1. Fire and Explosion

2. Fire Prevention Goals Life Safety Property Protection
The primary goal of fire safety efforts is to protect building occupants from injury and to prevent loss of life.
Property Protection
The secondary goal of fire safety is to prevent property damage.
Protection of Operations
By preventing fires and limiting damage we can assure that work operations will continue.

3. Fire Hazard 
The Fire Triangle
The essential elements for combustion are fuel, an oxidizer, and an ignition source.
These elements are illustrated by the fire triangle

4. Each of these three elements must be present at the same time to have a fire. A fire will burn until one or more of the elements is removed.
Fuel
Any combustible material – solid, liquid or gas
Heat
The energy necessary to increase the temperature of fuel to where sufficient vapors are given off for ignition to occur
Oxygen
The air we breathe is about 21% oxygen – fire needs only 16% oxygen

5. Sparks, flames, static electricity, heat
Various fuels, oxidizers, and ignition sources common in the chemical industry are:
Fuels
Liquids: gasoline, acetone, ether, pentane
Solids: plastics, wood dust, fibers, metal particles
Gases: acetylene, propane, carbon monoxide, hydrogen
Oxidizers
Gases: oxygen, fluorine, chlorine
Liquids: hydrogen peroxide, nitric acid, perchloric acid
Solids: metal peroxides, ammonium nitrite
Ignition sources
Sparks, flames, static electricity, heat

6. Distinction between Fires and Explosions
The major distinction between fires and explosions is the rate of energy release.
Fires release energy slowly, whereas explosions release energy rapidly, typically on the order of microseconds.
Fires can also result from explosions, and explosions can result from fires.
A good example of how the energy release rate affects the consequences of an accident is a standard automobile tire.
The compressed air within the tire contains energy.
If the energy is released slowly through the nozzle, the tire is harmlessly deflated. If the tire ruptures suddenly and all the energy within the compressed tire releases rapidly, the result is a dangerous explosion.

7. Definitions:
Flash point (FP): The flash point of a liquid is the lowest temperature at which it gives off enough vapor to form an ignitable mixture with air. At the flash point the vapor will burn but only briefly; inadequate vapor is produced to maintain combustion.

8. 2) Fire point: The fire point is the lowest temperature at which a vapor above a liquid will continue to burn once ignited; the fire point temperature is higher than the flash point.
3) Flammability limits: Vapor-air mixtures will ignite and burn only over a well-specified range of compositions.
The mixture will not burn when the composition is lower than the lower flammable limit (LFL); the mixture is too lean for combustion.
The mixture is also not combustible when the composition is too rich; that is, when it is above the upper flammable limit (UFL).
A mixture is flammable only when the composition is between the LFL and the UFL.
Lower explosion limit (LEL) and upper explosion limit (UEL) are used interchangeably with LFL and UFL.

9. Ignition Energy:
The minimum ignition energy (MIE) is the minimum energy input required to initiate combustion.
All flammable materials (including dusts) have MIEs.
The MIE depends on the specific chemical or mixture, the concentration, pressure, and temperature. .

12. Concepts to Prevent Fires and Explosions
A twofold strategy is used to limit the potential damage from fires and explosions:
prevent the initiation of the fire or explosion
minimize the damage after a fire or explosion has occurred.

13. How to prevent fires and explosion
1) Inerting:
Inerting is the process of adding an inert gas to a combustible mixture to reduce the concentration of oxygen below the limiting oxygen concentration (LOC).
The inert gas is usually nitrogen or carbon dioxide, although steam is sometimes used.
Inerting begins with an initial purge of the vessel with inert gas to bring the oxygen concentration down to safe concentrations.
A commonly used control point is 4% below the LOC, that is, 6% oxygen if the LOC is 10%.

14. 2) Static Electricity
A common ignition source within chemical plants is sparks resulting from static charge buildup and sudden discharge.
Static electricity is perhaps the most indefinable sources of ignitions.
Despite considerable efforts, serious explosions and fires caused by static ignition continue to plague the chemical process industry.
A charged object must be discharged to a ground or to an oppositely charged object

16. 3) Ventilation
Proper ventilation is another method used to prevent fires and explosions.
The purpose of ventilation is to dilute the explosive vapors with air to prevent explosion and to confine the hazardous flammable mixtures.
Open-Air Plants
Open-air plants are recommended because the average wind velocities are high enough to safely dilute volatile chemical leaks that may exist within a plant.
Although safety precautions are always practiced to minimize leaks, accidental releases from pump seals and other potential release points take place.
Plants Inside Buildings
Frequently, processes cannot be constructed outside. In this case local and dilution ventilation systems are required.

17. Sprinklers - The Principles
4.Sprinkler System
Sprinklers - The Principles
Water sprinklers provide an automatic spray dedicated to the area of fire outbreak. Sprinkler heads have temperature sensitive elements that respond immediately to heat, discharging the contents of the water main to which they are attached.
In addition to a rapid response which reduces and isolates fire damage, sprinklers use less water to control a fire than the firefighting service, therefore preventing further damage from excess water.

18. Sprinkler systems were initially credited to an American, Henry Parmalee, following his research during the late 1800s.

19. Quartzoid bulb

23. (1)main water tank
(2)main water pump
(3)main pilot valve (dry)
(4)pilot valve (wet)
(5)sprinkler head - standing configuration
(6)sprinkler head - hanging configuration
(7)pressure tank

26. 2) Using the Flammability Diagram To Avoid Flammable Atmospheres
A general way to represent the flammability of a gas or vapor is by the triangle diagram shown in Figure 6-6.
Concentrations of fuel, oxygen, and inert material (in volume or mole %) are plotted on the three axes.
Each apex of the triangle represents either 100% fuel, oxygen, or nitrogen.
The tick marks on the scales show the direction in which the scale moves across the figure. Thus point (A) represents a mixture composed of 60% methane, 20% oxygen, and 20% nitrogen.
The zone enclosed by the dashed line represents all mixtures that are flammable. Because point (A) lies outside the flammable zone, a mixture of this composition is not flammable.

29. The air line represents all possible combinations of fuel plus air.
The air line extends from the point where fuel is 0%, oxygen is 21% and nitrogen is 79% to the point where fuel is 100%, oxygen is 0% and nitrogen is 0%.
The stoichiometric line represents all stoichiometric combinations of fuel plus oxygen. The combustion reaction can be written in the form:
Fuel + z O2  combustion products (where z is the stoichiometric coefficient for oxygen)
The stoichiometric line extends from a point where the fuel is 100/(1 + z), oxygen is 100z/(1 + z) and nitrogen is 0%, to a point where fuel is 0%, oxygen is 0% and nitrogen is 100%.
The shape and size of the flammability zone on a flammability diagram change with a number of parameters, including fuel type, temperature, pressure, and inert species.
Thus the flammability limits and the LOC also change with these parameters.

33. How to understand the flammability diagram:
If two gas mixtures R and S are combined, the resulting mixture composition lies on a line connecting the points R and S on the flammability diagram. The location of the final mixture on the straight line depends on the relative moles in the mixtures combined: If mixture S has more moles, the final mixture point will lie closer to point S.
If a mixture R is continuously diluted with mixture S, the mixture composition follows along the straight line between points R and S on the flammability diagram. As the dilution continues, the mixture composition moves closer and closer to point S. Eventually, at infinite dilution the mixture composition is at point S.
For systems having composition points that fall on a straight line passing through an apex corresponding to one pure component, the other two components are present in a fixed ratio along the entire line length.
The LOC can be estimated by reading the oxygen concentration at the intersection of the stoichiometric line and a horizontal line drawn through the LFL

34. The flammability diagram is useful for tracking the gas composition during a process operation to determine whether a flammable mixture exists during the procedure.
For example, consider a storage vessel containing pure methane whose inside walls must be inspected as part of its periodic maintenance procedure.
For this operation the methane must be removed from the vessel and replaced by air for the inspection workers to breathe.
The first step in the procedure is to depressurize the vessel to atmospheric pressure. At this point the vessel contains 100% methane, represented by point A in Figure 6-7. If the vessel is opened and air is allowed to enter, the composition of gas within the vessel will follow the air line in Figure 6-7 until the vessel gas composition eventually reaches point B, pure air.

36. Note that at some point in this operation the gas composition passes through the flammability zone.
If an ignition source of sufficient strength were present, then a fire or explosion would result.
The elimination of ignition sources alone is not enough to prevent fires and explosions; ignition sources are too plentiful to use as the primary prevention mechanism.
A more robust design is to prevent the existence of flammable mixtures as the primary control, followed by the elimination of ignition sources as a secondary control.
The flammability diagram is important for determining whether a flammable mixture exists and for providing target concentrations for inerting and purging procedures.
So, the objective is to avoid the flammable region.