Chapter 7 Flashcards
Fire is a
- chain reaction
- chemical reaction
- Fireor combustionis a chemical reaction between oxygen and a combustible fluid
For combustion(burning)to continue, there must be
a constant source of:
- fuel,
- oxygen (air), and
- heat
Combustion (الإحتراق):
The process by which fire converts (changes)fuel and oxygen into energy, usually in the form of heat.
•The ignition (اشتعال)point or (combustion point):
The temperature at which a given fuel can burst (explode)into flame
Carbon
- Carbon is found in almost every flammable substance.
- When a substance burns, the carbon is released and then combines with oxygen.
- That produces either carbon dioxideor carbon monoxide.
Carbon dioxide (CO2)
- is produced when there is more oxygen than the fire needs. It is not toxic, but can be produced in such volumes that it seriously reduces the concentration of oxygen in the air surrounding the fire site…..
- Suffocation.
Carbon monoxide (CO)
- a colorless, odorless(no smell), fatal(deadly) gas,
- It is the result of incomplete combustion of a fuel.
- It is produced when there is insufficient (little or short) oxygen to burn the fuel completely
Combustion of liquids and solids
Liquids and solids such as oil and wood do not burn directly but must first be converted into a flammable vapor by heat.
Example: Burning a paper (look to the vapor area just above the surface of the paper).
Methods of heat transfer
Conduction (توصيل الحرارة)
Convection (move) (إنتقال الحرارة)
Radiation(spread) (الإشعاع)
Conduction (توصيل الحرارة)
is direct thermal energy transfer (move).Metals are very good conductors of heat. [The opposite are insulators such as Concrete, rubber and glass which are poor conductors].
Convection (move) (إنتقال الحرارة)
•is heat transfer through the movement of hot gases. Convection determines the general direction of the spread of a fire.
Radiation(spread) (الإشعاع)
Is electromagnetic wave transfer of heat to a solid. A fire in one oil tank can spread to nearby tanks through radiated heat, raising the temperature and pressure of the other tank contents.
e.g. sun’s radiation of heat.
Spontaneous combustion: الاحتراق التلقائي
- A classic example of spontaneous combustion is a pile (mass) of oil rags (wet old cloth). The fibers (tissues) of the rags expose a large surface area to oxidation. Theporous (spongy)nature of the rags allow additional oxygen to be absorbed(taken in), replacing the oxygen already consumed (used).
- When the temperature rises enough, the surfaces of the oil on the rags vaporize.
- Spontaneous combustion is rare, but it can happen.
Sources of Fire Hazards
- Almost everything in industrial environments can burn.
- Metal furniture, machines, plaster, and concrete block walls are usually painted. Most paints and polish will easily catch fire.
- The principal method of fire prevention is passive – the absence of sufficient heat
Packing material
•All of the packing materials such as cardboard (thick paper), Styrofoam, papers, bubble wrap and shrink wrap easily burn.
Classes of fires
- Class A fires: Solid materials such as wood, plastics, textiles and their products: paper, housing, clothing.
- Class B fires: Flammable liquids and gases.
- Class C fires: electrical – live electricity situations.
- Class D fires: Combustible, easily oxidized metals such as aluminum, magnesium, titanium and zirconium.
- Special Categories: extremely active oxidizers or mixtures, flammables containing oxygen, nitric acid, hydrogen peroxide, and solid missile(bullet)propellants (gun powder, pushing).
Flash point
The lowest temperature for a given fuel at which vapors are produced in sufficient concentration to flash (flame)in the presence of a source of ignition.