This standard provides guidelines for safely entering and working in and near confined spaces that have inert atmospheres and can aid employers in preparing specific procedures for working safely in inert confined spaces, recognizing that because of its unique nature, the hazards and requirements for inert entry are generally greater than for "normal" permit-required confined space (PRCS) entry. API 2217A applies to confined spaces that have been intentionally purged with an inert gas until:the oxygen level in the vapor space is too low to support combustion, and any gases in or flowing out of the confined space are below flammable or reactive levels. Typical inert entry work in the petroleum and petrochemical industry includes work to service or replace catalyst in reactors.