Question

Carbon dioxide is used for extinguishing fire because: (a) It is a colourless gas (b) It is neither combustile nor a supporter of combution (c) It has a relatively high critical temperature (d) In solid state, it is called dry ice

Short answer

(b) It is neither combustible nor a supporter of combustion.

Step-by-step solution

Identify Required Property

Understand the role of a fire extinguishing agent. A fire extinguisher must either remove heat, remove oxygen, or stop the chemical reactions at the fire's surface to be effective.

Analyze Each Option's Relevance to Fire Extinguishing

Evaluate each given option: - Option (a) states that CO2 is colorless, which does not contribute to extinguishing fire. - Option (b) indicates that CO2 is non-combustible and does not support combustion; this is crucial as it suffocates the fire by displacing oxygen. - Option (c) refers to its critical temperature, which is unrelated to fire extinguishing capabilities. - Option (d) mentions dry ice, which is relevant in cooling but not explicitly for extinguishing fire.

Determine the Most Effective Property

Option (b) is the most pertinent attribute for fire extinguishing purposes as CO2's non-combustibility prevents the fire from continuing to burn by displacing oxygen.

Conclusion: Choose the Correct Option

The best choice is option (b), as it directly addresses how CO2 extinguishes fires by preventing combustion through oxygen displacement.

Key concepts

Carbon Dioxide Properties

Carbon dioxide ( O_2 ) is a fascinating and versatile gas widely used in fire extinguishers. One of its striking properties is that it is colorless. This means it can be released without leaving any visible residue, which is advantageous when putting out fires inside buildings or around electronic equipment. Additionally, CO_2 is heavier than air. This property is particularly useful because it allows the gas to settle effectively over the flames, smothering the fire by cutting off its oxygen supply. Another important aspect of carbon dioxide is its state at different temperatures. In its solid form, it becomes what is commonly known as "dry ice." While dry ice is not the primary means of extinguishing fires, it serves other applications due to its cooling properties. Generally, the unique properties of carbon dioxide make it an excellent choice for quenching flames efficiently and safely.

Non-Combustible Gases

Non-combustible gases are integral in fire extinguishing because they do not catch fire or support combustion. Carbon dioxide is a prime example of a non-combustible gas. This characteristic is key when dealing with fires as it does more than just resist burning; it actively helps to stop fires. By not supporting combustion, carbon dioxide prevents a fire from sustaining itself.

• It's pivotal in displacing oxygen, which is necessary for a fire to keep burning.
• Being inert, CO_2 doesn't attempt to combine chemically with the burning materials.

When released over a fire, CO_2 effectively envelops the flames, depriving them of oxygen and consequently leading to their extinction. This principle underlies its widespread use in environments where the use of water or other agents might be problematic.

Oxygen Displacement

Oxygen displacement is a critical concept in the realm of fire extinguishing. Fires need oxygen to burn, and removing this vital element from the equation will cause the fire to die out. Carbon dioxide is exceptional at displacing oxygen because, when released from an extinguisher, it floods the area surrounding a fire. This effectively pushes out the oxygen present, without which the flames cannot sustain themselves.
A unique advantage of CO_2 is that it acts quickly, delivering its fire-stopping effects almost instantly upon release.

• It blankets the fire, denying it the oxygen it requires.
• Leaves no harmful residues or water damage in its wake, unlike some other extinguishing methods.

This is why carbon dioxide fire extinguishers are prevalent in settings that must avoid damaging sensitive equipment or properties.

Chemical Reactions in Combustion

Understanding the chemical reactions in combustion offers insight into why carbon dioxide is such an effective extinguishing agent. Combustion occurs when a fuel reacts with oxygen releasing heat and light. The key to stopping this reaction is to interrupt the availability of one of its components, primarily oxygen.
Carbon dioxide is effective because it does not actively participate in combustion reactions. By using CO_2 , we introduce a gas into the environment that displaces the oxygen around the fire.

• Without oxygen, the chemical chain reaction falters, halting the further release of heat and light.
• The chemical neutrality of carbon dioxide ensures that it does not add to the combustion process.

Thus, chemical reactions in combustion are effectively put on pause when CO_2 takes over the environment, showcasing its superior fire-extinguishing capabilities.