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June 2004
D
Draeger Safety
Entrada a espacios confinados
June 2004
D
Draeger Safety
Confined Spaces
 Que es un espacio confinado?
 American National Standards Institute (ANSI Z-117.1-1989)
– An enclosed area that has all the following characteristics: its primary
function is something other than human occupancy, has restricted entry
and exit, and may contain potential or known hazards
– Que su funcion primara se para otro uso y no para la ocupacion humana
que tenga entradas restringida como salidas y que puede tener conetener
sustancias potenciales riesgosas
 American Petroleum Institute
– Confined spaces are normally considered enclosures with known or
potential hazards and restricted means of entrance or exit
– Los espacios confinados normalmente se consideran los recintos con sabido o
peligros potenciales y medios restringidos de la entrada o de la salida
 OSHA (29 CFR 1910.146) General Industry
– A space that is large enough that an employee can bodily enter and
perform assigned work, has limited means for entry or exit, and is not
designed for continuous human occupancy
– Un espacio que es bastante grande que un empleado puede entrar en persona y
realice el trabajo asignado, ha limitado los medios para la entrada o la salida, y
no es diseñado para la ocupación humana continua
June 2004
D
Draeger Safety
Confined Spaces
 What is a confined space?
 OSHA (29 CFR 1915.4) Marine
– A compartment of small size and limited access such as a
double bottom tank, coffer dam, or other space which by its
size and confined nature can readily create or aggravate a
hazardous exposure (an enclosed space on the other hand is
any space other than a confined space which is enclosed by
bulkheads and overhead; it includes cargo holds, tanks,
quarters and machinery and boiler spaces.
– OSHA (29 CFR 1926.21) Construction
– Any space having limited means of egress, which is subject to
accumulation of toxic or flammable contaminants or has an
oxygen deficient atmospheres
June 2004
D
Draeger Safety
Confined Spaces
 What is a confined space?
 NIOSH
– A space which by design has limited openings for entry and
exit; unfavorable natural ventilation which could contain or
produce dangerous air contaminants, and which is not intended
for continuous human occupancy. NIOSH also classify confined
spaces:
– Class A spaces: those that present situations which are
immediately dangerous to life or health; includes deficient in
oxygen or contain flammable or toxic atmospheres
– Class B spaces: do not present an immediate threat to life or
health; however, they have the potential for causing injury or
illness if protective measures are not used
– Class C spaces: where any hazards posed are so insignificant
that no special work practices or procedures are required
June 2004
D
Draeger Safety
Confined Spaces
 OSHA also classifies confined spaces as permit-
required or non-permit required; a permit-required
confined space has one or more of the following
characteristics:
 contains, or has the potential to contain, a hazardous atmosphere
 contains a material that has the potential to engulf an entrant
 has an internal configuration such that an entrant could be
trapped or asphyxiated by inwardly converging walls or by a
floor that slopes downward and tapers to a smaller cross-section
 contains any other recognized serious safety or health hazard
June 2004
D
Draeger Safety
Simply put, a confined space is:
 Limited Access and/or Egress
 Able to be entered by humans
 Not designed for continuous human occupancy
 Real potential for life threatening
circumstances
Confined Spaces
June 2004
D
Draeger Safety
Confined Spaces
 Typical examples
Sewers
Underground
cable/electrical vaults
Water/storage
tanks
Aircraft wings during maintenance Process/mixing vessels Grain silos
Cargo holds
Construction and
excavation
Tunnels and pipes
Mobile tankers
June 2004
D
Draeger Safety
Confined Space Entry
What needs to be determined prior to entry, during
confinement and upon re-entry?
• Oxygen (19.5 to 23.5 % by vol.) 20.9% ambient
• Combustible Gas (Below 10% LEL)
• Toxic Gases (Known to be present)
June 2004
D
Draeger Safety
Dangers
• Oxygen - Too much or too little
• Toxic - Bodily Damage
• Combustible - Explosions
June 2004
D
Draeger Safety
What is Oxygen?
- Required to support life and support combustion
- 20.95% in ambient air
How is it Measured?
- Typically in % by volume scale
- Safe range from 19.5 to 23.5% by volume
Gas Detection Basics
June 2004
D
Draeger Safety
What is Toxic?
- Corrosive or poisonous or both
- Danger varies with each type of toxic in ambient air
How is it Measured?
- Typically in parts per million (ppm) scale
- Safe range determined by NIOSH for each gas
- Can be measured in Time Weighed Averages
(TWA). Typically 8 hour shifts.
- Can be measured in Short Term Exposure Level
(STEL). Typically 15 minutes
Gas Detection Basics
June 2004
D
Draeger Safety
What is a Combustible Gas?
- Explosive with ideal conditions
How is it Measured?
- Typically in % by vol. (%vol.) or
Lower Explosive Limit (LEL)
- Safe range determined by NIOSH for each gas
- Alarm warning set to 10 % LEL
Gas Detection Basics
June 2004
D
Draeger Safety
FIRE TRIANGLE
EXPLOSIVE
Fuel Oxygen
Spark / Ignition
Source
June 2004
D
Draeger Safety
Mixtures of Flammable Gases and Air
 It is a commonly held misconception that any
mixture of flammable gas and air is highly
dangerous and explosive. This is not the case
 For most flammable substances there is only a
relatively small range of gas-air mixtures which
are explosive (see below)
June 2004
D
Draeger Safety
Explosive Range, Some Examples
 Only the red ranges for the below substances are
explosive, the green regions will not sustain burning
and exhibit no danger of explosion!
Explosive Range
0% 20% 40% 60% 80% 100%
Pentane
Methane
Hydrogen
Acetone
% Vol. of Gas in Air
June 2004
D
Draeger Safety
The beginning of the red explosive
range is called the lower explosion limit (LEL)
Explosive Range
0% 5% 10% 15% 20% 25%
Pentane
Methane
Hydrogen
Acetone
% Vol. of Gas in Air
 Note that each of the substances listed below has a different LEL,
for example, methane’s LEL is 5% by volume and pentane’s is
1.4% by volume
Explosive Range
0% 20% 40% 60% 80% 100%
Pentane
Methane
Hydrogen
Acetone
% Vol. of Gas in Air
June 2004
D
Draeger Safety
The end of the red explosive
range is called the upper explosion limit (UEL)
Explosive Range
0% 5% 10% 15% 20% 25%
Pentane
Methane
Hydrogen
Acetone
% Vol. of Gas in Air
 Note that each of the substances listed below has a different UEL, for
example, methane’s is 15% by volume and pentane’s is 6.4% by volume
Explosive Range
0% 20% 40% 60% 80% 100%
Pentane
Methane
Hydrogen
Acetone
% Vol. of Gas in Air
June 2004
D
Draeger Safety
An Alternate Terminology for the
Red Explosive Range
 The explosive range of a gas is between the
LEL and the UEL of a gas
Explosive Range
0% 5% 10% 15% 20% 25%
Pentane
Methane
Hydrogen
Acetone
% Vol. of Gas in Air
June 2004
D
Draeger Safety
The % LEL Scale
 Since one normally references flammable-gas measurements to pure air, a
special set of units has been adopted called the %LEL scale
 This set of units is useful when the goal is to avoid explosive dangers by
staying under the LEL of the gas
 Pure air (without any flammable gas content) is assigned a value of 0%
LEL, the LEL of the gas is assigned a value of 100% LEL. Using
methane as an example, 5% by volume corresponds to 100 %LEL
Explosive Range
0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10% 11% 12% 13% 14% 15%
Methane
% Vol. of Gas in Air
0 – 100% LEL
June 2004
D
Draeger Safety
The %LEL Scale
 When working with the %LEL scale, you try to stay in the green
range, that is, between 0 and 100% LEL
 Over 100% LEL, there is a danger of explosion
 Remember, the % LEL scale corresponds to different absolute %
Vol. gas concentrations for different substances because the LEL of
each gas is different
Explosive Range
0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10% 11% 12% 13% 14% 15%
Methane
% Vol. of Gas in Air
0 – 100% LEL
June 2004
D
Draeger Safety
Lower Explosive Limit
 LEL is expressed as a percentage of the
volume needed to create combustion
Methane LEL = 5% methane by volume
0.5% methane by volume = 10% LEL
1.0% methane by volume = 20% LEL
2.5% methane by volume = 50% LEL
4.0% methane by volume = 80% LEL
+ =
5% CH4
= 100% LEL
June 2004
D
Draeger Safety
The %LEL Scale
 The LEL scale has the advantage that it focuses
on the explosion danger associated with the gas
 Under 100% LEL is safe
 Over 100% LEL is dangerous
 This is true regardless of the specific gas in
question
June 2004
D
Draeger Safety
FIRE TRIANGLE
EXPLOSIVE
Fuel Oxygen
Spark / Ignition
Source
June 2004
D
Draeger Safety
How can gases be detected?
With Draeger Safety Gas Detection Instrumentation
Using Draeger Safety Sensor and Glass Tube*
Technology
* Not discussed in this presentation
June 2004
D
Draeger Safety
DSensor Technology
June 2004
D
Draeger Safety
Sensor Technology
 Electrochemical Sensors (EC)
 Filter Media
 Catalytic Oxidation Sensors (Cat)
 Thermal Conductivity Sensors
 Infra-red Sensors (IR)
 CO2 & Ex Versions
June 2004
D
Draeger Safety
Electrochemical (EC) Sensors
June 2004
D
Draeger Safety
Electrochemical (EC) Sensors
 Based on a chemical reaction that
produces an electrical response/signal.
 The more gas that is present, the larger
the signal that is generated by the sensor.
 This signal is directly proportional to the
gas that is present.
June 2004
D
Draeger Safety
Electrochemical (EC) Sensors
1.) Gas to be Measured
2.) Dust & Mist Filter
3.) Diffusion Membrane
4.) Measuring Electrode
5.) Electrolyte
6.) Reference Electrode
7.) Counter Electrode
June 2004
D
Draeger Safety
Electrochemical (EC) Sensors
 How are the sensors made specific to one particular
gas or vapor?
 Choice of Diffusion Membrane, Electrolyte,
Electrodes, and Bias Voltage
 Draeger’s patented Three-Electrode Technology
maximizes response to the gas of concern and
minimizes the response to other chemicals.
 Gases with similar elements, chemical properties,
or chemical bonds may produce similar reactions.
 Gases with opposite chemical properties may
produce a negative reaction.
June 2004
D
Draeger Safety
Display
Circuitry
Current
Potential
Control
Sensor
Gas
The sensor produces a current proportional to the gas concentration.
EC Sensor Principle Overview
June 2004
D
Draeger Safety
Filter Media
 Chemical Filters
 D3T for CO Sensor
 OV’s and H2S
 B2T for Odor Sensor
 H2S
 K1T for SO2 Sensor
 H2S
June 2004
D
Draeger Safety
Electrochemical (EC) Sensors
 What is the expected life of a sensor?
 This varies with the type of sensor.
 The Draeger XS Sensors for CO, H2S & O2
have Three or Five-year Warranties, the
longest in the market.
 The XS stands for “eXtra Stability”, this
design allows the sensor to operate longer
and more stable over it’s life.
 Life is NOT determined by exposure to gas,
but is more dependant on time.
June 2004
D
Draeger Safety
Electrochemical (EC) Sensors
 How does Temperature effect the sensor?
 In general; these chemical reactions occur
quicker and stronger at higher temperatures and
slower and weaker at lower temperatures.
 A temperature compensation circuit inside the
sensor accurately compensates for changes in
ambient temperature.
 This internal compensation is better than PCB
mounted compensation, a feature exclusive to
Draeger-Sensors®
June 2004
D
Draeger Safety
Electrochemical (EC) Sensors
 Does Pressure make any difference on the
measurement by the sensor
 Higher ambient pressures will “force”
more gas into the sensor and thus
produce higher readings.
 The Draeger XS sensor have a pressure
compensation port which minimizes the
effects of pressure.
June 2004
D
Draeger Safety
Electrochemical (EC) Sensors
 Does Humidity effect the Sensor?
 Humidity by itself has minimal effect on
the sensor reading.
 However, should condensation occur, and
a layer of water covers the sensor, this will
prevent the gas from entering the sensor.
June 2004
D
Draeger Safety
Electrochemical (EC) Sensors
 Can Dust and other Particulate matter make a
difference?
 Should enough dust cover the sensor
inlet, it could slow down or block gas from
entering the sensor.
June 2004
D
Draeger Safety
Electrochemical (EC) Sensors
 What exactly is a “Smart” Sensor?
 Typically this means that when plugged
into a monitor, the instrument recognizes
what the sensor is designed to measure.
June 2004
D
Draeger Safety
Electrochemical (EC) Sensors
 What is special about the Draeger-Sensor?
 The XS,R and PS2 Sensors contain much
more data; Gas ID, Calibration Data,
Operating Parameters, Temperature
Compensation, Measuring Ranges, Alarm
Values, etc.
 This information stays with the sensor when
installed in another instrument.
 Transportable Calibration !!!
June 2004
D
Draeger Safety
Electrochemical (EC) Sensors
 How often do you need to calibrate the
Draeger XS Sensors?
 Per our specifications the CO, H2S and
O2, XS Sensors only require calibration
every 12 months (once a year)!
 Other XS Sensors, once every six months.
June 2004
D
Draeger Safety
Draeger-Sensor® Advantages
 Three or Five-year Warranty on CO, H2S, O2!!!
 The XS O2 sensor is NOT based on a
consumptive reaction.
 Interchangeable with other Draeger
Portables.
 Transportable Calibration Data.
 Long periods (up to 1 year) between routine
required calibrations.
 Widest variety of gases and vapors detected.
June 2004
D
Draeger Safety
• Oxygen
• Carbon Monoxide
• Hydrogen Sulfide
• Hydrogen Sulfide 1000
• Sulfur Dioxide
• Organic Vapors
• Organic Vapors - A
• Hydrides
• Hydrogen Peroxide
• Nitrogen Dioxide
• Nitric Oxide
• Phosphine 1000
• Hydrogen Cyanide
Available DrägerSensors XS EC
• Mercaptans
• Chlorine
• Carbon Dioxide
• Amines
• Hydrogen
• Hydrazine
• HF/HCl
June 2004
D
Draeger Safety
Electrochemical (EC) Sensors
June 2004
D
Draeger Safety
Catalytic Oxidation (Cat) Sensors
June 2004
D
Draeger Safety
Explosive Gas Measurement
Lean Explosive Rich
0-100 % LEL Explosive UEL Range
> 100%LEL
June 2004
D
Draeger Safety
Catalytic Oxidation (Cat) Sensors
 Metal Sinter Disk
 Compensating
Element
 Detection Element
 Wheatstone Bridge
June 2004
D
Draeger Safety
Lower Explosion Limits
Example: Methane 100% LEL = 5% Volume
Pellistor
Signal
Level
UEL
LEL
Gas concentration too
low to sustain flame
Explosive
region
Oxygen concentration too
low to sustain flame
Concentration of hazardous gas ( % Volume)
Possible source of danger: Same readings for two different concentrations ( A & B)
A B
0
Catalytic
Thermal
June 2004
D
Draeger Safety
Catalytic Oxidation (Cat) Sensors
 A catalyst facilitates the reaction between oxygen
in the air and combustible substances.
 This oxidation reaction produces heat.
 The heat of this reaction increases the resistance
of the element in the catalytic bead.
 The increase in resistance changes the flow of
electric current in the electrical bridge.
 More gas, causes more heat, causes a large
deflection of signal which is displayed as an
increase %LEL signal.
June 2004
D
Draeger Safety
Catalytic Oxidation (Cat) Sensors
 A compensation element negates
variations in temperature and humidity.
 Sensor reacts to any gas that is readily
oxidized by the catalyst.
 Methane, Propane, Gasoline, NH3, CO, etc.
 Sensitivity to any gas is dependant on the
chemical bonds within the substance.
June 2004
D
Draeger Safety
Catalytic Oxidation (Cat) Sensors
 In general, the heavier the compound, the lower the response
the catalytic sensor.
 CH4, C3H8, C5H12, etc.
 Relative Sensitivities of Common Compounds*
 **** Referenced to Methane Calibration ****
 Methane, CH4 100%
 Propane, C3H8 70%
 Pentane, C5H10 50%
 Gasoline, CxHy 55%
 Benzene, C6H6 33%
 Hydrogen, H2 100 %
June 2004
D
Draeger Safety
Catalytic Oxidation (Cat) Sensors
 Poisoning Compounds
 Sulfur-bearing compounds (H2S, SO2, etc.)
 Halogenated (CL2, F2, etc.) Hydrocarbons
 Inhibiting Agents
 Heavy-Metals Containing Compounds
– Leaded Gasoline (Pb)
 Silicone-bearing (Si) Compounds
 Long-Chained Polymers
 High Concentrations of Combustible Gases
June 2004
D
Draeger Safety
Draeger-Sensor® Advantages
 Poison Resistant Design
 Measures Heavier Hydrocarbons.
 Measures many compounds in ppm.
 Unambiguous Measurement of LEL
 With Thermal Conductivity Element
June 2004
D
Draeger Safety
Thermal Conductivity (TC) Sensor
Ambiguous Ex Sensor Operation
 As more combustible gas is present in the
ambient atmosphere, it displaces the
available oxygen needed to carry out the
catalytic oxidization reaction.
 Less oxygen to carry out the catalytic reaction
causes the sensor signal to drop.
 There will be a point at which the sensor will
produce the same signal for concentrations
over the LEL as under the LEL.
June 2004
D
Draeger Safety
Thermal Conductivity (TC) Sensor
0% LEL
Lean Explosive Rich
100%LEL
0 Vol. % 5 Vol. % 15 Vol. %
Sensor signal decrease due to lack of O2
thermal conductivity
catalytic oxidation
June 2004
D
Draeger Safety
Thermal Conductivity (TC) Sensor
 Different compounds have different thermal
conductivity (heat of transport) and will carry
away more heat from a heated source.
 Increased concentrations of methane (or
other combustibles) will conduct more heat
away from the thermal conductivity element in
the catalytic sensor. (vs. air).
 The Draeger Ex Sensor (thermal) prevents
ambiguous measurement and can accurately
measure CH4 up to 100 %Vol.
June 2004
D
Draeger Safety
Infrared (IR) Sensors
June 2004
D
Draeger Safety
Infrared (IR) Sensors
 Various compounds absorb infrared
energy.
 They absorb different wavelengths of IR
light energy in different degrees.
 Higher concentrations of gas will absorb
more IR light energy.
June 2004
D
Draeger Safety
Infrared (IR) Sensors
 1.) IR Light Source
 2.) Lens
 3.) Cuvette / Chamber
 4.) Mirror
 5.) Lens
 6.) Beam Splitter
 7.) Light Filter
 8.) Measure Detector
 9.) Light Filter
 10.) Comp. Detector
June 2004
D
Draeger Safety
Infrared (IR) Sensors
 Gas is pumped, or diffuses into a chamber
with an IR light source.
 The targeted gas(es) absorb the IR energy.
 The detector on the other side of the
chamber measures how much light is
absorbed by the targeted compound(s).
 A compensation detector corrects for
blockage by dust, water and other
physical factors.
June 2004
D
Draeger Safety
IR-Ex versus Cat-Ex
 Operates in environments with Low or No
Oxygen concentrations
 Completely Immune to Poisoning and
Inhibiting Compounds that affect Cat-Ex.
 Measures %LEL, ppm, and %Volume
Concentrations of various gases.
 Different responses to different
compounds vs catalytic sensor
(specifying).
June 2004
D
Draeger Safety
Draeger-Sensor ® Advantages
 Available for Ex or CO2.
 Can be coupled with a Cat-Ex.
 Qualified for more than Methane
 Does not require a Pump for operation.
 Compensation detector.
 Not affected by temperature, dirt, or
vibrations.
 Easily cleaned measurement chamber
June 2004
D
Draeger Safety
Questions?
Thank you.

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ESPACIOS CONFINADOS Y ATMOSFERAS PELIGROSAS.ppt

  • 1. June 2004 D Draeger Safety Entrada a espacios confinados
  • 2. June 2004 D Draeger Safety Confined Spaces  Que es un espacio confinado?  American National Standards Institute (ANSI Z-117.1-1989) – An enclosed area that has all the following characteristics: its primary function is something other than human occupancy, has restricted entry and exit, and may contain potential or known hazards – Que su funcion primara se para otro uso y no para la ocupacion humana que tenga entradas restringida como salidas y que puede tener conetener sustancias potenciales riesgosas  American Petroleum Institute – Confined spaces are normally considered enclosures with known or potential hazards and restricted means of entrance or exit – Los espacios confinados normalmente se consideran los recintos con sabido o peligros potenciales y medios restringidos de la entrada o de la salida  OSHA (29 CFR 1910.146) General Industry – A space that is large enough that an employee can bodily enter and perform assigned work, has limited means for entry or exit, and is not designed for continuous human occupancy – Un espacio que es bastante grande que un empleado puede entrar en persona y realice el trabajo asignado, ha limitado los medios para la entrada o la salida, y no es diseñado para la ocupación humana continua
  • 3. June 2004 D Draeger Safety Confined Spaces  What is a confined space?  OSHA (29 CFR 1915.4) Marine – A compartment of small size and limited access such as a double bottom tank, coffer dam, or other space which by its size and confined nature can readily create or aggravate a hazardous exposure (an enclosed space on the other hand is any space other than a confined space which is enclosed by bulkheads and overhead; it includes cargo holds, tanks, quarters and machinery and boiler spaces. – OSHA (29 CFR 1926.21) Construction – Any space having limited means of egress, which is subject to accumulation of toxic or flammable contaminants or has an oxygen deficient atmospheres
  • 4. June 2004 D Draeger Safety Confined Spaces  What is a confined space?  NIOSH – A space which by design has limited openings for entry and exit; unfavorable natural ventilation which could contain or produce dangerous air contaminants, and which is not intended for continuous human occupancy. NIOSH also classify confined spaces: – Class A spaces: those that present situations which are immediately dangerous to life or health; includes deficient in oxygen or contain flammable or toxic atmospheres – Class B spaces: do not present an immediate threat to life or health; however, they have the potential for causing injury or illness if protective measures are not used – Class C spaces: where any hazards posed are so insignificant that no special work practices or procedures are required
  • 5. June 2004 D Draeger Safety Confined Spaces  OSHA also classifies confined spaces as permit- required or non-permit required; a permit-required confined space has one or more of the following characteristics:  contains, or has the potential to contain, a hazardous atmosphere  contains a material that has the potential to engulf an entrant  has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or by a floor that slopes downward and tapers to a smaller cross-section  contains any other recognized serious safety or health hazard
  • 6. June 2004 D Draeger Safety Simply put, a confined space is:  Limited Access and/or Egress  Able to be entered by humans  Not designed for continuous human occupancy  Real potential for life threatening circumstances Confined Spaces
  • 7. June 2004 D Draeger Safety Confined Spaces  Typical examples Sewers Underground cable/electrical vaults Water/storage tanks Aircraft wings during maintenance Process/mixing vessels Grain silos Cargo holds Construction and excavation Tunnels and pipes Mobile tankers
  • 8. June 2004 D Draeger Safety Confined Space Entry What needs to be determined prior to entry, during confinement and upon re-entry? • Oxygen (19.5 to 23.5 % by vol.) 20.9% ambient • Combustible Gas (Below 10% LEL) • Toxic Gases (Known to be present)
  • 9. June 2004 D Draeger Safety Dangers • Oxygen - Too much or too little • Toxic - Bodily Damage • Combustible - Explosions
  • 10. June 2004 D Draeger Safety What is Oxygen? - Required to support life and support combustion - 20.95% in ambient air How is it Measured? - Typically in % by volume scale - Safe range from 19.5 to 23.5% by volume Gas Detection Basics
  • 11. June 2004 D Draeger Safety What is Toxic? - Corrosive or poisonous or both - Danger varies with each type of toxic in ambient air How is it Measured? - Typically in parts per million (ppm) scale - Safe range determined by NIOSH for each gas - Can be measured in Time Weighed Averages (TWA). Typically 8 hour shifts. - Can be measured in Short Term Exposure Level (STEL). Typically 15 minutes Gas Detection Basics
  • 12. June 2004 D Draeger Safety What is a Combustible Gas? - Explosive with ideal conditions How is it Measured? - Typically in % by vol. (%vol.) or Lower Explosive Limit (LEL) - Safe range determined by NIOSH for each gas - Alarm warning set to 10 % LEL Gas Detection Basics
  • 13. June 2004 D Draeger Safety FIRE TRIANGLE EXPLOSIVE Fuel Oxygen Spark / Ignition Source
  • 14. June 2004 D Draeger Safety Mixtures of Flammable Gases and Air  It is a commonly held misconception that any mixture of flammable gas and air is highly dangerous and explosive. This is not the case  For most flammable substances there is only a relatively small range of gas-air mixtures which are explosive (see below)
  • 15. June 2004 D Draeger Safety Explosive Range, Some Examples  Only the red ranges for the below substances are explosive, the green regions will not sustain burning and exhibit no danger of explosion! Explosive Range 0% 20% 40% 60% 80% 100% Pentane Methane Hydrogen Acetone % Vol. of Gas in Air
  • 16. June 2004 D Draeger Safety The beginning of the red explosive range is called the lower explosion limit (LEL) Explosive Range 0% 5% 10% 15% 20% 25% Pentane Methane Hydrogen Acetone % Vol. of Gas in Air  Note that each of the substances listed below has a different LEL, for example, methane’s LEL is 5% by volume and pentane’s is 1.4% by volume Explosive Range 0% 20% 40% 60% 80% 100% Pentane Methane Hydrogen Acetone % Vol. of Gas in Air
  • 17. June 2004 D Draeger Safety The end of the red explosive range is called the upper explosion limit (UEL) Explosive Range 0% 5% 10% 15% 20% 25% Pentane Methane Hydrogen Acetone % Vol. of Gas in Air  Note that each of the substances listed below has a different UEL, for example, methane’s is 15% by volume and pentane’s is 6.4% by volume Explosive Range 0% 20% 40% 60% 80% 100% Pentane Methane Hydrogen Acetone % Vol. of Gas in Air
  • 18. June 2004 D Draeger Safety An Alternate Terminology for the Red Explosive Range  The explosive range of a gas is between the LEL and the UEL of a gas Explosive Range 0% 5% 10% 15% 20% 25% Pentane Methane Hydrogen Acetone % Vol. of Gas in Air
  • 19. June 2004 D Draeger Safety The % LEL Scale  Since one normally references flammable-gas measurements to pure air, a special set of units has been adopted called the %LEL scale  This set of units is useful when the goal is to avoid explosive dangers by staying under the LEL of the gas  Pure air (without any flammable gas content) is assigned a value of 0% LEL, the LEL of the gas is assigned a value of 100% LEL. Using methane as an example, 5% by volume corresponds to 100 %LEL Explosive Range 0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10% 11% 12% 13% 14% 15% Methane % Vol. of Gas in Air 0 – 100% LEL
  • 20. June 2004 D Draeger Safety The %LEL Scale  When working with the %LEL scale, you try to stay in the green range, that is, between 0 and 100% LEL  Over 100% LEL, there is a danger of explosion  Remember, the % LEL scale corresponds to different absolute % Vol. gas concentrations for different substances because the LEL of each gas is different Explosive Range 0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10% 11% 12% 13% 14% 15% Methane % Vol. of Gas in Air 0 – 100% LEL
  • 21. June 2004 D Draeger Safety Lower Explosive Limit  LEL is expressed as a percentage of the volume needed to create combustion Methane LEL = 5% methane by volume 0.5% methane by volume = 10% LEL 1.0% methane by volume = 20% LEL 2.5% methane by volume = 50% LEL 4.0% methane by volume = 80% LEL + = 5% CH4 = 100% LEL
  • 22. June 2004 D Draeger Safety The %LEL Scale  The LEL scale has the advantage that it focuses on the explosion danger associated with the gas  Under 100% LEL is safe  Over 100% LEL is dangerous  This is true regardless of the specific gas in question
  • 23. June 2004 D Draeger Safety FIRE TRIANGLE EXPLOSIVE Fuel Oxygen Spark / Ignition Source
  • 24. June 2004 D Draeger Safety How can gases be detected? With Draeger Safety Gas Detection Instrumentation Using Draeger Safety Sensor and Glass Tube* Technology * Not discussed in this presentation
  • 26. June 2004 D Draeger Safety Sensor Technology  Electrochemical Sensors (EC)  Filter Media  Catalytic Oxidation Sensors (Cat)  Thermal Conductivity Sensors  Infra-red Sensors (IR)  CO2 & Ex Versions
  • 28. June 2004 D Draeger Safety Electrochemical (EC) Sensors  Based on a chemical reaction that produces an electrical response/signal.  The more gas that is present, the larger the signal that is generated by the sensor.  This signal is directly proportional to the gas that is present.
  • 29. June 2004 D Draeger Safety Electrochemical (EC) Sensors 1.) Gas to be Measured 2.) Dust & Mist Filter 3.) Diffusion Membrane 4.) Measuring Electrode 5.) Electrolyte 6.) Reference Electrode 7.) Counter Electrode
  • 30. June 2004 D Draeger Safety Electrochemical (EC) Sensors  How are the sensors made specific to one particular gas or vapor?  Choice of Diffusion Membrane, Electrolyte, Electrodes, and Bias Voltage  Draeger’s patented Three-Electrode Technology maximizes response to the gas of concern and minimizes the response to other chemicals.  Gases with similar elements, chemical properties, or chemical bonds may produce similar reactions.  Gases with opposite chemical properties may produce a negative reaction.
  • 31. June 2004 D Draeger Safety Display Circuitry Current Potential Control Sensor Gas The sensor produces a current proportional to the gas concentration. EC Sensor Principle Overview
  • 32. June 2004 D Draeger Safety Filter Media  Chemical Filters  D3T for CO Sensor  OV’s and H2S  B2T for Odor Sensor  H2S  K1T for SO2 Sensor  H2S
  • 33. June 2004 D Draeger Safety Electrochemical (EC) Sensors  What is the expected life of a sensor?  This varies with the type of sensor.  The Draeger XS Sensors for CO, H2S & O2 have Three or Five-year Warranties, the longest in the market.  The XS stands for “eXtra Stability”, this design allows the sensor to operate longer and more stable over it’s life.  Life is NOT determined by exposure to gas, but is more dependant on time.
  • 34. June 2004 D Draeger Safety Electrochemical (EC) Sensors  How does Temperature effect the sensor?  In general; these chemical reactions occur quicker and stronger at higher temperatures and slower and weaker at lower temperatures.  A temperature compensation circuit inside the sensor accurately compensates for changes in ambient temperature.  This internal compensation is better than PCB mounted compensation, a feature exclusive to Draeger-Sensors®
  • 35. June 2004 D Draeger Safety Electrochemical (EC) Sensors  Does Pressure make any difference on the measurement by the sensor  Higher ambient pressures will “force” more gas into the sensor and thus produce higher readings.  The Draeger XS sensor have a pressure compensation port which minimizes the effects of pressure.
  • 36. June 2004 D Draeger Safety Electrochemical (EC) Sensors  Does Humidity effect the Sensor?  Humidity by itself has minimal effect on the sensor reading.  However, should condensation occur, and a layer of water covers the sensor, this will prevent the gas from entering the sensor.
  • 37. June 2004 D Draeger Safety Electrochemical (EC) Sensors  Can Dust and other Particulate matter make a difference?  Should enough dust cover the sensor inlet, it could slow down or block gas from entering the sensor.
  • 38. June 2004 D Draeger Safety Electrochemical (EC) Sensors  What exactly is a “Smart” Sensor?  Typically this means that when plugged into a monitor, the instrument recognizes what the sensor is designed to measure.
  • 39. June 2004 D Draeger Safety Electrochemical (EC) Sensors  What is special about the Draeger-Sensor?  The XS,R and PS2 Sensors contain much more data; Gas ID, Calibration Data, Operating Parameters, Temperature Compensation, Measuring Ranges, Alarm Values, etc.  This information stays with the sensor when installed in another instrument.  Transportable Calibration !!!
  • 40. June 2004 D Draeger Safety Electrochemical (EC) Sensors  How often do you need to calibrate the Draeger XS Sensors?  Per our specifications the CO, H2S and O2, XS Sensors only require calibration every 12 months (once a year)!  Other XS Sensors, once every six months.
  • 41. June 2004 D Draeger Safety Draeger-Sensor® Advantages  Three or Five-year Warranty on CO, H2S, O2!!!  The XS O2 sensor is NOT based on a consumptive reaction.  Interchangeable with other Draeger Portables.  Transportable Calibration Data.  Long periods (up to 1 year) between routine required calibrations.  Widest variety of gases and vapors detected.
  • 42. June 2004 D Draeger Safety • Oxygen • Carbon Monoxide • Hydrogen Sulfide • Hydrogen Sulfide 1000 • Sulfur Dioxide • Organic Vapors • Organic Vapors - A • Hydrides • Hydrogen Peroxide • Nitrogen Dioxide • Nitric Oxide • Phosphine 1000 • Hydrogen Cyanide Available DrägerSensors XS EC • Mercaptans • Chlorine • Carbon Dioxide • Amines • Hydrogen • Hydrazine • HF/HCl
  • 44. June 2004 D Draeger Safety Catalytic Oxidation (Cat) Sensors
  • 45. June 2004 D Draeger Safety Explosive Gas Measurement Lean Explosive Rich 0-100 % LEL Explosive UEL Range > 100%LEL
  • 46. June 2004 D Draeger Safety Catalytic Oxidation (Cat) Sensors  Metal Sinter Disk  Compensating Element  Detection Element  Wheatstone Bridge
  • 47. June 2004 D Draeger Safety Lower Explosion Limits Example: Methane 100% LEL = 5% Volume Pellistor Signal Level UEL LEL Gas concentration too low to sustain flame Explosive region Oxygen concentration too low to sustain flame Concentration of hazardous gas ( % Volume) Possible source of danger: Same readings for two different concentrations ( A & B) A B 0 Catalytic Thermal
  • 48. June 2004 D Draeger Safety Catalytic Oxidation (Cat) Sensors  A catalyst facilitates the reaction between oxygen in the air and combustible substances.  This oxidation reaction produces heat.  The heat of this reaction increases the resistance of the element in the catalytic bead.  The increase in resistance changes the flow of electric current in the electrical bridge.  More gas, causes more heat, causes a large deflection of signal which is displayed as an increase %LEL signal.
  • 49. June 2004 D Draeger Safety Catalytic Oxidation (Cat) Sensors  A compensation element negates variations in temperature and humidity.  Sensor reacts to any gas that is readily oxidized by the catalyst.  Methane, Propane, Gasoline, NH3, CO, etc.  Sensitivity to any gas is dependant on the chemical bonds within the substance.
  • 50. June 2004 D Draeger Safety Catalytic Oxidation (Cat) Sensors  In general, the heavier the compound, the lower the response the catalytic sensor.  CH4, C3H8, C5H12, etc.  Relative Sensitivities of Common Compounds*  **** Referenced to Methane Calibration ****  Methane, CH4 100%  Propane, C3H8 70%  Pentane, C5H10 50%  Gasoline, CxHy 55%  Benzene, C6H6 33%  Hydrogen, H2 100 %
  • 51. June 2004 D Draeger Safety Catalytic Oxidation (Cat) Sensors  Poisoning Compounds  Sulfur-bearing compounds (H2S, SO2, etc.)  Halogenated (CL2, F2, etc.) Hydrocarbons  Inhibiting Agents  Heavy-Metals Containing Compounds – Leaded Gasoline (Pb)  Silicone-bearing (Si) Compounds  Long-Chained Polymers  High Concentrations of Combustible Gases
  • 52. June 2004 D Draeger Safety Draeger-Sensor® Advantages  Poison Resistant Design  Measures Heavier Hydrocarbons.  Measures many compounds in ppm.  Unambiguous Measurement of LEL  With Thermal Conductivity Element
  • 53. June 2004 D Draeger Safety Thermal Conductivity (TC) Sensor Ambiguous Ex Sensor Operation  As more combustible gas is present in the ambient atmosphere, it displaces the available oxygen needed to carry out the catalytic oxidization reaction.  Less oxygen to carry out the catalytic reaction causes the sensor signal to drop.  There will be a point at which the sensor will produce the same signal for concentrations over the LEL as under the LEL.
  • 54. June 2004 D Draeger Safety Thermal Conductivity (TC) Sensor 0% LEL Lean Explosive Rich 100%LEL 0 Vol. % 5 Vol. % 15 Vol. % Sensor signal decrease due to lack of O2 thermal conductivity catalytic oxidation
  • 55. June 2004 D Draeger Safety Thermal Conductivity (TC) Sensor  Different compounds have different thermal conductivity (heat of transport) and will carry away more heat from a heated source.  Increased concentrations of methane (or other combustibles) will conduct more heat away from the thermal conductivity element in the catalytic sensor. (vs. air).  The Draeger Ex Sensor (thermal) prevents ambiguous measurement and can accurately measure CH4 up to 100 %Vol.
  • 57. June 2004 D Draeger Safety Infrared (IR) Sensors  Various compounds absorb infrared energy.  They absorb different wavelengths of IR light energy in different degrees.  Higher concentrations of gas will absorb more IR light energy.
  • 58. June 2004 D Draeger Safety Infrared (IR) Sensors  1.) IR Light Source  2.) Lens  3.) Cuvette / Chamber  4.) Mirror  5.) Lens  6.) Beam Splitter  7.) Light Filter  8.) Measure Detector  9.) Light Filter  10.) Comp. Detector
  • 59. June 2004 D Draeger Safety Infrared (IR) Sensors  Gas is pumped, or diffuses into a chamber with an IR light source.  The targeted gas(es) absorb the IR energy.  The detector on the other side of the chamber measures how much light is absorbed by the targeted compound(s).  A compensation detector corrects for blockage by dust, water and other physical factors.
  • 60. June 2004 D Draeger Safety IR-Ex versus Cat-Ex  Operates in environments with Low or No Oxygen concentrations  Completely Immune to Poisoning and Inhibiting Compounds that affect Cat-Ex.  Measures %LEL, ppm, and %Volume Concentrations of various gases.  Different responses to different compounds vs catalytic sensor (specifying).
  • 61. June 2004 D Draeger Safety Draeger-Sensor ® Advantages  Available for Ex or CO2.  Can be coupled with a Cat-Ex.  Qualified for more than Methane  Does not require a Pump for operation.  Compensation detector.  Not affected by temperature, dirt, or vibrations.  Easily cleaned measurement chamber