Understanding fire characteristics is essential for effective firefighting. Develop strategies based on this knowledge and apply them on site.

If you don’t know how a fire starts, you won’t know how to extinguish it!

Definition of fire

A “fire” is a combustion phenomenon that occurs or expands contrary to human intent or arises from arson and requires extinguishing. It requires the use of fire extinguishing facilities or other means with equivalent effects. It also includes explosive phenomena that occur or expand contrary to human intent.

The Four Elements of Combustion (Fire Triangle)

For a substance to burn, the following four elements are needed. These are referred to as the four elements of combustion:

• Fuel
• Oxygen
• Heat
• Chemical chain reaction

Fuel

A combustible material is a “flammable substance.” This includes wood, paper, oil, etc.

As a firefighter, it’s important to know that smoke can also become a combustible material.

Oxygen

This refers to substances that contain or supply oxygen. Oxygen binds to combustible materials to burn them.

Heat (Energy)

This refers to sources of heat (ignition energy), such as flames, sparks, or static electricity. Examples include flames, sparks, static electricity, and frictional heat.

Chemical Chain Reaction

A continuous oxidation reaction is needed for combustion to persist. The chain reaction of oxidation is what sustains combustion.

Smoke

Understanding smoke can be beneficial for field activities and help in risk avoidance.

Smoke is air that contains solid or liquid particles generated by incomplete combustion.

Many people think of smoke as just a gas, but it actually contains both solids and liquids.

Imagine something burning; there are cases where smoke is generated and cases where it is not. When smoke is generated, this is called “incomplete combustion.”

Incomplete combustion occurs when there is not enough oxygen in the air for the carbon to fully combine. If carbon can combine properly with oxygen, it becomes carbon dioxide, but if there is not enough oxygen, carbon becomes carbon monoxide, a toxic gas.

Chemically, carbon dioxide is “CO2,” while carbon monoxide is “CO.” Carbon monoxide is produced in the absence of sufficient oxygen. Carbon monoxide is highly toxic and even a small amount can be very dangerous.

What are Black and White Smoke?

What is the identity of black and white smoke?

To conclude, black smoke is made of tiny particles of carbon, and white smoke is made of tiny particles of water. In other words, black smoke is composed of small solid particles of carbon, and white smoke is composed of small liquid particles of water.

Most black and white smoke fall into this category. White smoke can be thought of as water vapor, though not always.

When we think of smoke from a fire, we often imagine black smoke. Smoke, as mentioned earlier, is air that contains solid or liquid particles generated by incomplete combustion, typically referring to black smoke.

When something burns incompletely, not only are tiny particles of carbon produced but also carbon monoxide. (The tiny particles of carbon produced by incomplete combustion are called soot.)

When something burns with sufficient oxygen (complete combustion), carbon dioxide is produced, and when there is insufficient oxygen (incomplete combustion), tiny particles of carbon and carbon monoxide are produced.

To reiterate, black smoke is very likely to contain the toxic carbon monoxide.

Gases Produced During Building Fires and Their Toxicity

Carbon Monoxide (CO)

When inhaled, carbon monoxide binds strongly with hemoglobin (Hb) in the blood, reducing the blood’s ability to carry oxygen. This leads to a lack of oxygen in the body, first affecting brain cells that are highly sensitive to oxygen deficiency. About half of the substances in smoke from residential fires are carbon monoxide.

Hydrogen Cyanide (HCN)

Even in very small amounts, hydrogen cyanide is extremely toxic. It binds with the iron molecules in the body’s oxidative enzymes, inhibiting oxygen activity. This causes chest pain and breathing difficulties, eventually leading to death.

Other Gases

• Ammonia (NH3)
• Nitrogen Dioxide (NO2)
• Sulfur Dioxide (SO2)
• Formaldehyde

Ignition Points of Various Substances

The ignition point is the minimum temperature at which a substance will ignite without an external flame in the presence of air.

Important Points

• Black smoke often contains a lot of soot and carbon monoxide, so it is important to be cautious when dealing with it.
• Carbon monoxide, which is present in black smoke from incomplete combustion, has an ignition point, so it’s important to remember that smoke itself can burn.

Pushing Fire

Understanding the Flow of Smoke and Fire

When a large amount of water is sprayed or when the water flow is too strong, the expansion of steam and the force of the water can push the fire, causing it to spread further.

Example Video

In the video below, you can see how spraying water can cause the fire to spread. When a small amount of straight water is sprayed, the heat layer is not disturbed, and the fire does not spread. However, when water is sprayed in a mist, the heat layer is disturbed, and the force of the extra water pushes the fire.

As shown in the video, mist spraying has the disadvantage of pushing the fire. In contrast, properly controlled straight water spraying does not disturb the heat layer and prevents the fire from spreading.

Important Points

• Do Not: Spraying mist can cover windows and prevent the fire from passing through, potentially pushing steam and gases back into the structure.
• Mist spraying can disturb the heat layer and generate a lot of steam, increasing the risk of smoke blowback, which can injure firefighters. In contrast, straight water spraying does not push air into the space, helping to prevent turbulence.

Example from Japan

In a real fire video from Japan, the fire intensity increased after the firefighters arrived and started spraying water (after 1:40 in the video). It is likely that mist spraying from the back of the video pushed the fire and allowed air to flow in, increasing the spread of the fire.

At 30 seconds into the video, only part of one room on the first floor and part of the second floor are burning. However, incorrect water spraying caused the fire to spread.

Key Takeaways

• Firefighters should avoid causing the fire to spread!
• Use effective water spraying techniques!
• Smoke and fire are highly fluid and can easily spread.
• It is generally preferable to prioritize straight water spraying.

Why Does Water Extinguish Fire?

Water is an excellent fire extinguisher. This is because water absorbs heat and lowers the temperature needed for the fire to burn. Additionally, when water covers burning materials, it prevents oxygen from reaching them, which helps put out the fire. Moreover, as water evaporates, it absorbs a significant amount of heat, making it very effective in extinguishing fires.

Using Water Correctly

However, it is important to use water correctly. For example, if you pour water on a very hot substance, a large amount of steam can be generated. This steam rises, mixing with the surrounding air and releasing heat, which can cause the smoke near the ceiling to be pushed down. This can create dangerous situations for firefighters and others.

Overall, while water is a very effective fire extinguisher, it must be used carefully. Firefighting is complex, and there is no single perfect method.

Risks of Incorrect Use of Water

If water is used incorrectly, it can actually spread the fire and lead to fatal accidents for firefighters.

Why Does a Candle Burn?

A candle is made of paraffin, which is composed mainly of carbon and hydrogen.

How a Candle Burns

1. Ignition: When you light the candle, the wick catches fire first.
2. Melting: The heat from the flame melts the paraffin wax around the wick, turning it into a liquid.
3. Capillary Action: The liquid paraffin travels up the wick through capillary action.
4. Vaporization: As the liquid paraffin reaches the flame, it turns into vapor (gas).
5. Combustion: The paraffin vapor is further heated in the flame, breaking down into smaller molecules. Air (oxygen) from around the flame mixes with the vapor, causing it to burn.

The burning process releases a lot of heat, which melts more wax, allowing the candle to keep burning.

Important Points

• Not Just the Wick: It’s not just the wick that’s burning; the vaporized paraffin gas is what actually burns.
• Smoke Can Burn: As mentioned earlier, the smoke produced during a fire can also burn, so as long as there is a heat source, the flame will continue to burn.

Summary

• Prioritize Straight Water Spraying: Always choose straight water spraying first.
• Be Careful with Water Flow: Avoid breaking the heat layer and do not push the fire.
• Smoke is Flammable: Remember that smoke can catch fire.

Reference page: This training focuses on teaching firefighters to safely navigate wire entanglements and remove SCBA in emergency situations, ensuring effective response during critical scenarios.

References　National Fire Protection Association (NFPA)

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