An Experimental Investigation on the Effect of Nitrogen Enriched Air and Heat Transfer on the Maximum Experimental Safe Gap for Propane Gas Explosions

Abstract

Electrical apparatuses for use in potentially explosive gas atmospheres are required to be enclosed. There are two main requirements in the design of such enclosures. Firstly, they are required to withstand the pressure generated in an internal explosion. Secondly, any gap openings must be small enough to quench flames and to cool combustion products to prevent re-ignition of a surrounding explosive gas atmosphere. The largest gap opening that just prevents transmission of an internal explosion to a surrounding explosive gas atmosphere is called the maximum experimental safe gap (MESG). The MESG values is determined from standardised experiments. The purpose of the conducted experimental work was to investigate the influence of the gap material on the MESG value. Another aim was to find out if partial inertisation of the explosive gas influences the maximum experimental safe gap. The combustible gas used in the experiments was propane. The experiments were conducted in an apparatus with an interchangeable and adjustable gap opening. The gap materials tested was carbon steel, brass, aluminium and polyoxymethylene. The experiments with metal gaps show that the properties of the metals do not have a significant influence on the MESG value. However, a decrease of 0.01 mm was achieved when a flame gap of brass was used, compared to the value obtained using a steel gap. Temperature measured above the orifice of the gap opening supports the finding. At equal gap opening, a higher temperature was measures above brass gaps than above steel gaps. An increase of the MESG was achieved by partial inertisation of the explosive gas atmosphere. The MESG value of propane was doubled when the oxygen content of air was lowered to 15.04 volume percent.