[tzs]

Vinyl chloride tank car capacity is usually specified in gallons. E.g., [1].

It sounds like what the article is saying is that a 20000 gallon vinyl chloride tank car released all its load.

[1] https://www.gbrx.com/railcars/25800-gallon-vcm-pressure-tank...

[cmmeur01]

And it’s transported as a liquid in rail cars, so that 20,000 gallons of liquid turns into many many more gallons (lol) of gas.

Why not use mass? The reportable quantity is 1 pound.