In the field of protection against an explosion, every plant where flammable chemicals (liquids, gases, powders) are handled should build an explosion protection document. This document is a powerful tool to assess explosion management on the plant. Among other parts, it must include an ignition source analysis that assess the probability of explosion for every single place where a flammable atmosphere is expected.
The ignition sources to be considered as listed in various standards such as the EN 1127-1 (Secteur interdisciplinaire de normalisation, 2012) and the IEC 60079-0 (IEC, 2012). The trickiest ignition sources are often static electricity and sometimes, the general measures that could be defined for a fully new plant are extremely difficult to implement on an existing plant.
A common case deals with venting lines. Those lines are sometimes made of insulating plastics while a flammable atmosphere remains possible under normal operation. A strong charge build up can be generated on the inside surface of those lines and several hazards might happen. The charge build up in the inside part of the line will generate an electric field in its vicinity and will charge by influence the conductive parts that are not grounded. In that case, a spark discharges can occur in the working area. If a flammable atmosphere takes place at that point, an ignition could occur. The second main hazard would be a propagating brush discharge across the thickness of the venting line. In that case, an ignition of the vapours inside the pipes is possible.
This presentation describes an experimental approach to measure the charge build up generated during the different process steps of one chemical firm. The results showed large differences depending on the process step and a hazard of propagating brush discharge was identified at some point.