Fire Safety
Fire associates with extremes. Present in daily activities like cooking, barbecuing or in the fireplace, when uncontrolled may become real danger to human life or property.
What is it?
How can it be classified?
What are the fire stages and critical points?
FIRE - a chemical reaction involving rapid oxidation or burning of a fuel occurs only when three elements are present in the proper conditions and proportions.
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FUEL - Fuel can be any combustible material - solid, liquid or gas. Most solids and liquids become a vapour or gas before they will burn. HEAT - Heat is the energy necessary to increase the temperature of the fuel to a point where sufficient vapours are given off for ignition to occur. |
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HOW FIRES ARE CLASSIFIED? |
COMBUSTION CLASSES |
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| Ordinary combustible materials, such as wood, paper, cloth, rubber and some plastics. | Flammable or combustible liquids such as gasoline, kerosene, paint, paint thinners and propane. | Energized electrical equipment, such as appliances, switches, panel boxes and power tools. | Certain combustible metals, such as magnesium, titanium, potassium and sodium. |
Fire development depends mostly on room geometry and ventilation, the fuel type, the amount and surface area of the fuel. Fire is often discussed in terms of the temperature development and can be divided into different stages: Incipience (Ignition), Growth, Flashover, Fully developed fire and Decay.
| INCIPIENCE / IGNITION | The process with an exothermic reaction with an increase in temperature greatly above the ambient. It can occur either by flaming match, spark or other source or by spontaneous ignition. The process can be either flaming or smouldering combustion. |
| GROWTH | The fire may grow fast or slow depending on the type of combustion, the fuel, access to oxygen etc. The smouldering combustion produce hazardous amounts of toxic gases even if the energy release rate is relatively low. The growth period for such a fire may be very long. The growth stage may be very fast with flaming combustion if the fuel is flammable enough. The heat flux from the first burning part is sufficient to ignite adjacent fuel surface and sufficient oxygen and fuel are available. The fire is said to be fuel-controlled. |
| FLASHOVER | The transition from the growth period to the fully developed fire. The stage before flashover is called the pre-flashover. The stage after flashover is called post-flashover. Flashover is not a precise term or mechanism but a phenomenon associated with thermal instability. (see picture below) |
| FULLY DEVELOPED | The energy release in the room is at maximum and the process is limited by the availability of oxygen. This is called ventilation-controlled burning. At this stage unburnt gases can collect under the ceiling and as these gases leave the room they burn in contact with oxygen outside the room. The gas temperature in the room during this stage is very high and in the range of 700-1200 °C. |
| DECAY | The stage when the fuel becomes consumed and the energy release diminishes and thus the gas temperature decrease. During this stage the fire go from ventilation-controlled to fuel controlled. |
| FLASHOVER - according to ISO, the rapid transition to a state of total surface involvement in a fire of combustible material within an enclosure. For pre-flashover phase Reaction to Fire classification reflects product contribution to the fire growth. In post-flashover phase Fire Resistance of building partitions determines level of protection against spread of fire, structural stability and safety of fire fighter. |