SAF13-P10
20 February 2013
Subject: Laser pen safety
Origin: Health and Safety Manager, Catherine Moore
University Laser Safety Advisor, Professor John Tyrer
Purpose of the report
To advise the Committee of a recent incident involving the misuse of a laser pen and make recommendations to reduce future risk from unintentional or deliberate misuse of such devices.
Incident report:
A member of the design school staff reported to Security that he had been targeted by a person in Towers deliberately shining a laser into his face as he walked to his car in a bay adjacent to the Towers building. The laser was confiscated by Security staff and Professor
Tyrer, the University’s Laser Safety Advisor, was asked to comment on the power of the laser. Professor Tyrer established that the pen, which had been purchased from eBay, was
45 times more powerful than those legally available in the UK and 9 times more powerful than the label had suggested. Lasers are classified from into 7 classes based on power, wavelength and beam divergence. This laser should be classified as 3B – the second highest rating.
Professor Tyrer commented that given the power of the laser and the quality of the beam produced, the expectation is that permanent injury would have been caused by a direct strike on the back of the eye. Professor Tyrer made contact with the person who had reported the incident and established that he had indeed received the beam directly into his eye, but by a unique stroke of good fortune the weather had been misty on the night in question. The mist had disrupted the beam, scattering some light and reducing its impact on the light sensitive cells in the retina. Additional inadvertent protection was afforded by the fact that the laser was quite dirty. Professor Tyrer carried out further tests on the beam to ensure that the Duty of Care owed to the victim to ensure that he did not have latent eye damage has been discharged and he was able to prove by testing the device using an eyeball simulator that the energy received by the eye was less than that normally produced by a laser of such power and was below the level at which an injury could have occurred. The need for a further assessment by a specialist eye clinic, as would normally be required, was thankfully avoided.
It has been alleged that other incidents occurred last year with staff in offices on the top floor of the design school being targeted through their windows.
Outcome
A student from Towers was spoken to by his Warden and fined £20.

Comment
Laser pointers bought over the internet can be significantly more powerful than the classification permitted by UK regulations. The risk is not widely recognised and if used incorrectly, there is a possibility of permanent injury. The Health Protection Agency provides information about laser pens pointers on its website: http://www.hpa.org.uk/web/HPAweb&HPAwebStandard/HPAweb_C/1195733794576 .
The reckless use of laser pointers has been treated as a criminal offence with particular concern over lasers directed at motorists, aircraft and Police officers. It is also likely that had a permanent injury resulted from this incident the matter would have been reported to the
Police to consider appropriate charges.
Given the potential for accidental injury and deliberate misuse, staff and students should be given information about using laser pointers/pens on campus – see
appendix 1 for a suggested poster design. This information should be publicised
through Schools, brought to the attention of Hall Wardens and shared with the LSU. If this information is made widely available then the deliberate misuse of laser pens should be considered as a major offence under the University’s Ordinances – see recommended policy.
Recommended Policy
Class 1 and Class 2 laser pens and pointers may be used in teaching and demonstrations without prior registration; the only restriction in use is that the beam must not be directed towards anyone. The advice of the University Laser Safety Advisor must be sought before the purchase of pointers or devices with any other classification. If the need for such a device is approved the device must be registered with the University’s Health and Safety
Office.
Devices labelled as Class 1 or 2 must only be sourced from UK based suppliers. Devices brought over the internet have been shown to be potentially unsafe and may exceed the expected power rating resulting in permanent eye injuries if shone directly into the eyes.
Misuse of laser pointers/pens
“Recreational” use of laser pens and pointers is strictly prohibited. Misuse of a laser pointer in such a manner that it could cause harm to anyone on or in the vicinity of campus shall be considered as gross miscon duct and the appropriate penalty as laid down in the University’s ordinances shall be applied.
Appendix 2
Report by Professor Tyrer of the tests carried out on the confiscated laser.

Appendix 1
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Appendix 2
Measurement of the laser pointer
Abstract
The purpose of this report is to examine the laser beam from the laser pointer and determine the structure of the beam at a distance similar to that in the incident (90m). Once we know the structure it is possible to identify the hazard potential of the beam and from that work out the beam density at the most hazardous region. This beam density will then be compared with levels laid down in the relevant
Control of Artificial Optical Radiation at Work Regulations 2010.
Introduction and description of method used
A laser beam in the eye can be considered as a point source, which is traditionally defined as;
A source whose angular extent is so small that it cannot be measured with existing equipment, eg a star
An extended so urce, ie a beam which doesn’t appear to be a point source is defined as;
A source whose angular size exceeds the resolution of the instrument being used to observe it. Extended sources, such as many galaxies and nebulae, can be resolved by telescopes, whereas most stars cannot and are therefore are classified as a point source.
Retinal spot size effects are related to the differential effects of conduction of heat away from the image which are a function of both exposure time and image size. For long exposures, the large and small image size damage thresholds are different because of thermal conduction. By thermal conduction, in this context it is meant the cooling of laser heated tissue by contact with surrounding tissue and by circulation of the blood.
Significant is the fact that in this case the resulting retinal irradiance produced while viewing can be shown to be independent of the distance between the source and viewer. The best way I have found for practically determining this is to use an eyeball simulation rig schematically outlined below. Why is this important? It modifies the actual Maximum Exposure Value with a simple multiplication of the relevant value from the table in BSEN 60825 which is used as the basis for the Regs. We can increase the exposure value by the ratio of the target beam image size divided by a high quality point source image size.
Diagram of eye simulator

6 pixels wide
Image of a high quality scientific laser
12 pixels wide
Actual image from eye ball simulator of the student laser pointer
Analysis of measured data
The circled part is the main beam of the pointer; the additional bright components are caused by dirt on the laser output, presumably from the hair/lint from inside the owners pocket diffracting the beam.
A diffraction limited laser ie the best quality and smallest focussing laser would produce a beam on the retina of 6 pixels as shown above. Therefore, as stated earlier, we can modify the threshold limit by the ratio of the actual laser compared to the point source (12/6 = 2), we are able to increase the
Maximum Exposure Level to 2mW from 1mW.
At 90m distance the main beam diameter was just over 40mm in diameter, because the occurrence happened at night we can assume the iris of the victim’s eye was dilated, so a 7mm aperture will be considered appropriate. If we assume the 43mW to be spread throughout the 40mm diameter beam then the beam density is 0.043/(πx0.020
2 ) = 34.2 W/m 2 .
The 1mW limit we modified to 2mW is a beam density of 2 x 25.4 W/m 2 i.e. 50.8 W/m 2 . So in this case using the modified threshold limit the laser pointer could be considered to be just inside that level. If the student had been at a distance of less than 74m this threshold would have been exceeded. I doubt this level of awareness would be known to the student. Fortunately the mist which was prevalent during the evening of the incident

added a reasonable attenuation to the beam which brought it well below any limits. In discussion with the member of staff who was targeted he reported no after image of the beam or other impairments.
So the mist attenuation was significant.
Conclusion
The measurements indicate that without introducing a beam intensity modifier i.e. the laser is a simple point source, which is a likely case for the police position to take, and then this laser was above national threshold values. We can make a reasonable argument to modify this threshold value to reduce it, based on the actual laser beam configuration. The mist conditions on the night mitigated the situation such that the beam intensity was below any threshold. I doubt any of this information was available to the student and he simply targeted the member of staff with the beam deliberately aimed at his face. If the evening conditions had been clear we would be in a more serious situation with a member of staff likely to consider his vision to possibly be impaired. He certainly would have sustained significant dazzle effects which would have lasted for a significant time. If the member of staff had then driven home in that state again his awareness and judgement would have been impaired. If this had been a medical procedure he would not have been allowed to drive for several hours.
So the question to resolve is did the student have intent to cause injury, he certainly had intent to illuminate the victims eyes. He may not have realised this laser pointer could be considered a weapon, but the situation is that this is a highly powerful laser which could be used as a weapon.
John Tyrer
University Laser Safety Adviser
19 th January 2013