Analysis of experimental hydrocarbon localised fires with and without engulfed steel members

Localised fires can represent an important hazard to structural safety of buildings where a fully generalised fire cannot develop or when it is at its early stage. Plume correlations given in the codes are valid for undisturbed plume and it is not known whether the presence of a structural element engulfed into the localised fire can affect the validity of such correlations. In structural design, this may lead to highly conservative assumptions or, even, to possible misuses of the correlations. In order to provide insight into this issue, a comprehensive experimental programme aimed at providing data on hydrocarbon localised fires with and without engulfed vertical steel members was performed. In detail, a series of 22 tests of circular hydrocarbon pool fires in well-ventilated conditions of diameters ranging from 0.6 m to 2.2 m were performed with diesel and heptane. The particular aspect of these tests is that they were performed by means of a system that controlled the fuel flow and thus the rate of heat release (RHR) of the fire. The flame length and the temperatures of the fire plume measured experimentally were compared with existing plume correlations, data in the literature and the Eurocode correlations. The results show that: the presence of the column contributed to straighten the flame; although pool fires with same diameters were characterised by the same RHR, the flame length was different depending on the fuel type; experimental gas temperatures were lower than the temperature correlation given in the Eurocodes. In stun, the correlations included in the Eurocodes provided reasonable predictions in terms of flame length and of fire plume temperature rise around a steel vertical element located along the centreline of the localised fire.