From shitty Wikipedia. On vinyl chloride transport and storage. (Emphasis mine).

"Storage and transportation

Vinyl chloride is stored as a liquid. The accepted upper limit of safety as a health hazard is 500 ppm. Often, the storage containers for the product vinyl chloride are high capacity spheres. The spheres have an inside sphere and an outside sphere. Several inches of space separate the inside sphere from the outside sphere. The interstitial space between the spheres is purged with an inert gas such as nitrogen. As the nitrogen purge gas exits the interstitial space it passes through an analyzer that detects whether any vinyl chloride is leaking from the internal sphere. If vinyl chloride starts to leak from the internal sphere or if a fire is detected on the outside of the sphere then the contents of the sphere are automatically dumped into an emergency underground storage container. Containers used for handling vinyl chloride at atmospheric temperature are always under pressure. Inhibited vinyl chloride may be stored at normal atmospheric conditions in suitable pressure vessel. Uninhibited vinyl chloride may be stored either under refrigeration or at normal atmospheric temperature in the absence of air or sunlight but only for a duration of a few days. If for longer periods, regular checks should be made for the presence of polymers.[14]

Transporting VCM presents the same risks as transporting other flammable gases[citation needed] such as propane, butane (LPG) or natural gas (for which the same safety regulations apply). The equipment used for VCM transport is specially designed to be impact and corrosion resistant.[15]"

https://en.wikipedia.org//wiki/Vinyl_chloride