Authorised Gas Tester Assessed Competency

Course

Presented by: Presented by:

John M Sonley, C.Sci C.Eng John M Sonley, C.Sci C.Eng MIGEM MEI C.Chem FRSCMIGEM MEI C.Chem FRSC

JMS Consultants

Gas Molecules

Properties of Flammable GasesFLAMMABILITY AND IGNITION

Most natural gases are mainly methane - typically 70 - 90 % methanemixed with smaller amounts of the other hydrocarbon gases

Flammability Limits for Methane in Air

Ignition of methane

Flammable mixtures of methane and air may ignite if heated above the auto-ignition temperature , which for methane is 538oC

- without any other source of ignition being presentFlammability of Other Gases – BS EN 61779-1:2000

GasEthane - Propane -Butane -Pentane -Hydrogen -

LEL2.5 %vol.1.7 %vol.1.4 %vol.1.4 %vol.4.0 %vol.

0% Methane( Clean Air)

LEL 4.4%

% Vol. Methane % LEL Methane

20% LEL = 0.88% methane in air

40% LEL = 1.76% methane in air

60% LEL = 2.64% methane in air

80% LEL = 3.52% methane in airUEL 17%

‘BUMP’ Test

2.2% methane in air

= 50% LEL

Response Factorsof the catalytic flammable gas sensor

to a range of hydrocarbons

Gas at its LEL Concentration Meter Reading % LEL

Methane 100

Ethane 68

Propane 55

n-Butane 59

n-Pentane 46

Hexane 37

Heptane/Octane 38

Nonane 31

Hydrogen 77

Condensate

or Solvent

Vapour Cloud

Containment of hazard

……. use sampling system

Containment of:

Gases/Vapour/Liquids

Other ‘heavy’ gases:

Carbon dioxide: R.D. = 1.5

Chlorine: R.D. = 2.5

Units of Measurement

Oxygen Flammables Toxics

10 10 10

10% vol 10% LEL 10 ppm 0.44% vol 0.001% vol

Clean Air

Oxygen = 20.95% vol.

Nitrogen = 78.08% vol.

Properties of Harmful and Toxic Gases

Large amounts of natural gas and some other gases displace oxygen from the air we breathe and cause suffocation

APPLICATION / WHERE FOUND

Pipeline and vessel purging operationsPipe freezing operations

Argon arc welding

GAS

Nitrogen

Argon

ASPHYXIANT GASES

Hazards of Oxygen

<19% Oxygen

‘Deficiency’

>23% Oxygen

‘Enrichment’

TOXIC GASES

GAS APPLICATION / WHERE FOUND

Condensate / heavyhydrocarbon vapours

Hydrogen sulphide

Carbon monoxide

Carbon dioxide

Sulphur dioxide

Chlorine

Benzene

Hydrazine

Crude oil residues, oil condensate residuesand sludges

Found widely in reservoir gas, crude oil vapours and around stagnant water

Associated with combustion processes

Fire extinguishers and deluge systems

Sulphur recovery plants, flare stacks - formed when hydrogen sulphide is burned

Water purification processes

Occasionally found in crude oil gases and vapours

Used in water treatment processes

Small amounts of some gases and vapours found in the oil industry poison our bodies- we measure these amounts in parts per million - ‘ppm’.

For example : 10 ppm = 0.001% 1000 ppm = 0.1 %

Properties of Harmful and Toxic Gases

For Toxic Gases …

C.O.S.H.H.

Control of Substances Hazardous to Health

Workplace Exposure Limit

WEL

8 HOUR LIMIT 15 MINUTE LIMIT

WELs published in HSE document EH40 each year

Control of Substances Hazardous to Health - COSHHWorkplace Exposure Limits for Toxic Gases

WEL

8 Hour Limit 15 Minute Limit

GAS

Carbon Monoxide

30 ppm 200 ppm

Hydrogen Sulphide 5 ppm 10 ppm

Light PetroleumHydrocarbons( Condensates )

500 ppm -

Medium PetroleumHydrocarbons( Sludges)

250 ppm -

Carbon Dioxide 5000 ppm 15000 ppm

Sulphur Dioxide No longer listed No longer listed

Chlorine 0.5 ppm 1 ppm

Benzene 3 ppm(1 ppm – 2003)

-

Hydrazine 0.02 ppm 0.1 ppm

A number of the listed Workplace Exposure Limits are cancer causing, carcinogenic. As a principle, no exposure to concentrations greater than the WEL shall be permitted, and for carcinogenic compounds, ‘adequate control’ should be to as low a level ‘as is reasonably practicable’.

Properties of Hydrogen Sulphide

Occurrence Important Properties•In crude oil - ‘Sour’ crude•In reservoir gas - ‘Sour’ gas•In stagnant water

•Deadly toxic gas at high concentration•Colourless•Smells of bad eggs at low concentrations•Paralyses sense of smell at high concentrations

Effects and Symptoms of H2S

0.15ppm -------------------------------- threshold of smell - 0.000015% vol.5ppm ----------------------------------------------------- 8 hour exposure limit10ppm ------------------------------------------------- 15 minute exposure limit20ppm ---------------------------- strong ‘bad - eggs’ smell, eye irritation100ppm ------------------------------- loss of sense of smell in 3 - 15 mins200 - 300ppm ----------------------- instantaneous loss of sense of smell (that’s why you cannot use your nose as a gas detector!)700ppm or more -------breathing ceases, loss of consciousness and death unless resuscitated

REMEMBER! - 700ppm sounds a lot but its only 0.07% vol.- -there may well be 99.93% vol. fresh air as the remainder

H2S

Physical Properties of Hydrogen Sulphide

1.Flammable gas:

LEL = 4.0% vol = 40,000 ppm!

2. Reacts with iron in an inert atmosphere to create : ‘Pyrophoric Iron Sulphide’ – a fire and explosion hazard

3. Heavier than air:

Relative Density = 1.2

(Air = 1)

Industries with SRB Problems

Hazards of Carbon Monoxide - CO

1. Produced by incomplete combustion

2. Haemoglobin in your blood prefers CO to oxygen – 240 times more! – to form carboxyhaemoglobin

3. Colourless gas of neutral density

4. Odourless gas – it doesn’t smell of exhaust fumes!

5. Flammable gas: LEL = 10.9% vol. in air

6. Smokers have 5 – 10% of their blood permanently complexed as carboxyhaemoglobin

The Catalytic Gas SensorUSED IN PORTABLE AND FIXED GAS DETECTORS

TO DETECT AND M EASUREMETHANE AND OTHER FLAMMABLE GASES IN AIR

The Catalytic Gas Sensor ( Pellistor )

Pellistors measure combustible gases in air at concentrations of upto the Lower Explosive Limit. Flammable gases are burnt on the hot

catalytic detector element and the resulting heat generated increasesthe electrical resistance of the platinum wire coil. This change inresistance produces a reading on the detector which is directly

proportional to the amount of flammable gas present in the atmosphere

Limitations

( Hot work and Confined Space Entry Gas Testing )

Catalyst Platinum wirecoil

1. Cannot be used in inert gas atmospheres - needs 13% or more oxygen

2. Fails - to - danger due to Poisons and Blockage of the flame arrestor Silicones Water De-greasing fluids Drilling fluids Hot lube oils / WD40 Oil 3. Methane calibrated detectors seriously under-read concentrations of the higher hydrocarbon gases and vapours e.g. condensate vapours

4. Older gas detectors can give ambiguous readings at high gas concentrations

Approx. 1 mm

550 oCApprox.

‘Old Wives’ Tale’ – Don’t ‘bump’ test the detector too often because it ‘wears out the sensor’ – untrue!

Catalytic Sensors - EEV ‘pellistors’

A Simple ‘Explosimeter’

Gas Detectors don’t like water !

Corrosion of catalytic sensors

Catalytic fixed gas sensor

The Thermal Conductivity Gas SensorUSED IN PORTABLE GAS DETECTORS TO MEASURE THE PERCENTAGE

OF FLAMMABLE GAS MIXED WITH AN INERT GAS ( NITROGEN )DURING PURGING OPERATIONS

Principle

Thermal conductivity sensors detect a gas by comparing the heat conducting propertiesThermal conductivity sensors detect a gas by comparing the heat conducting propertiesof that gas with the heat conducting properties of a ‘ reference’ gas, usually nitrogenof that gas with the heat conducting properties of a ‘ reference’ gas, usually nitrogen

Typical Application - entry into a vessel that contains natural gas

Natural gas

Purge vessel

with nitrogen

Less than7.5% methane

Purge vessel

with air

20.9%oxygen

(a) Permit to Enter issued

(b) Entry made, work completed

20.9%Oxygen

Purge vessel

with nitrogen

Less than 7.7% oxygen

Purge vessel

with natural gas

Natural gas

Step 1. Step 2. Step 3.

Step 4. Step 5. Step 6.

Limitations

1. For accurate results, the detector should be calibrated with the natural gas in use and be zeroed with the inert (purge ) gas being used

2. The detector is sensitive to changes in sample gas flow rate

IMPORTANT

Thermal conductivity based gas detectors are calibrated ‘ % volume ’and CANNOT be used for Hot Work and Confined Space Entry gastesting - - - - - - they are too insensitive!

in nitrogen

Principle of Infra-red Gas Detection

Sieger ‘Searchpoint’infra-red ‘point’ detector

Sieger ‘Searchline’Open-path detector for

flammable gases

PLMS ‘Line of Sight’Infra-red Flammable Gas

Detector

Installation ofOpen Path Gas

Detection

Draeger Multiwarn II- infra-red flammable

gas sensor

The Infra Red Gas SensorUSED IN PORTABLE AND FIXED GAS DETECTORS

TO DETECT AND MEASURE HYDROCARBONS AND CARBON DIOXIDE

Broad-band infra red light from a source shines through a window and into a cuvette where ambient air to be monitored diffuses or is pumped. The light is reflected from a concave mirror, back through the window on to an angled beam splitter. Part of the light penetrates the beam splitter, passes through a narrow band interference filter tuned to the absorbtion wavelength of the gas being detected and through to a detector. The remainder of the light is reflected by the beam splitter through an equivalent filter tuned to a reference wavelength, slightly away from the absorbtion wavelength of the gas being detected and through to a reference detector.

Features• Can be configured to be Fail – Safe, unlike catalytic detectors• Electrically more stable than catalytic detectors• Will operate in inert gases as well as air – purging applications• Cannot be used to detect hydrogen• Interference filters available for several gases• Widely used in ‘Line of Sight’ or ‘Open Path’ gas detectors

Electrochemical Oxygen Sensor

Oxygen electrochemical cells are self powered, metal - air ‘batteries’ consisting of an anode, a gel electrolyte and an air permeable cathode. Oxygen within the air supply diffuses in a controlled manner through a barrier, chemically reacts within and the reaction produces a voltage proportional to the concentration of oxygen

Limitations• Selective, but some ‘cross-sensitivity’ •Gas ‘batteries’ which become ‘flat’ and need replacement •Temperatures greater than 400C cause rapid failure and leakage •Toxic gas sensors - radio transmitter interference •Oxygen sensors - air pressure pulses cause false alarms

USED IN PORTABLE AND FIXED GAS DETECTORSTO DETECT AND MEASURE : % OXYGEN

AND TOXIC GAS CONCENTRATIONS (ppm) OF:

HYDROGEN SULPHIDE CARBON MONOXIDE SULPHUR DIOXIDE CHLORINE

+ + + + + + + + + + + + +CATHODE + + + + + + + + + + + + +

ELECTROLYTE

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ANODE _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

LoadResistorV

4e-

Capillary DiffusionBarrier

Air

The Electrochemical Cell

H2S Paper Tape Detector

Chemical Stain Tubes

Chemical Stain Tubes

Draeger Chemical Detector TubesUSED MAINLY WHEN TESTING CONFINED SPACES AND VESSELS

FOR TOXIC AMOUNTS OF THE FOLLOWING SUBSTANCES :(a) Vapours from crude oil residues, condensates and sludges

(b) Residual motor spirit vapours(c) Paint and other solvent fumes and vapours

(d) Carbon monoxide and carbon dioxide(e) Hydrogen sulphide and mercaptans

(f) Benzene and other aromatics

Limitations1. Tubes are gas specific, choose the correct tube2. Tubes are concentration specific, choose the correct tube3. Instructions enclosed with each box of tubes4. Tubes can only be used once5. Accuracy only plus/minus 25%, don’t use for oxygen tests6. Single test only - not a continuous monitor7. Shelf life - typically 2 years, see ‘use-by’ date on box

Kitagawa Chemical Stain Tube

Gastec Chemical Stain Tube

Calibration Gases

2.2% methane in air – stable gas mixture

Low ppm mixtures of many reactive toxic gases in air – NOT stable

Examples: H2S, SOx, NOx Cl2 – these gas mixtures require special cylinders,

regulators and tubing

Explosive Atmospheres Certification

1. The EEx label is on the outside of the certified product – some detectors need leather cases

2. Don’t infringe the EEx certification by a ‘cowboy’ repair

GAS DETECTOR APPLICATIONSAND

TYPES OF PORTABLE GAS DETECTOR

1. HOT WORK Gas Testing

Gas Test

Flammable GasDetector Principle Unit of

MeasurementMethane

( and otherflammable gases)

Catalyticor

Infra-red – NOT for Hydrogen!

% LEL

2. CONFINED SPACE OR VESSEL ENTRY Gas Testing

Gas Test Detector Principle Unit of Measurement

Oxygen

Methane or other

flammable gases

Toxic gases or vapours

Electrochemical cell

Catalytic orInfra-red

Electrochemical cellChemical stain tube

% O2

% LEL(flammable gas in air)

ppm toxic gas

3. INERT GAS PURGE Gas Testing

Oxygen

Methane

Electrochemical cell

Thermal conductivity % volume methane in inert gas

% O2

Pre-issue Testing of DetectorMechanical Checks

BEFORE USING A PORTABLE ELECTRICAL GAS DETECTOR 1. Check body of detector for physical damage and loose components

2. Check gas inlet port for water / mud / oil contamination

3. Check that flammable atmospheres safety label (BASEEFA or others) is attached and recalibn. date is OK

4. Connect and check aspirator bulb and tubing for wear, blockage, leakage or water / oil contamination

5. Check any user accessible filters for dust, oil or water contamination BEFORE USING A DRAEGER CHEMICAL TUBE DETECTOR

1. Check that bellows spring(s) is not broken or dislodged by squeezing bellows and observing

2. Check that you have chosen the correct tube for your application - - correct gas, correct concentration and correct ‘use-by’ date

3. Check that the bellows do not leak by inserting unbroken tube into the aspirator ( with or without the extension tube )compress bellows and confirm that bellows do not expand.

- - - and if your detector fails any one of these checks return it to the issuing authority

Pre-issue Testing of DetectorElectrical / Gas Checks

BEFORE USING A PORTABLE ELECTRICAL GAS DETECTOR1. Switch on and study any diagnostic messages

2. Check condition of battery using built - in indicator

3. Check functioning of audible and visual alarms during warm - up (when applicable) - cancel alarms

4. Note reading in clean air to be 20.9 or 21% for oxygen and ‘zero’ for flammable and all toxic gases

5. If detector has an electrical aspirating pump, seal gas inlet with finger and check the operation of the flow failure indicator or note change in sound of the pump

6. Check correct functioning of a catalytic sensor by aspirating a standard test gas through the detector and noting : (a) activation of both audible and visual alarms at the set alarm level, usually 20% LEL (b) meter indicates plus/minus 5% LEL of the correct reading : with 2.2% methane in air reading is 45 - 55% LEL with 1.1% methane in air reading is 15 - 25% LEL7. Check correct functioning of a thermal conductivity sensor by aspirating a 50% by volume methane in nitrogen gas mixture through the detector and noting a reading of 50 plus / minus 2 % vol. - - - and return faulty detectors to the issuing authority

VA 16

TRUSTTRUST THE INDICATION THE INDICATION ON YOUR GAS DETECTOR - -ON YOUR GAS DETECTOR - -

- - - PERHAPS THAT LITTLE - - - PERHAPS THAT LITTLE READINGREADING IS NOTIS NOT

‘‘JUST ZERO DRIFT’JUST ZERO DRIFT’ ! !

TRUSTTRUST THE INDICATION THE INDICATION ON YOUR GAS DETECTOR - -ON YOUR GAS DETECTOR - -

- - - PERHAPS THAT LITTLE - - - PERHAPS THAT LITTLE READINGREADING IS NOTIS NOT

‘‘JUST ZERO DRIFT’JUST ZERO DRIFT’ ! !

- - and finally- - and finally ! !- - and finally- - and finally ! !

Why are you carrying out a gas test?

Answer : To certify that the atmosphere is safe to work in