[235711]

Hello Everyone, Its good to be back on this great forum!

I would like to share some of the more interesting facts about the gas in hopes that it will help persons understand the risks and thus work safer and more aware.

SELF DECOMPOSITION

It is widely accepted that the lower explosive limit of acetylene is about 2.3 % Vol. and an upper limit of 82% Vol; however, this is not the entire truth since these values only consider a combustion reaction (burning with oxygen) and not the self decomposition reaction which acetylene is capable of in certain conditions. Self decomposition basically means, the gas molecules begin to break apart and in doing so release energy in the form of heat.

The heat produced by the self decomposition reaction produces, rapidly expands the gaseous mixture increasing the pressure inside the containment vessel. The increased pressure and heat may burst the containment vessel resulting in an explosion ( i.e. deflagration). It is worth mentioning as the heat and pressure increase inside the vessel so does the rate of the decomposition reaction. This results in a runaway reaction or chain reaction inside the containment vessel.

Since the above described reaction can occur without the presence of oxygen, in certain conditions, truly puts acetylene's upper explosive limit at 100% Vol.

Pure acetylene under a pressure greater than 0.8 Bar (11.6 Psi) has a potential to self decompose. As the pressure increases the probability of self decomposition increases. This also holds true for temperature increases of the gas. The point at which self decomposition occurs is a function of many factors which include but are not limited too pressure, temperature and the shape of the containment vessel. There are also many other factors that also play a role.

The presence of an ignition or activation energy source, for example, is one of these additional factors that will influence the initiation of a self decomposition reaction of acetylene.

Some examples of activation energy sources include:

Electro Static Discharge ( e.g. improperly grounded equipment)
Mechanical Shock Waves ( e.g. dropping a cylinder off a truck; hammer blows)
Hot Surfaces (e.g. hot-working to close to a cylinder, hot parts touching a cylinder)
Heat from rapid compression (e.g. improper regulators / defective regulators)

Basically any source that provides energy for acetylene's endothermic nature can pose an issue. Microwave energy from cell phones may also contribute to the initiation of a self decomposition reaction.

SELF IGNITION / AUTO IGNITION

Acetylene gas also has the ability to self ignite (combustion / oxidation reaction). Self ignition requires the presents of air (oxygen). Self ignition is a result of the self decomposition reaction explained above. Self ignition occurs when the heat generated by the self decomposition reaction is sufficient to initiate a combustion reaction with the oxygen present in the gas mix. An minimum gas mixture consisting of 10% AIR Vol. is required for self ignition.

Acetylene has a one of the lowest ignition energy requirements for the initiation of a combustion reaction with oxygen. It is similar to the ignition energy requirements of hydrogen. The ignition temperature of an air gas mix with a 38% Acetylene is about 305 °C (518 °F) at atmospheric pressure.

However the presence of one or more of the afore mentioned activation energy sources can lower the ignition temperature too as low as 160°C (320°F) at atmospheric pressure.

INCOMPATIBILITIES and TOXICITY.

Acetylene gas itself has little toxicity to humans in a pure form. Excess inhalation of the pure gas can lead to headaches, stupor, nausea and eventual loss of consciousnus. Acetylene in its pure form is orderless and colourless. Impurities, associated with the production of the gas from calcium carbide, are always present in the gas mixture for industrial grades. These impurities are also responsible for the gas's distinct odor. Common impurities, two of which are extremely toxic to humans, found in industrial grade acetylene gas are:

Arsenic
Phosphine
Hydrogen Sulfide
Ammonia

Acetylene gas, when in contact with copper has the potential to form a highly explosive salt called Copper(I) acetylide.
(Personally I found this rather interesting since some torch nozzles are made from copper or a copper balanced alloy)
The salt is a reddish brown colour and extremely sensitive to heat and shock. It is considered a high explosive. Acetylene's contact with silver also forms an explosive salt.

In Conclusion

So to some it up and to put in the words of my American friend....

“This stuff will eat your lunch if you let it”

but, the gas ,when understood and handled properly, posses a manageable risk. After all entire industries that employ millions throughout the world are based on this gas.

There are many more interesting things about the gas. Like its behavior when dissolved in acetone and stored in gas bottles. The use of porous calcium silicate hydrate in modern gas bottles,which helps to prevent self decomposition by a flashback for example.

It is important, in my opinion, that all shops have at least 3 hours of safety training with the gas. The training should be followed by written or oral examination of the information presented to ensure understanding. Critical is, again in my opinion,that all person working with the gas understand its characteristic. The gasses properties should be elevated to "common sense" level through training.

Most of this information here can be found on the German Wikipedia site under “Ethin”. I just translated it and summarized it for the forum. I have done research on this gas for some calcium carbide processing tooling we fabricated. If anyone would like more detailed information on the gas and its properties, let me know and I will point you to some good literature.

again it is nice to b back on the forum. a shout out to Mr. Steve S for helping me to get my account squared!


Cheers
235711

[WerkSpace]

I refilled my 'B size' hobby tank of acetylene yesterday for $75 CAD in Calgary, Alberta.

When I got home, the girlfriend had a surprise for me. Two more 'B size' (40 cu/ft) tanks of acetylene for free from her work place. They wanted to get rid of them, so I got them for free.

I also got three very tiny tanks, one argon, one oxygen and one hydrogen. The metal safety cap was almost as big as the tank itself. These tanks came in a special metal holder that resembled what the milk man used to deliver glass bottles of milk door to door with.

[Antorcha]

I refilled my 'B size' hobby tank of acetylene yesterday for $75 CAD in Calgary, Alberta.

When I got home, the girlfriend had a surprise for me. Two more 'B size' (40 cu/ft) tanks of acetylene for free from her work place. They wanted to get rid of them, so I got them for free.

I also got three very tiny tanks, one argon, one oxygen and one hydrogen. The metal safety cap was almost as big as the tank itself. These tanks came in a special metal holder that resembled what the milk man used to deliver glass bottles of milk door to door with.

That'll be nice having . Easy to move around and no worries about running out in the middle of something.
I'd trade one off for(towards) a second O2 tank and you're all set.

[gnuuser]

I refilled my 'B size' hobby tank of acetylene yesterday for $75 CAD in Calgary, Alberta.

When I got home, the girlfriend had a surprise for me. Two more 'B size' (40 cu/ft) tanks of acetylene for free from her work place. They wanted to get rid of them, so I got them for free.

I also got three very tiny tanks, one argon, one oxygen and one hydrogen. The metal safety cap was almost as big as the tank itself. These tanks came in a special metal holder that resembled what the milk man used to deliver glass bottles of milk door to door with.

That'll be nice having . Easy to move around and no worries about running out in the middle of something.
I'd trade one off for(towards) a second O2 tank and you're all set.

got that right nothing more of a pita. than running out of oxy or fuel half way into a job