In-Line Flame Arrester Application Limits and Matrix Concept for Process Plant Safety from Flash Back of Thermal Combustion Units
Authors: Davies Michael , Heidermann Thomas 
Published: November 2019

Abstract
To reduce envirnonmental impact from emissions of upstream, midstream and downstream operations enivironemental laws have been tightened and reinforced through the industry. The goal to reduce emissions globally is not just focused on onshore operations but also heavily extended to offshore operations. Vapor recovery and vapor combustion are two measures to comply with environmental regulations.
To effectively use vapor recovery or vapor combustion systems it is required to install vent header systems in tank terminals, tank process units and other areas where liquids and gases are stored or processed. Both systems increase the risk of potentially creating an ingnition source. The vapor combustion systems operate with a permanent ignition source at the burner port.
Flame arresters are a safe measure to avoid potential flashback to create a deflagration or a detonation in the vent header system that can end in a catastrophic explosion and bring harm to people and the envirnonment. The safe use of flame arresters requires a detailed understanding of this technology and the limits of application.
Different standards have been developed over decades, but also have limitations that many users are not aware of. Through lessons learned and research work new standards improve the safety of these devices if the application limits are known.
Research work in [1] and [2] details the risk of burner systems and application limits of some of the most commonly used flame arrester test standards. The impact of process pressure, temperature and oxygen concentration as well as the turbulence created through other devices in the vent header system call for conservative testing of flame and detonation arresters.
An additional risk that is often overseen is the use of flame or detonation arresters to stop the explosion of self decomposing gases (e.g. Ethylene Oxide, Acetylene). The standard clearly states that these gases are not covered within the test procedures, but this is often ignored or disregarded.
To date many end of line or so called in-line vent line flame arresters are installed in vent header systems, which need to be replaced by true in-line flame or detonation arresters to reach an acceptable level of safety.
Beside effectively mitigating in-line deflagration or detonation, a major risk that occurs is a continuous flame that settles on the flame arrester element and burns for a long period of time. From incidents that are reported the continuous burning needs to be detected and safety measures need to be put in place to prevent in-line arresters from potentially failing.
During the selection of flame arrester, the impact of process temperature, pressure, oxygen concentration and turbulence created by blower systems are often underestimated or not taken care of during a HAZOP. We asure the proper selection of a flame arrester and we are providing guidance and solutions within this paper.
In addition, a safety matrix concept that is part of the operational instructions of the TRGS 509 (German Tanks Safety Standard) and ATEX will be introduced. In this concept, three independent measures are required for waste gas zone 0 if a permanent operational ignition source (e.g. incinerator, flare) is present.