Generic selectors
Termine esatto
Cerca per termine
Cerca nel contenuto

Preliminary Hazard Analysis

PHA. Preliminary hazard analysis. Activity carried out in the initial design phase (conceptual phase) of a safe system during which, starting from a preliminary list of generic hazards identifiable in the railway sector (PHI), possible dangers are identified (Hazard), with the related risks (Risk) of damage (Harm) in case of normal or emergency operation. Once the dangers connected to the system have been identified, the qualitative category of the Risk and the related protection actions (QRC-A) are analyzed and determined for each of them. In particular, for each cause of high qualitative Hazard (“intolerable” or “undesirable”), the measures (countermeasures) that must be adopted for the reduction of the relative risks are identified, and therefore the qualitative category of residual Risk is redefined; the measures must be such that the residual category is not yet “intolerable” or “undesirable”, but “tolerable” or “negligible”. Then the Risk assessment and acceptance (REA) is carried out according to the frequency of the dangerous events (FHE or HFR) and the level of danger severity (HSL). In this conceptual phase, the safety level that the system must have globally (pSysSIL or pSIL,) in terms of self-protection (immunity) is also defined, by way of the safety Integrity Level Definition (SIL-D)) from dangerous failures (Safety integrity, Inerranza, V.); for example, if there are dangers that can present themselves with a high level of probability (FHE) and with serious effects (HSL), the system must have characteristics such that its level of security, for immunity from dangerous failures, is equal to 4 (pSysSIL or pSIL 4). When the project is fully executed, before the realization, the system is assigned both the global and final integrity level (SysSIL or SIL), and the level of integrity that the various hardware parts (HwSIL.) And software (SwSIL) components of the system itself. The preliminary SIL (pSIL) of the system, defined in the conceptual phase, can be reduced at the end of the design following, for example, the adoption of specific regulatory constraints or procedures, so that it will be possible to have a definitive SIL system less than the pSIL . On the basis of these preliminary analyzes, the requisites and constraints (Requirements, SRB) necessary for the security of the system and which contribute to defining the detailed design criteria, for the realization of the necessary protections to face the identified dangers, can also be identified. During the PHA the cataloging of the cases of danger is also set, together with the decisions and the solutions adopted (Hazard log). Once the project and product have been completed, a detailed analysis of the hazards and risks of damage called hazard analysis (ha) is carried out, in order to verify that the system implemented meets the established safety Requirements. The methods used for hazard analysis in the preliminary project phase can be of Top down type: HAZOP and FTA; while the method to be used when the project is completed is normally Bottom up: ETA and FMECA. More qualitative aspects of Risk analysis are defined by the ALARP, GAMAB and MEM techniques

Link... for your business

WikiRail

WikiRail