Restrictions to Use of Cellars, Pits, and Trenches

This Standard provides the minimum mandatory requirements for the use of below-grade unventilated enclosures such as cellars, pits, valve boxes,
telecommunication service points and trenches in which hazardous vapors may collect. This applies for all on-site and off-site facilities, pipeways, cross-country transportation pipeline corridors, flowlines, trunklines, gaslift pipelines, and test pipelines.