Which of the following is not considered a container when in active use?

Pipes are not categorized as containers when in active use because they are typically part of a system designed for transporting gases or liquids rather than storing them. In laboratory settings, containers generally refer to items specifically designated for holding or storing flammable gases or liquids. Barrels, drums, and bottles are all containers since they serve the primary function of containing substances, especially when they are not in transit.

In contrast, pipes actively facilitate movement and flow within systems involving the handling of flammable substances. Their design and function differ fundamentally from that of static containers, emphasizing their role in distribution rather than containment. This distinction is critical in laboratory safety protocols, as it impacts how flammable materials are stored, handled, and assessed for risks.