Preamble to Slide Series. “Fire is no Accident” Fire Chemistry for Construction Workers.

Preamble to Slide Series

“Fire is no Accident”

Fire Chemistry for Construction Workers

3 States of Matter

• Solid• Liquid• Gas

What is fire?

• Answer : Fire is a phenomena that occurs when a substance combines with oxygen from the air and typically gives out heat, smoke and bright light.

• But it is not all that simple!

What is fire?

• For fire to start, a combustible substance must be present, the temperature must be high enough to cause combustion, and enough oxygen must be present to sustain rapid combustion. It gets more complicated!

Chemistry of Fire

• Oxygen combines with other substances to produce new products – this is called “oxidation”

When it is real slow it can be called “rusting”

Chemistry of Fire

• Stored chemical energy is converted to energy in the form of heat and light.

• The energy in these chemical reactions comes from the breaking and formation of chemical bonds.

Chemistry of Fire

• Once a fire starts it will continue to burn until the supply of oxygen is exhausted or until the fuel is removed or consumed

• or• Someone extinguishes it

How Hot is Hot?

• The heat of combustion is an exothermic reaction – it gives off heat.

Activation energy

–the minimum energy necessary for a specific chemical reaction to occur i.e. matches, electrical discharges, sparks, and chemicals.

How Hot is Hot?

• Ignition Temperature: Minimum temperature at which a fuel will spontaneously ignite.

Definitions of Termsfor Solid Fuels

• Ignition Temperature- The temperature to which a fuel must be heated to initiate combustion

• Sometimes called the “autoignition” temperature.

• Every fuel has an ignition temperature!

•

Heat and Fuel

• Fuel needs to be in gaseous state to ignite – temperature must be high enough to vaporize the fuel.

Spontaneous Combustion

Is a type of combustion which occurs without an external ignition source.

• Heat builds up to the point of ignition• Uses chemicals to supply oxygen –

such as oxidizing agents

Requirements for Combustion

• A fuel must be present• Oxygen must be available in

sufficient quantity• Heat must be applied to initiate

combustion, and sufficient heat must be generated to sustain the reaction.

Requirements for Combustion

• Rate of oxidation (reaction): • Rate of oxidation of a fuel must be

capable of sustaining a flaming fire.

Pyrolysis

• The chemical decomposition of a substance through the action of heat

Definition of TermsFlammable Liquids and Gases

• Flash Point: Minimum temperature at which a liquid fuel will produce enough vapor to burn.

• Flammable Range: The (range of) composition of fuel-air mixture required for combustion.

• Flammable range of gasoline is 1.3- 6%.

What is the difference between and Fire and a Explosion?• Detonation• The speed at which explosives

decompose (detonation) varies greatly and permits the classification of explosives as high and low explosives.

What is the difference between and Fire and a Explosion?DeflagrationLow Order Explosives: Low explosives

have velocities of detonation less than 1,000 m/s. Less than the speed of sound

What is the difference between and Fire and a Explosion?• Detonation• High Order Explosives: High

explosives have velocities of detonation more than 1,000 m/s. More than the speed of sound

Production of Smoke

• Carbon monoxide• Carbon particles• Carcinogens

Fire is not an accident- It is the presence of two behaviors

• Acts by individuals to allow the right combination of components to be present

• Or• Omissions by individuals that allows the

right combination of components to be present

All Fire have “causes”

The Fire Triangle

• This combination is sometimes called the fire triangle because it has three sides.

http://en.wikipedia.org/wiki/Image:Fire_triangle.svg

What three components are required to have a fire start?

• Fuel • Heat• Air

http://en.wikipedia.org/wiki/Image:Fire_triangle.svg

Fuel can be solid, liquid or gas

• The more finely divided the fuel is the more likely it can be easily ignited.

Specific Solid Fuel Conditions

• On the basis of specific surface and fire susceptibility, all combustible solids can be classified into three categories:

»Tinder»Kindling»Bulk fuel


• Surface Area• Volume• Density

TINDER : Solids with specific surface ofTinder can be ignited by very small heat sources



KINDLING : Solids with specific surfaceThat can be ignited fairly easilyKindling requires a burning tinder for ignition.



BULK FUEL : Solids with specificBulk Fuel requires burning Kindling for ignition.


Surface AreaVolumeDensity

Combustion

Liquid or Gaseous Fuels

• Liquid fuels have physical properties that increase the difficulty of extinguishment and hazard to personnel.

• Specific Gravity is important

Liquid or Gaseous Fuels

• Gases tend to assume the shape of their container but have no specific volume.

Heat is the Enemy

Heat• Now let’s go back and review the concept

of how heat plays a part in the starting of fires.

Sources of Heat

• 4 General Categories• Chemical Heat Energy• Electrical Heat Energy• Mechanical Heat Energy• Nuclear Heat Energy

Sources of Heat

• Heat of Combustion• Spontaneous Heating• Heat of Decomposition• Heat of Solution

Sources of Heat

Electrical Heat Energy

Sources of HeatElectrical Heat EnergyResistance Heating-Dielectric HeatingInduction HeatingLeakage Current HeatingHeat from ArcingStatic electricityLighting

Sources of HeatMechanical Heat Energy

Frictional Heat – Friction Sparks -.Heat of Compression -

Sources of Heat

Nuclear Fission and Fusion

Heat !!!!!!!!!

• Heat is a form of energy that is measured in degrees of temperature to signify its intensity.

• Flame is the visible, luminous body of a burning gas

The Dynamics of Fire

Oxygen (oxidizing agent) Fuel HeatAnd a Self sustained chemical reaction (also referred to as the chain reaction)

Fire Prevention

• Consists of keeping these three things separated.

Fire Prevention

• This is where “best management applies

What are some of the “Causes?”• Cutting• Grinding• Welding• Smoking• Food preparation• Vandalism• Arsonist

Fire Suppression consists of separating them

• Cooling• Smothering• Starving

This will be revisited during our discussion of Fire Extinguishers

Cooling

• Temperature Reduction

Smothering

• Extinguishment by Oxygen Dilution

Starving

• Extinguishment by Fuel Removal

Flame Inhibition

• Dry Chemicals and Halons

How does a Fire Spread?

• A rate of combustion or the spread of fire depends on several variables:

How Does a Fire Spread?

• The area of solid/liquid in contact with air.

• The amount of heat generated to raise the temperature of un-burnt portion.

• The ability of materials to conduct heat away.

How Does a Fire Spread?

• Atmospheric humidity.• Wind velocity.• Air Temperature.• Atmospheric pressure.

What are the methods of Heat Transfer?

• Conduction - Heat may be conducted from one body to another by direct contact of the two bodies or by an intervening heat-conducting medium.


• Radiation Although air is a poor conductor, it is obvious that heat can travel where matter does not exist. This method of heat transmission is known as radiation of heat waves.


• Convection - Convection is the transfer of heat by the movement of air or liquid.

Phases that a fire goes through

• Incipient Stage• Low challenge• High Challenge

How can a small fire become a big one in such a short time?

• Incipient Phase


• Incipient Phase• Smoldering Phase


• Incipient Phase• Smoldering Phase• Low Challenge Open Flame


• Incipient Phase• Smoldering Phase• Low Challenge Open Flame• High Challenge Open Flame

Point of Origin

• The location where a fire begins

Area of Origin

• The area of a fire site where the combination of heat and fuel has resulted in damage or destruction

How are Fires Classified?• Class A Fires involving ordinary

combustible materials, such as wood, cloth, paper, rubber and many plastics.

• Water is used in a cooling or quenching effect to reduce the temperature of the burning Class A material below its ignition temperature.

How are Fires Classified?• Class B - Fires involving

flammable liquids, greases and gases.

• The smothering or blanketing effect of oxygen exclusion is most effective. Other extinguishing methods include removal of fuel and temperature reduction.

•

How are Fires Classified?• Class C - Fires involving energized

electrical equipment.

How are Fires Classified?

• Class D - Fires involving combustible metals, such as magnesium, titanium, zirconium, sodium and potassium.


• Class D - The extremely high temperature of some burning metals makes water and other common extinguishing agents ineffective..


• Class K - a new classification of fire as of 1998 and involves fires in combustible cooking fuels such as vegetable or animal fats.


• Class K - Its fuels are similar to Class B fuels but involve high temperature cooking oils and therefore have special characteristics.

• Use the right type of extinguisher for the right class of fire

Products of Combustion

Fire gases

Flame

Heat

Smoke

Fire is never “An Accident”

Keeping Heat away from FuelOr

Keeping Fuel away from HeatIs What

Fire Prevention is all about

The Importance of Time

Delay of Alarm is Deadly.

Examination

The End

Can an Ounce of Prevention be worthA pound of cure?

Preamble to Slide Series. “Fire is no Accident” Fire Chemistry for Construction Workers.

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Transcript of Preamble to Slide Series. “Fire is no Accident” Fire Chemistry for Construction Workers.