The Civil service has asked YARA to justify the relevance of the number and arrangement of the ammoniac detectors as regards the demands of Article 2.3 of the Order of the Prefect of March 15th 1996 and the hypotheses retained for the evaluation of the accident scenarios of the danger analysis of the site.

APSYS has thus carried out the validation study of the establishment of the ammoniac detectors by relying on:

• the technical characteristics of the detectors (detection period),
• the geographical cover linked to the type of scenario, to the weather conditions and to the desired concentration.

In order to that, the modelling tool PHAST was used.

APSYS has brought to YARA its expertise in terms of knowledge of the accidental phenomena and its command of the modelling tool PHAST. Moreover, through the other files conducted by the YARA group, APSYS had at its disposal good knowledge of the installations and of the risks inherent to the installations.