The AT&T Standard Section 620-140-501 (often referred to as Bell System Practice, or BSP, 620-140-501), published in June 1976, is a foundational safety document for the telecommunications industry. It outlines the strict procedures for testing, purging, and ventilating manholes and other confined spaces before and during employee entry. Because telecommunications workers frequently operate in underground manholes that could harbor toxic gases, combustible atmospheres, or dangerous dust, AT&T developed this comprehensive standard to prevent injuries and fatalities.
Here is a breakdown of the standard’s primary guidelines and its lasting impact: