Chapter 11

LASER SAFETY

Michelangelo Carano, Claudia Caprioglio, Giovanni Olivi

Although laser systems are safe, they are not hazard-free. They are associated with risks mainly to the eyes and skin.

The use of medical lasers is subject to compliance with certain safety regulations in force at European level.

In Italy, these regulations are dictated by the law D.Lgs.81/08, art. 28, which makes provision for:

• the appointment of a head of the Prevention and Protection Service, who is responsible for assessing the risks present in the workplace and for compiling the risk assessment report.
• the appointment of a Workers’ Safety Representative, who monitors equipment and machinery, informs the operator about periodic maintenance checks, and supervises the working area and the protection systems used. The workers’ safety representative also carries out investigations and checks in the event of accidents of any kind.
• it is also compulsory to provide all operators, both medical and non-medical, with training and updating on workplace safety.

The lasers currently in use can be classified, on the basis of their intensity (power) and potential hazardousness, in accordance with the international and European laser safety standards, IEC 60825-1 and EN 60825-1.

There exists a specific value called the “maximum permissible exposure” (MPE). Determined experimentally, the MPE, which differs for the skin (W/m2) and eyes (J/m2), is the maximum level of laser radiation to which the human organism can be exposed without the risk of adverse biological effects on the eyes and skin.

Three main factors contribute to the determination of this value:

• the wavelength
• the quantity of energy (beam divergence)
• the duration of the exposure

In the case of pulsed lasers it is also important to consider other parameters, namely:

• the pulse duration
• the pulse repetition frequency
• the characteristics of the pulse train

The nominal hazard zone is the area in which the level of laser radiation (direct, reflected or scattered) exceeds the applicable MPE.

Lasers can be divided into four categories:

• Class 1: these lasers, which are not powerful (below 40 µW in blue light range, or 400 µW in red light range), remain within MPE limits even after prolonged use. These devices are not dangerous providing their case is not opened or broken: examples include CD players. They do not require any protective measures.
• Class 2: these are slightly more powerful than class 1 lasers; they emit visible light and, when operated in continuous mode, have a maximum power of 1µW. Accidental exposure of the eye is harmless. Examples of Class 2 lasers include laser pointers and bar code readers.
• Class 3 A: updated safety standards have replaced this category with Classes 1 M and 2 M.

The level of exposure is comparable to that of Class 2 in the visible light range and to that of class 1 in the invisible light range.

M denotes “magnifying instruments” and it means that these lasers are safe if the eye is protected, but that they can be dangerous if optical aids (lenses or telescopes) are used.

When operated in continuous mode, they emit less than 5 mW, with an intensity of less than 25W/cm2 in the visible range, or 5 times the threshold value of Class 1 in the invisible light range.

This class includes laser measurement instruments and lasers used in the building sector. These lasers are hazardous if viewed directly.

• Class 3 B: the updated EN 60825-1 safety standard has renamed this class as Class R.

Harmful to eyes and skin in specific cases.

Continuous lasers with a power of emission below 0.5 W (UV-A to far-IR) and wavelengths > 315 nm.

This class includes laser measurement instruments used in the building sector, lasers used in shows and lasers used in sighting/guidance systems.

In this category, protective systems are required: goggles, the application of precautionary measures in the hazard zone, special courses for users, the presence of a workers’ safety representative/head.

• The new Class 3 R (where R stands for “relaxed”) this class includes some safety characteristics of Class 2 although they are as harmful for the eyes as the other Class 3 lasers. For wavelengths in the 400-1,400 nm range (Class 3 R) it is advisable to avoid direct exposure of the eye. For all the other wavelengths (still Class 3R) exposure to the radiation must be avoided.

• Class 4: these are lasers with power greater than 0.5 W.

The eyes and skin can be harmed even by reflected scattered radiation.

The presence of flammable substances in the path of the beam constitutes a fire hazard; furthermore, interaction of flammable with other substances can result in the emission of toxic products.

This class includes medical lasers used for therapeutic purposes and lasers used in industry. Protection systems are required: specific technical equipment and measures in the at-risk working area, special courses for users, the presence of a workers’ safety representative and attention to the possible fire hazard.

I. Regulations and safety measures in the working area

• Laser instruments must be kept in an enclosed, monitored environment (where unauthorised access is forbidden).
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