Mayo Gas Info

There was a gas leak in the building at work today. The plumber, gas company, and other people said that the gas is denser than the air, so it sinks. I accept that fact, I know there are dangers of using propane heaters in a duck boat because the gas can settle in the bottom of the boat.

But when I was in 8th grade, we did a science experiment. We filled up drycleaning bags with the natural gas that comes from the spigots of each lab table (for the bunsen burners). Then we put in a SASE in each bag, taped them shut, and released them outside. All the bags floated off. They were made of transparent plastic. That implies the gas is lighter than air.

So why are there warning about the natural gas settling in a basement or other low areas? I natural gas composed of methane, ethane, propane, butane, etc but in diminishing percentages?

Usually the composition f natural gas is as follows:
Component Typical Analysis(mole %) Range(mole %)
Methane 94.9 87.0 – 96.0
Ethane 2.5 1.8 – 5.1
Propane 0.2 0.1 – 1.5
iso – Butane 0.03 0.01 – 0.3
normal – Butane 0.03 0.01 – 0.3
iso – Pentane 0.01 trace – 0.14
normal – Pentane 0.01 trace – 0.04
Hexanes plus 0.01 trace – 0.06
Nitrogen 1.6 1.3 – 5.6
Carbon Dioxide 0.7 0.1 – 1.0
Oxygen 0.02 0.01 – 0.1
Hydrogen trace trace – 0.02

Specific Gravity 0.585 0.57 – 0.62
GHV(MJ/m3), dry* 37.8 36.0 – 40.2

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