Lasers to understand these hazards and implement effective

Lasers are powerful tools
which not only aid in scientific research but also everyday living. Without the
right knowledge of how to operate lasers safely, they can cause serious injury.
It is therefore very important to lay down strict protocol and establish what
different classes of lasers are considered safe. It is important to categorise
lasers into group which represent  hazards
a specific group of lasers can cause. This happens in the form of standards
such as the IEC 60825-1. Lasers can operate in safety and not cause anyone any
harm if the right precautions are taken. LiDAR is an innovative piece of
technology which allows us to use light to trace out a surrounding environment,
with major military, surveying, robotic applications, and of course LiDAR is
extremely useful in the autonomous car industry. Since LiDAR can map out the
environment, it can aid the autonomous car in navigation to get from one point
to another. Although LiDAR is an ideal piece of technology for the autonomous
car, it is unwise to forget about the safety concerns with use of lasers used
on board a car. Autonomous cars are paving the way for future transport, so it
is beneficial to everyone to ensure that these cars are safe for the public

Lasers are hazardous. There
are two types of hazards associated with the use of lasers, beam and non-beam. It
is important to understand these hazards and implement effective precautions
while working with lasers.
Beam hazards can be resultant from direct exposure to the beam or from
reflected exposure. The main concerns for laser injury are to the skin and
eyes. Damage from lasers on biological tissue can be caused from either
thermal, acoustical or photochemical processes.
Thermal effects are the most likely danger for lasers. This is the processes of
temperature rise on the surface in which the laser is exposed to. This is due
to absorption of the laser energy. The scale of the damage is dependent on
several factors including wavelength of the laser, length of exposure, energy
of the beam, and the area of the tissue exposed to the light. Heating and
burning of the retina is a major concern when it comes to this type of hazard.
Acoustical effects are caused by the mechanical shockwave that propagates
itself through human tissue, which results in damage to the tissue. This
happens when localized vaporization of tissue occurs due to the laser.
A laser’s beam may also cause photochemical effects, which occur when photons
of light interact with tissue cells. This may change the cells chemistry which
causes cell damage or cell malfunction. Photochemical effects depend heavily on
the wavelength of the laser. Both the skin and eye can be affected from
wavelengths in the ultraviolet range (200nm-280nm) to the infrared C range (3.0
?m – 1000 ?m). Some of the biological effects caused by a laser beam include,
but are not limited to; photo keratitis, skin cancer, accelerated skin aging,
sunburn, cataract and retinal burn, corneal burns, and skin burn.
In relation to the types of beams which can cause these hazards, direct
exposure is not the only concern. In certain cases, exposure to reflected beams
may be just as damaging as the direct beam. Intrabeam exposure relates to the
direct exposure of skin or the eye to all parts of the beam. The skin tissue is
exposed to the full irradiance.
Specular reflections can nearly be as harmful as direct exposure. Curved
surfaces spread the beam so that the exposed eye or skin does not receive the
full impact of the beam. A diffuse surface is a surface in which the beam will
be reflected in many directions. Non-flat surfaces such as jewellery may cause
diffuse reflections of the laser beam. These reflected beams do not carry full
irradiance, but are nonetheless still a hazard especially for high powered
lasers.
Although beams present dangerous hazards, they are not the only component of
the laser.
Non-beam hazards also need to be accounted for, as in some cases they can be
more dangerous than beam hazards.
Oftentimes laser systems require large power supplies. This leads to the
potential of electric shocks. Shocks usually occur when the laser equipment and
power supplies are not cased properly, grounded properly, or have a large
capacitor bank that was not discharged. This is the most common injury
sustained while working with lasers. Protective measures should be used while
working with laser to prevent electrical shocks, such as ensuring that all
electric wires are covered, use of the “buddy system”, and ensuring that all
workers have the proper training.
Since lasers use equipment such as; high-pressured arc lamps, filament lamps,
and capacitor banks, there may be concern for an explosive hazard. To ensure no
injury or damage to other components of the laser occurs, it is important to
enclose any type of equipment with the potential to explode in housing that
could, if need be, withstand the high pressures of any exploding components.
Class 3B and class 4 lasers are powerful and may lead to laser generated air
contaminants, when there is an interaction between the beam and the target
material, there may be contaminants released into the surrounding air, such as
metallic fumes, dust, chemical fumes, and aerosols. To protect against these, certain
protocols must be in place whilst working with lasers within these categories.
Controls are set up to prevent any damage or injury to the operators. Exhaust
ventilation, respiratory protection, and isolation of the process are controls
that can be used to prevent any damage that may occur by laser generated air
contaminates.
Other hazards include laser dyes and solvents, fire hazards, noise hazards, and
X-ray radiation hazards

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Infrared radiation is not
overly dangerous in most cases. IR light only has enough energy to get
molecules moving, not enough to break molecules apart which would cause damage
in the skin or eye. IR radiation may cause a person to feel warmer and, in some
circumstances, it can be hazardous. In most cases, it is only extreme cases of
IR exposure that result in injury, for example workers who work with molten
steel or glass for many years may have issues with cataracts. The main issue
with IR lasers is they do not prompt a blink reflex as they do not emit visible
light.4
Infrared light can be subdivided into 3 sections; infrared A(780nm-1400nm),
infrared B(1.4 ?m -3.0 ?m), infrared C(3.0 ?m -1000 ?m).
Infrared A lasers can lead to burns when skin is exposed to the beam. While
prolonged exposure of infrared A light to the eye can cause photic retinopathy,
which is damaging to the retina. This damage can lead to vision loss, though
recovery periods last about 2 months.
Infrared B lasers may lead to corneal burns, aqueous flare, and cataracts.
Infrared C lasers cause corneal burns when exposed to the eye.

As lasers are hazardous
and can cause severe injuries in certain circumstances, it is important to
implement standards to ensure the safety of any operators using laser systems.
For this purpose, laser safety standards are used to set out rules and
regulations to identify different classes of lasers and to regulate the amount
of protocols that need to be used when dealing with the lasers of certain
classes. The role of standards is to establish the maximum permissible exposure
for each class of laser. The MPE is defined as the level of laser radiation a
person can be exposed to without hazardous effect or any biological change to
the eyes or skin. The nominal hazard zone can also be defined as the space
within which the level of direct, scattered, or reflected radiation exceeds the
MPE.

Most international
standards divide lasers into four major categories called the laser hazard
classifications. The European norms are the standards adopted by the
international electrotechnical commission. This is used for countries in the
European community. The USA has standards based on the US FDA code of federal
regulation, and the American national standard institute (ANSI).
For Europe standards, there are four different classes each with subsections.
Class 1 lasers are safe under all operating conditions. This may include high
power lasers that prevent exposure to radiation due to an enclosure that shuts
off the laser once opened.
Class 1M is safe to view with the naked eye but may be hazardous when viewed
with an optical instrument.
Class 2 lasers are visible. They are safe for viewing under all operation
conditions. However, if the operator intentionally stares into the beam for
longer than 0.25s, then there is a hazard risk. This must be done by overcoming
their natural aversion response to very bright light. Class 2M lasers are
visible lasers but may be hazardous when viewed accidently.
Class 3R lasers are considered low risk but they are potentially hazardous.
Continuous wave lasers emitting between 1 and 5 mW are normally classed as 3R.
Class 3B lasers are very dangerous and pose a serious risk for a hazard. For a
continuous wave laser, the maximum must not exceed 500mW. Viewing a diffuse
reflection is safe. Protective eyewear is required. All Class 3B lasers must be
equipped with a key switch and a safety interlock.
Class 4 lasers are very dangerous and viewings of diffuse light is also
considered dangerous. There is a possibility of a fire hazard as these lasers
can ignite combustible material. They must be equipped with a key switch and
safety interlock.
From these different classes, standards can be implemented. All international
standards take these different categories into account. The classes are based
on graded risk, they are based on the ability of the laser to cause biological
damage to the skin or eye. The classification of a laser is based on the
concept of accessible emission limits. This is determined as the product of the
maximum permissible exposure limit and the area of the limiting aperture.

LiDAR stands for light
detection and ranging. The way LiDAR works is straight forward; light is
emitted from a source, hits an object and is reflected to where it is detected.
A LiDAR instrument emits rapid pulses of laser light at a certain surface, up
to 150,000 pulses per second. The LiDAR system then detects the reflected beam
and calculates the amount of time it took for the laser light to return. As the
speed of light is known, LiDAR can accurately calculate the distance the light
travelled and the time it took to return so a LiDAR system has the capabilities
to sketch out its entire surrounding which is obviously a requirement in the
autonomous car industry.
There are two types of LiDAR detection methods, incoherent detection and
coherent detection. Coherent detection is best for phase sensitive
measurements. It uses heterodyne detection, meaning they can operate at much
lower power but they have more expensive transceiver requirements. For each
type of LiDAR systems, there are two main pulse models, micro pulse and
high-energy systems. Micro pulses require high computation power. However, with
advancements in processors, it is now achievable and affordable. Micro pulses
use low powered lasers and as a result are considered “eye safe”. This means
that micro pulses can be used with fewer safety precautions and thus are very
suited to the role of the autonomous car.
Almost every LiDAR system uses four main components. The first component of
LiDAR are the lasers. Lasers are categorised by their respective wavelength.
600nm-1000nm are typically used for non-scientific purposes. However, lasers
with this range of wavelengths tend to be focused and absorb by the eye, thus
rendering them not “eye safe”. To prevent this, lasers with wavelength 1550nm
are used as an alternative as they are not focused or absorbed by the eye, making
them “eye safe” even at much higher power levels.
The second set of components of LiDAR systems are scanners and optics. The
speed at which the images are developed is affected by the speed at which the
signal can be scanned into the system. The type of optics used determines the
range and resolution that can be detected by LiDAR  
The third set of components of a LiDAR system are photodetectors and receiver
electronics. The photodetector is used to read the return signal. Currently
there are two main type of photodetectors, solid state detectors and
photomultipliers.
The fourth set of components of LiDAR systems are the navigation and
positioning systems. It is useful to retain the position and orientation of the
sensor for reusable data especially for the use of the autonomous car. GPS and
an inertia measurement unit record precisely the position and orientation of
the LiDAR system at a specific location. These systems are safe with no risk of
hazards.

 
The potential problem with the use of LiDAR for autonomous cars is that there
are multiple lasers on LiDAR systems and some day, if there are as many
autonomous cars as there are manual cars on today’s roads, there may be a
potential risk to pedestrians who may pass hundreds of cars in a few minutes.
Laser safety standards are assembled based on the MPE (maximum permissible
exposure) and this is tested with the idea of worst case scenario in mind. It
is measured for a given wavelength with a given exposure time. However, this does
not take into account repeated or multiple exposures as there would be in a
world full of LiDAR based autonomous cars. It is not only important to test
lasers at a given exposure time but also with repeated exposure. There is also
a concern with the use of LiDAR on autonomous cars as LiDAR only uses infrared
lasers, meaning that the exposure time might not be limited to 0.25 seconds in
accordance with the human blink reflex which is only reactive with visible
light. There might be a possibility that the exposure time will be considerably
longer than this 0.25 second exposure time limit in a real-world situation. If
the human eye was exposed to infrared radiation from a LiDAR system, the person
would not notice, and the person’s eye may receive more than what would be
considered “safe” in accordance with the MPE. So, in conclusion, with multiple
LiDAR system operating in public, there is a potential risk of over exposure of
infrared radiation. The laser safety standards may need to be reconsidered as
they are geared more towards lab safety and use in controlled environments and
not towards a real-world environment where safety equipment is not so prominent.

The international laser
product standard IEC 60825-1 categorises lasers into their respective
categories based on their danger factor and risk of causing damage to the skin
and eyes. In 2014 the international electrotechnical commission made changes to
the IEC 60825-1 which, as a result, will change the future classification of
many laser products. Prior to 2014, many laser products were limited in their
capabilities due to the regulations. For example, in Europe consumers are limited
to class 1 and class 2 laser products, while the use of class 3R and 3B lasers
require a laser safety officer. The IEC 60825-1 brought in new changes as the
previous decade resulted in better understanding of physics and biology of
lasers leading to more knowledge of ocular hazards and laser safety. As a
result, some laser classes were not as strict allowing new laser products onto
the market. Laser classes such as Class 1 and class 2 were given more freedom,
which would be used for LiDAR system on cars. 

LiDAR is almost an ideal
tool to be used to optimise the autonomous car. It takes advantage of the use
of lasers and their potential. However lasers can cause harm to the human body,
mainly the skin and eyes, so it is important to analyse how harmful the lasers
used in LiDAR are to human. With the aid of standards such as IEC 60825-1,
there needs to be laws which limit the power of these lasers based on the risk
factors of causing harm.

4https://healthfully.com/dangers-infrared-8239296.html Accessed 18 Jan.
2018

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