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Gas Detector Selection and Calibration Guide

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Gas Detector Selection and Calibration Guide

Sponsored by the DTI, this industry guide concentrates upon safety systems designed to protect users from the harmful effects of flammable, toxic or asphyxiant gases. Will aid users and manufacturers in considering relevant factors when selecting and monitoring a gas detector or detection system so that its performance remains within acceptable limits throughout the intended product life.

CONTENTS

Foreword

Acknowledgement

1 Industrial Flammable and Toxic Gas Detection
1.1 Aim of the Guide
1.2 Scope
1.3 Object
1.4 Safety

2 Concise Guide to the Selection of a Suitable Gas Detection System
2.1 Introduction
2.2 Nature of the Gas Hazard
2.3 Anticipated Concentration Range
2.4 Type of Apparatus Required
2.5 Environmental Considerations

3 Introduction
3.1 Purpose of the Guide
3.2 Relevant Gas Properties
3.3 Gas Distribution
3.4 Units of Measurement
3.5 Routinely Monitored Gases
3.6 Health and Safety Issues
3.6.1 Gas Detectors and Their Role in Safety Management
3.6.2 Flammable Gases
3.6.3 Toxic Gases
3.6.4 Staff Training

4 Sensor Technologies
4.1 Electrochemical sensor
4.1.1 Liquid Electrolyte Cells
4.1.2 Solid Electrolyte Cells
4.1.3 Calibration
4.2 Infra-red (IR) Photometry
4.3 Pellistor
4.4 Chemiluminescence
4.5 Colourimetry
4.5.1 Detector Tubes
4.5.2 Paper Tape and Dosimeter Badges
4.6 Electrical Conductivity
4.7 Electron Capture Detector
4.8 Flame Ionisation Detector
4.9 Flame photometric Detector
4.10 Flame Temperature Analyser
4.11 Gas Chromatography
4.12 Ion Mobility Spectrometry (IMS)
4.13 Mass Spectrometry
4.14 Open-path Measurement Systems
4.15 Paramagnetic Oxygen Analyser
4.16 Photo-ionisation Detector
4.17 Semiconductor Sensor
4.18 Thermal Conductivity
4.19 Ultra-violet /Visible Photometry (spectrometry)

5 Guide to Gas Detector Selection
5.1 Introduction
5.2 Components of a Gas Detection System
5.2.1 Sampling Strategies
5.2.2 Typical Monitoring Tasks
5.3 Factors in the Selection of a Suitable Gas Detection System
5.3.1 Purpose
5.3.2 Type of Apparatus Required
5.3.3 Gas(es) to be Detected
5.3.4 Anticipated Concentration Range
5.3.5 Performance Requirements
5.3.6 Environmental Considerations
5.3.7 Other Species Present in the Sampled Atmosphere
5.3.7.1 Selectivity Required
5.3.7.2 Presence of Sensor Poisons
5.3.7.3 Balance Gas
5.3.8 Use in Potentially Explosive Atmospheres
5.3.9 Cost
5.3.10 Other Factors
5.3.10.1 Complexity of Calibration
5.3.10.2 Instrument Lifetime
5.3.10.3 Personnel Training Requirements
5.3.10.4 Data Logging
5.3.10.5 Number of Monitors
5.3.10.6 Compliance with Regulatory Requirements
5.3.11 Miscellaneous Factors
5.4 Explanation of Instrument Specifications
5.4.1 Accuracy
5.4.2 Resolution
5.4.3 Operating Environment
5.4.4 Interferences
5.4.5 Warm-up time
5.4.6 Response time
5.4.7 Instrument Drift

6 Performance Evaluation
6.1 Introduction
6.2 Results of Gas Detector Performance Evaluation Testing
6.2.1 Instruments Tested
6.2.2 Tests Performed
6.2.2.1 Calibration Curve/Measurement of Deviations
6.2.2.2 Time of Response
6.2.2.3 Time of Recovery
6.2.2.4 Humidity (of test gas)
6.2.2.5 Poisoning/Cross-Sensitivity
6.2.2.6 Wind Velocity
6.2.2.7 Long Term Stability
6.2.3 Summary of Results
6.2.3.1 Calibration Curve/Measurement of Deviations
6.2.3.2 Time of Response And Time of Recovery
6.2.3.3 Humidity (of test gas)
6.2.3.4 Poisoning/Cross-Sensitivity
6.2.3.5 Wind Velocity
6.2.3.6 Long Term Stability
6.2.4 Comments
6.2.4.1 Calibration Curve/Measurement of Deviations
6.2.4.2 Response Time
6.2.4.3 Poisoning
6.2.4.4 Wind Velocity

7 Calibration
7.1 Introduction
7.2 Defining Calibration
7.3 Importance of Calibration
7.3.1 Calibration Frequency
7.3.2 Functional Testing
7.4 Calibration Methods
7.4.1 Competence of Personnel and Organisations
7.4.2 Selection of Calibration Gas Mixture and Source
7.4.3 Factors Influencing Gas Detector Calibration
7.4.3.1 Pressure /Flowrate
7.4.3.2 Temperature
7.4.3.3 Humidity
7.4.3.4 Warm Up Time
7.4.3.5 Gas Mixture Composition
7.4.3.6 Operator Error
7.4.3.7 Instrument Errors
7.4.3.8 Setting of Instrument Zero
7.4.4 Documentation of Results
7.5 Calibration Gas Mixture Production Techniques
7.5.1 Commercial Gas Mixtures
7.5.1.1 Volumetric Production Techniques
7.5.1.2 Gravimetric Production Techniques
7.5.1.3 Cylinders
7.5.2 Flow Meters
7.5.3 Volumetric Pumps
7.5.4 Permeation Tubes
7.5.5 Capillary Calibration Devices
7.5.6 Gas Generators
7.5.6.1 Electrochemical Generators
7.5.6.2 Ozone Generators
7.5.7 Ampoules
7.5.8 Gas Sample Bags
7.6 Maintaining Gas Mixture Composition from the Source to the Instrument
7.6.1 Leakage Out
7.6.1.1 Practical Advice
7.6.2 Air/Moisture Ingress
7.6.3 Internal Corrosion/Reaction/Absorption/Adsorption
7.6.3.1 Practical Advice
7.6.4 Exposure to Extreme Environmental Conditions
7.6.5 Low Cylinder Gas Pressure
7.6.6 Gas Control Equipment
7.6.6.1 Pressure Regulators
7.6.6.2 Flow Control Valves
7.7 Accuracy and Traceability of Commercial Gas Mixtures
7.8 Errors and Uncertainty
7.8.1 Introduction
7.8.2 Volumetric Pumps (Iso 6145-2)
7.8.3 Continuous Syringe Injection Method (Iso 6145-4)
7.8.4 Capillary Calibration Devices (Iso 6145-5)
7.8.5 Critical Orifices (Iso 6145-6)
7.8.6 Thermal Mass-Flow Controllers (Iso 6145-7)
7.8.7 Diffusion Method (Iso 6145-8)
7.8.8 Saturation Method (Iso 6145-9)
7.8.9 Permeation Method (Iso 6145-10)
7.8.10 Static Volumetric Method (Iso 6144)
7.8.11 Other Sources of Uncertainty
7.9 Benefits of Accredited Calibration
7.10 Scope for Improvement of Calibration Methods
7.10.1 Selection of Gas Supplier
7.10.2 Checking the Gas on Receipt
7.10.3 In-House References
7.10.4 Application of Gas
7.10.5 Control of Materials Used for Gas Supply
7.10.6 Response Time Issues
7.10.7 Proficiency Testing
7.10.8 Analysis of Calibration Data
7.10.9 Review of Uncertainty Budgets

8 Reference Documents
8.1 Other Useful Information Sources

Appendices
A.1 List of Detector Manufacturers
A.2 Gas Handling, Transportation and Safety
A.2.1 Gas Handling
A.2.2 Cylinder Handling
A.2.3 Gas Cylinder Transportation
A.3 Domestic Carbon Monoxide Detectors
A.4 Affects of Oxygen Depletion on the Human Body
A.5 Results of Independent Analyses of Commercial Gas Mixtures