UNIT 4 –FUNDAMENTALS OF FIRE SAFETY

COURSE : INTRODUCTION TO CIVIL ENGINEERING

DEPT OF CIVIL ENGINEERING, DBCE, FATORDA

INSTRUCTOR: ANNAPURNA SAKHARDANDE

What is Fire

Fire, the common term given to the combustion reaction

which results from interaction of HEAT + FUEL + OXYGEN. This

combination is called ‘Triangle of Fire’.

Fuels involved can be in three states: SOLID, LIQUID, GAS.

HEAT, SMOKE, LIGHT, GASES are by-products of the reaction.

Triangle of Fire

Types of Fire

Class A – Solids Solid combustibles like Wood, Paper, Cloth, Rubbish, Plastics

Class B – Liquids Liquids like Gasoline, Oil, Petrol, Diesel, Grease, Acetone

Class C – Gases Gases like LPG, Methane, Propane

Class D – Metals Metals like potassium, sodium, aluminum, magnesium

Class E – Electrical Fires involving electricity and electrical components

THEORY OF FIRE Extinguishment

• Extinction of a fire may be achieved in a number of ways:

1. stopping the supply of fuel vapours

2. quenching the flame by chemical extinguishers (inhibiting)

3. removing the supply of air (oxygen) to the fire (smothering)

4. “blow-out”.

Fire Extinguishers Fire extinguishers put out fires by taking away one or more

elements from the ‘triangle of fire’.

Oxygen Removed

“ SMOTHERING”

Fuel Removed

“ STARVING”

Heat Removed

“ COOLING”

REMEMBER: Extinguishers Will have a label indicating what type of fire it can

extinguish. Not all extinguishers can be used for all types of fires.

DO NOT USE AN EXTINGUISHER IF YOU DON’T KNOW ITS USE OR

HOW TO USE IT

EXTINGUISHING AGENTS AND SYSTEMS

• Fire Suppression Systems

a) Gas based systems — Systems that use gaseous agents as fire suppression media, such as, all agents alternate to Halon gases, listed and approved for use by relevant Indian Standards; other methods/types of gas based systems where their protection is equal to or better than what is suggested above for the type of application subject to the acceptance of Authorities concerned may also fall under such systems.

Water based systems — Systems • Hydrant System — A distribution system having a

network of piping installed underground/aboveground around and/or through inside of a building with internal and/or external hydrants fitted with landing valves at regular intervals according to the occupancy. The distribution system is connected to water supply system for firefighting.

• Automatic Water Spray Systems — A special fixed pipe system connected to a reliable source of fire protection water supply and equipped with water spray nozzles for specific water discharge and distribution over the surface or area to be protected. The piping system is connected to the water supply through an automatically actuated deluge valve which initiates flow of water. Automatic actuation is achieved by operation of automatic detecting equipment installed along with water spray nozzles. There are two types of systems namely high velocity and medium velocity systems.

Water based systems — Systems

• Automatic Sprinkler System — A system of water pipes fitted with sprinkler heads at suitable intervals and heights and designed to actuate automatically, control and extinguish a fire by the discharge of water.

• Water Mist Systems — A distribution system connected to a pumping and water supply system that is equipped with nozzles capable of delivering water mist to the part/entire enclosure or area, intended to control, suppress, or extinguish fire and is capable of meeting the specified performance requirements.

• Water Mist extinguishers are a recent development that extinguish the fire by taking away the heat element of the fire triangle. They are an alternative to the clean agent extinguishers where contamination is a concern.

• Water mist extinguishers are primarily for Class A fires, although they are safe for use on Class C fires as well.

Water based systems — Systems

Water based systems — Systems • Foam Protection System — Firefighting

systems where foam is made by mechanically mixing air with a solution consisting of fresh water to which a foaming agent (liquid concentrate) has been added. Firefighting foam is a stable aggregation of small bubbles of density lower than oil or water, and shows tenacious qualities for covering horizontal surfaces. There are three types of foam applications that is, low, medium and high expansion foams depending upon the application.

• Wet Riser — An arrangement for firefighting within the building by means of vertical rising mains not less than 100 mm nominal diameter with landing valves on each floor/landing for firefighting purposes and permanently charged with water from a pressurized supply.

Powder Based Fire Extinguishers • Dry Powder Dry Powder extinguishers are similar to dry chemical except that they extinguish the fire by separating the fuel from the oxygen element or by removing the heat element of the fire triangle. However, dry powder extinguishers are for Class D or combustible metal fires, only. They are ineffective on all other classes of fires

Cost ranges from Rs.600 – Rs.5000.

CHEMISTRY AND PHYSICS OF FIRE

• Fire is a manifestation of uncontrolled combustion

Controlling the flow of fuel vapours • applicable to a gas-jet fire in which the supply of the fuel can simply be turned off

• most common and safest method of extinguishing a fire involving condensed fuels

• In the case of a fire involving a solid, this requires the fuel surface to be cooled below the firepoint, when the flow of vapours becomes too small to support a flame. (achieved most effectively by the application of water, either manually or by means of an automatic system sprinklers, water spray, etc.).

• liquid fires cannot be dealt with in this manner: liquid fuels with low firepoints simply cannot be cooled sufficiently, while in the case of a high-firepoint fuel, vigorous vaporization of water when it comes into contact with the hot liquid at the surface can lead to burning fuel being ejected from the container. This can have very serious consequences for those fighting the fire. (There are some special cases in which an automatic high-pressure water-spray system may be designed to deal with the latter type of fire, but this is not common.)

• Liquid fires are commonly extinguished by the use of fire-fighting foams (Cote 1991). This is produced by aspirating a foam concentrate into a stream of water which is then directed at the fire through a special nozzle which permits air to be entrained into the flow. This produces a foam which floats on top of the liquid, reducing the rate of supply of fuel vapours by a blockage effect and by shielding the surface from heat transfer from the flames. The foam has to be applied carefully to form a “raft” which gradually increases in size to cover the liquid surface. The flames will decrease in size as the raft grows, and at the same time the foam will gradually break down, releasing water which will aid the cooling of the surface. The mechanism is in fact complex, although the net result is to control the flow of vapours.

• There are a number of foam concentrates available, and it is important to choose one that is compatible with the liquids that are to be protected. The original “protein foams” were developed for hydrocarbon liquid fires, but break down rapidly if brought into contact with liquid fuels that are water soluble. A range of “synthetic foams” have been developed to tackle the entire range of liquid fires that may be encountered. One of these, aqueous film-forming foam (AFFF), is an all-purpose foam which also produces a film of water on the surface of the liquid fuel, thus increasing its effectiveness.

PROCEDURES IN THE EVENT OF A FIRE

• The Rules for Fighting Fires • Just remember the three A's • ACTIVATE the building alarm system or notify the fire department

by calling 911. Or, have someone else do this for you. • ASSIST any persons in immediate danger, or those incapable on

their own, to exit the building, without risk to yourself. • Only after these two are completed should you ATTEMPT to

extinguish the fire.

• Only fight a fire if: • The fire is small and contained • You are safe from toxic smoke • You have a means of escape • Your instincts tell you it's OK

TYPES OF DETECTING DEVICES

• Automatic Fire Detection and Alarm System — A system comprising components and sub-systems required for automatically detecting smoke, heat or fire initiating an alarm and other actions as appropriate. This system also includes manually operated electronic fire alarm (MOEFA) system. NOTE — MOEFA system (with or without automatic fire detection and alarm system) includes all or some of the components such as manual call stations (initiating an alarm for fire and other actions as required), talk-back system and public address system.

Firefighting installations

Fundamentals of industrial safety

Different types of safety systems and equipments

Recognition of possible fire sources and emergency

Explosive ACT

Electricity ACT

Factories ACT 1948

References

• https://www.femalifesafety.org/types-of-extinguishers.html