Gas welding safety — storage of acetylene: In which form is acetylene safely stored inside its cylinder for oxy–acetylene welding and cutting?

Introduction / Context:
Acetylene is a highly energetic fuel gas used in oxy–fuel welding and cutting. Safe storage is critical because free acetylene becomes unstable above modest pressures and can decompose explosively. Understanding the correct storage method is a core safety competency for welding operations.

Given Data / Assumptions:

• Industrial acetylene cylinders used with regulators and flashback arrestors.
• Goal is safe, stable storage under usable pressure.
• No external refrigeration is used in common shop practice.

Concept / Approach:
Acetylene is stored by dissolving it in a solvent (typically acetone or dimethylformamide) contained in a porous mass inside the cylinder. This solution storage greatly increases the safe pressure range and suppresses decomposition. The cylinder is used upright so the gas exits above the solvent; excessive withdrawal rates risk solvent carryover, which must be avoided.

Step-by-Step Solution:
Recognise acetylene instability at pressure when free (gaseous).Adopt solution storage: porous filler + acetone dissolve acetylene safely.Use upright cylinders and moderate withdrawal to prevent solvent entrainment.Hence, acetylene is stored dissolved in acetone within a porous mass.

Verification / Alternative check:
Cylinder labels and safety data clearly indicate acetone-filled porous mass; regulators are sized for solution storage performance.

Why Other Options Are Wrong:
Pure compressed gaseous acetylene above low pressure is hazardous.

Liquefaction by compression alone is not used; acetylene has no practical ambient-pressure liquefaction pathway for cylinders.

Solid carbide blocks (e.g., calcium carbide) are for generating acetylene on demand in older generators, not for cylinder storage.

Cryogenic storage is impractical and unnecessary in workshops.

Common Pitfalls:
Laying cylinders horizontally (causes solvent carryover); withdrawing gas too fast; using copper tubing with acetylene (risk of explosive copper acetylide formation above certain percentages).

Final Answer:
dissolved in acetone within a porous mass (solution storage)