At construction sites in chemical plants, acetylene is frequently used for welding and cutting operations. However, acetylene is an extremely hazardous gas. It should not be used simply because “it burns well.”
This article explains why acetylene is selected for welding and cutting, outlines its key characteristics, and summarizes essential safety precautions in plant environments. The chemical background is also explained in a way that mechanical engineers can easily understand.
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Why Acetylene Is Used: High Flammability
Why is acetylene used for welding and cutting?
Because it burns easily and produces a large amount of heat. It can also be described as having high energy efficiency. Even a small mass can release substantial thermal energy, making it an efficient heat source.
Why can it release so much heat? Because it is the simplest hydrocarbon containing a triple bond. From an energy-efficiency standpoint, this unstable bond structure provides significant energy release.
In practice, however, the reasoning is often reduced to “it’s dangerous, so handle it carefully.” While welders usually understand its properties, other workers on construction sites may not. Hoses and related equipment are sometimes handled carelessly.
Extremely Wide Explosive Limits
The term “explosive limits” should be basic knowledge for engineers working in chemical plants.
Generally, substances with wider flammable ranges are considered more hazardous. Hydrogen, for example, has a flammable range of 4.0–75%. Acetylene has an even wider range of 2.5–81%. It exceeds even hydrogen, which is often regarded as one of the most hazardous gases.
In practice:
- Chemical engineers may underestimate the presence of acetylene at construction sites.
- Mechanical engineers may not fully understand how hazardous acetylene is compared with other chemicals.
This gap in awareness makes welding-related acetylene risks harder to manage.
For reference, propane—commonly used in households—has a flammable range of 2.2–9.5%, significantly narrower than acetylene.
Low Autoignition Temperature
The autoignition temperature is the temperature at which a substance ignites without an external ignition source. This differs from flash point, which requires an ignition source.
Acetylene’s autoignition temperature is approximately 299°C.
Hydrogen: 585°C
Propane: 466°C
Although safety measures are not determined by autoignition temperature alone, this comparison shows that acetylene requires strict temperature control.
Avoid Direct Sunlight
Acetylene is far more flammable than propane. Cylinders exposed to direct sunlight may reach temperatures of 60–70°C.
While propane cylinders may tolerate such temperatures under certain conditions, 60–70°C should be considered dangerous for acetylene.
Because acetylene and propane cylinders look similar, some contractors may handle them with the same assumptions—this can be a serious mistake.
Prone to Self-Decomposition
Acetylene is highly unstable and prone to self-decomposition. As a general rule, compounds with triple bonds should be assumed to have instability risks.
Under shock or certain conditions, acetylene can self-ignite or explode. This instability is precisely what makes it useful as a high-energy welding fuel.
To store acetylene safely in cylinders, it is dissolved in acetone or DMF. The cylinder is filled with porous material to increase surface area and dissolution capacity. This design stabilizes the gas through gas–liquid contact within a porous matrix.
Avoid Contact with Copper and Silver
Acetylene reacts with copper and silver to form metal acetylides, which are extremely sensitive and explosive.
In chemical plants, particular caution is required if copper tracing lines or copper-containing materials are nearby.
The same precaution applies to other chemicals containing triple bonds.
Summary
Acetylene used for welding and cutting in chemical plants has the following characteristics:
- High flammability
- High heat release
- Extremely wide explosive limits
- Low autoignition temperature
- Risk of self-decomposition
- Hazardous reactions with certain metals
Understanding these properties is essential for safe handling. It is not enough to focus only on energy efficiency—stability and hazard characteristics must also be carefully considered.
If you have questions regarding plant design, maintenance, or operation, feel free to leave a comment.
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