NGA 85: Meter Assembly and Abnormal Operating Conditions (AOCs) Practice Test

Specific gravity is a comparison of a substance’s density to a reference density. For gases like propane, the reference is air, so the specific gravity tells you how much heavier or lighter the gas is than air.

Propane gas has a density about 1.5 times that of air, so its specific gravity is roughly 1.5. It is heavier than air, but not anywhere near 3.5. The number 3.5 would imply a density far greater than typical propane gas, which isn’t correct under normal conditions. Even if you consider temperature or pressure changes, propane’s gas specific gravity remains around 1.5, not 3.5. (For propane in liquid form, the specific gravity relative to water is about 0.5, not 3.5.)

So the statement is false.