This regulatory clarification explains when quantities of hazardous substances of the same subclass should be aggregated for determining if a hazardous substance location should be established.

The term ‘Hazardous substance location’ (HSL) is defined in regulation 3(1) of the Health and Safety at Work (Hazardous Substances) Regulations 2017 (the HS Regulations).

For classes 2, 3, 4, 5, 6 or 8 substances, HSL means an ‘area’ where a quantity of the substance exceeds the prescribed quantity for more than the prescribed period of time.

The regulations that require a hazardous substance location to be established depend on the hazard classification of the substance(s) (regulations 10.26, 12.8, 12.34 and 13.34).

If there are two or more areas at a workplace where there are hazardous substances of the same subclass, it is necessary to consider how these areas relate to each other and whether the quantity of substances held in those areas is to be aggregated to determine if the threshold quantity is exceeded.

If areas are:

1. separated from each other such that an incident in one area would not impact on another area (that is, the areas can be considered ‘adequately separated’) the quantity of the substance held at each of the areas is not aggregated
2. not adequately separated, such that an incident in one area could adversely impact on another area, then the quantities in those areas are to be aggregated, and this would include the quantity in any area that is, on its own, below the threshold quantity.

If the quantity of substance held at an adequately separated area does not exceed the threshold quantity for establishing a HSL, that area is not a HSL and location compliance certification is not required.

However, the PCBU with management or control of a place within a workplace must still ensure an adequately separated area complies with all other relevant provisions of the HS Regulations, including, for example, hazardous areas in the case of flammable liquids or gasses.

Campgrounds are a common example where there may be multiple areas containing hazardous substances. Here, LPG is commonly used for heating, cooking and hot water. Consider, for example, a campground with accommodation units each having 2 x 45kg cylinders, and a communal kitchen with over 100kg of LPG.

Where each area is adequately separated (Cabins 2, 3, and 4 in Figure 1), these can be treated as individual areas and wouldn’t be required to be designated as hazardous substance locations or used to calculate the aggregate quantity.

The communal kitchen would require a location compliance certificate, and as Cabin 1 is not adequately separated from the kitchen, this quantity would be aggregated with the quantity at the kitchen. In this case, a location compliance certificate would be issued for 270kg LPG.

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* Refer: Groups of cylinders installed for use – cylinder and tank security signage(external link) GasNZ, January 2022, for guidance on when cylinders may be considered adequately separated.