What gases can be detected with PRISM
Gas Detection equipment?
How far apart should the
sensors be ?
What should the
mounting height of the sensors
be?
Are there other
considerations for locating
sensors?
What is the breathing
zone?
Are some gases heavier
or lighter than others?
What are the densities of
gases?
Are there many types of
sensors used for gas detection?
Why are different kinds
of sensors used?
What are the advantages and
disadvantages of Solid State (MOS)
sensors?
What are the advantages
and disadvantages of Electrochemical
sensors?
What are the advantages
and disadvantages of Catalytic
sensors?
What are the advantages
and disadvantages of Infrared
sensors?
What are the advantages
and disadvantages of Galvanic
sensors?
Does gas detection
equipment need maintenance and
calibration?
What is
calibration?
Can gas detection
equipment produce energy savings?
What is
cross-sensitivity?
What are combustible
gases?
Where does CO come
from?
I get confused between
CO and CO2 — what’s the
difference?
Where do NO and NO2 come
from?
What is
Nox?
What are Nitrogen
Oxides?
Where does CO2 come
from?
Where does H2S come
from?
What does % LEL
mean?
What does ppm
mean?
What does % volume
mean?
What are the most common
commercial and institutional
applications
?
What gases are present in parking
garages?
What gases are present
in swimming pools?
What gases are present
in chiller rooms?
What gases are present
in repair garages?
What gases are present
in warehouses?
What gases are present
in repair garages?
If you don't see your question !
How far apart should the sensors
be?
Refer - Technical Note
TN1002
SITING OF FLAMMABLE GAS SENSORS
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What should the mounting height of the
sensors be?
This depends on the density of the gas relative to air. Heavier than air gases like LPG
should be detected 6 inches from the floor, for lighter than air gases like Methane,
sensors should be placed on or near the ceiling, and gases which have a
density close to that of air should have sensors installed in the
‘breathing zone’ 4 to 6 feet from the floor. Consider accessibility for
calibration when locating sensors.
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Are there other considerations for
locating sensors?
Sensors should not be placed near ventilation fans or openings to
outside, but not in the path of rapidly moving air. Pay particular
attention to ‘dead air spots’ where there is little or no air
movement.
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What is the breathing zone?
The breathing zone refers to the area 4 to 6 feet from the floor,
where most human breathing takes place. This is a good default location
for sensors.
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What gases can be
detected with PRISM Gas Detection equipment?
| Ammonia |
NH3 |
| Carbon
Monoxide |
CO |
| Carbon
Dioxide |
CO2 |
| Chlorine |
Cl2 |
| Combustible
Gases |
N/A |
| Ethylene
Oxide |
C2H4O |
| Hydrogen |
H2 |
| Hydrogen
Sulphide |
H2S |
| Methane
|
CH4 |
| Oxygen |
O2 |
| Ozone |
O3 |
| Nitric
Oxide |
NO |
| Nitrogen
Dioxide |
NO2 |
| Propane |
C3H8 |
| Refrigerants |
CFC, HCFC,
HFC |
| Sulphur
Dioxide |
SO2 |
| Cigarette
Smoke |
N/A |
Don’t see what you’re looking for? There are
more….contact us!
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Are some gases heavier or lighter than
others?
All substances have a molecular weight determined by the number and
type of atoms in the molecule. In a gaseous state, the larger and heavier
the molecule, the heavier the gas.
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What are the densities of
gases?
Vapour Density of some common gases:
| Air |
. |
1 |
| Ammonia |
NH3 |
17 |
| Carbon Monoxide |
CO |
28 |
| Carbon Dioxide |
CO2 |
44 |
| Hydrogen |
H2 |
0.2 |
| Hydrogen Sulphide |
H2S |
34 |
| Methane |
CH4 |
0.6 |
| Propane |
C3H8 |
2.2 |
| Oxygen |
O2 |
1 |
| Ozone |
O3 |
48 |
| Chlorine |
Cl2 |
71 |
| Nitric Oxide |
NO |
30 |
| Nitrogen Dioxide |
NO2 |
46 |
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Are there many types of sensors used
for gas detection?
There are many sensors used to detect gases. Types of popular
sensors include Solid State ( Metal Oxide Semiconductor),
Electrochemical, Catalytic, Infrared, Galvanic, Photoaccoustic, PID.
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Why are different kinds of sensors
used?
Different sensors use different physical or
chemical properties of different gases for detection and
measurement. Toxic gases are generally detected using
Electrochemical Sensorss. Flammable gases are generally detected
using Catalytic Sensors. Most gases can only be detected by one or two sensor types.
Sensor choice also depends upon required accuracy and specificity, sensor
life expectancy and cost.
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What are
the advantages and disadvantages of Semicoductor sensors?
Advantages: Low cost, long life, quite resistant to
poisoning
Disadvantages: Broad spectrum, non-specific, not as accurate as
other types
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What are the advantages and
disadvantages of Electrochemical sensors?
Advantages: Accurate, repeatable, more gas specific, defined cross
sensitivities
Disadvantages: Relatively short life, moderately
expensive
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What are the advantages and
disadvantages of Catalytic sensors?
Advantages: Range 0 — 100% LEL for many combustible gases,
accurate, long life
Disadvantages: Moderately expensive, can be poisoned
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What are the advantages and
disadvantages of Infrared sensors?
Advantages: Very gas specific, can measure upto 100% gas, best way to detect CO2, very
accurate & stable, long life
Disadvantages: Expensive
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What are the advantages and
disadvantages of Galvanic sensors?
Advantages: Range 0 to 100% volume Oxygen, long life
Disadvantages: Expensive, poor low-end accuracy
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Does gas detection equipment need
maintenance and calibration?
Yes. Maintenance on a properly installed, quality system is minimal and need only
consist of a visual inspection and verification of operation. Calibration frequency
depends on sensor type and application. Typical frequency for
commercial applications is 1 to 2 times per year. For areas where
health hazards may exist, 3 to 4 times per year and for critical
Industrial applications 4 to 6 times per year or even
monthly.
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What is calibration?
This process verifies that the instrument is
operating properly and adjusts for any sensor drift or loss of
sensitivity.This involves exposing the sensor to a known concentration of the target
gas, usually from a calibration gas cylinder, and resetting the instrument
to adjust for sensor drift.
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Can gas detection equipment produce
energy savings?
Yes. A properly installed, maintained and calibrated gas detection
system can produce significant energy savings by running ventilation fans
only when required, minimizing energy usage and expense.
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What is cross-sensitivity?
Cross-sensitivity refers to the response of a sensor to a gas other
than the target gas (also called an interference gas).
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What are combustible
gases?
Combustible gases are those that are monitored because they present
a risk of explosion or fire.
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Where does CO come
from?
Usually occurs as a product of combustion of an organic compound.
Most commonly found in vehicle exhaust.
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I get confused between CO and CO2
— what’s the difference?
CO is the chemical symbol for Carbon Monoxide which usually comes
from vehicle exhaust in commercial applications.
CO2 is the chemical symbol for Carbon Dioxide which usually comes
from human respiration in commercial applications and is used as an
indicator for Indoor Air Quality.
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Where do NO and NO2 come
from?
Nitric Oxide (NO) and Nitrogen Dioxide (NO2) usually occur as a
byproduct of combustion, often from vehicle engines. (see Nitrogen
Oxides)
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What is Nox?
Nox is an abbreviation for Nitrogen Oxides. (see Nitrogen
Oxides)
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What are Nitrogen
Oxides?
A group of compounds most commonly found in vehicle exhaust, where
Nitrogen Oxides are a byproduct of combustion formed from the Nitrogen and
Oxygen in the air. In exhaust, the most common is Nitric Oxide (NO)
followed by Nitrogen Dioxide (NO2). Other Nitrogen Oxides found in much
smaller quantities are N2O, N2O3, N2O4, N2O5, N3O4 AND NO3.
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Where does CO2 come
from?
Carbon Dioxide is a naturally occurring gas in air (less than 1 %)
and since it is exhaled during respiration, it is often used as an
indicator of Indoor Air Quality. CO2 is produced in the combustion of
organic compounds and it is also formed during fermentation. CO2 is used
in many industrial and food & beverage applications and may present a
hazard if it leaks from cylinders.
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Where does H2S come
from?
Hydrogen Sulphide is commonly produced from decay of organic matter
and in industrial processes such as Pulp & Paper and Oil & Gas. It
is often found in ‘Sewer Gas’.
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What does % LEL mean?
Combustible gases form flammable mixtures with air. For each gas
there is an explosive range within which the fuel to air mixture will
support combustion. LEL is an abbreviation for Lower Explosive Limit,
which is the minimum concentration of each gas in air that must be present
for combustion or explosion to occur.
% LEL refers to a method of measuring the concentration of a
combustible gas where the range of the sensor is set to correspond with
the concentration of gas that is below the explosive range. In this case
the Lower Explosive Limit equals 100 % LEL.
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What does ppm mean?
Parts Per Million. 100 % volume equals 1,000,000 ‘parts’ , 1 %
volume equals 10,000 ‘parts’ .
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What does % volume
mean?
The percentage of a gas in the total volume of mixture.
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What are the most common commercial and
institutional applications?
For more
information on applications
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What gases are present in parking
garages?
Vehicle exhaust gases: CO, Nitrogen Oxides
Combustible gases
from fuel leakage: Propane, Gasoline, Methane
Interference gases:
Solvent fumes from paint or sealer
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What gases are present in chiller
rooms?
Chiller room gases: Ammonia, Refrigerants
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What gases are present in swimming
pools?
Water purification chemicals: Chlorine, Ozone
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What gases are present in
warehouses?
Forklift or truck exhaust gases: CO, Nitrogen
oxides
Interference gases: Solvent fumes from warehoused
products
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What gases are present in repair
garages?
Vehicle exhaust gases: CO, Nitrogen Oxides
Combustible gases
from fuel leakage: Propane, Gasoline, Methane
Interference gases:
Solvent fumes
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