Transporting or handling flammable liquids and gases very often entails the danger of the formation of potentially explosive atmospheres. Such situations require safety measures which provide preventive explosion protection. One such measure, apart from many other regulations, is the installation of safety fittings to all connections and exposed vents and openings for manipulation to avoid reignitions or the propagation of flames and explosions.

 

Depending on the existing operating conditions, various types of combustion processes - explosions, detonations or continuous combustion – can occur, which in turn require appropriate flame-arresting fittings. At present, the development of universal flame-arresting fittings, which can be used for all types of combustion processes, is technically not possible apart from very small devices for special purposes.

 

The ignition of mixtures of gas or process vapours and air in enclosed spaces (containers and pipework) can, depending on the operating conditions (i.e. type and concentration of ignitable mixtures, initial pressure and temperature) and depending on the run-up distances of the flame front, cause deflagrations or detonations. These differ mainly in their flame propagation speeds and combustion pressure and hence in their ability to transmit internal ignition.

 

A key factor in the occurrence of deflagrations and detonations is the length of the run-up distance of a flame front in relation to the inner diameter of the pipe (L/D ratio). Depending on the inner pipe diameter, relatively short run-up distances (L/D ratio > 50) will be enough to cause detonations with ram pressures in the direction of the flame front of more than 50 bar, and flame propagation speeds of approx. 1800 m/s are possible.

 

The transition phase from a pipe deflagration to a stable detonation is called “unstable detonation” and is characterised by particularly high pressure pulses and flame propagation speeds.

 

One of the most important components of flame-arresting fittings is the flame barrier, an element which prevents the propagation of flames caused by explosions (deflagrations), detonations or continuous combustion and the resulting flame flashback. Today, a number of very diverse constructions are used as flame barriers.

 

The majority of flame-arresting fittings used today – including those of Universal-Sicherungstechnik GmbH - are fitted with static dry flame arresters. These elements function on the basis that flames are no longer reactive in narrow gaps of an appropriate length and at suitable approved limit dimensions and will hence extinguish.

 

The Universal-Sicherungstechnik flame arrester element is a strip winding barrier consisting of one smooth and one corrugated strip of suitable material being wound up and creating a predefined gap width.