Ask the Expert: Safety Reviews of Machines that Include Laser Systems

Powerful lasers are becoming prevalent in manufacturing, not just for cutting and welding applications but also for marking.  Laser marking is now much more common than inkjet printing or dot peening. What this means is that many more small-scale (but powerful) lasers are being implemented within many different types of machines, and many more people working near them. In our experience, it seems there is a misconception that lasers are not that much of a hazard. It is, for the most part, an invisible hazard and if you can't see it then it is difficult to recognize it. It doesn't help that most people have little experience with lasers beyond low-power convenience store pointers. There is an overwhelming and unfortunate lack of understanding of laser hazards.

Lasers can cause injuries by various mechanisms, depending on the wavelength of radiation emitted. The importance of this is how far different wavelengths penetrate the skin or eye.

• UV C (180- 280 nm) and some UV B (280 - 315 nm) is absorbed in the cornea.
• UV B and some UV A (315- 400 nm) is absorbed in the lens.
• Visible (400- 780 nm) and IR A (780- 1400 nm) are transmitted to the retina, amplified by the cornea and lens 100,000 times.
• IR B (1400 - 3000 nm) is absorbed in the lens and cornea.
• IR C (3000 - 10,000 nm) is absorbed in the surface of the cornea.

There are several negative effects that lasers can have on human tissue:

• Thermal for exposures under 10s, typically IR. (cooking your tissues)
• Photochemical for exposures over 10s, typically UV. (sunburns, or worse)
• Photo ablation, typically pulsed lasers in a wide range of wavelengths. (literally vaporization)

Some of the types of injuries include:

• Photo keratitis (welders flash) is a photochemical "burn" of the corneal epithelium. Full recovery may be possible but requires treatment and rest.
• Corneal thermal injuries, which may be superficial and recoverable, or deeper burns causing permanent opacity.
• Cataracts, or opacity of the lens, are caused by the heating effects of IR or the photochemical effects of UV. 
• Retinal burns or hemorrhages, with differing lasting effects depending on where the laser strikes the retina. At the macula, macular degeneration or a permanent loss of central vision would result. Strikes on other parts of the retina would affect peripheral vision. A strike at the optic nerve might result in total blindness of the eye. 

Pulsed lasers are used in the majority of industrial applications we have seen. With these the laser energy is repeatedly built up to a high level and released, resulting in a series of pulses. The peak energy of a pulse can be much higher than a continuous beam. Many older industrial laser systems are of the CO2 type (IR C, or deep infrared) which would be absorbed in the cornea, and is absorbed by most common polycarbonate windows (destructively). Almost all the lasers we have been reviewing in the last few years, however, are the fibre-optic type which typically has an operating wavelength of around 1064nm. This wavelength is easily transmitted through common polycarbonate window materials and is capable of causing retinal injuries.

Although injuries could occur in the skin or eyes, laser eye injuries in my opinion have the capability of being much more life-altering.  For skin, think of 1st, 2nd, or 3rd degree burns depending on the depth of penetration but focused on a small area compared to other ways that people might commonly be burned. Eye injuries could occur at the cornea, lens or retina, all three potentially resulting in blindness.

The goal of a laser evaluation is to make sure that workers outside of the laser nominal hazard zone are protected. When we review laser systems we look for a few very simple things:

• the laser beam direction and potential paths of reflected or scattered laser beams. 
• the enclosure intended to contain the laser beam and any openings that might allow a beam to escape. 
• safety circuits and enclosure interlocks. 
• the rated optical density (OD) of windows if present the requirements of which depend on the laser power and wavelength. 
• the presence of exhaust of fume extraction. Laser-generated air contaminants (LGAC) could potentially be toxic. 

Laser beams cannot be seen unless they are directed or reflected into the eye. They can however be felt when an injury occurs, sometimes taking several days to develop into something noticeable. By that point, it is too late. Employers need to educate their workers about the hazards related to lasers, make sure their guarding and safety equipment is compliant and functional, and be vigilant to make sure that laser injuries are prevented.