Question

Propane and methane are commonly used for heating in winter, and the leakage of these fuels, even for short periods, poses a fire danger for homes. Which gas leakage do you think poses a greater risk for fire? Explain.

Short answer

Answer: Propane leakage poses a greater risk for fire. This is because propane is flammable at lower concentrations than methane, has a lower ignition temperature, and has a lower explosive range, making it more hazardous in terms of fire risk than methane leakage.

Step-by-step solution

Investigate propane and methane flammability

Propane (C3H8) and methane (CH4) are both flammable hydrocarbon gases that can pose a fire risk. Flammable gases mix with air, and if the concentration is within the flammable range, a source of ignition can cause a fire or an explosion. Both gases have different flammability ranges in air, so let's consider their flammability limits.

Analyze flammability limits of propane and methane

The flammability limits of a gas represent the concentration range within which a gas in the air is capable of burning. For propane, the lower flammability limit (LFL) is 2.1% and the upper flammability limit (UFL) is 9.5%. For methane, the LFL is 5.0% and the UFL is 15.0%. This means that propane is flammable in air at lower concentrations than methane.

Investigate the ignition temperatures of propane and methane

The ignition temperature of a gas refers to the minimum temperature at which the gas will spontaneously ignite (without a spark or flame). The ignition temperature of propane is 493°C (920°F) and that of methane is 537°C (1000°F). Hence, propane ignites at a lower temperature than methane.

Determine the explosive ranges of propane and methane

The explosive range of a gas shows the concentration range within which the gas, when mixed with air, can result in an explosion if ignited. The explosive range of propane is 2.1% to 9.5%, while the explosive range of methane is 5.0% to 15.0%. Propane has a lower explosive range, which means it can explode at lower concentrations in the air compared to methane.

Conclusion: Which gas leakage poses a greater risk for fire?

After analyzing the flammability limits, ignition temperatures, and explosive ranges of propane and methane, we can conclude that propane leakage poses a greater risk for fire. This is because propane is flammable at lower concentrations than methane, has a lower ignition temperature, and has a lower explosive range. Therefore, propane leakage can be considered more hazardous in terms of fire risk than methane leakage.

Key concepts

Flammability Limits

Flammability limits are crucial for understanding the safe handling and risk assessment of gases. These limits, often referred to as explosive limits, are expressed as the percentage by volume of the gas in air. The lower flammability limit (LFL) indicates the lowest concentration of a gas capable of producing a flame upon ignition, while the upper flammability limit (UFL) signals the highest concentration beyond which the gas-air mixture is too rich to burn. Gases with a wider range of flammability between LFL and UFL can be more dangerous because they have the potential to ignite over a broader range of concentrations.

For instance, in the case of propane and methane, propane's LFL of 2.1% means that even a slight leak can result in a flammable mixture and represents a significant fire risk. In contrast, methane's LFL of 5.0% suggests that a slightly larger volume is necessary to reach a flammable state. Moreover, understanding the concept of flammability limits also helps in designing safety measures such as proper ventilation to keep gas concentrations below hazardous levels.

Ignition Temperature

Ignition temperature is another important aspect to consider when evaluating the fire risk of gases. This is the minimum temperature at which a gas will catch fire without an external ignition source, such as a spark or flame. A lower ignition temperature indicates that the gas can start burning more easily and thus, represents a higher risk of accidental combustion when compared to gases with higher ignition temperatures.

Propane, with an ignition temperature of 493°C, can ignite more readily than methane, which has an ignition temperature of 537°C. This means in environments where temperatures can rise, such as near heaters or engines, propane poses a higher fire risk. It is also crucial to ensure that storage and usage areas for such gases are kept well below their ignition temperatures to prevent self-ignition.

Explosive Range

The explosive range of a gas is closely related to its flammability limits, encompassing the range between the LFL and UFL. A mixture within this range has the potential to explode if an ignition source is present. The explosive range is an indicator of the severity of potential incidents that could occur if proper safety measures are not maintained.

Notably, propane's explosive range of 2.1% to 9.5% indicates that propane-air mixtures are capable of producing an explosion over a smaller range of concentrations compared to methane (5.0% to 15.0%). The narrow explosive range of propane means that even small leaks could lead to dangerous situations. Safety protocols, such as leak detectors and emergency shutoff mechanisms, are essential to prevent reaching concentrations within the explosive range.