With the efforts of the Security Department and Administrative and Support Management, a training course was held at Qom University of Technology, focusing on specialized fire extinguishing training. The key topics covered in this course are outlined below.
Familiarization with different types of fire extinguishers and fire-generating factors.
A fire is a series of rapid chemical reactions and oxidation of combustible materials, typically manifesting as heat and flame. The occurrence of any fire requires specific physical and chemical conditions. There are several factors involved in causing a fire.
However, to initiate a fire, the presence of three essential elements known as the fire triangle is crucial, and utilizing various fire extinguishers can halt the fire if at least one of these elements is removed. These factors include: oxygen, heat, and a combustible material (flammable substances), as well as recently recognized chain reactions.
Factors that cause fire
Generally, three elements are required to create a fire; that is, if these three elements gather (in adequate amounts), a fire will occur. These factors are as follows:
1- Combustible materials
2- Heat
3- Oxygen (Air)
1- Combustible materials
Materials found in nature are generally divided into two categories:
• Non-combustible materials
These materials cannot burn under normal conditions and do not react with the oxygen in the air, such as clay, sand, stone, and many limestone rocks and natural mineral soils, etc. The presence of these materials not only does not lead to any combustion but can sometimes assist in extinguishing a fire.
• Combustible materials
Combustible materials exist in three forms in nature:
1. Solid fuels, such as wood, charcoal, paper, cloth, etc.
2. Liquid fuels, such as petroleum products, alcohols, and other flammable liquids.
3. Gas fuels, such as various combustible gases, butane, acetylene, etc.
2- Heat
Combustion occurs when the temperature reaches a sufficient level based on the type and nature of the combustible materials, referred to as the ignition temperature (Point Fire). The ignition temperature varies among different materials. When a body reaches this temperature, it begins to burn. In this state, if the heat source is cut off, the combustible material will continue to burn.
However, when heated, the body reaches another temperature, which is lower than the ignition temperature; if the heat source is cut off at this temperature, combustion will not continue, and this point is called the flash point. At the flash temperature, lighter elements of a solid or liquid convert to gas, and the combination of this gas with atmospheric oxygen leads to combustion.
3- Oxygen
It should be noted that combustion is facilitated by the oxygen present in the air. For combustion to occur, the flammable material and air must be in proximity. The greater the surface area of the material in contact with oxygen, the easier and faster the combustion and ignition occur. It is also essential to note that during the oxygen absorption process from the air, the more air available, the more intense the combustion. If there is no oxygen, the fire will be extinguished.
Chain Reaction
Recent studies have shown that the three elements of oxygen – fuel – heat cannot create fire on their own; a fourth factor is also involved. This factor is the chain reaction between the molecules of the combustible substance and oxygen, which causes the breaking and recombination of molecules with the surrounding oxygen, leading to fire formation.
Methods of Heat Transfer
• (Conduction) Direct or Conduction method
In this method, an object is heated due to proximity to a fire source. This means heat is transferred from an object with a higher temperature to another with a lower temperature.
• (Convection) Indirect or Displacement method
In this method, heat is transferred due to the displacement and movement of warm air.
• (Radiation) Radiation
In this method, heat is transferred in the form of thermal waves (light).
Classification of Fire Types
Based on the type of combustible materials that initiate fires, they are classified into various categories. This classification varies among countries, but the definitions and nature of types of fire remain unchanged. They are divided into five categories, as follows: A, B, C, D, and E.
: A This class includes fires that leave ashes resulting from the combustion of various combustible materials.
: B This class consists of fires that originate from the combustion of flammable liquids and do not leave ashes upon burning.
: C This class includes fires caused by the combustion of flammable gases, such as natural gas, acetylene, etc.
: D This class comprises fires arising from the combustion of flammable metals like sodium, potassium, magnesium, aluminum, etc.
E: This class represents fires caused by electricity, such as fires occurring in devices like thermal power generators, dynamos, etc.
Methods for Extinguishing Fires
Cooling (removing heat)
The cooling method actually entails eliminating the heat factor. As previously mentioned, combustion begins at a specific temperature. If we can lower the temperature of a combustible material through cooling, we remove one element of the fire triangle, ultimately extinguishing the fire. It should be noted that not all fires can be extinguished with water.
Smothering (cutting off oxygen)
The smothering method involves hindering oxygen from reaching the combustible material. This process is known as smothering. In this case, fire extinguishers, wet blankets, or any other means that can block oxygen from the fire source are utilized.
The process works by covering the fire with a layer of extinguishing materials in gas or powder form, preventing oxygen from reaching the fire source and halting the combustion. These materials remain on the fire's surface until the temperature of the combustible materials drops below the ignition point.
Blocking (cutting off fuel)
If we can prevent fuel from reaching the ignition source, we accomplish blocking, such as turning off the gas valve that caused the fire.
Methods for Extinguishing Classified Fires
A: According to safety and protection studies, the best method to extinguish fires in this class, which arise from combustible materials that leave ash, involves removing the heat element of the fire triangle through cooling; the most economical and rapid means is water. Water lowers the temperature of the burning material to a level where combustion stops. It should be noted that the water flow should continuously run until the fire is completely extinguished.
:B The best method for extinguishing fires is to eliminate the oxygen element of the fire triangle, which is done by smothering. For these types of fires, powder and gas extinguishers, halogenated hydrocarbons, foams, and other smothering techniques such as sand, gravel, and blankets can be employed.
:C The best method for extinguishing fires of this class, as explained in prior sections, is blocking, which means preventing flammable gases from reaching the fire source. Typically, this involves turning off the valve related to the gas flow or using any possible means to stop gas leakage.
:D For extinguishing flammable metal fires, specialized extinguishers corresponding to the type of metal are used.
E: The best method for quenching electrical fires is to cut off oxygen from the fire triangle through smothering. For these types of fires, water is entirely unsuitable, and the best type of extinguisher is foam, which should not be used.
Classification of Types of Fire Extinguishers
Below, we review the types of fire extinguishers in detail:
A – Water-based extinguishers
Water is one of the most familiar materials for extinguishing fires. However, if not used correctly, it can be more dangerous than the fire itself. A fire extinguisher that operates using water can extinguish fires caused by wood, paper, or cardboard.
However, if a fire is caused by electricity or flammable liquids, water is not an effective means of controlling it since water can conduct electricity and cause electric shocks. Additionally, flammable liquids can spread with water, exacerbating the fire spread.
B – Powder-based extinguishers
The best types of fire extinguishing materials are powders, primarily made from sodium bicarbonate, potassium bicarbonate, or monoammonium phosphate. Potassium bicarbonate begins to decompose and releases carbon dioxide when it reaches 70 degrees Celsius. This carbon dioxide covers the fire and smothers it.
C – Foam extinguishers
Foam extinguishers are used to quench flammable liquid fires; when sprayed on burning materials, they quickly cover the fire and prevent flammable gases from escaping, effectively blocking oxygen from reaching the fire.
D – Carbon dioxide extinguishers
One of the most popular fire extinguishing materials is pure carbon dioxide. In fire extinguishers that use carbon dioxide, it is stored as a liquid under high pressure in a cylinder. When the container is opened, carbon dioxide expands and turns into gas in the atmosphere.
Carbon dioxide is heavier than oxygen, effectively replacing the surrounding oxygen of the combustible material. These types of extinguishers are commonly used in restaurants because they do not contaminate food or cooking equipment.