Acetylene Properties

Acetylene is a colorless gas with a pleasant odor. It usually contains traces of phosphine that cause an unpleasant garlic like odor. It is stored in a high pressure cylinder filled with a porous material that contains acetone. Acetylene can be decomposed to its elements with the liberation of heat. It can decompose spontaneously when the pressure exceeds 15 PSIG.

Acetylene is manufactured by the reaction of water with calcium carbide. It is also manufactured by thermal cracking of hydrocarbons, or by partial combustion of methane and oxygen.

Formula - C2H2
Molecular Weight - 26.04
Physical Properties of Acetylene - It is a colorless and flammable gas.
It has a ginger like odor · Acetylene of 100% purity is odorless.
Specific Heat : 10.53 BTU/lbmol-deg F@ 70 deg. F
Specific Gravity : .920
Gas Density : .0677 lb/ ft3 @ 70 deg. F. 14.7 PSIA
Psa t: 586.2 psia @ 70 deg F
Liquid Density : 23.61 lb/ ft3 @ 70 deg F
Boiling Point : Temperature: -120.6 deg. F ( deg. C)
Critical Point :Temperature: 95.36 deg. F, Pressure: 897.8 PSIA
Melting Point : Temperature: -113.0 deg. F, Pressure: 18.5 PSIA
Chemical Properties of Acetylene
Flammable Limits : 2.3-100%
Specific Gravity : 0.91@70F

Together with air it easily forms an explosive mixture. Thermal decomposition produces carbon monoxide that is poisonous. It possess a reactive triple bond between carbon and carbon. which means that acetylene is VERY reactive.

Acetylene is not especially toxic but when generated from calcium carbide it can contain toxic impurities such as traces of phosphine and arsine. It is also highly flammable (hence its use in welding). Its singular hazard is associated with its intrinsic instability; samples of concentrated or pure acetylene will explosively decompose. Acetylene can explode with extreme violence if the pressure of the gas exceeds about 200 kPa (39 psi) as a gas or when in liquid or solid form. It is therefore shipped and stored dissolved in acetone or dimethylformamide (DMF), contained in a metal cylinder with a porous filling (Agamassan), which renders it safe to transport and use, given proper handling.

Acetylene Incident 1

This is reportedly the result of a leaking acetylene cylinder that was stored inside of a plumber’s work van. It is believed the ignition source was a remote door-lock device. [Is that really possible?] Note that the acetylene cylinder is considerably smaller than those used on most burning/cutting rigs found in maintenance shops.

Acetylene Incident 2

Non-Coal Mining Near Miss Accident Involving Acetylene Cylinder

This incident happened on Monday the 29th of September 2003. A fitter with a work van left an E size Oxygen and Acetylene cylinder on the back seat of a Toyota dual cab over the weekend. The Acetylene cylinder valve was not fully closed and a leak occurred.

Over the weekend the Acetylene accumulated in the van. On Monday morning the fitter approached the van and opened the door, a large explosion took place. The ignition may have been caused by either the internal light circuitry, the automatic door control, mobile phone which was on the front seat of the van, or lighting a cigarette. The fitter was also a smoker. He has damage to his ear drums and facial damage. As you can see by the attached photo he was very lucky. Don't let safety be something you learn by accident.

Compressed and liquid gas cylinders shall be secured in a safe manner. 30 CFR 77.208 (d).

Materials that can create hazards if accidentally liberated from their containers shall be stored in a manner that minimizes the danger. (Never store cylinders in an enclosed vehicle or area.) 30 CFR 77.208 (b).

Remember that all gases have different properties. Some are lighter than air and others are heavier. Knowing the difference can make the difference between life and death. Always have a healthy respect for something cooped up in a bottle under pressure, regardless of the product.

Stay safe and Merry Christmas to you and yours. CBz