"Orsan" stands for French: organisation de la réponse du système de santé en situations sanitaires exceptionnelles, i.e. "organisation of the healthcare response system in exceptional public health situations".
See: References The French disaster white plans are the new trend for the SAMU national network and integrated EMS (IEMS) towards a modern medical sanitary civil defence.
The scheme of the white plans for the département is made by the director of public health (directeur départemental des affaires sanitaires et sociales), with the technical collaboration of the SAMU (French emergency medical service) and the regional public health authority.
It is initiated by the medical regulator doctor decision of the SAMU who alerts public health authority for extension.
Terrorist acts are most likely to happen at the end of the afternoon, to benefit from the mass media coverage of the evening news (at 8 pm, "le 20h").