15._SGW -_GAS_TESTING__MONITORING .pptx

OBJECTIVES
The objectives of this presentation are:
• To identify the causes of hazardous atmospheres.
• To review the principles of gas testing.
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Contents
Why Carry out a Gas Test
What Defines A Safe Atmosphere
Properties of Flammable, Explosive and Toxic Gases and Vapours
Properties, Effects and Symptoms of Hydrogen Sulphide
Control of Substance Hazardous to Health
Density of Gases and Vapors
Characteristics of Gas
Application and types of Portable Gas Detectors and Operation

Introduction
Many fatalities have
occurred because gas
testing had not been
conducted or the tests
have been inadequate.
Gas testing must be
completed by trained
competent personnel.
However, it is important
that everyone understands
the basic requirements.

Categories
In the oil/gas and petrochemical industries, gas hazards are of particular importance. These hazards can be
split into 3 main categories
• The first are oxygen hazards, in the air we breathe if there’s too much or not enough oxygen you or
your work mates may die.
• Secondly explosive gases and flammable vapours, which, when mixed with air in certain proportions
can lead to fires or explosions.
• And finally harmful or toxic gas hazards; these cover everything from inert gases like nitrogen, used in
purging operations, which, simply displace the oxygen out of the air we are breathing, right through
to the nerve gases like Hydrogen Sulphide, which chemically interfere with the cells in our body.
Each one of these hazards are serious and life threatening.

Type of Gas
Detector

The following abbreviations are used:
AGT-
Authorized Gas
Tester.
CH4-
Methane (a
flammable
hydrocarbon gas).
H2S-
Hydrogen Sulphide
(a toxic gas).
LEL-
Lower Explosive
Limit.
UEL-
Upper Explosive
Limit.
PPM-
Parts Per Million.

To prevent an
incident 3 main
types of gas
testing are
undertaken:
• Before enteringa confinedspace or
vessel
• Before undertaking any type of hot-
work
• During inserting

The following
definitions are
used in this
presentation:
• Gas - any substance of very low density
and viscosity. ( No shape, fills the free
space of container)
• Vapor - mist or fumes suspended in air.
• Liquid- any flowing substance with
little tendency to disperse. ( No
shape, takes shape of container)

Gas testing is involved with the following activities:
Hot work of any type where heat is used or generated,
e.g.. by welding, flame cutting and grinding, etc.
Work which may generate sparks or other sources of
ignition.
Work which may cause an uncontrolled release of
hydrocarbons, other flammable or toxic materials.
Electrical instrumentation work which may cause
sparks
Entry into confined spaces and Gas alarm investigation

WHY CARRY OUT A GAS CHECK?
Confined Space and Vessel Entry Gas Testing
OXYGEN
DEFICIENCY …
SUFFOCATION /
DEATH
01
OXYGEN
ENRICHMENT …
FIRE / EXPLOSION
HAZARD
02
GAS OR
FLAMMABLE
VAPOUR …FIRE OR
EXPLOSIVE
HAZARD
03
TOXIC GAS …
POISONING
HAZARD
04

To certify that the
atmosphere within a
confined space is free
from Flammable,
Explosive or Toxic
substances and that the
Oxygen content is 20.9%
IN OTHER WORDS, TO CERTIFY
THAT THE ATMOSPHEREIS SAFE
TO WORK IN!

WHY CARRY OUT
A GAS CHECK?
Hot Work Gas Testing
To certify that there are no leaks
or accumulations of Flammable
Vapours or Explosive gases at the
worksite when Hot work is being
under taken

WHAT DEFINES A SAFE ATMOSPHERE?
Looking at all the essential needs
of our body, sufficient oxygen is
the most urgent, immediate and
basic need we have. Without
sufficient oxygen we will lose
consciousness quickly and die in a
few Minutes.
THE CORRECT FIGURES FOR
OXYGEN IS 20.9%, BELOW OR
ABOVE THIS FIGURE IS
POTENTIALLY HAZARDOUS.

LOW OXYGEN EFFECT AND SYMPTOMS
15 to 19%
12 to 14%
Strenuous work is difficult
Respiration and pulse increases,
co-ordination and judgment impaired
Nausea, fainting, blue lips,
unconsciousness
Death within 8 minutes, recovery if
resuscitated within 4 minutes
9 to 11%
6 to 8%
Remember! that rusting of steelwork and some
chemicals in confined spaces can reduce the oxygen in
the atmosphere to dangerous levels very quickly.

HIGH OXYGEN EFFECTS AND SYMPTOMS
Above 23% oxygen serious fire risk causing some materials to
spontaneously combust, for example oily cloth and steel wool >(30%)
Prolonged exposure causes damage to breathing processes and an
intoxication which seriously disturbs judgment with (industrial 02 gas)
Most gas detection apparatus is uncertified if the oxygen content is
increased above atmosphere levels
Note: The minimum content of Oxygen required for a Catalytic Gas
detector reading LEL, is 13% or more to read accurately.

PROPERTIES OF EXPLOSIVE GASES AND
FLAMMABLE VAPOURS
All combustible gases and vapors are characterized by explosive limits between which,
the gas or vapor mixed with air is capable of sustaining the spread of flame. These can
be referred to as the Explosive or Flammable limits

SUBSTANCE LEL
(Vol%)
UEL
(Vol%)
ACETONE 2.15 13
ACETYLENE 2.4 88
BUTANE 1.5 8.5
ETHANE 3 15.5
ETHYLENE 2.7 34
HEXANE 1.2 7.4
HYDROGEN 4 75.6
METHANE 5 15
PROPANE 2 9.5
Explosive
ranges of
other gases
The Lower Explosive Limit (LEL) of methane is 5%
by volume i.e. 5 volumes of methane mixed with
95 volumes of air. This is the minimum quantity of
Methane in a methane/air mixture that will ignite
to produce a self propagating flame if exposed to
a hot source or a spark from electrical or
mechanical equipment. if there is less than 5% of
Methane in the air by volume the mixture is too
lean to support combustion.
The Upper Explosive Limit ( UEL ) refers to the
highest concentration of a gas in the atmosphere
which results in a combustible mixture. For
example, the UEL of Methane in air is 15% by
volume, which means that if there is more than
15% of Methane in the air by volumethe mixture
is too rich to support combustion.

For example, our list of L.E.L.s shows that Methane has an L.E.L. of 5.0%. This means that a
mixture of 5.0% Methane and 95.0% air, equals 100%, the
L.E.L. for Methane

The most important point to remember is that any indication between 5 – 10% LEL on
the detector means caution and possible danger

Properties of Harmful & Toxic Gases
Within the oil and gas industry a wide range of harmful and toxic gases
can be encountered generallythey can be sub-dividedinto Asphyxiant
and Toxic Gases.
ASPHYXIANT GASES:
• Simple displacement of oxygen from the air we breathe by any
one of these gases can lead to suffocation, remembernitrogen is
widely used in purging applications.
• This heightensthe importance of the oxygen gas test at the
entrance to any confined space, remember20.9% oxygen is the
correct figure.

TOXIC GASES
Toxic gases chemically interfere with the vital processestaking place within our
bodies,only minute amounts of these gases need to be present in our breathing
air to cause catastrophic effects..
As the amount needed to poison us, is well below 1% in quantity, the expression
‘parts per million’ is used to measure these very small quantities of gas.
• examples:
• 10 ppm is the same as 0.001%
• 10,000 ppm is the same as 1%
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23

PROPERTIESOF HARMFULAND TOXIC GASES YOU MAY COME ACROSS
GAS Application And Were Found
Condensate or heavy Hydrocarbonvapours Crude oil residues, oil condensate and Sludges
Hydrogen Sulphide Reservoirgas, crude oil vapour and stagnant water.
Carbon Monoxide Associatedwith combustion process.
Carbon Dioxide Fire extinguishers and Deluge systems
Sulphur Dioxide Sulphur recovery plants and Flare stacks
Chlorine Water treatment
Benzene Sometimes found in crude oil and vapours.
Trichloroethane Solvent sometimes used in de-greasing fluids and dye- penetrants.

PROPERTIESOF HARMFUL AND TOXIC GASES YOU MAY
COME ACROSS
GAS APPLICATION AND WHERE FOUND.
Sulphur Dioxide Sulphur recovery plants and Flare
stacks.
Water treatment.
Sometimes found in crude oil and
vapours.
Solvent sometimes used in de-greasing
fluids and dye- penetrants.
Chlorine
Benzene
Trichloroethane

PROPERTIES OF
HYDROGEN
SULPHIDE
27
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Hydrogen Sulphide is found widely in
the oil industry, it is found in crude oil,
it is found in some natural gases and it
can even be found in stagnant water,
particularly sea water.
Hydrogen Sulphide is a ‘nerve gas ; its
almost as toxic as cyanide and whilst at
very low concentrations it is not
considered to be harmful to us, at high
concentrations it is lethal.

HYDROGEN SULPHIDE
gas is referred to by a
variety of names:
• Sour gas
• Rotten egg gas
• Sulphurated Hydrogen
• H2S

MAIN CHARACTERISTICS OF H2S:
• Potentially lethal.
• Colourless.
• Heavier than air.
• Readily dispersed by wind or air currents.
• Flammable - burns with a blue flame.
• Odour of rotten eggs (below concentration of 100 ppm).
• Highly corrosive to certain materials (eg. steel).

EFFECT OF H2S ON PERSONNEL
The way in which H2S affects you depends on the following:
• Duration: the length of time the individual is
exposed.
how often the individual has been
exposed.
the concentration of exposure.
Frequency:
Intensity:
Susceptibility: the individual’s physiological make up.

EFFECT OF H2S ON PERSONNEL
0.0025 ppm Minimum concentration which produces
odour
Eye and respiratory tract irritation,
especially in vulnerable workers.
Inflammation, blistering and opacity of the
eye, loss of the sense of smell, headache,
cough and nausea.
Respiratory difficulty, respiratory depression and
irritation (exposures of 30 minutes to 8 hours).
10 - 20 ppm
20 - 100 ppm
100 - 300 ppm

0.0025 ppm Minimum concentration which produces
odour
Eye and respiratory tract irritation,
especially in vulnerable workers.
Inflammation, blistering and opacity of the
eye, loss of the sense of smell, headache,
cough and nausea.
Respiratory difficulty, respiratory depression
and irritation (exposures of 30 minutes to 8
hours).
10 - 20 ppm
20 - 100 ppm
100 - 300 ppm
EFFECTS ANDSYMPTEMSOF H2S

300 - 700 ppm Central nervous system effects , eg
tremors, weakness, numbness of
extremities, unconsciousness and
convulsions.
700 - 1000 ppm Rapid (one to several breaths will result
in unconsciousness)
Above 1000 ppm Cessation of breathing (instantaneous)
followed by death.
EFFECTS AND SYMPTEMS OF H2S

If a person inhales H2S, it passes directly through the
lungs in to the bloodstream. To protect itself, the body
’oxidises’ (breaks down) the gas as rapidly as possible
into a harmless compound.
If the person breathes in too much H2S, the body cannot
oxsidise all of it, it builds up in the blood and the person
becomes poisoned. The areas of the brain which control
breathing become paralysed, the lungs stop working and
the person is asphyxiated.
Effect of H2S on personnel

REMEMBER!
700ppm sounds a lot, but
it is only 0.07% vol.,
There may well be
99.93% vol. of fresh air
as the remainder.

EXPOSURE LIMITS AND THE COSHH REGULATIONS
The maximum amount of any toxic gas
that you’re allowed to be exposed to in
the workplace is controlled by law.
The Control Of Substances Hazardous to
Health in the UK or COSHH which states
how much of a particular toxic material
you are allowed to be exposed too and
for how long.

DENSITY OF GASES AND VAPOURS
1.Relative Density of Pure Gas
Gases when pure and concentrated are
either lighter than air, neutral in density
or heavier than air. To simplify an
understanding of the density of gases,fresh
air is given a density which = 1.

So gases, can then be compared with
air to see if they are lighter ( less dense )
or heavier ( more dense ).
Methane, the main component of natural
gas is lighter than air about half the
weight of air.

Ethane
Propane
Butane
Pentane
H2S
Carbon Monoxide
Methane
1.05
1.55
2.00
2.50
1.18
0.97
0.55

Densities of Gas Clouds
The density of a flammable or toxic
gas cloud formed during a gas leakage
incident will depend not only on the
type of gas but more importantly on
its concentration within the gas cloud.

Popular Myth Toxic H2S gas clouds are heavier
than air, usually not true!
(a) 1000 ppm H2S in pure natural gas is
lighter than air.
(b) 1000 ppm H2S in a gas cloud formed
from a high pressure release is neutral.
(c) 1000 ppm H2S entrapped in a condensate
vapour cloud is heavier than air.

ATMOSPHERIC COMPOSITION
CARBON MONOXIDE
Same molecular weight as air (
same density as air)
HYDROGEN SULPHIDE
Heavier than air
(more dense)
METHANE
Lighter than air
(less dense)

CHARACTERISTICS OF GASES
·Remember the flammable and toxic limit
values for gases such as hydrogen sulphide
require relatively large mounts to produce a
flammable mixture where as the quantity
necessary to produce a toxic gas mixture is
extremely small.

APPLICATIONS AND TYPES OF PORTABLE GAS DETECTOR
Detector Principle Measurement
Electrochemical Cell % Volume
Gas Test
Oxygen
Methane or other
Flammable gases
Catalytic or Infra-red
Infra-red or Tank scope
% L.E.L.
% Volume
Electrochemical Cell
or
Chemical stain tube
Toxic gases or Vapours ppm

Used in portable and fixed gas detectors to
detect and measure % oxygen and other toxic
gas concentrations of Hydrogen Sulphide
(H2S), Sulphur Dioxide, Carbon Monoxide,
Chlorine etc,
ELECTROCHEMICAL SENSOR

Platinum
Wire
• The catalytic sens
operate on the
combustion principl
they must be used
environments
containing oxygen
Catalytic Sensor
Catalytically-Treated
Metal oxide material

THE CATALYTIC GAS SENSOR

A methane calibrated gas detector will detect many other flammable
gases and vapours, but may seriously under-read the concentration
present.
For example, on a methane calibrated catalytic gas detector:-
100% LEL propane or butane will only indicate about
50-60% LEL on the display
100% LEL pentane or hexane will only indicate about
35-45% LEL on the display
SUBSTANCE LEL (Vol%) UEL (Vol%)
ACETONE 2.15 13
ACETYLENE 2.4 88
BUTANE 1.5 8.5
ETHANE 3 15.5
ETHYLENE 2.7 34
HEXANE 1.2 7.4
HYDROGEN 4 75.6
METHANE 5 15
PROPANE 2 9.5

Limitations:
1. Cannot be used in an inert gas atmospheres – needs 13% or
more Oxygen.
and Blockage of flame
2. Fails to danger due to Poisons
arrester
Silicones Water
Drilling fluids
Oil
De-greasing fluids
Hot lube oils
WD40
3. Methane calibrated detectors under-read concentrations of
higher hydrocarbon gases & vapours e.g. condensate vapours.
4. Older detectors can give ambiguous readings at high gas
concentrations

Catalytic sensors are most
commonly calibrated to
methane for 0-100% LEL
full scale range
Why?

Methane gas is a very common gas
and is often encountered in many
applications

HOW FREQUENT SHOULD YOU CALIBRATE YOUR
GAS DETECTOR?
• The only way to know that the readings are accurate is to expose t
instrument to known concentration test gas;
• To check the accuracy of the instrument on a regular basis

• Any instrument which may be used in a potentially hazardous locat
should be checked with a known concentration test gas before any
daily period of use.
• Normally 2.5% Methane in Air
HOW FREQUENT SHOULD YOU CALIBRATE
YOUR GAS DETECTOR?

PREMIXED CALIBRATION GAS

WHAT ARE THE BENEFITS FOR CALIBRATION?
Gas detectors are designed to help keep
your safe in potentially life threatening
environments.
If you test your instrument on a daily
basis you know that your readings are
accurate.
Confined spaces and other areas where
the air is potentially dangerous are
environments where you want to be sure

Don’t take a chance
with your life.
Verify accuracy
daily!

Summary

Flammable gas
Sensor range
0%
in volume
UEL
100%
in volume
NO COMBUSTION (lack of oxygen)
LEL
Upper Explosion Limit
HAZARDOUS AREA
Lower Explosion Limit
No combustion (lack of gas
EXPLOSIVERANGE

PERMIT TO WORK
Prior to Hot-Work in zones 1 or 2 or a Enclosed Space, the areas
must be checked to make sure that it is safe for work to be carried
out.
This work is carried under the Permit to Work system,
part of this includes the signing by a competent person
that the atmosphere is safe to work in.
A. Hot Work in Zone 1 and 2 and near an enclosed
space
B. Enclosed Space Entry
C. Inerting Operations

DETAILS OF METER
1. Meter Serial numbers
2. Last Calibration date: (within one month of
today’s date.
3. Battery Check ( Condition)
4. Zero Check in fresh air
5. Check of hand or electrical operated pump
operation
Test for:
Oxygen, Flammable / Explosive and Toxic
vapours and gases
GAS TEST

Operating The Various Combustible Gas Detectors.
Some basic rules for operating gas detectors:
• Ensure you select a gas detector you know how to
operate.
• Check that it has been calibrated within the last
month.
• Look for any signs of damage or misuse.
• Turn it on and confirm the battery and
battery voltage are acceptable.
• Operate it in a safe and atmosphere area to ensure
it "zeros“ properly.

Operating The Various Combustible Gas Detectors.
Refer to and perform the checks listed on the
instrument checklist.
• Know the limitations of each instrument
• Perform the procedures and retests, required by the
work permit or work plan.
• Go over the safety procedures and cover any special
safety "know how" with the men doing the work.
• Always allow at least 3 seconds for every metre of
hose for the sample to reach the sensor.
• Always approach and begin testing from upwind and in
the open fresh air.

Sampling Considerations:
• Oxygen level
• Type of combustibles
• Vapor density
• Temperature
• Wind and air movements
• Possible leak points and size
• Possible traps
REMEMBER .. Gas accumulations may be found
anywhere!

Possible leakage points:
• FLANGES
• VALVE PACKING
• INSTUMENTS
• PUMP & COMPRESSOR SEALS
• TANK & MAHHOLES
• DECK DRAINS

Gas testing only to be carried ou
by Authorised Gas Tester

Sign Apparatus Out/ In in
LOG
Report Any Defects
Report Any Anomalies
Know Your Permit!

POTENTIAL HAZARDS

FIRE
The combination of fuel, air and
heat results in fire.
FLASH FIRE
The combination of an
accumulation of vapor with air
and heat in an open area will
result in a flash fire.
EXPLOSION
The combination of an
accumulation of vapor air and
heat in the right proportion in a
confined space results in
explosion.
You may not SEE
You may not SMELL
You may not TASTE
But COMBUSTIBLES
can cause an unexpected

THANK YOU FOR YOUR ATTENTION

Conclusion.. Its just beginning
QUESTIONS

Thank You

15._SGW -_GAS_TESTING__MONITORING .pptx

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