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Part 2Part 2Direct ReadingDirect ReadingInstrumentationInstrumentation
Direct Reading InstrumentsDirect Reading Instruments
• Many different instruments• Many different operating principles including:
– Electrochemical– Photoionisation– Flame ionisation– Chemiluminescence– Colorimetric– Heat of combustion– Gas chromatography
• May sample many different gases & vapour• From relatively simple to complex
• Many different instruments• Many different operating principles including:
– Electrochemical– Photoionisation– Flame ionisation– Chemiluminescence– Colorimetric– Heat of combustion– Gas chromatography
• May sample many different gases & vapour• From relatively simple to complex
Uses of Direct Reading InstrumentsUses of Direct Reading Instruments
• Where immediate data is needed
• For personal exposure monitoring• Sample air in confined spaces
• Help develop comprehensive evaluationprograms
• Evaluate effectiveness of controls
• Prepare for emergency response
• Where immediate data is needed
• For personal exposure monitoring• Sample air in confined spaces
• Help develop comprehensive evaluationprograms
• Evaluate effectiveness of controls
• Prepare for emergency response
Calculation of resultsCalculation of resultsPassive/Diffusion sampling:
Conc (mg/m3) = W (µg) x Ar x t
where W = contaminant weight (µg)A calculation constant = 1000 / Sampling rater = recovery coefficientt = sampling time in minutes
Conc (ppm) = W (µg) x Br x t
where W = contaminant weight (µg)B = calculation constant = 1000 x 24.45 / Sampling rate
x mol wtr = recovery coefficientt = sampling time in minutes
Passive/Diffusion sampling:Conc (mg/m3) = W (µg) x A
r x twhere W = contaminant weight (µg)
A calculation constant = 1000 / Sampling rater = recovery coefficientt = sampling time in minutes
Conc (ppm) = W (µg) x Br x t
where W = contaminant weight (µg)B = calculation constant = 1000 x 24.45 / Sampling rate
x mol wtr = recovery coefficientt = sampling time in minutes
Uses of Direct Reading Instruments (cont)Uses of Direct Reading Instruments (cont)
• For difficult-to-sample chemicals
• Multi sensors
• Multi alarms
• For stationary installations
• Use for fit testing of respirators
• Video monitoring
• For difficult-to-sample chemicals
• Multi sensors
• Multi alarms
• For stationary installations
• Use for fit testing of respirators
• Video monitoring
LimitationsLimitations
• Often costly to purchase• Need for frequent and regular calibration• Lack of specificity – too generic• Effect of interferences• Cross sensitivity• Need for intrinsically safe instruments in many
places• Battery life• Sensors
– Finite life, poisoning, lack of range
• Often costly to purchase• Need for frequent and regular calibration• Lack of specificity – too generic• Effect of interferences• Cross sensitivity• Need for intrinsically safe instruments in many
places• Battery life• Sensors
– Finite life, poisoning, lack of range
AdvantagesAdvantages
• Direct reading
• Continuous operation
• TWA, STEL & Peaks
• Data logging (recording)
• Direct reading
• Continuous operation
• TWA, STEL & Peaks
• Data logging (recording)
Other LimitationsOther Limitations
• E.g. Catalytic combustion detectors– React with other flammable gases– Poisoned by
• Silicones• Phosphate esters• Fluorocarbons
• E.g. Catalytic combustion detectors– React with other flammable gases– Poisoned by
• Silicones• Phosphate esters• Fluorocarbons
Single Gas MonitorSingle Gas Monitor
• Interchangeable sensors including:• O2, CO, H2S, H2, SO2, NO2, HCN
Cl2, ClO2, PH3• STEL, TWA, peak• Alarm if exceeding limits• Data logging
• Interchangeable sensors including:• O2, CO, H2S, H2, SO2, NO2, HCN
Cl2, ClO2, PH3• STEL, TWA, peak• Alarm if exceeding limits• Data logging
Source: Industrial Scientific Inc – reproduced withpermission
Multigas MonitorMultigas Monitor
• 1 – 6 gases• Interchangeable sensors:
LEL, CH4, CO, H2S, O2, SO2,Cl2, NO, ClO2, NH3, H2, HCl, PH3
• STEL, TWA, peak• Alarm• Data logging
• 1 – 6 gases• Interchangeable sensors:
LEL, CH4, CO, H2S, O2, SO2,Cl2, NO, ClO2, NH3, H2, HCl, PH3
• STEL, TWA, peak• Alarm• Data logging
Gas BadgesGas Badges
• Two year maintenance free• For single gas monitor• Sensors include CO, H2S, O2 SO2• Turn them on & let them run out• Alarms• Some data logging ability
• Two year maintenance free• For single gas monitor• Sensors include CO, H2S, O2 SO2• Turn them on & let them run out• Alarms• Some data logging ability
Source: Industrial Scientific Inc – reproduced withpermission
PhotoPhoto IonisationIonisation Detectors (PID)Detectors (PID)
• Dependent on lamp ionisation potential• Typically for non specific VOCs
or total hydrocarbons– Some specific eg benzene, NH3, Cl2
• Not for CH4 or ethane• Affected by humidity, dust etc.
• Dependent on lamp ionisation potential• Typically for non specific VOCs
or total hydrocarbons– Some specific eg benzene, NH3, Cl2
• Not for CH4 or ethane• Affected by humidity, dust etc.
Source: Airmet Scientific-reproduced withpermission
FlameFlame IonisationIonisation MonitorMonitor
• Similar to PID but using flame• Non specific, broad range• Less sensitive to humidity &
other contaminants• Poor response to some gases• Needs hydrogen (hazard)
• Similar to PID but using flame• Non specific, broad range• Less sensitive to humidity &
other contaminants• Poor response to some gases• Needs hydrogen (hazard)
Source: Airmet Scientific-reproduced withpermission
Portable Gas ChromatographPortable Gas Chromatograph– Highly selective for certain chemicals– Range depends on type of detector used– Complex instrument requiring
extensive operator training– Non continuous monitoring
– Highly selective for certain chemicals– Range depends on type of detector used– Complex instrument requiring
extensive operator training– Non continuous monitoring
Source: Airmet Scientific-reproduced withpermission
InfraInfra--redred AnalyserAnalyser
• For organic vapours• Specific gases• Portable• Expensive
• For organic vapours• Specific gases• Portable• Expensive
MercuryMercury VapourVapour DetectorsDetectorsTwo principles:
• UV– Interferences:
OzoneSome organic solvents
• Gold Film– High cost– Gold film needs regular cleaning
Two principles:
• UV– Interferences:
OzoneSome organic solvents
• Gold Film– High cost– Gold film needs regular cleaning
Maintenance & CalibrationMaintenance & Calibration
Source: Industrial Scientific Inc – reproduced withpermission
Guidelines for Using Gas DetectionGuidelines for Using Gas DetectionEquipmentEquipment
• Bump or challenge test– Daily before use, known concentration of test gas to
ensure sensors working correctly
• Calibration– Full instrument calibration, certified concentration of
gas(es), regularly to ensure accuracy & documented
• Maintenance– Regular services provides reassurance instruments
repaired professionally & calibrated & documented
• Bump or challenge test– Daily before use, known concentration of test gas to
ensure sensors working correctly
• Calibration– Full instrument calibration, certified concentration of
gas(es), regularly to ensure accuracy & documented
• Maintenance– Regular services provides reassurance instruments
repaired professionally & calibrated & documented
Typical Basic Instrument ChecksTypical Basic Instrument Checks
• Physical appearance• Ensure instrument is within calibration period• Turn instrument on and check battery level• Zero the instrument – recorded data• Bump test (functionality test) instrument• Clear the peaks
• Physical appearance• Ensure instrument is within calibration period• Turn instrument on and check battery level• Zero the instrument – recorded data• Bump test (functionality test) instrument• Clear the peaks
Standard Gas AtmospheresStandard Gas Atmospheres
Primary Gas Standards• Are prepared from high purity 5.0 (dec pt.) gases (99.99999%) or
6.0 gases (99.999999%) by weighing them into a gas cylinder ofknown size
Secondary Gas Standards• Are prepared volumetrically from these (primary gases) using gas
mixing pumps or mass flow controllers (mixture of gases)
Primary Gas Standards• Are prepared from high purity 5.0 (dec pt.) gases (99.99999%) or
6.0 gases (99.999999%) by weighing them into a gas cylinder ofknown size
Secondary Gas Standards• Are prepared volumetrically from these (primary gases) using gas
mixing pumps or mass flow controllers (mixture of gases)
Source: University of Wollongong
Intrinsic SafetyIntrinsic Safety
IECEx Standards
• Equipment for use in explosive areas e.g.– Underground coal mines– Oil refineries– Petrol stations– Chemical processing plants– Gas pipelines– Grain handling– Sewerage treatment plants
IECEx Standards
• Equipment for use in explosive areas e.g.– Underground coal mines– Oil refineries– Petrol stations– Chemical processing plants– Gas pipelines– Grain handling– Sewerage treatment plants
Intrinsic Safety (cont)Intrinsic Safety (cont)
Gases,vapours, mists
Dusts Explosive atmosphere ispresent
Zone 0 Zone 20 Most of the time
Classification of zones
Zone 1 Zone 21 Some time
Zone 2 Zone 22 Seldom or short term
Source: TestSafe – reproduced withpermission
Intrinsic Safety (cont)Intrinsic Safety (cont)
• Group 1 Equipment used undergroundeg methane & coal dust
• Group II Equipment used in other (aboveground) hazardous areas
IIA - least readily ignited gaseseg propane & benzeneIIB – more readily ignited gaseseg ethylene & diethyl ether
IIC – most readily ignited gaseseg hydrogen and acetylene
Gas or Explosive Groups• Group 1 Equipment used underground
eg methane & coal dust• Group II Equipment used in other (above
ground) hazardous areasIIA - least readily ignited gaseseg propane & benzeneIIB – more readily ignited gaseseg ethylene & diethyl ether
IIC – most readily ignited gaseseg hydrogen and acetylene
Intrinsic Safety (cont)Intrinsic Safety (cont)Temperature classesGroup I Surfaces exposed to dust @ less than 150°C
Group II Temp Class Max permissiblesurface temp °C (auto
ignition)
Max permissiblesurface temp °C (auto
ignition)T1 450T2 300T3 200T4 135T5 100T6 85
Source: TestSafe – reproduced withpermission
Intrinsic Safety (cont)Intrinsic Safety (cont)
Levels ofprotection
Suitable for use in
“ia” Zones 0, 20 (safe with up to 2 faults)
Levels of Protection & Zones
“ia” Zones 0, 20 (safe with up to 2 faults)
“ib” Zones 1, 21 (safe with up to 1 fault)
“ic” Zones 2, 22 ( safe under normaloperation)
Source: TestSafe – reproduced withpermission
Intrinsic Safety MarkingsIntrinsic Safety MarkingsExample Smith Electronics
Model TREEx ia IIC T4Cert 098XSerial No. 8765
ia equipment suitable for zone 0 applicationIIC equipment is suitable for Gas Groups IIA,IIB,
IICT4 equipment is suitable for gases with auto
ignition temp greater than 135°C
Example Smith ElectronicsModel TREEx ia IIC T4Cert 098XSerial No. 8765
ia equipment suitable for zone 0 applicationIIC equipment is suitable for Gas Groups IIA,IIB,
IICT4 equipment is suitable for gases with auto
ignition temp greater than 135°C
Detector TubesDetector Tubes -- Colorimetric TubesColorimetric Tubes
Change in colour of a specific reactant whenin contact with a particular gas or vapour
Source: Dräger Safety – Reproduced withpermission
AdvantagesAdvantages
• Relatively inexpensive & cheap
• Wide range of gases and vapours – approx 300
• Immediate results
• No expensive laboratory costs
• Can be used for spot checks
• No need for calibration
• No need for power or charging
• Relatively inexpensive & cheap
• Wide range of gases and vapours – approx 300
• Immediate results
• No expensive laboratory costs
• Can be used for spot checks
• No need for calibration
• No need for power or charging
LimitationsLimitations
• Interferences from other contaminants
• Need to select correct tube & correct range
• Results should NOT be compared to TWA• Correct storage
• Limited shelf life
• Interferences from other contaminants
• Need to select correct tube & correct range
• Results should NOT be compared to TWA• Correct storage
• Limited shelf life
ColourColour Tubes / Badges Available ForTubes / Badges Available For
• Instantaneous short term measurement• Long term measurements – pump• Long term measurements – diffusion
• Instantaneous short term measurement• Long term measurements – pump• Long term measurements – diffusion
End of Part 2End of Part 2End of Part 2End of Part 2
Part 3Part 3
Personal Air SamplerPersonal Air Sampler
Air SamplingAir Sampling
• There are various locations at which one may wish to take anintegrated sample of a chemical in the plant air.
• A general plant air sample is useful to give an overall measureof plant contamination.
• One might also be concerned with escape of chemical at aknown or suspected point source, such as an open vat, aspraying operation, or a valve.
• Measurements made at a source of contaminant escape shouldnot be used as values representing overall contamination ofplant air.
• Air collected at a point source will later be diluted by plant airor may be removed effectively by the ventilation system.
• Such a reading indicated hazard to a worker at the location andestimates the effectiveness of systems that clear the air.
• There are various locations at which one may wish to take anintegrated sample of a chemical in the plant air.
• A general plant air sample is useful to give an overall measureof plant contamination.
• One might also be concerned with escape of chemical at aknown or suspected point source, such as an open vat, aspraying operation, or a valve.
• Measurements made at a source of contaminant escape shouldnot be used as values representing overall contamination ofplant air.
• Air collected at a point source will later be diluted by plant airor may be removed effectively by the ventilation system.
• Such a reading indicated hazard to a worker at the location andestimates the effectiveness of systems that clear the air.
Air SamplingAir Sampling
• A variety of stationary devices are available that either collect asample for later analysis of give a direct reading of thecontamination of the air at that location.
• Such devices may depend on appearance of a specificabsorption of infrared light, change in the transparency of afilter, change in the pressure drop across a filter, scattering oflight by airborne particulate of variety of other techniques.
• Devices are available to take samples automatically at timedintervals.
• A variety of stationary devices are available that either collect asample for later analysis of give a direct reading of thecontamination of the air at that location.
• Such devices may depend on appearance of a specificabsorption of infrared light, change in the transparency of afilter, change in the pressure drop across a filter, scattering oflight by airborne particulate of variety of other techniques.
• Devices are available to take samples automatically at timedintervals.
PERSONAL AIR SAMPLERSPERSONAL AIR SAMPLERS
• The most important air to sample is the air inhaled by theindividual worker. Such air must be collected near the face.
• Unless we wish to attach the worker by a tube to a largestationary device, which would restrict the free movement ofthe worker and thereby distort the results of the study, theentire apparatus must be small and lightweight enough to becarried about conveniently by the worker.
• Such personal air samplers are available and are in commonuse. They consist of a small, battery-powered air pump thatcan be worn on the belt , to which a trapping device is attached.A tube pinned to the clothing near the face carries the air to thetrapping device.
• The most important air to sample is the air inhaled by theindividual worker. Such air must be collected near the face.
• Unless we wish to attach the worker by a tube to a largestationary device, which would restrict the free movement ofthe worker and thereby distort the results of the study, theentire apparatus must be small and lightweight enough to becarried about conveniently by the worker.
• Such personal air samplers are available and are in commonuse. They consist of a small, battery-powered air pump thatcan be worn on the belt , to which a trapping device is attached.A tube pinned to the clothing near the face carries the air to thetrapping device.
End of Part 3End of Part 3
