the density of acetylene is 0.6181 whilst that of DRY air is 1.0
Thus acetylene is lighter than air".
John, sorry mate, …but for the first time in the many years
that I have been reading your posts, I have to disagree with you.
I do agree with you that acetylene is indeed lighter than air, I
,just don’t quite agree with your density comments. When quoting the
density of a gas, the temperature and pressure are quite important
as gas density is directly proportional to pressure and inversely
proportional to temperature. Meaning, that unless you know the
temperature and pressure at which the density was measured, it is
meaningless. Further, unless the air density you quote above is
measured at the same temperature and pressure as the acetylene
density, a comparison between the two is also basically meaningless.
The density of air at Standard Conditions (60F and 14.7 psia) is
0.0763 lb/ft3. The density of acetylene at standard conditions is
0.0686 lb/ft3 The density of propane at standard conditions is 0.1162
A gas with a density greater than air (propane) will generally sink
to the ground in calm conditions. A gas with a density lighter than
air (acetylene) will generally rise in calm conditions.
A measure of the relative density of gases is called specific
gravity. Specific gravity is basically the ratio of the density of
a gas divided by the density of air. If the specific gravity of a
gas is greater than 1 it is heavier than air, if it is less than 1
it is lighter than air.
The specific gravity of air is 1 ie 0.0763/0.0763
The specific gravity of acetylene is 0.899 ie 0.0686/0.0763
The specific gravity of propane is 1.523 ie 0.1162/0.0763
Note that specific gravity can also be calculated by calculating the
ratio of molecular weights of the gasses. (My source for this data is
Gas Processors Association Engineering Data Book.
Now, after having spewed a bunch of technical mumbo jumbo, I believe
that most of the above is somewhat irrelevant. As I mentioned in my
post yesterday, whether a gas is lighter or heavier than air is not
the only consideration in determining its relative safety. All
combustible gasses (light or heavy) if allowed to accumulated in
enclosed and unventilated spaces ( like many home studios) have a
real good chance of exploding if they are exposed to an ignition