Flat roofs renovation: a life cycle approach for environmental impact assessment and economic effectiveness

The high energy consumption caused by the building sector and the continuous growth and ageing of the existing housing stock show the importance of housing renovation to improve the quality of the environment. This research compares the environmental performance of flat roof systems (insulation, roofing membrane and covering layer) using Life Cycle Assessment (LCA). The aim is to give indications on how to improve the environmental performance of housing. This research uses a reference building located in the Netherlands and considers environmental impacts related to materials, energy consumption for heating and maintenance activities. It indicates impact scores for each material taking into account interconnections between the layers and between the different parts of the life cycle. It compares the environmental and economic performances of PV panels and of different materials and thermal resistance values for the insulation. These comparisons show that PV panels are convenient from an environmental and economic point of view. The same is true for the insulation layer, especially for materials as PIR (polyisocyanurate) and EPS (expanded polystyrene). It shows that energy consumption for heating causes a larger share of impact scores than production of the materials and maintenance activities. The insulation also causes larger impact scores comparing to roofing membrane and covering layer. The results show which materials are preferable for flat roof renovation and what causes the largest shares of impact. This gives indication to the roofers and to other stakeholders about how to reduce the environmental impact of the existing housing stock.

Comparative study of the different models for the calculation of BLEVEs overpressure effects

The BLEVE, acronym for Boiling Liquid Expanding Vapour Explosion, is one of the most dangerous accidents that can occur in pressure vessels. It can be defined as an explosion resulting from the failure of a vessel containing a pressure liquefied gas stored at a temperature significantly above its boiling point at atmospheric pressure. This phenomenon frequently appears when a vessel is engulfed by a fire: the heat causes the internal pressure to raise and the mechanical proprieties of the wall to decrease, with the consequent rupture of the tank and the instantaneous release of its whole content. After the breakage, the vapour outflows and expands and the liquid phase starts boiling due to the pressure drop. The formation and propagation of a distructive schock wave may occur, together with the ejection of fragments, the generation of a fireball if the stored fluid is flammable and immediately ignited or the atmospheric dispersion of a toxic cloud if the fluid contained inside the vessel is toxic. Despite the presence of many studies on the BLEVE mechanism, the exact causes and conditions of its occurrence are still elusive. In order to better understand this phenomenon, in the present study first of all the concept and definition of BLEVE are investigated. A historical analysis of the major events that have occurred over the past 60 years is described. A research of the principal causes of this event, including the analysis of the substances most frequently involved, is presented too. Afterwards a description of the main effects of BLEVEs is reported, focusing especially on the overpressure. Though the major aim of the present thesis is to contribute, with a comparative analysis, to the validation of the main models present in the literature for the calculation and prediction of the overpressure caused by BLEVEs. In line with this purpose, after a short overview of the available approaches, their ability to reproduce the trend of the overpressure is investigated. The overpressure calculated with the different models is compared with values deriving from events happened in the past and ad-hoc experiments, focusing the attention especially on medium and large scale phenomena. The ability of the models to consider different filling levels of the reservoir and different substances is analyzed too. The results of these calculations are extensively discussed. Finally some conclusive remarks are reported.