```
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

lb/ft3

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

source.

Regards

Milt Fischbein

Calgary, Canada