THIS IS A SUMMARY COURSE REGARDING GAS TESTING REQUIRMEMENTS AND EXPOSURE .. RECOMMENDED AS AN

1. ISO 9712 cert

3. Course aim
• To provide you with a full understanding of the role of a Gas Tester
• To provide you with a full understanding of the different types of gas test that can be
conducted
How this will be achieved?
• Through PowerPoint, DVD and practical demonstration
• By taking notes as the lesson progresses
Confirmation of understanding
• There will be a short test at the end of this presentation to confirm your understanding
of the material presented

4. INTRODUCTION TO GAS TESTING
Q, Why do we test need to test for gas?
Some of the gasses we work with can be very
dangerous, so we need to make sure the
atmosphere is safe to work in before any work
start AND during the time the work taking
place

5. Upper
Explosive
Limit
Explosive
Envelope
Why are gas tests required?
To:
• Determine if an area is
hazardous due to the
presence of gas
• Provide monitoring of an
area to ensure the
continued safety of a
workplace
• Determine the type of work
that can take place in an
area
• Determine any worksite
restrictions that may be
necessary

6. When will “gas tests” be required?
• Hot work
• Naked flames
• Welding and grinding
• Flame cutting and burning
• Use of flare guns in hazardous areas
• Use of equipment or work on pipelines or
vessels contaminated with pyrophoric scale

7. When will “gas tests” be required?
• Hot Work (Spark potential in hazardous areas)
• Use of non IS electrical equipment, soldering
• Opening of junction boxes in hazardous areas
• Pneumatically or hydraulically operated tools capable of generating a spark
• Explosives and perforating guns
• Cartridge operating fixing tools
• Dry grit, shot blasting
• Portable diesel engines
• Use of battery operated cameras

8. When will “gas tests” be required?
• Confined Space Entry
• Definition of a ‘Confined Space’:
• Limited access or egress
• Poorly ventilated
• Not designed for human occupancy
• Dangerous by design, through products held, vessel shape or if there are
known hazards contained
• If any doubt is present then it should be classified as a confined space
• Cold work:
• Where there may be a potential for hydrocarbon leakage

9. Three main types of test
• Flammable gas tests
• Hydrocarbon gas is explosive
• Toxic or harmful gas tests
• Toxic gases are dangerous to health
• Oxygen content tests (deficiency or enrichment)
• We need oxygen to breathe
• Enrichment is a fire hazard

10. Gas testers
• Must ensure that equipment used is:
• suitable for the atmosphere to be tested
• an approved type
• properly calibrated and maintained
• within its validation period

11. Gas testers
• Must also be:
• adequately trained
• sufficiently knowledgeable to interpret and record the results correctly
• aware of the likely contaminants
• sure that gas tests are carried out at the correct time
• authorised and registered on the rig or installation that they are currently
working on

12. Gas meter users
• Must also be:
• able to interpret meter readings and
alarms
• know the actions to take should an alarm
activate
• know who to contact should a problem
arise
• know the local hazards which may affect
the worksite

13. Gas meter users
• Read the manufacturers meter instructions
• Know the instrument limitations
• Check the general condition of the meter
• Check the meter is within its calibration date
• Ensure the battery has been charged
• Ensure that the sensor intakes are not blocked
• Check that any sample probes or aspirators are in good condition

14. Basic instrument checks
• Switch on the meter
• Check the readings in normal air
• Meter should show:
• Oxygen 20.9% v/v
• Hydrocarbons 0 %LEL
• Hydrogen Sulphide 0 ppm
• Carbon Monoxide 0 ppm
• Zero the meter in normal air if there are any deviations
• Meter function and alarms may be checked with test gas prior to use

15. Typical gas meters

16. ..and not so typical

17. Portable gas detectors
Disadvantages
• May be contaminated by:
• silicones
• sulphur compounds
• welding fumes
• chlorine
• high levels of hydrocarbons
• ‘catalytic’ gas detectors
• There must be at least 16% Oxygen present
in the atmosphere to be measured before
hydrocarbon gas concentrations can be
accurately detected

18. The fire triangle
Air Fuel
Ignition

19. • Gas in correct concentration
• Sufficient Oxygen
• Sufficient ignition energy
Gas ignition

20. Flammable limits of hydrocarbon gas
• Lower Explosive Limit (LEL)
• Lowest concentration of gas that can ignite
• Below this level the mixture of gas in air is too lean
• Upper Explosive Limit (UEL)
• The highest concentration of gas that can ignite
• Above this limit the mixture of gas in air is too rich
• The maximum range used in most gas meters
• Between these limits, hydrocarbon gas is explosive
• Known as the explosive envelope

21. Flammable limits of hydrocarbon gas

22. Flashpoints
• The lowest temperature at which a liquid will
emit ignitable vapours
• The flashpoint of Methanol
is very low at 11°C

23. Ignition temperatures
• Gas within it’s flammable range will ignite if the temperature is raised to a
certain value
• Known as the ignition temperature
• Normally caused by a spark or flame
• Ignition temperatures for gases vary
• Approx 635° C for methane and 460° C for butane
• A match-head burns at around 1500° C
• Naked flame hot work ignites all of the flammable gases and vapours

24. Auto ignition
• Combustible materials may ignite without a spark or flame
• Caused by heating or contact with a hot surface
• Known as the auto ignition temperature

25. Expansion of NGL to gas
• A small volume of Natural Gas Liquid (NGL) gives a large hydrocarbon
gas vapour cloud, for example:
• Butane expands 225 times when changing from liquid to gas
• Propane expands around 250 times
• L.E.L. of Butane is approximately 2%(v/v) in air
• An explosive gas cloud approximately 11,000 times the volume of liquid
escaping may develop
• The gas cloud will expand again, up to fifty times and still be explosive

26. Flammable gas testing
• Gas is never likely to be distributed evenly
• Some gases are lighter than air and some are heavier
• Lighter than air gases will rise and may be trapped below ceilings
• Gases that are heavier than air will tend to hug the ground and fall to lower
levels
• Distribution depends on the area layout (equipment)
• Atmospheric conditions must also be considered (temperature, wind speed and
direction)
• For ‘Hot Work’ there must be NO hydrocarbon gas present

27. Oxygen
• Level required for normal breathing is 20.89%
• Low levels of oxygen may be caused by:
• rusting
• welding, burning or a fire
• displacement by another gas
• chemicals
• vacuum
• High levels of oxygen can be caused by:
• leaking oxygen hose (oxy/acetylene)
• vents on nitrogen generators
• chemicals

28. Ventilation in a confined space
• A good supply of fresh air required in a vessel to be entered without BA
equipment
• Air movers may be needed
• Air supply from a safe, clean source
• The air should be vented safely
• Note:- 20.9% Oxygen in a vessel does not on it’s own mean that the
vessel is safe to enter

29. Oxygen levels
• Reduced oxygen levels
• Reduces explosive envelope
• At around 8% oxygen it drops to zero
• During purging operations look for
6% oxygen prior to admitting
hydrocarbons

30. High oxygen content
Risks to personnel
• Increased fire risk
• Human intoxication
• Risk to IS equipment

31. Ignition energy
The third element needed for fire / explosion
• Energy is needed to ignite a gas
• Ignition energy required varies for each gas
• Energy varies within the flammability envelope
• Dependant on amount of Oxygen available

32. Ignition energy

33. Hydrogen Sulphide (H2S)
• H2S is measured in ‘Parts Per Million’ (ppm) in air
• Lethal at concentrations of only 700 ppm or 0.07% v/v
• Meter alarm settings
• Evacuate area upwind and across wind if alarm sounds
• H2S is highly corrosive
• Causes stress cracking in steel
• Flammable at high levels, (LEL of 4% UEL of 45%)
• May be absorbed by sample tubes
• Heavier than air
• Insoluble in water (creates acid)

34. H2S generation
• Generated by bacteria (aerobic and anaerobic)
• Some oil and gas reservoirs produce (H2S)
• May be found where oil/water interfaces
• Common in drains and sewers
• Found in light end gas systems

35. Physiological properties of H2S
• Smell of rotten eggs at low concentrations
• Sense of smell is LOST at around levels of only 100 ppm
• Eye irritation
• Throat irritation
• Coughing
• Dizziness
• Loss of vision
• Unconsciousness
• Death (levels of around 700ppm)

36. Note: Never depend on your sense of smell to detect gas
Other harmful gas
• Benzene (found in some hydrocarbon systems)
• Carbon monoxide (found in exhaust flues)
• Carbon dioxide (gas blankets on storage tanks, fire fighting)
• Nitrogen (inert gas purging, blankets etc)
• Chlorine ( found in water systems)
• Hydrogen (emitted by battery systems)

37. Toxic gas exposure limits
• Meters alarm at Maximum Exposure Limits
• Long Term Exposure Limit or Time Weighted Average (TWA) is taken over an 8
hour period within 24 hours
• Short Term Exposure Limit is taken over a 15 minute period
• Toxic exposure limits may be found in HSE document EH40

38. Exposure limits
The 8 Hour reference period covers any 8 hours in 24, time weighted average
Formulae used:
C1T1 + C2T2 = CnTn
8
Where C is the occupational exposure and T is the exposure time in hours

39. Exposure limits
Within a 24 hour period a worker was exposed to the following levels of H2S:
4.0 ppm for a period of 4 hours, then
4.5 ppm for a period of 3 hours
This gives an exposure level of
(4 x 4) + (4.5 x 3) = 3.69
8
Which is below the 8 hour occupational exposure limit (TWA) of 5ppm for
Hydrogen Sulphide

40. Chemical tubes
• Used to test various gases
• Two common systems :
• Draeger
• Kitagawa
• Gas sample sucked into a tube containing chemicals by
pump or bellows
• Chemical changes colour depending on gas concentration
• Scale indicated on tube and also dependent on the
number of pump strokes
• Errors may be caused if:
• Tubes are out of date
• Contamination occurs due to mists/particles

41. Where to test
• ‘Risk Assessment’ to determine possible gases
• Check at all levels of the worksite in the area specified by the work permit
• High for methane
• Low for heavier hydrocarbons
• Select the type of gas on the meter or apply a correction factor
• With a vessel, approach from upwind, testing all the time
• Never expose yourself to unknown gas concentrations

42. Where to test?
Areas to check on equipment include the following:
• In tanks or vessels
• In cellars
• Behind weir plates or barriers in vessels
• Pipe flanges
• Vents and drains
• Loop seals leading to drain systems
• Screwed fittings
• Valve packing
• Pump seals

43. When to test?
• Immediately before work begins
Testing Frequency’ depends on:
• Nature of the work
• Time elapsed since the last test
• Requirements of the work permit
• Atmospheric conditions
• Area classification
• Company requirements
• Continuous ‘sentry’ testing may be required by work
party

44. Recording results
When recording test results:
• Remember to insert the correct units of measurement
• Hydrocarbons % LEL
• Oxygen % v/v
• Hydrogen Sulphide ppm
• Carbon Monoxide ppm

45. Vessel entry
• Good mechanical and electrical isolation procedures
• Consider LSA scale, radiation from instruments, hazardous substance
requirements, loose equipment, slippery surfaces
• Gas monitors
• Correct vessel entry procedures
• Sentry duties clearly defined
• Good communications system (internal and external)
• Good access/egress
• Inertia reels and retrieval facilities
• Certified lighting required
• Barriers and signs
• No pressurised cylinders within vessel
• External risks considered (drains, vents etc)
• Air moving equipment if required

46. Vessel procedures
Use correct vessel entry procedures
Test for:
• Oxygen Content
• Hydrocarbons
• Toxic gases
• Special gases as required

47. Respiratory Equipment
• Breathing apparatus
• Provides an independent source of breathable air
• Self Contained Breathing Apparatus (SCBA)
• Air line breathing apparatus

48. Respiratory Equipment
• Respirators
• Provides filtration or absorption of atmospheric
contaminants
• Filter mask
• Filter and cartridge
• Canister type
• Will not remove high levels of gas

49. Gas Type New Colour RAL Code
Acetylene Maroon RAL 3009
Argon Dark Green RAL 6001
Oxygen White RAL 9010
Nitrogen Black RAL 9005
Gas cylinders
• Several gases arrive on board in cylinders
• Clear identification is critical
• New colour coding system introduced
• Colour code applies to shoulder of cylinder
• Identification label on neck of bottle
• Some Gas cylinder ‘Colour Codes’

50. Personal Protective Equipment
• Protection required for:
• Head
• Eyes and Face
• Hearing
• Body and limbs
• Hands
• Feet
• Additional equipment (e.g. BA, paper suits;
may be required for entering confined spaces)

51. Training aims and goals
• You should now be able to:
• decide where and when gas tests will be required list the types of gas tests
carried out
• describe gas testing principles
• identify and use various types of gas detectors
• describe pre-checks to be carried out on a meter
• explain the hazards and effects of flammable, toxic(H2S) and inert gases
• identify the hazards of oxygen deficiency and enrichment

52. Summary
• Gas tests can be divided into three types:
• Flammable
• Toxic or harmful
• Oxygen
• Always pre-check the tester or analyser
• Consider carefully where and when to test
• Hydrogen Sulphide is highly toxic and is a poisonous gas
• Oxygen levels above and below 20.89% are hazardous
• Be aware of the dangers of high nitrogen concentrations