FIRE AND GAS DETECTION

SYSTEMBY

ISMAIL ALI MOHAMED

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.

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.

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

Gas HazardsThere 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

Flammable Risk

• Fire TriangleThree factors are always needed to cause combustion:

1. A source of ignition2. Oxygen3. Fuel in the form of a gas

or vapour

fuel

oxyg

en

heat

FIRE

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.

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.

Vapour density

-It is the relative density of a gas or vapour when air = 1.0

vapour density <1, gas will risevapour density >1, gas will fall

Examples

methane..................................... 0.55carbon monoxide ..................... 0.97hydrogen sulphide ................... 1.19petrol vapour (approx) ............. 3.0

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.

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

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

Safety Certification

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.

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.

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.

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..

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.

TURBINE CHALLENGES Turbine Air Intake Acoustic Turbine Enclosure Hydrogen Cooling System

LOGIC CONTROLLER OR FIRE

ALARM SYSTEM

SHUTDOWN SYSTEM

HMI GRAPHIC

REPRESENTATION AND ALARM

LISTS

FIRE SUPPRESSION SYSTEM

ALARM NOTIFICATIO

N BEACONS

AND LAMPS

GAS DETECTION

TOXIC FLAMMABL

EMANUAL

CALL POINT

FIRE DETECTION

SMOKE HEAT

FLAMEMANUAL

CALL POINT

BASIC F&G LOGIC PHILOSOPHY:

FIRE PROTECTION MAPPING GRAPH

Bhopal Gas Tragedy, IndiaThe 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

Rig: Mumbai (Bombay) High North Platform

Date: 27 July 2005Location:

Mumbai High, Indian Ocean

Operator:

Oil and Natural Gas Corporation (ONGC)

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.