Influence of a Wall Close to a Vent Outlet

It is well known that the US NFPA 68 (2013) and the EU standard (EN14994:2007), based on the work of Bartknecht (1993), for gas venting do not agree and the EU standard will require a much larger vent area for the same Pred. The present work offers a possible explanation of the difference in these guidelines: the experimental results of. Bartknecht (1993) were carried out with the bottom of the vented vessel on the ground, so that the vent exit was relatively close to the ground and the interaction increased Pred. In the present work a 0.2 m3 cylinder of 0.5m diameter with end wall ignition was free vented into a large dump vessel with a 0.5m diameter connecting pipe. The wall of the 0.5m connecting pipe was close to the vent and the results showed that there was a wall interaction that gave Pred close to those of Bartknecht (1993) at low Kv. In the vented explosion work of Fakandu (2016b) using a 10L vessel, the discharge area was connected to a dump vessel with a 0.5m diameter pipe, which was much bigger than the 162mm diameter of the vented vessel and this gave overpressures close to those predicted in NFPA 68 (2013) with the turbulence parameter λ set to unity. The critical ratio of the centerline distance of the vented vessel to the external surface (ground in most cases) as a ratio of the distance from the edge of the vent to the external surface (DR) was shown to be 1.8 in this work, with lower values indicating no interaction. The present results show that Bartknecht’s experimental results had high Pred probably due to the presence of the ground as a nearby surface.