The Quantification of Hazards at LPG Installations

Abstract

The literature relating to properties, utilisation, storage and transportation of LPG has been surveyed. Potential hazards were reviewed, particularly those related to fireballs arising from unconfined vapour clouds, boiling liquid / expanding vapour and pool fires. These confirmed the need for quantitative techniques for hazard evaluation and a critical analysis of such techniques, their applications and limitations was carried out. The main parameters innvolved in evaluating thermal radiation hazards were: mass of fuel, equivalent spherical diameter, duration, height and surface temperature of the fireball. Published empirical correlations for fireball size and radiation were compared with theoretical models and observations and the best fitting models were established, accurate to ± 5%. Three new correlations have been proposed to fit published experimental data which relate radiation intensity on human skin to exposure time and to tissue damage, within ±8%. Thermodynamic considerations have been applied to calculate the theoretical flame temperature of a fireball, giving good agreement with previous models. A proposed correlation for radiation from pool fires also shows reasonable agreement with published results. However, many factors for pool fires remain unpredictable, such as: shape and size of flame envelope, its temperature and emissivity. Four methods to find acceptable spacing distances between vessels in hazardous areas are discussed. The results show spacing distance related to fuel released and to explosion yield factor for different damage overpressures. The maximum predicted spacing distances are to be preferred because of the relative unpredicability of unconfined vapour cloud explosions. The quantitative methods discussed enable a reasonable assessment of major LPG hazards. The possibility of a major fire or explosion at an LPG installation may be minimised by recommended safety measures. The available hazard evaluation methods have been collected, compared and their limitations assessed in a manner which should be useful to engineers and safety and loss prevention personnel.