Technical Description
TM888300 Rev. (Al), August 2019
19
3.3.3
Optical Path
The presence of toxic airborne vapors, gases, or aerosols in a monitored area is
detected when the defined substance crosses/enters the optical path between the
radiation source unit and the detector.
Toxic gases/vapors present in the atmosphere cause absorption of the radiation
pulse at specific wavelengths in the optical path between the radiating source and
the detector unit. This causes a change in the signal intensity received by the
detector, which is translated into an output related to the d
etector’s measur
ing
scale.
The system analyzes the defined open path at the spectral bands specific to the
materials being monitored. The Automatic Gain Control (AGC) unit compensates
for environmental disturbances such as fog and rain through a constant
comparison with its dual spectral beam.
3.3.4
Detected Gases
The following toxic gases and vapors are detected by the UV SafEye models
according to their unique spectral absorption in the UV solar blind range:
•
Ammonia
(NH
3
): A flammable and toxic gas that is highly irritant, colorless,
and with a pungent odor. The lower limit of human perception is 17ppm.
Ammonia
’s
TLV-TWA is 25ppm.
The early detection of NH
3
at concentrations of up to 25ppm is essential in
order to prevent its toxic effects, such as respiratory tract paralysis. In the UV
band, NH
3
gas has a typically strong absorption in the solar blind range of
189
–
210nm that enables its fast and reliable detection at low concentrations.
•
Hydrogen Sulfide
(H
2
S): A flammable, poisonous gas with a characteristic
smell of rotten eggs. It is perceptible in air at concentrations of 0.001
–
0.1ppm, with a sweetish taste, and a TLV-TWA of 10ppm.
H
2
S is heavier than air and very dangerous to humans, causing collapse,
coma, or death from respiratory failure within a few seconds of inhalation.
Early detection of H
2
S at concentrations of up to 10ppm is essential to
prevent its toxic influence.
In the UV band, H
2
S has a characteristically strong absorption in the solar
blind range of 189
–
270nm, which enables its fast and reliable detection at low
concentrations.
•
Aromatic Hydrocarbons
: Benzene, toluene, xylene, styrene, etc., have the
unique “conjugated double bonding” chemical configuration responsible for
their spectral absorption in the UV band. These substances, which are usually
in the liquid phase, are volatile, and their vapors are highly explosive and
toxic. Some of them have narcotic effects and/or are considered carcinogens.
Odor is perceptible in the air at 12ppm. The TLV-TWA is 10ppm.
In the UV band, the aromatic compounds have a typically strong absorption in
ranges of 200
–
230nm and 250
–
270nm, which enables fast and reliable
detection at low concentrations.