2. What is fire?
Fire is continuous oxidation of combustible material in exothermic chain reaction between fuel and
oxygen or oxidiser or air as catalyst when exposed to sufficient amount of heat or ignition source
giving out smoke, heat, light energy in the form of electromagnetic spectrum and other by products
such as sound and pressure.
Fire produces different colours of flame depending on type of fuel is consumed.
3.
4. What is gas?
The name gas comes from the word chaos.
Gas is a swarm of molecules moving randomly
and chaotically, constantly colliding with each
other and anything else around it.
Gases fill any available volume and due to the
very high speed at which they move will mix
rapidly into any atmosphere in which they are
released.
VAPOUR-A gaseous form of a substance that
is liquid or solid at normal temperatures and
pressures
FUME-airborne dispersion consisting of
minute particles that come from heating a solid
(often an oxide resulting from a chemical
reaction between the particles and oxygen.
5.
6. Why do we need fire and gas detection system??????.....
Fire & Gas detection is mainly used to monitor areas where hazardous levels of
gas or flammable substance that are not present at normal operation.
They are designed to give early warning of the build up of gas or fire before it
becomes a hazard to people, infrastructure and environment.
Various national and international laws exist that demand the use of gas or fire
detection to protect people and plant
Many local codes of practice also exist that ensure health and safety policies are
employed
Insurance companies may not provide cover to businesses that cannot prove that
they have taken appropriate safety measures to detect hazardous gases and
detection of flame, smoke, heat, or fire
7. Gas Hazards
There are three main types of gas hazard
1. Flammable
– Risk of fire and or explosion,
e.g. Methane, Butane, Propane
2. Toxic
– Risk of poisoning,
e.g. Carbon Monoxide, Hydrogen Sulfide, Chlorine
3. Asphyxiant
– Risk of suffocation,
e.g. Oxygen deficiency, Nitrogen, Carbon Dioxide
8. Flammable Risk
• Fire Triangle
Three factors are always needed to cause
combustion:
1. A source of ignition
2. Oxygen
3. Fuel in the form of a gas
or vapour
fuel
FIRE
9. What is Flash Point?
Flash point is the lowest temperature at which a liquid
can form an ignitable mixture in air near the surface of
the liquid.
The lower the flash point, the easier it is to ignite the
material.
10. What Is Ignition Point
The minimum temperature at which a substance will continue to
burn without additional application of external heat. Also called
kindling point.
11. Vapour density
-It is the relative density of a gas or vapour when air = 1.0
vapour density <1, gas will rise
vapour density >1, gas will fall
Examples
methane..................................... 0.55
carbon monoxide ..................... 0.97
hydrogen sulphide ................... 1.19
petrol vapour (approx) ............. 3.0
12. LIMITS OF FLAMMABILITY
LOWER FLAMMABLE/EXPLOSIVE LIMIT (LFL/LEL):
• THE MINIMUM CONCENTRATION OF A GAS OR VAPOR MIXED IN AIR THAT WILL BURN.
• BELOW THIS CONCENTRATION THE MIXTURE WILL NOT BURN (“TOO LEAN”).
• EXPRESSED AS A PERCENTAGE OF THE GAS IN AIR.
UPPER FLAMMABLE/EXPLOSIVE LIMIT (UFL/UEL):
• THE MAXIMUM CONCENTRATION OF A GAS OR VAPOR MIXED IN AIR THAT WILL BURN.
ABOVE THIS CONCENTRATION THE MIXTURE WILL NOT BURN(“TOO RICH”)
• EXPRESSED AS A PERCENTAGE OF THE GAS IN AIR.
13.
14.
15. Toxic Risk
• Some gases are poisonous and can be
dangerous to life at very low
concentrations.
• Some toxic gases have strong smells like
the distinctive ‘rotten eggs’ smell of
H2S
• Others are completely odourless like
Carbon Monoxide
16. Toxic Risk
• The measurement most often used for
the concentration of toxic gases is parts
per million (ppm).
• For example 1ppm would be equivalent
to a room filled with a total of 1 million
balls and 1 of those balls being red. The
red ball would represent 1ppm.
1 million balls
1 red ball
20. Gas Detection
In general, gas detection is divided into combustible gas detection and toxic gas detection. This is a
broad separation that breaks down in some cases, e.g. some gases are both toxic and combustible in the
concentrations expected. Historically there has also been a separation in technology between combustible
and toxic detection.
Below are some of the issues you need to consider when choosing gas detectors.
·Most devices used in the oil and gas industry are set to detect methane (CH4) or hydrogen sulphide
(H2S).
·Many detectors show cross-sensitivity; i.e. a detector for detecting one gas will also detect another, at
different readings. So at the time of purchase it is important to specify the gas that is to be detected and
consider other gases that may be present that may affect the readings.
·The nature of the gas should be considered – e.g. H2S is heavier than air, methane rises, propane sinks.
However they may not behave like that under a high pressure discharge.
·Altitude affects the readings of some detectors.
21. Combustible Gas Detection:
Two mainstream technologies are available – infra-red absorption and catalytic types. Other types are
available and in development; e.g. metal oxide semiconductor sensors.
Point detectors are calibrated against the lower explosive limit (LEL) of a certain gas, frequently methane.
The lower explosive limit for methane mixed in air is achieved at a 5% concentration. Typical alarm
settings are 20% LEL and 40% LEL. Confusion can arise as these levels are traditionally labelled low
gas and high gas, whereas control instrument engineers would use the term high alarm and high-high
alarm.
Open path gas detectors are calibrated in LEL metres (LELm). This setting has evolved as an analogue
with the LEL range used in point detectors.
22. Infra-red Absorption Combustible Gas Detection:
Hydrocarbons have special properties which can be used for infrared
measurement of their concentration.
The technology uses the absorption characteristics of the
hydrocarbon molecules to infra-red light. The more hydrocarbon
molecules are present, the higher the absorption of infra-red
radiation. More than one type of hydrocarbon gas may be detected.
This technology is more expensive than catalytic detection, but it is
used for many applications as it doesn’t need field calibration and
proof test intervals are considerably better (longer) than for catalytic
types. Speed of response is quicker than for catalytic types. The
measured value doesn’t drift unlike catalytic detectors. And unlike
catalytic types, the detector doesn’t need oxygen for
operation.9066814650.
23.
24. Catalytic Bead Sensors:
One pellistor alone is not suitable for the detection of flammable gases and vapours. It needs a second one to
compensate for environmental parameters (especially temperature and humidity). And it needs to be explosion
protected. By means of a flameproof enclosure and a sinter disk.
Working principle: Uses a catalytic bead to oxidize combustible gas; a Wheatstone Bridge converts the resulting
change in resistance into a corresponding sensor signal..
25.
26.
27.
28.
29. Instrument Calibration:
“Calibration” refers to an instrument’s measurement accuracy relative to a known concentration of gas.
Gas detectors perform relative measurements: rather than independently assessing the quantity of gas present,
they measure the concentration of the air sample and then compare it to the known concentration of the
gas that the instrument is configured. This “known concentration” serves as the instrument’s measurement scale,
or reference point.
If the instrument’s reference point has moved, then its reading will also move. This is called “calibration
drift” and it happens to most instruments over time. (Common causes of calibration drift include the normal
degradation of sensors, exposure of the sensor to poisons, and harsh operating conditions.)
When an instrument experiences calibration drift it can still measure the quantity of gas present, but it cannot
convert it into an accurate numerical reading. Regular calibration with a certified standard gas concentration
updates the instrument’s reference point, re-enabling it to produce accurate readings.
There are two methods of verifying instrument calibration: through a functional or “bump” test (or span check)
or by performing a full calibration.
33. Bhopal Gas Tragedy, India
The worst industrial tragedy ever known was a result of utter negligence on part of a pesticide
manufacturing company and incompetence of the government authorities. Over 500,000 people
were exposed to the deadly methyl isocyanate and other chemicals leaking from the pesticide plant
of Union Carbide India Ltd at Bhopal, India on the night of December 2-3, 1984. The gas leaked
spread in the town through air and water killing 8000 people within two weeks and injuring 558,125
of which of which approximately 3900 were seriously and permanently disabled. UCC had been
warned before of potential leakages though no real efforts were made to improve the situation
finally leading to a disaster which claimed thousands of life.
Bhopal Gas
Tragedy, India
34. Rig:
Mumbai (Bombay) High
North Platform
Date: 27 July 2005
Location: Mumbai High, Indian Ocean
Operator:
Oil and Natural Gas
Corporation (ONGC)
35. RISK ASSESMENT:
Certain plant operations and maintenance may require that one or more leak
detection devices are inhibited for a short time, and it is important to understand the
degree of cover that remains during this time and that the risks have been assessed
correctly.
Construction work may result in long term inhibits (more than one shift) and it may
be appropriate to revise the safety case for such activities.
