Overview
There are many lasers in the CLF that can cause permanent damage to the eye or burns to the skin through even a momentary exposure to the beam or reflected beam.
Lasers emit radiation at wavelengths spanning the ultraviolet (UV) to the far infrared (IR). For lasers in the visible or near infrared part of the spectrum, there is a particular risk of damage to the retina of the eye and permanent visual impairment.
The power of laser beams, particularly pulsed lasers, can be so high that not only the main beam, but also weak reflections and diffusely scattered radiation, can be hazardous. Constant awareness is needed.
In a research laboratory there may be multiple lasers operating at different wavelengths, from the UV through the visible and IR. What may seem to be a steady beam may be a pulsed laser operating at a high pulse repetition rate, with peak powers in the individual pulses that are more than a million times the average power of the beam. What may seem to be weak blue or red beams may be operating at wavelengths at the extreme of the visual response range of the eye, where the eye’s sensitivity is several thousand times below its peak sensitivity. UV and IR beams cannot be seen at all.
Beam hazards associated with laser use
Over the wavelength range in which many lasers operate, the skin is a strong absorber, and thereby protects the organs of the body; however, damage to the eyes is a major risk.
There are three principal types of tissue damage mechanisms for laser radiation: thermal, photochemical, and thermo-mechanical. The nature of an injury that results from laser exposure is determined by the laser wavelength, the duration of exposure, and the type of tissue that is exposed.
Ocular hazards
| Spectrum | Wavelength range | Primary tissue at risk of damage |
| Ultraviolet | 180 nm – 400 nm | Cornea or lens (302 – 315 nm) |
| Visible Near Infrared | 400 nm – 1.4 µm | Retina |
| Medium & Far Infrared | 1.4 µm – 1 mm | Cornea or lens (1.4 – 3.0 µm) |
Retinal eye damage from laser radiation can occur at very low power levels due to the focusing effect of the cornea and lens of the eye, and the coherence of laser radiation.
For very short exposures (< 10 to 6s), damage arises primarily from thermo-acoustic transients. Simple heating effects predominate in the range 100ms to 10s. For exposures longer than 100 s, photochemical effects can predominate if the wavelength is less than 600nm.
Skin hazards
The biological effects of skin exposure to laser radiation are simpler to assess than those of eye exposure. The primary injury is surface burning, which can occur in just a fraction of a second. Photochemical burns can result from skin exposure to UV laser beams and could result in longer term issues, such as a higher risk of skin cancer. Unlike retinal eye burns, skin burns can usually be treated. They are sterile and generally heal quickly.
Laser damage mechanisms for skin tissue are similar to those for the eye, in terms of the effect of wavelength and duration of exposure.
Laser safety eyewear
Laser protective eyewear is not a substitute for other precautions. It must, however, be used if, after applying control measures, adequate protection for the eyes has not been achieved.
Laser safety eyewear is marked to show the wavelength(s) for which it provides protection and the level of protection it offers. The level of protection required for each laser type will be listed on the safety sheets displayed on the door to the laser area.
Classes of laser – Low-risk lasers
Lasers are classified by their manufacturers, according to a universal rating system. The following pages provide a brief summary of the classifications for low-risk lasers & the suggested control measures.
Low-risk lasers
Class 1
Class 1 laser products are safe in normal use under most conditions.
Class 1M
Class 1M laser products are safe in normal use under most conditions. They can, however, be dangerous if lenses, mirrors, or other such optical devices are used to focus the laser beam or assist viewing.
Class 2
Class 2 laser products emit low levels of visible radiation (i.e. in the wavelength range 0.4 to 0.7 μm). They are safe for normal use, because of the natural aversion response of the eye to bright light which generally limits the duration of any exposure to 0.25 s. Nevertheless, Class 2 lasers present a dazzle hazard.
Class 2M
Class 2M laser products emit visible radiation (i.e. in the wavelength range 0.4 to 0.7 μm). They are safe for normal use, because of the natural aversion response of the eye to bright light, but they can be dangerous if lenses, mirrors, or other such optical devices are used to focus the laser beam or assist viewing. Class 2M lasers also present a dazzle hazard.
Class 3R
Class 3R laser products are unsafe for direct viewing of the laser beam, whether in aided or unaided viewing. The risk of injury is, however, still low.
Control measures for low-risk lasers
Low-risk lasers can be used anywhere on site, as long as the following conditions are met:
- horizontal beams are not located at eye level
- there are no upwardly-directed open beam paths
- the beam terminates at the end of its useful range
If these conditions cannot be met, then special authorisation will need to be given. Discuss this with your link scientists if it applies to your experiment.
The use of optical viewing aids and optical components (magnifiers, eye loupes, concave mirrors, binoculars and telescopes) is dangerous and must be strictly controlled, even around Class 1M and 2M lasers.
Some low-risk lasers present an extreme dazzle hazard and must not be used in areas where people could be working at heights or driving vehicles. More generally, visible laser beams must not be deliberately pointed at people or into any areas where people unconnected with the laser work may be present.
Under no circumstances should anyone stare into a beam.
Classes of laser – High-risk lasers
Lasers are classified by their manufacturers, according to a universal rating system. The following pages provide a brief summary of the classifications for high-risk lasers & the suggested control measures.
High-risk lasers
Class 3B
Class 3B laser products are medium-power laser-based devices. Direct ocular exposure to these beams is unsafe, although diffuse reflection might be safe under certain conditions. The beam presents a minor skin hazard, especially when focused.
Class 4
Class 4 laser products are high-power laser-based devices. Even diffuse reflection of these beams is hazardous. Class 4 lasers can cause skin burns. They also present a fire hazard.
Control measures for high-risk lasers
High-risk lasers must only be operated by authorised persons and in approved areas. Beamline staff will ensure that the following conditions are met:
- Lasers and optics that define the beam path are securely mounted
- Main and hazardous secondary beams are enclosed
- Beam paths are as short as possible, with a minimum number of directional changes
- Open beam paths are clear of surfaces that could produce hazardous reflections
- Open beam paths do not cross walkways.
If you notice that any of the above conditions are not met, leave the room immediately, along with your colleagues, and contact beamline staff to have the problem fixed.
Users may not undertake changes to the beam path under any circumstances.
When you are in a room with high-risk lasers, you must remove or cover watches, rings and other items of jewellery that could specularly reflect a laser beam. You must also keep all optical benches free from clutter. Note that many types of surface that appear visually dull are specularly reflecting for infrared radiation.
Laser safety eyewear must be worn in accordance with instructions from beamline staff.
Optical fibre systems
Optical fibres provide, typically, complete enclosure of laser radiation, but if a fibre is disconnected or a fibre break occurs, hazardous levels of laser exposure can occur.
Do not stare with unprotected eyes at the fibre ends or connector faces, and do not use any unapproved collimating device.
Fibre ends must be individually or collectively covered when they are not being used, and prior to connecting high-risk laser equipment, to prevent accidental exposures.
Laser safety appointed roles
Within your user group, “laser nominated persons” (LNPs) might be authorised to undertake specific, well-defined tasks. This authorisation must be made in writing.
If you are designated by your link scientists as an LNP – for example, as a “target area operator” (TAO) – you are responsible for the safety and control of hazards on your experiment. Therefore you must:
- be familiar with and abide by the operating procedures in your work area. These procedures will be provided to you by the beamline staff in the form of “standing orders” that you must read and follow
- work within the official constraints placed upon your activities, as communicated in the standing orders and by the link scientists
- undertake training, which will be given to you by beamline staff
- not make any significant changes to laser beam paths, beam wavelengths, or safety devices. Furthermore, you may not introduce new lasers to the laboratory without specific CLF authorisation and previous discussion with the beamline staff
- declare any pre-existing eye conditions you might have
Designated laser areas (DLAs)
Basic explanatory information combined with the laser hazard warning triangle (black star-burst on yellow background) is displayed at all points of entry to a designated laser area where high-risk lasers are in operation.
Clearly visible warning lights or a monitor screen are also displayed at all entry points to indicate when high-risk lasers are in operation. The following colours may be visible:
- green: safe to enter
- amber: restricted access. Read warning signs before entering. Laser safety eyewear may be required. (This mode usually refers to a state where hazards exist in a specific, controlled region within the DLA)
- red: restricted access. Read warning signs before entering, and take note that there will be special access restrictions. Laser safety eyewear required
Medical inspections, accident and incident reporting
Pre-existing eye conditions
If you have any eye conditions, you must declare them in advance of your experiment. Eye conditions that could affect your work include (but are not limited to) the following:
- a vision defect that cannot be corrected by the use of simple prescriptive lenses
- a vision defect that prevents effective use of both eyes
- untreated glaucoma
If you have medically impaired vision, it is likely that you will not be allowed to work with high risk laser systems.
Accident and incident response
If you suspect that you or another member of your team has sustained a laser injury of any kind, you must seek medical examination as soon as possible, and certainly within 24 hours. You must also notify CLF staff immediately.
Laser eye damage can include: pain or discomfort, blurring of vision, loss of ability to read small print, or any unusual appearance or sensation, such as persistent after-images.
In some cases, a protective measure in the laboratory fails, but does not actually lead to injury. In this case, even though no injury has occurred, terminate laser emission immediately and halt the experiment until a full assessment of the failure has been made and corrective action has been taken. Report any such incident to your link scientists.
