The compressed gas industry recognizes that the filling process for U.S. Department of Transportation (DOT)/Transport Canada (TC) cylinders used to contain nonliquefied gases is subject to variations and regulatory requirements that affect the settled pressure. The industry follows DOT and TC regulations that specify filling requirements for compressed gases. Industry practice is to fill compressed gas cylinders to achieve a specified settled pressure that does not exceed the authorized service pressure at reference temperature in accordance with DOT regulations found in 49 CFR 173.301a(c) or Canadian regulations found in Transportation of Dangerous Goods Regulations and CSA B340, Section 5, “Selection and filling of containers for transportation.”

This publication describes the variations that can occur during the filling of cylinders with nonliquefied gases. This publication contains methods to minimize the effect of these variations on the settled pressure. In addition, it identifies the variability in the specified settled pressure that fillers can reasonably expect.