When purging, one should avoid applying a vacuum to containers that may have contained?

When purging, it is crucial to avoid applying a vacuum to containers that may have contained propane due to the flammable nature of the gas. Propane is a highly volatile substance, and if a vacuum is applied to a container with residual propane, it can lead to a rapid release of gas as the pressure decreases. This could create an explosive atmosphere if the propane ignites, presenting significant safety hazards.

Additionally, purging with a vacuum in such cases can result in the drawing of propane vapors into the vacuum system, which might not be designed to handle flammable gases, further increasing the risk of fire or explosion. Therefore, safety protocols emphasize the need to avoid generating a vacuum in containers associated with hazardous flammable substances like propane during purging operations.