Laser Safety

In this guide, you will find the guidelines for working with lasers at the Department of Chemistry. The guidelines are updated on an ongoing basis according to the knowledge available at all times in the field. The guidelines apply only to the daily use of the lasers and do not include service or inspection thereof. If you are going to do laser service, first read the laser service manuals. For more information, read the Working Environment Institute's excellent Executive Order on Laser Safety No. 30/1990, and Danish Standard EN 60825-1.

It is important to know this guide before entering one of the laser laboratories at the Department of Chemistry, even if you are only on a short visit. The laser laboratories are marked with yellow warning signs on the doors as well as red lights above the doors. If the lasers are running in the laboratory, the red lights will light up.

The guide covers eye damage, skin damage, electric shock and poisoning, as well as mechanical damage such as fractures and sprains and how to avoid them. To help you quickly find the section dealing with your question, the injuries are written in italics, while instructions on how to avoid that damage are written in bold.

EYE DAMAGE

Of the serious injuries, eye injuries are by far the most common. Eye damage varies from passing irritations such as red spots on the eyes and “welder’s flash” (severely itchy or stinging eyes) to permanently impaired vision or blindness.

The damage can be acute, because of short-term exposure to the eye, but it can also occur after a long period of accumulated exposure, such as welder’s flash (minutes - hours) and cataracts (months - years).
The location of the eye damage depends primarily on how far the laser beam penetrates the eye, and this in turn depends on the wavelength of the laser. If the laser emits ultraviolet or far-infrared light, the laser beam only reaches the cornea and the lens of the eye, and so the damage occurs here. On the other hand, if the laser light is visible or near-infrared, the laser beam passes through the eye and focuses on the retina, resulting in a blind spot on the retina. However, with minor damage to the retina, it can heal partially or completely.

 

The vast majority, if not all, damage to the eyes can be avoided by the use of laser-protective glasses. You can find the right laser glasses in all the laser laboratories at the Department of Chemistry. However, it is important that you know how the glasses are used. The glasses cover only certain spectral ranges (wavelengths) and only dim the light a finite amount of magnitude. Spectral range and dimming are usually indicated on the glasses themselves. The dimming is most often indicated in optical density, OD, defined by

OD = log (I / I0)

where I0 and I are the intensity of the laser beam before and after the glasses. Always make sure that the glasses work at the laser wavelengths you are working with and that they sufficiently dampen the beam. As a rule of thumb, you can assume that if the laser's average power after the glasses is

I <0.1 mW

it does not damage your eyes. For example, on laser glasses for a 10 mW helium-neon laser, OD> 2 (or more) must be at a wavelength of 632.8 nm (HeNe laser wavelength), while on glasses for a 10 W neodymium: YAG laser must be OD > 5 (or more) at 1064 nm.

 

Now it is not always applicable to work with laser glasses. For example, if working with an experimental set up that uses both green, red and blue laser light, an appropriate glasses must dim the entire visible spectrum - but then the glasses would be black!

Therefore, you must follow a number of additional security requirements as listed below.

  • Shield all the laser beams and their reflection. Even a faint reflection from a lens surface can damage an eye.
  • Block all laser beams with appropriate beam stop. Remember that the beam stop should be non-reflective.
  • All laser beams must run horizontally and at the height of the stomach.
  • Vertical laser beams must be limited and shielded with utmost care.
  • The laser beams must be kept within a limited space, e.g. the edge of the laser table.
  • Do not wear watches, bracelets or finger rings when working with laser light. Even a faint reflection from a watch’s glass can damage an eye.
  • Do not put tools, such as a screwdriver, into the laser beam. Block the laser beam before screwing.
  • Block the laser beam before inserting new optics.
  • Provide good background lighting so that the pupil is closed as much as possible.
  • Warn everyone in the room about the laser rays, especially if they are invisible.

SKIN DAMAGE

Another common type of injury is skin damage.
Skin damage includes burns due to excessive heating of dermis and hypodermis tissue, redness (sunburn) caused by ultraviolet light as well as cell changes and probably skin cancer due to prolonged exposure to ultraviolet light. At the time of writing, however, we are not aware of cases of skin cancer due to laser light.

As in the case of eye damage, the position and extent of the damage depends on the depth of light penetrating the skin. Ultraviolet light (<400 nm) penetrates less than 1 mm into the skin, while near-infrared light (750-1000 nm) can pass through several centimeters of skin and underlying tissue. This means that a light effect of e.g. 1 W at 300 nm is deposited in a very small volume and results in vigorous local heating resulting in painful combustion, whereas the same power at 800 nm can hardly be felt.

You can minimize the risk of skin damage, in addition to following the safety requirements above, by

  • Wear long sleeved clothing.
  • Use sun protection factor 20 or more when working with ultraviolet laser light
  • Keep your hands out of the laser beams.

 

ELECTRICAL SHOCK

Many lasers use high voltage with deadly current. Access to the high voltage is only available if the laser safety circuit is bypassed. This may be necessary when servicing.

  • In such cases, first read the laser service manual and ask for qualified help. Never bypass the laser safety circuit until you are absolutely sure about what to do. It may be the last thing you see of this world!

POISONING

Some lasers use toxic gases such as Chlorine and Fluorine. These lasers must always be connected to a strong ventilation system.

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