Sulfur hexafluoride question

I work in a cancer center. Our radiotherapy department has 12 linear accelerators, and they all use SF6 gas as an electric insulator. Sometimes during routine maintenance the gas needs to be purged and replaced with fresh stock. Recently, there was big debate on how it should be disposed. SF6 is flagged as the most potent greenhouse gas, and the sale of it is starting to become strictly regulated. If the hospital did not provide proof that acceptable procedures were put in place to get rid of it in a green fashion they would deny us gas. Which brought about this question:

If SF6 is 5 times heavier than air, how does it get into the atmosphere? If I filled a bag full of the gas and opened it outside, wouldn’t it stay in a perpetual state of being picked up by the wind and falling to earth? Could it stay in the Stratosphere long enough to trap rising heat and be a serious threat?

The hospital’s solution was to pay a significant amount of money to have it properly disposed. Couldn’t that money have gone to better use?

The atmosphere of the earth goes all the way down to the ground. If you released a bag of it outside, that would be it getting into the atmosphere.

And although it’s a heavier gas than others in the mix, the point is, it’s already a mix of gases with different weights - this one would become part of the mix.

Maybe I should rephrase the question.

Does the height of gas in the atmosphere have any impact how much “heat” it retains?

In a word, no. If it’s just a matter of it being a heat-retaining gas (instead of an ozone-depleting gas like CFCs, also known as a ‘greenhouse gas’) it doesn’t matter what altitude it’s at, it’ll still retain heat. A mild hijack, you guys ever get to do this with it?

I never have…don’t get to purge the machines myself. I imagine the medical physics people have some fun with it. You could discreetly pour some in their drink while they weren’t looking. It would just sit in the glass on top of the liquid. Don’t know how well that would work, but you would imagine they would drink a certain amount unknowingly. Would be fun to see their reaction once their voice started changing :slight_smile:

[hijack]Do note that Adam is wrong about either one changing the fundamental frequency of the voice. The voice itself is the same pitch, but the harmonics it gets from echoing inside your head are emphasized differently. Hence why he doesn’t sound like a female or a contrabass.[/hijack]

A cloud of sulfur hexafluoride may sink to the ground, but released into the air it is soon going to mix fairly thoroughly, and molecules of it will be carried to high altitudes, and will contribute to the greenhouse effect.

It is the same as with CO2. It is also heavier than air, and clouds of it can accumulate in low lying areas under some circumstances, but once it is mixed in with the air as a whole it does not separate out simply because the individual molecules weigh more than molecules of N2 and O2.

Yes given a chance, a mixture of gases will eventually become homogenous.

I think we have an ozone layer because cosmic radiation forms it high in the atmosphere.

The atmosphere is well mixed enough that even heavier gases eventually find themselves in the upper atmosphere.

This is why ozone-depleting CFCs are a problem. Despite the fact that they consist of large molecules, traces of CFCs still find themselves in the stratosphere where they damage the ozone layer.