threat comes from surface reflections off the lenses from beams directed towards the side of the face. In effect, glasses make the user's eyes bigger targets.

By design, beams produced by stray reflections and diffuse scatter travel mostly in a plane at waist height and parallel to the floor. You must never allow your open eyes to intersect this plane. For example, if you drop a tool on the floor, you put yourself at risk when you bend down to pick it up. You can protect yourself by simply keeping your eyes closed until you are below this plane - make this a habit. Often, you will want to look at some part of your apparatus that requires you to place your eyes in a dangerous position if the lasers are present. Do not depend on electronically controlled beam stops to protect your eyes and do not use your hands as beam blocks. Use a beam block - a stable mounted shield, or a "beam eater" - a box designed to contain laser beams.

There will be times when you wish to view your experiment in progress, and can do so only by placing your eyes near a beam. This is unacceptable. You must be willing to take the time to devise a safe means to view it.

Laser Protective Eyewear

Historically, the most common eye protection has been the use of special colored glass absorbing filters. These are generally the most effective in resisting damage from general use as well as from exposure to intense laser sources.

The advantage of using reflective coatings is that they can be designed to selectively reflect a given wavelength while transmitting as much of the remaining visible spectrum as possible. However, some angular dependence of the spectral attenuation factor may be present.

It should be stressed that there are few known materials that can withstand laser exposures, which exceed 105 W/cm2 since the electric fields associated with the beam will exceed the bonding forces of matter. Most materials will begin to degrade at levels far below these field strength levels due to thermal or shock effects.

While direct raw beam exposure onto eyewear is certainly not recommended under any normal condition, it does occur. At least one intra-beam eye accident with thermal puncture of plastic laser eyewear has been reported with a Nd:Yag laser in a research laboratory.

Protective Clothing

Where personnel may be exposed to levels of radiation that clearly exceed the MPE for the skin, particularly in the ultraviolet, the LSO shall recommend or approve the use of protective clothing. Where personnel may be subject to chronic skin exposure from scattered ultraviolet radiation, as may occur during excimer laser processing, skin protection should be provided even at levels below the MPE for the skin. Consideration should also be given to the use offire resistant material when using Class IV lasers.

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