Classification of hazardous areas produced by maintenance interventions on n.g. distribution networks and in presence of open surface of flammable liquid

The safety and protection of workers is a duty of their employer. In case of presence of hazardous areas due to the risk of explosion, an area classification has to be performed to identify the shape and size of the locations where an explosion may happen. Two typical cases that can produce hazardous areas are gas emissions from a containment system, because of normal operation or because of a failure, and vapors emissions from an open surface pool of flammable liquid. In this paper two studies are presented: the first deals with the problem of natural gas releases during maintenance work on the gas distribution network, the second with vapors emissions from a pool of flammable liquid. In the first case experimental measures have been performed to easily calculate the size of the hazardous area; in the second case computer simulations are used to derive a simplified model to determine it. The results of the two studies presented are examined and commented in the light of the International and national Standards.