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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
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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
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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
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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
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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
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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
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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)
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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
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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
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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
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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)
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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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
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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.
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Draeger Safety
Filter Media
Chemical Filters
D3T for CO Sensor
OV’s and H2S
B2T for Odor Sensor
H2S
K1T for SO2 Sensor
H2S
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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.
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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®
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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.
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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.
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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.
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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.
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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 !!!
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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.
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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.
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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
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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.
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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.
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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 %
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Draeger Safety
Draeger-Sensor® Advantages
Poison Resistant Design
Measures Heavier Hydrocarbons.
Measures many compounds in ppm.
Unambiguous Measurement of LEL
With Thermal Conductivity Element
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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.
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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
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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.
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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.
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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.
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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).
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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
