A hazard assessment comprises several components
The description part of the assessment presents the industrial site with its installations, its volume of activity, its organisation and its administrative situation. It describes the environment near the site (natural areas, transport routes, climatology, etc.). Finally, it cites the populated areas and the neighbouring industrial sites.
There are six risk analysis methods.
PHA (Preliminary Hazard Analysis)
is a general-purpose method that is used to identify risks at the preliminary stage of project design.
FMEA (Failure Modes and Effects Analysis)
examines a situation where an element or system is no longer capable of fulfilling a required function. It analyses the effects through which a failure is observed on an element or system. It is centred on how the installation’s components work.
FMECA (Failure Modes, Effects and Criticality Analysis)
includes the main stages of the FMEA and a semi-quantitative assessment of criticality.
HAZID is a HAZard IDentification
and risk analysis review. It identifies the causes and consequences (leak, fire, explosion, etc.) and identifies planned and additional compensatory measures. It is based on accidentology and identifies potential accident scenarios.
HAZOP (HAZard Operability)
is an analysis of the effects of deviations in operating conditions on the safety and operability of the project (centred on the workings of the process). It considers potential drifting of the main parameters linked to running the installation. The process is broken down into sections with an analysis form for each one. The keywords used are “More”, “Less”, “No” and “Too much (or too many)”. The parameters analysed are temperature, pressure, level, flow rate and concentration. It may be coupled with a semi-quantitative estimate of criticality.
“What-if”
is a method derived from HAZOP but offering a more superficial analysis of events. It considers the consequences without examining the causes. The question that the analysis asks is: “WHAT IF this parameter or the behaviour of that component differs from what is normally expected?”. It identifies parameters or components of which the object of the questions is free.
The dangerous phenomena modelled may be related to thermal effects, excess pressure or toxicity. The models map the distances of effects and identify third parties subjected to the effects. This can be used to define severity. We use PHAST software.
We use “bowtie” analyses to study probabilities. This consists in analysing the frequency of initiating events based on lessons learned or literature. Risk control measures are both technical in nature (especially with the safety instrumented systems (SIS)) and organisational. They enable the confidence level to be defined.
The SIL method defines the Confidence Level (CL). This is the class of probability at which a barrier, in its operating environment, fails to fulfil the safety function for which it has been chosen.
e.g. CL = 2
Probability of failure: 10-2 or 1%
The risk control measure will not fulfil its safety function in 1% of cases.
The confidence level of an SIS may be derived from the SIL (Safety Integrated Level) defined in standards IEC 61508 and IEC 61511.
Hazard assessment acts as a basis for the implementation of urban planning or building measures (public utility easements, technological risk prevention plan, etc.) It lays the foundations for emergency and contingency plans (fire control plan, internal operations plan and emergency response plan (ERP)). Finally, it establishes a framework for communication with staff and the public (Social and Economic Council (CSE), Local Information and Consultation Committee (CLIC), etc.) and encourages the emergence of a risk culture.
The hazard assessment offers a conclusion on the acceptability of the risk to the population and the environment generated by the classified facility.
Upper-tier Seveso sites are a special case as they must undergo a five-year re-examination with mandatory instructions and an updated hazard assessment (if necessary).