Risk analysis - Mission: Laser glare
Worldwide the number of laser incidents grow rapidly.
1In the US i.e., the numbers doubled from 2009 to 2010 to a total of more than 2.800 incidents.
These attacks are usually regarded as dangerous intrusion and require the use of the police, especially police helicopters, to identify the perpetrators.
While on mission, investigating police-helicopters had been targeted by laser-offenders several times. The crews suffered from health impairments, such as teary eyes, disorientation and short time visual impairments, due to flash-blindness.
Because, depending on power and exposure time, lasers can harm eyes permanently, it is necessary to analyse the risks and to look for measurements to minimize these risks.
While doing this, one has to consider the rapid developing of lasers, while legislation, trade restrictions and laser-classification are lagging behind.
2Especially mentioned here is the so called the blink reflex, which was used to specify the older laser-grades. Newer research showed, that only a minority of people showed the „blink reflex“, when blinded by a laser and should no longer been taken into account.
The following impairments and injuries could be caused by lasers.
• Pilots / Crew members could be startled by the sudden, often flashing, laser light – until it can be identified as a laser attack instead of an operational aircraft failure.
• distraction / annoyance from the normal cockpit tasks
• blinding with impairment of the visual perception of instruments and obstacles within the
flight path (i.e. transmission tower)
• 3flash-blindness, from a few seconds up to minutes. At night, due to the wider opend pupils,
flash-blindness tends to occur much more easy and lasts longer. Often combined with
disorientation and the feel of sickness. Continued flight might not be possible for the pilot.
• permanent eye-damage due to burns inside the eye: 4Already relative small power (few
milliwatt) of a wavelength, which is transparent to the eye (around 350 to 1200 nm [green Laser around 523 nm]) can lead to blind spots, cause the parallel laser-beam will be focused by the lens of the eye. Damages will often not be recognized by the person straight away, but will be found by surgery.
(Further dangers, which occur on other wavelength, are not listed here.)
Further factors are:
• the laser-power – more power – more effect / damage
• the divergence of the laser (widening) – the less the divergenz, the higher the risk.
• the wavelength of the lasers (infra-red- ultraviolet-parts of a lasers can ́t be recognized by a
pilot, but can also harm).
• the colour of the lasers (yellow and green laser are recognized brighter than red or blue laser
1 USA – Departement of Transportation, 19.01.2011 - Siehe LaserUSA2010.pdf
2 Aus Wikipedia: Die Bundesanstalt für Arbeitsschutz und Arbeitsmedizin stellt fest, dass unter typischen Laserklasse-2-Bedingungen nur 17% der Probanden mit einem Lidschlussreflex reagierten und somit dieser Reflex als einziger Schutzmechanismus bei Expositionen durch Laserstrahlung dieser Klasse keineswegs ausreicht.[1] In der BGI
(Berufsgenossenschaftliche Information) 832 "Betrieb von Lasereinrichtungen" vom April 2003 heißt es: "Von dem Vorhandensein des Lidschlussreflexes zum Schutz der Augen darf in der Regel nicht ausgegangen werden. Daher sollte man, falls Laserstrahlung der Klasse 2 ins Auge trifft, bewusst die Augen schließen oder sich sofort abwenden". Die Lidschlussreflexzeit ist von zahlreichen Einflüssen abhängig, u. a. von der Größe des Lichtfleckes auf der Netzhaut. Die Unfallverhütungsvorschrift (UVV) "Laserstrahlung" BGV B 2 geht hingegen noch von einem Lidschlussreflex nach 250ms aus und steht damit neuen Erkenntnissen aus der Forschung entgegen.
3
Flash blindness - Wikipedia, the free encyclopedia 4
Laser ? Wikipedia

with the same power)
• pulsating or constant beam - with a pulsating laser more energy will be transmitted in a short
time and increases the risk of eye-damage
• movement and speed of the aircraft – has influences on targeting the aircraft
• the distance to the aircraft
• the angle in relation to the cockpit
• the flight-phase (start/landing/cruise)
• the pilot-estimation / - reaction
• optical parts, like i.e. binoculars and or glasses, which will focus the laser additional
Laser-grades, 5Classified according to EN 60825-1
Due to threats to the humans, lasers are listed in grades. It ́s done by the manufacturer. (The old grades according to DIN VDE 0837 are not longer valid for new lasers)
Grade Power Wavelength
Description
The laser isn ́t harmful or the laser is in a closed case/box
The laser isn ́t harmful, if no optical lenses, like magnifying glasses, are used
The laser-beam is only in the visible lightarea (400 nm bis 700 nm). It isn ́t harmful, if the exposure-time for the eye is under 0,25 s.
As grade 2, as long, as no optical lenses are used to view the beam
1 1M
2 2M
< 25 μW < 25 μW
≤ 1mW ≤ 1 mW
400... 700 nm
302,5... 4000 nm
400... 700 nm
400... 700 nm
3R 1 bis 5 302,5 nm... The laser is dangerous for the eye mW 106 nm
3B
5 bis 302,5... The laser ist dangerous for the eye and in some cases also for the 500 mW 106 nm skin. Stray-light isn ́t dangerous in most cases.
> 500mW 302,5... The laser-power is very dangerous for the eye and dangerous for 106 nm the skin. Even stray-light is dangerous for the eye and for the skin.
For the blinding of aircraft the offenders normally use lasers grade 3R and 3B. You can easily buy them in the worlds wide web.
To have some facts and not only theoretical views, a green laser was ordered in China.
For € 17.74 and € 1.54 postage/package a „30mW super-bright green Laser-Pointer with Li- Ionen-Akku (tra416)“ was bought.
After four weeks it arrived.
It had to be collected at customs – but it was no problem to get it!
First trials showed, that the power of the beam dropped after a short time (visible beam reduced in brightness). It was thought, that it was due to the akku, so a bigger power-source was installed to have the full power through all the tests.
The tests showed, that it was powerful enough to burst a balloon after a few seconds, which was placed about 50 cm away from the laser.
At a distance of about 60 meters the laser-beam was widened to an area of about 6 x 9 cm. 5
Laser ? Wikipedia
4

Calculating with a straight factor that would mean, you would have a light-spot from around 1 meter at 1000 meters distance and a 2 meter spot at 2000 meters.
Additional findings were, that the laser didn ́t fit the safety standards. It wasn ́t label d at all and it strayed infra-red light.
To prevent risk or damage while doing a set of tests, the appropriate authorities were informed. (tower, ground-handling, airport-safety, fire-brigade, police and ATC.
After closing of the airport, a BK117 was parked on a taxiway in vicinity of the runway, facing north.
A small video-camera was set up and the helicopter lasered from the runway from different distances (measured by GPS)
Later a video-camera was set up on the pilots seat, (eye high) and further tests done.
In the video it can be seen, that the laser is coming in shaky, cause you can ́t hold the laser rock steady. So it ́s producing a lot of flashes instead of a steady blinding.
NM km Hitting diameter around stillshots of the video
0,32
0,59
100 cm
0,46
0,85
150 cm
0,82
1,52
200 cm

1
1,85
240 cm
1,18
2,19
300 cm
Calculations were made for power on the eye on an area of 0,3 cm and 0,5 cm and because you can buy stronger laser in the web and you don ́t know, what laser is used, also for lasers with 100 mW, 200 mW and 500 mW.
Calculations were made by pretending, that all lasers would widen up their beam the same way the tested laser-beam did. Videos in the internet show, that that isn ́t always to be expected, cause there are „better“ lasers around.
That would mean, even more power on the eye.
There were no calculations for pulsed lasers.
From inside the cockpit

Entfernung m Durchmesser cm 0 0,3 607 100 10 500 50
Kreisfläche cm r2*π 0,4712289 10,995341 15,70763 78,53815 157,0763 314,1526
Kreisfläche cm r2*π 0,4712289 10,995341 15,70763 78,53815 157,0763 314,1526
Kreisfläche cm r2*π 0,4712289 10,995341 15,70763 78,53815 157,0763 314,1526
Kreisfläche cm r2*π 0,4712289 10,995341 15,70763 78,53815 157,0763 314,1526
Leistung mW bei 0,3cm Ø
10,0000
0,4286 0,3000 0,0600 0,0300 0,0150
Leistung mW bei 0,3cm Ø
30,0000
1,2857 0,9000 0,1800 0,0900 0,0450
Leistung mW bei 0,3cm Ø
100,0000
4,2857 3,0000 0,6000 0,3000 0,1500
Leistung mW bei 0,3cm Ø
500,0000
21,4286 15,0000 3,0000 1,5000 0,7500
Leistung mW bei 0,5cm Ø
10,0000
0,4547 0,3183 0,0637 0,0318 0,0159
Leistung mW bei 0,5cm Ø
30,0000
1,3642 0,9549 0,1910 0,0955 0,0477
Leistung mW bei 0,5cm Ø
100,0000
4,5474 3,1832 0,6366 0,3183 0,1592
Leistung mW bei 0,5cm Ø
500,0000
22,7369 15,9158 3,1832 1,5916 0,7958
1000 2000
Entfernung m 0 60 100 500 1000 2000
Entfernung m 0 60 100 500 1000 2000
Entfernung m 0 60 100 500 1000 2000
100 200
Durchmesser cm 0,3 7 10 50 100 200
Durchmesser cm 0,3 7 10 50 100 200
Durchmesser cm 0,3 7 10 50 100 200
Due to an expert report in an court trial, the exposure limit is t=0,25 sec for a wavelength of 532nm and 5 mW power.
Additional wavelength (i.e. infra-red) have to be considered and shorten the time.
Regarding the calculations and findings (flashing hits, widening of the beam) you can assume, that your eyes are more or less safe, if you are at least 1 km away from the attacking laser and you are only hit in a „flashing manner“
Flash-blindness, which may impair a pilot in a way, which may inhibit his possibilities to fly the aircraft are not only possible but even on greater distances – probable.
(From authors experience)
According to Pythagoras (a2+b2=c2), at a height of around ~ 2300 feet – height being equal to distance to the laser on the ground, with normal lasers used and only flashing hits, your eyes are fairly safe.
If you don ́t use laser-protection-goggles, you better fly around 2500 feet or higher, if you expect a laser blinding.
While doing the tests, it was also found, that NVG aren ́t very useful to search for an offender, cause green light isn ́t amplified and it is hard to identify the laser between other city lights.
The laser-beam, which often can be seen with the naked eye, won ́t be seen with the NVG.
Both pictures were made at the same position, on the left you can see the beam, on the right, with NVG, you only see the light-source, not the beam.
If you expect laser blinding, you should be prepared to ensure the safe operation of the aircraft. You could use the autopilot, if fitted, or have the copilot ready (also if fitted ;-))
Switching of all lights may also be an option, to reduce the risk of further laser-hits, but has to be coordinated with ATC – may be in advance.
In this context there are some words necessary regarding NVG.
Even so, due to their design, they won ́t let a laser through and therefore give a certain amount of protection, this protection is only given for a direct hit.
Because pilots need to check the instruments, the NVG aren ́t directly in front of the eye – they are at a certain distance, so that a pilot can look underneath them.
If the pilot isn ́t looking straight through the NVG or is hit from an angle, a laser can hit the eye and permanent damage can occur!
„6With normal scanning movements critical areas of the eye are exposed to possible laser-damage. Throughout protection requires ... mechanical cover or laser-protection-glasses or visors, which cover at least 90°.“
If you get hit by a laser while flying lower than 2500 feet and you can ́t get hold of the laser, to get information about it ́s properties, you should see the doc to check your eyes.
FLY SAFE!
ISO 6161:1981-02
Individueller Augenschutz; Filter und Augenschutz gegen Laserstrahlung
DIN EN 207:1998-12
Persönlicher Augenschutz - Filter und Augenschutzgeräte gegen Laserstrahlung (Laserschutzbrillen); Deutsche Fassung EN 207:1998
DIN EN 208:1998-12
Persönlicher Augenschutz - Augenschutzgeräte für Justierarbeiten an Lasern und Laseraufbauten (Laser-Justierbrillen); Deutsche Fassung EN 208:1998
6 USAARL Report No. 90-3, Laser Protection with Image Intensifier Night Vision Devices, by David J.Walsch 2 ́1990