The dangers of process seals

When designing a petrochemical facility, one must consider the possibility of primary seals failing. Where electrical devices are isolated from pressurized processes by primary (process) seals, failure of the primary seal can result in conduit or cable seals being subjected to the process pressure, with the result that explosive gas or vapor can be transmitted to safe areas. Conduit and cable seals are designed to prevent the passage of flames from one portion of an electrical installation to another. While they may restrict the flow of gas or vapor, they are not intended to prevent the passage of gas or vapor under continuous pressure, even at very low pressures. This paper is intended to make consultants and end users more aware of the potential results if designs do not consider the possibility of primary seal failures. This paper will discuss three examples where explosions occurred as the result of primary seal failures, review the NEC and CEC requirements and present solutions to prevent gases under high pressure from migrating through conduit systems or interstices of cable conductors.