What does it mean when a fire is transmitted by convection

The best way of protecting yourself in a fire is to understand the behaviour of fire and how it spreads.

Fire is fast, hot and deadly. Every day people are experiencing the horror of a fire. With a lack of understanding, it can end in tragedy.

Once you can recognise how fire behaves, you can help to prevent a fire and stay safe.

It’s easy to overlook just how quick a small fire can spread. You won’t have time to rescue valuables. It can take only 5 minutes for a whole property to go up in flames.

There are 6 ways in which a fire will commonly spread:

Initially, this is how fires normally spread until the heat builds up.

Fire will either travel along or through any combustible or flammable material it comes in contact with.

For example, a stack of cardboard boxes will enable a fire to quickly spread and build.

This is the process we use when we light a candle with a match. But it also how a candle can cause curtains to go up in flames.

As a fire increases in intensity, it will give off more heat.

Heat can transfer through electromagnetic waves. This is what makes us feel hot when we stand outside in the sun.

From a fire, this can cause nearby objects to catch alight if enough radiated heat reaches it.

This is why you should never place combustible materials near a radiator or build a bonfire near a fence or shed.

This is another way in which a fire can spread via heat transfer.

Any materials, such as metals, which can absorb and transfer heat are thermal conductors. An example of this is when your saucepan handle gets hot.

This allows a fire to spread through walls or steelwork.

And if there is a flammable material on the other side, it can heat up and cause a fire to spread into a neighbouring room or building.

When trying to escape a fire, you should always stay as low as possible. This is because hot gas and smoke rise above any cold air.

Ceilings then trap and prevent it moving any higher, which then causes everything to build up.

Not only is this dangerous if breathed in, but this too can cause a fire to spread.

If enough heat, fuel and oxygen build up in this area, it will create its own fire away from the original.

Once this happens, the fire will quickly engulf a whole room in seconds.

When convection has caused a hot layer of gas to establish, it will then begin to radiate the heat downwards.

The temperature in the room will continue to rise to around 500oC. Breathing in the air at this temperature will quickly scorch your lungs.

At these temperatures, any combustible materials in the room, such as furniture, will start to give off flammable gases.

A near-simultaneous ignition can then begin and change a ‘fire in a room’ to a ‘room on fire’.

A well-established fire has plenty of heat and fuel, but will often lack oxygen if there is no ventilation.

This causes the fire to begin to ‘die’ and fill a room of partially burnt particles in the form of soot.

But if a door opens or a window breaks, air will rush into the room. This can then re-ignite the fire, gases and soot with an explosive force.

This will send the fire out of the door or window and cause its spread.

It is for this reason then, that no-one should ever go back into a burning building. And if you ever suspect a fire on the other side of a door, don’t open it. Instead, find an alternative means of exit.

Having this basic understanding means you understand how to best prevent a fire. But also, how you should react in the event of a fire.

The Fire Triangle is a model that is used to understand the elements that are necessary for a fire to occur. The model consists of three elements: heat, fuel, and oxygen. All three of these elements must be present in order for a fire to occur.

When all three elements are present in the right proportions, a fire will start. If one of the elements is removed, the fire will go out. For example, if there is no fuel, there can be no fire. If there is no oxygen, the fire will eventually suffocate. And if the heat is removed, the fire will cool down and go out.

The type of fire that results from a particular combination of fuel, heat, and oxygen depends on the proportions of each element. A fire with more fuel will burn hotter and produce more smoke. A fire with more oxygen will burn hotter and produce less smoke. And fire with more heat will burn hotter and produce less smoke.

Principles of Fire

The basic principles of fire and combustion can be represented by the fire triangle.

For a fire to exist, three things must be present:

• Heat
• Fuel
• Oxygen

Sources Of Heat

Workplaces have numerous sources of ignition, some of which are obvious but others may be hidden inside machinery. Most of the sources may cause an accidental fire from sources inside but, in the case of arson (about 13% of industrial fires), the source of ignition may be brought from outside the workplace and will be deliberately used. The commonest type of fire in the workplace is caused by heat or light energy igniting materials like paper, wood, cloth, or chemicals. Other types of ignition include electricity, static electricity, friction, and enzymes.

The control of ignition sources is a key element in preventing fires in the workplace. To minimize the risk of fire, employers should carry out a fire risk assessment and put in place appropriate controls. Employees should be trained in how to identify and control ignition sources in their workplace. In the event of a fire, everyone should know what to do to ensure their safety.

The following are potential sources of ignition in the typical workplace:

Naked Flames: Naked flames are the leading cause of ignition for fires in the home and workplace. They can come from smoking materials, cooking appliances, heating appliances, and process equipment. naked flames can ignite flammable materials and start a fire very quickly.

External Sparks: External sparks are also common sources of ignition for fires and explosions. They can come from a variety of sources, including grinding metals, welding, impact tools, and electrical switchgear. When these sparks come into contact with flammable or combustible materials, they can easily ignite a fire or explosion.

Internal Sparking: Internal sparking is a major source of ignition for many fires. It can come from electrical equipment, machinery, and lighting. While some of these sources are faulty or normal, others may be due to poor maintenance or improper installation.

Hot Surfaces: Hot surfaces are one of the most common sources of ignition for fires. They can come from many sources, including lighting, cooking, heating appliances, process equipment, poorly ventilated equipment, faulty and/or badly lubricated equipment, hot bearings, and drive belts. All of these can create a risk of fire if they are not properly used or maintained.

Static Electricity: One of the most common sources of ignition in industrial settings is static electricity. This can occur when materials such as unwinding plastic, pouring highly flammable liquids, walking across insulated floors, or removing synthetic overalls come into contact and then separate. The resulting sparks can be enough to ignite nearby combustible materials.

Sources Of Fuel

If it will burn it can be fuel for a fire. The things which will burn easily are the most likely to be the initial fuel, which then burns quickly and spreads the fire to other fuels. The most common things that will burn in a typical workplace are:

Solid: When it comes to fires, solids are often the source of fuel. That’s because they can easily catch fire and spread quickly. Wood, paper, cardboard, plastics, rubber, and foam are all examples of solid materials that can easily ignite. Even textile materials like furnishings and clothing can be flammable if they’re not properly taken care of. In addition to being the source of ignition, solids can also be the fuel that feeds a fire. That’s why it’s important to be careful with materials like wood shavings, dust, and paper. If they’re not properly disposed of, they can easily become a fire hazard.

Liquids: Liquids are often the source of fuel for fires. This is because they can easily catch fire and spread quickly. Common liquids that are flammable include paint, varnish, thinners, adhesives, petrol, white spirit, methylated spirits, paraffin, toluene, acetone, and other chemicals. Most flammable liquids give off vapors that are heavier than air so they will fall to the lowest levels. This means that if there is a spill, the vapors will settle in low areas and can easily be ignited by a spark or flame.

Gases: Flammable gases are a major source of fuel in many industrial accidents. The most common flammable gases include (liquefied petroleum gas in cylinders, usually butane or propane), acetylene (used for welding), and hydrogen. An explosion can occur if the air/gas mixture is within the explosive range.

Oxygen

Oxygen is required for a fire to burn. The most common source of oxygen in a fire in the air around us. However, there are other sources of oxygen that can be used to make a fire burn hotter and faster. These include compressed oxygen cylinders (used for welding), liquid oxygen tanks (used in some chemical processes), and oxygen-enriched air (used in some industrial processes).

In addition, some chemicals such as nitrates, chlorates, chromates, and peroxides can release oxygen as they burn and therefore need no external source of air.

How Do Fire Spread?

There are several ways that fire can spread, each of which needs to be understood in order to prevent and fight fires effectively. Heat can be transmitted by convection, conduction, radiation, and direct burning.

Convection

Convection is the process of heat transfer by the movement of fluids. The heated fluid rises and the colder fluid sinks, causing a continuous circulation. This process is responsible for the transfer of heat from the Sun to the Earth’s surface, and also for the movement of heated air or water in a room or body.

Convection can be either forced or natural. Forced convection occurs when a fluid is moved by an external force, such as a fan or pump. Natural convection occurs when the fluid is moved by buoyancy forces, which occur when the density of the fluid decreases with increasing temperature.

Conduction

Conduction is the transfer of heat through a material by direct contact between particles. This process of heat transfer occurs without the material actually changing phase. In other words, conduction takes place rate of conduction depends on the material, its temperature, and the area of contact between the particles.

For example, metal is a good conductor of heat, so if you touch a hot metal object, you will feel the heat immediately. This is because the heat is being conducted from the hot metal object directly to your skin. Other materials, such as concrete and brickwork, have a low thermal conductivity. This means that they are not very effective at conducting heat. As a result, these materials are often used to insulate buildings. Insulation materials have a very low thermal conductivity, which makes them excellent at preventing heat from escaping.

When it comes to fire protection, it is important to use materials that are either poor conductors or good insulators. This helps to prevent the spread of fire by slowing down the transfer of heat. Asbestos is one material that fits this description, as it is a very poor conductor of heat and is also incombustible. However, asbestos can cause serious health problems, such as lung cancer, so it is no longer used as a fire protection material. 

Radiation

Radiation is the transfer of heat by electromagnetic waves. This process does not require a material to be in contact with the object that is emitting the radiation. Radiation can travel through a vacuum, which makes it very efficient at transferring heat over long distances.

The Sun is a good example of how radiation can be used to transfer heat. The Sun emits electromagnetic radiation, which travels through space and is then absorbed by the Earth’s atmosphere. This absorbs the heat, which is then radiated back towards the surface of the planet. This process warms the Earth’s surface and makes it habitable for life.

Fire also spreads by radiation. Hot gases radiate heat, which can then ignite nearby combustible materials. This is why it is important to keep flammable materials away from heat sources.

Direct Burning

Direct burning is the process of fire spread by direct contact between the flame and the material. This is the most common form of fire spread, as it only requires a small amount of heat to ignite most materials.

For example, paper is a very flammable material and it only takes a small flame to set it alight. Once the paper is burning, the heat from the flame will cause it to ignite other nearby materials. This can then create a chain reaction, with the fire spreading rapidly through a room or building.

Common Causes of Fires in Workplaces

There are many different causes of fires in workplaces, but some of the most common include:

• Electrical equipment: Faulty or poorly maintained electrical equipment is a common cause of workplace fires. This includes items such as electrical cables, plugs, and sockets.
• Smoking: Smoking is the leading cause of fatal fires in the home, and it is also a significant cause of workplace fires.
• Heating equipment: Faulty or poorly maintained heating equipment, such as radiators and boilers, can also be a fire hazard.
• Arson: Arson is a common cause of fires in commercial premises, such as shops and offices.

The consequences of fires in workplaces can be devastating. They can cause injuries, death, and damage to property. In addition, fires can also disrupt businesses and lead to financial losses.

Conclusion

The conclusion is that the three main ways fires spread are by convection, conduction, and radiation. Direct burning is also a common way for fires to spread. All of these methods require some form of contact with an ignition source in order to start the fire. Once the fire has started, it can quickly spread through a room or building, causing extensive damage. It is important to be aware of these methods of fire spread in order to help prevent the spread of fire.

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