How does a HAAZ form and what do the zones mean?
A Hazardous Area Atmosphere Zone (‘HAAZ’) is an area where flammable gas/vapour/mist hazards is present (or could be present) as a result of use/storage of flammable liquids/gases at a location where containers are open, occasionally open, decanted or mixed.
A HAAZ needs to be managed to prevent the risk of ignition of the flammable vapour/gas. AS/NZS 60079.10.1:2009 outlines the HAAZ for different locations.
How does a Hazardous Area Atmosphere Zone form?
Through an osmosis process - particles from inside the container move outside the container. This is sometimes, but not always, detected by a smell.
Once particles are outside a container, they can:
Fall to the ground and spread if they are heavier than air e.g: LPG
Waft upwards and outwards if they are lighter than air e.g: petrol
Hazardous areas are classified into zones based upon the frequency of the occurrence and duration of the flammable vapour/gas:
Zone 0: Present continuously / for long periods /frequently (always)
Zone 1: Likely to occur in normal operation occasionally (regularly)
Zone 2: Not likely to occur in normal operation but, if it does occur, will exist for a short period only (sometimes)