What is a primary hazard associated with acetylene gas when stored in cylinders?

The primary hazard associated with acetylene gas when stored in cylinders is the risk of combustion under high pressure. Acetylene is a highly flammable gas that can form explosive mixtures with air. When stored in cylinders, it must be kept under specific conditions to prevent it from becoming unstable, particularly at pressures above 15 psi. Under such high pressure, acetylene can decompose explosively, especially if it comes into contact with certain materials or if there is a sudden release of pressure. This necessitates strict adherence to safety protocols during storage and handling to mitigate the risk of fire and explosion.

The other options highlight different safety concerns that are not the primary focus regarding acetylene. Oxygen deficiency involves the absence of enough oxygen for safe breathing, which is a concern in confined spaces but not directly related to acetylene's storage. Pseudomonas contamination pertains to microorganisms, which not only are irrelevant to gas storage but typically do not pose a hazard with gases like acetylene. Low flammability is inaccurate because acetylene is one of the most flammable gases, making it crucial to handle it with care.