1          Additional aspects regarding the selection of risk reduction measures for laser devices

1.1      Introduction

After a risk assessment using checklists and finding the existence of the following risks:

-          high - measures should be immediately taken to reduce risk to a low level considering these checklist items that indicate the causes of these risks,

-           medium – measures are recommended to be taken to reduce the risk to a low level considering these checklist items that indicate the causes of these risks,

The type and scope of risk reducing measures does not depend on whether this is an initial, periodic or special assessment, but only on the causes of the occurring risk. An action plan to reduce the risk to a low level is implemented for all nonconformities identified in the risk assessment checklist presented below.

If the manufacturer fails to provide the laser device with additional protective guards or screens, and the risk assessment shows a necessity for such protective measures, they should be designed by an expert with appropriate expertise in this area. Usually, it is the manufacturer’s responsibility to select protective guards, while the user may have to select protective screens, safety goggles and other protective measures, such as a safety interlocks, light curtains, etc. The selection and design of engineering control measures should be assigned to appropriate specialists or experts. User responsibilities include checking their proper operation (e.g. the interlock) and their correct selection (based on the marking of the screen or safety goggles). However, the use should be able to independently select suitable safety goggles.

1.2      Selection of protective screens

When designing laser screens take into account the safety requirements of the standard PN-EN 12254. Each marking on the screen (from AB1 to AB10) corresponds to the maximum spectral transmission rate and resistance to laser radiation for the corresponding wavelength band and the laser mode of operation as well as the power density or radiation energy that may fall on the screen. Proper marking consists of a sequence of the following characters:

PN-EN 12254 - laser operation mode (D, I, R or M) – AB (appropriate number from 1 to 10) - X (manufacturer’s mark) – wavelength or wavelength range – ZZ (certification mark, if applicable)

Example: PN-EN 12254 I AB8 POL 990-1100 means protection of laser radiation operating in pulse mode, emitting radiation with a range of 990-1100 nm and resistance to laser radiation AB8 (i.e. a beam with an energy density up to 5·105 J/m2 for a manufacturer identified by POL).

For screen design it is important to adopt the maximum reasonably foreseeable exposure, i.e. the maximum power density or radiation energy, which may fall on the screen. It is recommended that power density or energy averaged over the area of ​​a circle with a diameter of not more than 1.13 mm be determined for this purpose.

Keep in mind that the protection provided by the screen depends on several factors, such as: laser power, beam surface, pulse repetition frequency, energy density distribution, exposure duration and the condition of the screen surface.

1.3      An example of the use of protective screens

When using hand-held instruments for laser processing, if it is not possible to completely shield the beam and the device operator may inadvertently direct the beam into empty space, it is important to properly isolate the work station from the environment and use protective screens as well.

Fig. 4.1. View of a workstation for operating a handheld device for laser processing.

1.4      Selection of safety goggles

The selection of goggles depends on whether they are used for normal operation of the device (EN 207) or for adjusting lasers (EN 208).

1.4.1    Selection of protective filters in safety goggles for normal operation of a laser device

The selection of protective filter for safety goggles, like in the case of protective screens depends on the laser operation mode (D, I, R, M) and beam parameters: wavelength, power density and radiation energy. Each marking on goggles (from LB1 to LB10) corresponds to the maximum spectral transmission rate and resistance to laser radiation for the corresponding wavelength band and the laser mode of operation as well as the power density or radiation energy that may fall on the filter. Proper marking consists of a sequence of the following characters:

wavelength or wavelength range - laser operation mode (D, I, R or M) – LB (appropriate number from 1 to 10) - X (manufacturer’s mark)

Example: 10600 D LB3 + IR LB4 means goggles protecting against radiation with a wavelength of 106 000 nm, and the continuous mode of operation and resistance to laser radiation LB3 (i.e. a beam with a power density up to 10⁶ W/m²) and the pulsed laser operation and Q-switched laser with resistance to laser radiation LB4 (i.e. a beam with an energy density up to 10⁶ J/m²).

Examples of the use of safety goggles for protection against laser radiation is shown in Fig. 4.2.

Fig. 4.2. Examples of the use of safety goggles

1.4.2    Selection of protective filters in safety goggles for laser device adjustment

Selection of protective filters in safety goggles for laser device adjustment is different than for normal operation and protective screens. For their selection the maximum power of a continuous operation laser or the maximum energy of pulsed laser shall be important, regardless of the type of pulsed operation (R and M). Each marking on goggles (from RB1 to RB5) corresponds to the maximum spectral transmission rate of a filter and frame and the maximum or radiation which may fall on the goggles. Proper marking consists of a sequence of the following characters:

Maximum laser power – maximum pulse energy – wavelength RB (appropriate number from 1 to 5) – X (manufacturer’s sign) – ZZ (certification mark, if applicable)

Example: 1 W 2x10^-4 J 514 RB3 means goggles protecting against radiation with a wavelength of 514 nm, and the continuous mode of laser operation up to 1W or the maximum pulse energy 2x10^-4 J and resistance to laser radiation RB3 (i.e. a beam with a power density up to 1x10⁶ W/m²) and energy density up to 200 J/m²).