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Laser Safety Standards

Laser Safety Standards

The Word of Laser Safety Standards - Optical Densities and More

The US laser safety standard ANSI Z136 requires that laser safety eyewear be specified according to optical density (OD) only. The OD is the attenuation of light that passes through an optical filter. The higher the OD value, the higher the attenuation. Optical density is the logarithm (to the base ten) of the reciprocal of the transmittance. For example, an OD of 1 means 10%, an OD of 2 means 1% and an OD of 3 means 0.1% transmittance (and so on). ANSI also allows a Nominal Hazard Zone (NHZ) which is to be determined by the laser safety officer (LSO). Outside of the NHZ, diffuse viewing eyewear is allowed. Most Asian countries refer to ANSI regulations.

In Europe, EN 60825/207/208 require that a second criteria must be taken into consideration - the power or energy density of the laser beam. This is the power or energy per unit beam area, expressed in Watts per square meter or Joules per square meter. A “diffuse viewing” condition is not allowed and laser safety glasses must be chosen to protect against a direct laser exposure. Protection accordinging to optical density alone is not sufficient and the filter and frame of the eyewear must be capable of withstanding a direct hit. The applicable European standards are in fact legal requirements and enforceable. Other legal requirements (e.g. the regulations for industrial safety as well as the medical equipment regulations) refer to them as well. Australia has adopted laser safety regulations that are based upon the European regulations.

EN 207 Full Protection Laser Safety Eyewear

Laser eyewear requires laser damage testing in order to achieve certification in according with EN 207. The safety eyewear - both filter and frame - must withstand (under standardised conditions) a direct hit from the laser for which they have been specified for at least 10 seconds (cw) or 100 pulses (pulsed mode). As a result of a successful test laser, glasses are awarded the CE mark to indicated compliance with the standard. A copy of the test certificate can be requested by any user of the laser safety eyewear.

The protection rating of EN 207 laser safety eyewear does not refer to optical densities (although OD is taken into account in the rating). Instead, eyewear is labelled in a manner that indicates the maximum power or energy density which the eyewear can withstand in the specified wavelength range and for the specified laser operating mode. The protection rating of the eyewear as a whole will be the lower of that for the filter and frame. This is why you may see that the same filter achieves a different protection rating when fitted to two different frames.

For example, consider the rating D 10600 L5. In this, D refers to a continous (cw) laser, 10600 to the wavelength 10600nm (or 10.6µm - the wavelength of a CO2 laser) and L5 means that the eyewear can withstand a 10 second exposure to a power density of 100 MW/m2 (see table below). Optical density is not stated explicitly in the specification, although the OD value will never be less that the power handling rating of the eyewear (the OD would be at least 5 in the example given above). To be clear, in countries which follow the European standard for personal protection, it is not acceptable to select laser glasses according to OD alone.

Table of Protection Levels per EN 207

 

 

Max. Power Density (E, W/m2) & Energy Density (H, J/m2) in Specified Wavelength Range

 

 

180-315nm

 

> 315-1400nm

 

> 1400nm-1000µm

   

For Pulse Duration (seconds)

Scale
Number

T

D
>3
10-4

I, R
10-9 to 3
10-4

M
<10-9

D
>5x10-4

I, R
10-9 to 5
10-4

M
<10-9

D
>0.1

I, R
10-9 to 0.1

M
<10-9

L1

10-1

0.01

3•102

3•1011

 102

 0.05

 1.5•10-3

104 

103

1012

L2

10-2

0.1

 3•103

 3•1012 

 103

 0.5

 1.5•10-2

 105

104

1013

L3

10-3

1

3•104

3•1013

104

5

0.15

106

105

1014

L4

10-4

10

3•105

3•1014

105

50

1.5

107

106

1015

L5

10-5

102

3•106

3•1015

106

5•102

15

108

107

1016

L6

10-6

103

3•107

3•1016

107

5•103

1.5•102

109

108

1017

L7

10-7

104

3•108

3•1017

108

5•104

1.5•103

1010

109

1018

L8

10-8

105

3•109

3•1018

109

5•105

1.5•104

1011

1010

1019

L9

10-9

106

3•1010

3•1019

1010

5•106

1.5•105

1012

1011

1020

L10

10-10

107

3•1011

3•1020

1011

5•107

1.5•106

1013

1012

1021

EN 208 Alignment Protection Laser Safety Eyewear

Alignment filters provide partial blocking of low power, visible wavelength (400-700nm) laser beams. This allows the wearer to safely view the visible beam spot for laser beam alignment. Alignment filters are assigned an R rating in accordance with BS EN 208. The principle of alignment protection filters is that they attenuate the power of the laser such that if the beam were to accidentially hit the filter directly, the only light that would be transmitted would be equivalent to a class 2 exposure, less than 1mW for a continuous wave laser. Class 2 lasers are those low power, visible devices for which the eye's blink reflex affords sufficient protection.

Alignment glasses are not intended for direct viewing of the laser beam, rather for diffuse, indirect viewing (i.e. reflections from a scattering surface). Alignment glasses must also withstand a direct hit from the laser for which they are chosen for at least 10 seconds or 100 pulses under standardised conditions.

Table of Protection Levels per EN 208

Scale Number

Maximum Power (Watts)
CW & pulsed lasers (pulse duration > 2•10-4 s)

Maximum Energy (Joules)
Pulsed lasers (pulse duration >10-9 to 10-4 s)

R1

0.01W

2•10-6

R2

0.1W

2•10-5

R3

1W

2•10-4

R4

10W

2•10-3

R5

100W

2•10-2

EN 60825 Protection Based Upon Optical Density

EN 60825 requires that laser safety eyewear provide sufficient optical density (OD) to reduce the power of a given laser to equal or less than the Maximum Permissible Exposure (MPE) levels. It permits the selection of protective eyewear according to optical densities in extreme situations, but recommends the application of EN 207 with a third party laser damage test.

It should be noted that neither EN 207 nor EN 60825 allows for a nominal hazard zone. This means that the protection required must be determined based upon the worst case scenario - which is a direct hit by the laser beam. If there is no filter available that fulfils the necessary requirements according to EN 207, LASERVISION will only then offer eyewear according to EN 60825. A filter will be offered that comes as close as possible to the requirements of EN 207. This means that the optical density is always sufficient, but that the stability time of 10 seconds or 100 pulses cannot be guaranteed. In cases such as this, we recommend that the laser safety officer contact the employer’s liability insurer to discuss this issue.

Labelling of Eyewear - CE & DIN GS

The CE mark serves as a demonstration of conformity to applicable standards. A manufacturer or importer must mark their products with the CE logo to certify that the product meets the relevant regulations. In the case of laser safety eyewear, this is the European Directive on Personal Protective Equipment, 89/686/EC. However, the CE mark is only proof of a single, type approval test This must be conducted by an independent testing institiute (a Notified Body). The CE mark does not infer any onging guarantee that the product and production process maintain their compliance with the regulations.

The additional GS (Gepruefte Sicherheit = tested safety) mark goes beyond the minimum requirements necessary for the CE mark. In a similar way to CE marking, the GS mark is applied to a product according to German law when a notified body (e.g. DIN CERTCO) carries out a prototype test to confirm that the product meets the required minimum safety requirement. In addition, GS marking requires that a certified quality management system is in place at the manufacturer’s plant, which serves to verify the manufacturer’s test equipment and in-house quality assurance. The GS mark is only allocated when products are re-tested at regular intervals. With the CE mark alone, the quality of the product or the production process is not guaranteed, nor are there any checks in place to prevent a manufacturer pre-selecting the sample they submit for the type approval tests required for the CE mark.

The LASERVISION Philosphy - Beyond CE Marking

The EC Directive 89/686/EEC has been in force for over 10 years now. Most people will now be familiar with the concept that eye protectors in general, and laser safety eyewear in particular, can only be sold within the EU if the product carries the CE mark. The Directive classifies three categories of protective equipment which relate to the exposure to danger, with Category 1 the lowest and Category III the highest risk. Eye protectors – with very few exceptions – fall into Category II of the Directive. Laser safety eyewear is not amongst these exceptions and has also been classified into Category II. In our opinion, the application of Category II requirements for laser eyewear leaves some very important gaps in safety and quality. Category II CE testing requires one single type approval test only. Neutral and objective sampling is not mandatory, which means the specimen can be selected by the manufacturer and  can be pre-tested. Thus, independent quality assurance is not achieved.

LASERVISION’s first priority has always been offering products of the higest safety and quality. Therefore LASERVISION has voluntarily committed itself to follow the more stringent requirements of DIN GS which provides for a higher level of assurance. To obtain the GS mark, the product must be subjected to CE type approval testing, as well as re-tests at regular intervals, neutral sampling at the manufacturer’s plant, checking of the manufacturer’s test equipment and an in-house quality management system.

Additional Requirements

According to EN 207/208, optical density cannot be used as the sole criteria for determining the suitability of laser safety eyewear. Account must also be taken of the stability of the OD throughout a direct laser expsoure to the full laser beam. The frame and filter of the eyewear must withstand the laser beam for which they have been selected for 10 seconds (for a continuous mode laser) or 100 pulses (pulsed mode) under standardised conditions. In addition, the filters and frame of the eyewear must satisfy the following requirements:

  • No Q-switch effect (EN 208/ EN 208)
  • Low dioptic effects (EN 167)
  • Quality of materials and surface (EN 167)
  • Stray light < 0.5cd/m2.lx (EN 207/EN 208)
  • No secondary radiation (EN207 / EN 208)
  • UV resistance (EN 207/EN 208, EN 168)
  • Thermal resistance (EN 207/EN 208, EN 168)
  • Field of vision > 40° (EN 208/ EN 208)
  • Shatter resistance (EN 166)

Nomenclature - EN 207 Full Protection Eyewear

EN 207 Eyewear Label

Nomenclature - EN 208 Alignment Protection Eyewear

EN 208 Eyewear Label 

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