The two industrial location classes are provided to allow recognition of land uses that don’t fit neatly into the four primary location classes. Unfortunately it seems that the definitions of Industrial (I) and Heavy Industrial (HI) are not always well understood, perhaps because the definitions in the Standard could be refined a bit.
Industrial (I) should be simple – it’s meant to cover urban industrial areas where there are multiple industries set in an ordinary streetscape. This is usually (but not always) light industry – warehouses, small factories, car yards, industry-related retail outlets, etc. Usually there will be quite a few offices as well as take-away food outlets scattered through the area if it is large. The area is generally accessible to the public. This image of Laverton North in Melbourne is typical of a large Industrial area, but they can be smaller too.
Industrial areas are reasonably well populated by workers and the public, and they are accessible to all the service providers who might pose a threat to pipelines by digging in the streets for maintenance or new installation of their utilities. For these reasons AS 2885 requires that they be treated the same as T1 (Residential) areas.
Heavy Industrial (HI) areas are different. These tend to be locations where there is only a single large industrial plant (or perhaps a few at most). As implied by the description in the Standard these areas may have quite diverse characteristics. Examples might include the land near a waste dump, a mine, a major mineral or coal processing facility, a process plant such as a refinery or a petrochemical facility, or a tank farm. I also once encountered a plant that manufactured aluminium power (highly flammable).
Because HI areas may be diverse there is no simple rule for them – they may need to be treated as R2, T1 or T2 depending on circumstances. The point of this location classification is to highlight that there is an unusual land use and make you think about it. The Standard highlights that HI areas may contain either unusual threats, or present unusual consequences in the event of a failure, the latter meaning escalation such as might occur if there is a major pipeline failure next to a tank farm and the tanks catch fire too.
To clarify this last point, I’ve seen confusion over whether a small store of drums containing flammable fluids would require a classification of HI and be treated as T2 because of the potential for escalation. In that particular case the fire from an ignited pipeline rupture would have been much bigger than any possible fire from the drums, so the escalation would have been insignificant. On the other hand another couple of kilometres along the same pipeline was a large refinery tank farm, and that was definitely a case of potential escalation.
At the other end of the scale mineral processing plants or waste dumps would only need to treated as if they are R2, and even that might be conservative in some cases.
As I’ve said before, getting the location classification exactly right isn’t critical because it’s only an intermediate stage in getting the design and risk assessment right. Sometimes there might be more than one way of classifying a particular location, which doesn’t matter as long as the design and safety management study identify all the relevant threats and treat them and the possible consequences properly.