A simplified approach to the assessment of passive fire protection systems

Accidental fires impinging equipment or pipes may cause severe secondary scenarios due to escalation events [1-3]. Several accidents in the chemical and process industry, as well as in the framework of the transportation of hazardous materials, presented this feature. Thus, an important issue for the assessment of fired-domino effect hazards is the detailed knowledge of the behaviour of target equipment during fire exposure, and the effect of the available mitigation and protection systems [4]. Several technical standards suggest to evaluate the possible damage to process equipment caused by fire using threshold values for radiation intensity, that do not take into account safety and site-specific factors, as the presence of improved thermal protection systems or the possible mitigation due to effective emergency response. An alternative to this oversimplified approach are very complex and time consuming models available for the detailed calculation of the time to failure (ttf) of the equipment items, requiring a detailed description of vessel geometry and other design data. An important benefit to the safety management of possible domino hazards would come from the availability of an approach to the calculation of the probability of vessel damage following external fires, based on simplified correlations able to take into account specific mitigative factors and the implemented fire protection systems [5]. The present work was focused on the development of a simplified methodology for the characterization of the behaviour of equipment items subjected to fire exposure, aimed at the assessment of passive fire protection systems performances. This allowed estimating the effective damage probability of fired process vessels, used for the quantitative assessment of fired-domino effect. The approach evidenced that important differences in the probability of domino effect triggered by external fires should be expected if differences among vessel characteristics and protection systems are taken into account. This was confirmed by the quantitative assessment of the risk caused by fired-domino events performed using the damage probability models developed. The application of the approach to the quantitative risk analysis of actual industrial lay-out evidenced that the application of fire passive protection systems, able to prevent or reduce the risk related to fired-domino effect escalation, resulted critical to enhance the safety performances in the storage, transport and process operations involving hazardous materials.