How is flammable range related to the relative danger of a substance?

• A. The narrower the range, the more dangerous the substance
• B. The wider the range, the less dangerous the substance
• C. The range has no impact on danger
• D. The wider the range, the more dangerous the substance

Answer: (D)

Flammable range is the span of vapor concentrations in air that can ignite if an ignition source is present. It’s bounded by the lower flammable limit (the minimum concentration needed for ignition) and the upper flammable limit (the maximum concentration above which combustion can’t be sustained). A wider range means ignition is possible over a larger set of conditions, so there are more realistic scenarios where a flammable mixture can exist. That makes the substance more dangerous because, in many real-world environments, you could encounter a vapor concentration within that range. If the range is narrow, ignition only occurs within a small window, making flammable conditions less likely.