Outlast the Blast, Avert the Loss

Abstract

Buildings that are manned and/or housing critical equipment are ideally conceived to be sited at safe distance away from potential explosion sources of the gas processing facilities. However it is not always possible to maintain the required stand-off distance due to several layout/operational constraints in brownfield projects and hence plant buildings are invariably subjected to the blast effects. The paper discusses challenges confronted and best practices followed in GASCO for blast protection of plant buildings. Quantitative Risk Assessment study forms the basis for blast considerations on the building, wherein potential Vapor Cloud Explosion scenarios are identified and blast overpressure are quantified in the form of contours on the plot. Buildings located within the blast contours and are manned/housing critical equipments are classified as blast-resistant to ensure safety to occupants and facilitate safe shutdown of process units during explosion. Building performance requirement defining acceptable level of damage is determined based on criticality of the facility/expected occupancy (control room, FAR, etc.). Structural system/material appropriate to blast intensity is chosen and a dynamic or equivalent static analysis is performed. Blast resistant design followed for buildings in GASCO plants incorporates a practical approach blending past experiences with best known practices in the industry. Building Blast Design Requirements (BDR) data sheet is introduced at early stages of the project and specific requirements such as blast load parameters, building configuration, structural system & foundation type, building response range and other special requirements are developed and firmed up before the commencement of detailed design. Single-storied regular shaped buildings with no windows or minimum windows with special features are preferred. Elevated ground floor is permitted in certain cases such as Substation to create cable vault. However this presents unique challenges in establishing blast pressure distribution due to lack of guidelines for such set-up, which is overcome by own novel solutions. For low blast loads, simplified static approach is adopted for structural analysis, while dynamic analysis with SDOF approach yields economical design for medium to high blast loads. In specific cases where SDOF idealization is inappropriate (as in multi storied building), a MDOF non-linear FE analysis is carried out. RC framed structure with reinforced masonry walls, or steel structure is adequate for low blast, while RC shear wall structure is found most effective to sustain moderate to high blast. The paper presents best practices and unique approach followed in GASCO for such design amid growing challenges of achieving high performance at low cost. These requirements are common for similar expansion projects and hence can be adopted across the industry.