Fire Fighting System And Fire Protection Facilities

Introduction

We will learn in this chapter in which way a system should be designed and executed through to get the best performance of system even in emergency.

A) Chemicals present a very substantial hazard due to fires and explosions.

The three most common chemical plant accidents are:

1. Fire
2. Toxic release
3. Explosions

B) The essential elements for combustion are

1. Fuel
2. Oxidiser
3. Ignition-source

C) Fuels, oxidisers, ignition source in chemical industry.

Fuels :-

Liquids : Gasolene, Acetone, Ether, Pentane etc.

Solids : Plastics, Wood, Dust, Fibers,

Gases : Acetylene, Propane, Hydrogen.

Oxidiser

Gases : O2, F2, Cl2

Liquids : HNO3/H2O2/ Some acids.

Solids : Metal Peroxides/ NH4NO2

Ignition Sources

Sparks, Flame, Static Electricity, Heat.

What is Fire? 

It is a chemical reaction in which a substance combines with an oxidant and releases energy, part of the energy releases is used to sub stain the reaction.

Flash Point

It is the lowest temperature at which it gives off enough vapour to form an ignitable mixture with air. The flash point generally increases with increase in pressure.

Chemical Explosion

It is a rapid expansion of gases resulting in a rapidly moving pressure or shock wave. The expansion can be mechanical in sudden exposure of a pressure vessel or it can be a result of a rapid chemical reaction.

Mechanical Explosion

It is due to the sudden failure of a vessel containing high-pressure gas. Designs to Prevent Fires and Explosions

1) Inerting- process of adding inert gas to a combustible mixture to reduce the concentration of oxygen below the limit- n2 gas is generally used.

2) Curbing of production of static electricity

3) Prevent sparks.

4) Explosion proof electrical equipments.

5) Ventilation open air plant.

6) Sprinkler system.

Fire Protection Facilities

Compliance of the tariff advisory committee rules or OISED i.e. that is Oil Industry Safety Directorate (established in 1986) . Rules will not only obtain appropriate discount is the fire insurance premium but will also instill that feeling of security in the minds of staff. Direct loss from fire and the resultant wastage is always serious but indirect loss of business is much more serious.

Types of Fire Protection Facilities

1) Internal appliances
2) Mechanically driven fire engines and trailer pumps
3) A well designed and laid hydrant system.

Internal Appliances

Generally consist of “hand appliances” and “hose reels”

A) Hand appliances buckets and extinguishers.

B) List of approves manufactures.

C) These are essentially “first-aid” equipments only meant for attacking small fires in their initial stages and are not intended to deal with large outbreaks of fires.

D) It is recommended that extinguishers installed in any one building or single occupancy be similar in shape and appearance as far as possible.

E) Boards

1) Nature of contacts of a building

2) Process carried out

3) Types of fires which may occur.

Fire Water Supply

1) It shall be stores in underground lines reservoir or above ground steel, concrete or masonry.

2) Effective capacity above the level of the foot valve seat in case of negative suction.

3) Reservoirs of above 2,25000 lit capacity as calculated for 2 hrs/3hrs/4hrs aggregate pumping capacity shall be in the compartments to facilitate cleaning and repairs.

Pumps

1) Pumps shall be exclusively used for fire-fighting purpose.

2) Pumps shall be direct couples belt driven pumps are not accepted.

3) Part of pumps like impeller, shaft sleeve, wearing rings shall be of noncorrosive metal preferably of brass or bronze.

4) Pump capacity would depend on whether tapping for water spray or foam protection for tanks is taken from the hydrant service.

Capacity for Hydrant System

Are acceptable
Number of hydrants equivalent
Double hydrant – 2 hydrants
Monitors 63MM – 3
75 MM – 4
100 MM- 6

Where storage tanks containing flammable liquids are protected by MVWS medium vel. Water spray system tapped from hose hydrant system, the water requirement of the spray system shall be calculated for tanks located in common dyke which have the rate of10 lit/min/sq.mt. Of the tank shell surface area.

+
Loaded for supplementary hose streams 

 
Largest tank in a Sykes has diameter 

 
UPTO 10M 1700 LIT/MIN
11-20 2250 LIT/MIN
21 AND ABOVE 4500 LIT/MIN

If total of MVWS = hose stream > hydrant this pumping capacity cover’s.

Fixed Foam System

Water requirements shall be considered for the largest protected tank at the rate of 5 lit/min sq. mt. of liquid surface area.

Where sphere/bullets containing LPG are protected by MVWS the water requirement shall be calculated for upto 3 spheres/bullets having largest aggregate surface area located within r +15 of each other at the rate of 10 lit/min/ Sq. Mit.

Jockey pump: High hazards (b) capacity to be 180 LPM pumps shall be capable of furnishing not less than 150%of rated capacity @ head not less than 65% of the rated head.

Suction velocity

High hazard (b) pump shall be 30 mt. Clear of all equipments containing hydrocarbons.

Mains

1) Is 1239 up to 6" ERW is 3589 for 8" and above size ERW.

2) Supported @ 3.5. Internals

3) 10% radiography

4) 6mt. Away from face of building and open storage area for light and ordinary hazards and 15m in case of high hazards.

5) Mains shall be in rings.

6) The mains shall not traverse ground that is under the control of the owner.

7) The velocity at any point should not exceed 3 mt/ sec.

8) Gate valves confirming to is 780 p.n.1.6 and is 2906 pn 1.6 will be used.

9) The hole system may be stress analyzed.

Hydrants/fixed monitors

1) Connection for any purpose other than fire fighting are not permitted from hydrants.

2) All hydrants outlets shall be 1 m above ground level.

3) Stand post shall be 80 mm for single headed and 100 mm for double headed.

4) 100 mm stand post for monitors 63 and 75 mm size and 150 mm for 100mm monitor and painted ‘fire red’

5) Distance between two hydrants

Light hazards – 60 mt.

Ordinary hazards –45 mt.

High hazards – 30 mt.

6) Hydrants/monitors shall not be installed with in dyked enclosures not can the main line pass through it.

Summing Up

For the fire fighting system, there are certain guidelines fixed by the statutory body. These guidelines are to be followed and the piping engineer has to identify the ‘Hazardous Areas’ and take corrective action. This is again a network to be laid along with the rest of the piping of the plant and care has to be taken during the preparation of the plant layout. Head and quantity balancing is again important for the fire fighting system.

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