Risk Assessment Helps Buildings Outlast the Blast

Blast wave striking a plant building.

Buildings that are manned or house critical equipment are conceived ideally to be a safe distance from potential explosion sources at gas-processing facilities. Maintaining the required stand-off distance, however, is not always possible because of several layout/operational constraints in brownfield projects, hence plant buildings are invariably subjected to blast effects. This paper discusses challenges confronted and best practices followed by GASCO, now ADNOC Gas Processing, for blast protection of plant buildings.

A quantitative risk assessment, wherein potential vapor-cloud-explosion scenarios were identified and blast overpressure was quantified in the form of contours on a plot, forms the basis of blast considerations. Buildings that are within the blast contours and are manned or house critical equipment must be classified as blast-resistant to ensure the safety of occupants and facilitate safe shutdown of process units during an explosion. The building-performance requirement defining the acceptable level of damage is determined on the basis of the criticality of the facility and expected occupancy. Structural systems and material appropriate for the blast intensity is chosen, and a dynamic or equivalent static analysis is performed.

Blast-resistant design incorporates a practical approach blending past experiences with best known practices in the industry. A Building Blast Design Requirements datasheet is introduced in the early stages of the project, and specific requirements such as blast-load parameters, building configuration, structural system and foundation type, building response range, and other special requirements are developed and solidified before detailed design begins.

Single-story regular-shape buildings with no windows or minimum windows with special features are preferred. An elevated ground floor is permitted in certain cases, such as a substation, to create a cable vault. However, this presents challenges in establishing blast-pressure distribution because of the lack of guidelines for such a set-up. These challenges are overcome with novel solutions.

For low blast loads, a simplified static approach is adopted for structural analysis, while dynamic analysis with a single-degree-of-freedom (SDOF) approach yields an economical design for medium to high blast loads. In specific cases where SDOF idealization is inappropriate (e.g., a multistory building), a multiple-degree-of-freedom nonlinear finite-element analysis is conducted.

A reinforced-concrete (RC) framed structure with reinforced masonry walls or a steel structure is adequate for a low blast, while an RC shear-wall structure is most effective in sustaining moderate to high blasts.

This paper presents best practices and the unique approach followed for such designs 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.

Find paper SPE 188275 on the HSE Technical Discipline Page free for a limited time.

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