Which statement describes CNG vapors in a compartment?

Which statement describes CNG vapors in a compartment?

• A. Heavier than air and sinks
• B. Lighter than air and rise to the top; opening a hatch or window helps dissipation
• C. They react with water
• D. They create toxic fog

Answer: (B)

CNG vapors are lighter than air, so they rise to the top of a compartment. When there’s a leak, these vapors tend to accumulate near the ceiling, and opening a hatch or window creates ventilation that allows the gas to dissipate and dilute, reducing the concentration and the chance of ignition. The idea that CNG would sink to the bottom is not correct for methane, which is lighter than air. CNG vapors don’t react with water under normal conditions, and while natural gas is not inherently toxic, concentrating it in a space can still pose asphyxiation and explosion risks.

CNG vapors are lighter than air, so they rise to the top of a compartment. When there’s a leak, these vapors tend to accumulate near the ceiling, and opening a hatch or window creates ventilation that allows the gas to dissipate and dilute, reducing the concentration and the chance of ignition. The idea that CNG would sink to the bottom is not correct for methane, which is lighter than air. CNG vapors don’t react with water under normal conditions, and while natural gas is not inherently toxic, concentrating it in a space can still pose asphyxiation and explosion risks.