Evaluating accidental risk

One of Ineris’ core areas of expertise is on the risk of industrial technological accidents. The methodological framework applicable to this type of risk was established by the decree of July 16, 1976, which requires that hazard studies (EDDs) be carried out for high-risk facilities. These methodological principles underwent a major change in 2003 with the introduction of law on the Prevention of Natural and Technological Risks.


The hazard studies required by the decree of September 21, 1977, is a diagnosis of the risks an industrial installation may pose to its surroundings in the event of an accident. Before 2003, the methodological approach used to carry out these studies was considered “deterministic.” It was based on analysing predefined accident scenarios, called “reference scenarios,” which were likely to generate the most significant effects. Because of this, scenarios that were potentially more likely, but had lesser consequences, were excluded from the study.
The “Bachelot” law of July 30, 2003, which was enacted in the wake of the explosion at the AZF factory in Toulouse, introduced the “probabilistic” approach to hazard studies. This approach requires an exhaustive analysis as possible of potential accident scenarios, which are then evaluated in terms of probability and severity.

> Technological risks with a chemical origin

The steps for evaluating industrial risks

The purpose of risk evaluation is to demonstrate the level of control of major accident risk management at industrial facilities. This evaluation is under the responsibility of the operator, and in the case of hazard studies, supervised by the French government through inspections of Classified Facilities. This evaluation must drive the reduction of risk at source to an acceptable level by implementing risk management measures (whether technical, organizational or human) as part of a continuous improvement process.

  • The first step is context analysis, which consists of collecting information required to identify dangerous substances and vulnerable targets (or stakes) and understanding the operations of dangerous facilities.
  • The second phase in preparation for risk analysis, based on the previous step, involves taking inventory of hazardous sources (or “potentials”) that may cause dangerous phenomena and lead to an accident. Ideas on how to reduce the hazard potential are then formulated, considering production requirements (for example, reducing quantities in storage, replacing dangerous substances with less dangerous ones, etc.).
  • The third step is the core of the evaluation: the purpose of the analysis is to identify all possible accident scenarios. These scenarios focus attention on the most undesirable events (most often a loss of containment), the potential causes of these events, the nature of the dangerous phenomena that result from them, the behaviour of these phenomena (slow or fast kinetics), the effects and consequences they may produce, and what technical, human, and organizational risk management measures (or safety barriers) can be mobilized to reduce the probability of these events occurring (the “probability of occurrence”). In regulatory hazard studies, the scenarios retained are those where the dangerous phenomena are likely to have an effect off-site, whether directly or indirectly via the domino effect (such as potential sources of a second accident at a neighbouring facility).
  • The fourth step in the process estimates the intensity of dangerous phenomena’s effects and the severity of their consequences for potential targets. This stage involves evaluating the severity of each potential accident. The risk manager ranks the accidents against each other and defines an objective in terms of probability of occurrence.
  • The fifth step consists of evaluating the probability of each accident, integrating the performance of risk management measures (i.e., safety barriers correctly performing their role of prevention or protection).
  • The final step uses the severity and probability forecasts from the two previous steps to grade risks on an evaluation scale (predefined by public authorities for regulatory hazard studies). If the risk is deemed to be insufficiently managed, actions must be determined to reduce the risk to an acceptable level. If the risk is considered to be managed, a risk reduction study must still be conducted for the purposes of continuous improvement.

Industrial risk evaluations were initially done on an individual, site-by-site basis. The law of 2003 introduced technological risk prevention plans (PPRTs) for existing sites with the highest level of risk and expanded the scope of evaluation to entire areas. Based on the model of regulatory plans for natural risks, plans to manage urban areas in proximity to industrial facilities are established with the goal of protecting the safety of people and goods. A PPRT is drawn up as part of a concerted effort with the stakeholders involved, in two technical stages: analysing and mapping hazards, which is done using the risk evaluation in the hazard study (or studies, if there are multiple operators); and analysing and mapping the stakes that must be considered in the region.

> Dangerous accident phenomena