French to English Tech/Engineering Human Resources workplace health and safety

from a safety document for working in enclosed spaces, usually with dangerous substances and conditions.
CAN french:

Mesures de prévention pour les risques identifiés
Nettoyage, vidange et retour intempestif


Then it gives a list of procedures to follow on cleaning, draining etc.

I am guessing it means unexpected or accidental....reaction? recovery?
It's really the first time I've ever seen that phrase and i've done a few of these documents.

Thanks for your help!