Categories 2a and 2b capture pollutants formed when fuel or waste is burnt. Because the trigger is fuel or energy use rather than the mass of a substance, many facilities with diesel fleets, boilers or power generation trip these thresholds without handling large quantities of any listed substance.
Key points
- Category 2a: 400 tonnes of fuel or waste a year, or 1 tonne in an hour
- Category 2b: 2,000 tonnes a year, 60,000 MWh of electricity or a 20 MW rating
- About 478,000 litres of diesel a year trips Category 2a
- Explosives such as ANFO count as fuel
- Lighting and motive electricity are excluded
What the categories cover
Category 2a covers common combustion pollutants such as oxides of nitrogen, carbon monoxide, sulfur dioxide and particulate matter. Category 2b covers all Category 2a substances plus certain metals and their compounds, magnesium oxide fume, and dioxins and furans.
Fuel equivalents
The NPI Guide converts the tonnage thresholds into typical fuel volumes using standard densities:
| Fuel | Category 2a (per year) | Category 2a (in any hour) | Category 2b (per year) |
|---|---|---|---|
| Diesel | 478,000 L | 1,200 L | 2,390,000 L |
| Petrol | 541,000 L | 1,350 L | 2,710,000 L |
| Fuel oil | 444,000 L | 1,110 L | 2,220,000 L |
| LPG | 784,000 L | 1,960 L | 3,920,000 L |
| Natural gas | 17,800,000 MJ | 44,400 MJ | 88,800,000 MJ |
| Solid fuel, explosives and waste | 400 t | 1 t | 2,000 t |
Where a facility burns several fuels, their masses are added together. DCCEEW treats explosives as fuel, so the full mass of an explosive such as ammonium nitrate fuel oil (ANFO) counts towards the threshold.
The electricity limbs
Category 2b is also tripped by consuming 60,000 megawatt hours or more of electricity in the reporting period, or by a maximum potential power consumption rated at 20 megawatts or more. Electricity used for lighting or motive purposes is excluded from both tests.
Transfers are treated differently
Tripping only a Category 2a or 2b threshold does not require transfers to be reported. Transfer reporting applies only where a substance also exceeds a Category 1, 1b or 3 threshold.
Why it matters
Because diesel use alone can trip Category 2a, fleets, generators and processing plants at sites with no other NPI inputs often have a reporting obligation. Tracking fuel and explosives by facility each month makes the annual threshold test straightforward.
References & sources
Primary regulatory documents and authoritative references underpinning this answer.