Most critical power backup solutions rely on a standby generator and a fuel source to keep power running for the required number of hours during an outage. For data centres, healthcare facilities, and large commercial buildings, diesel remains the most practical choice: other backup power sources are being researched, but diesel is still the simplest to specify, install, and manage today. With a generator on site, you'll very likely need to store that fuel supply within a building.
Standby diesel generators show up at a wide range of sites, including power plants, and industrial, commercial, medical, and educational facilities. Wherever power is generated, diesel storage tends to follow, and it needs to be stored correctly and safely.
For New Zealand projects, the relevant regulation is the Health and Safety at Work (Hazardous Substances) Regulations 2017, available free from legislation.govt.nz. Its objective is to protect people, property, and the environment wherever flammable or combustible liquids are stored or handled — in effect, it sets out how to correctly store fuel in a building.
This article walks through the three options available under AS1940 for storing fuel within a building, and what each one involves in practice.
Tank location: three options under AS1940
Clause 5.6 of AS1940 covers the location and capacity of indoor tanks, and clause 5.6.2 sets out three positions within a building where a tank can be placed (the equivalent section in the NZ regulations is 17.63, Stationary tank for certain Class 3.1C and 3.1D substances):
- A double-walled tank below the lowest floor level, installed per clause 5.12 - commonly known in the industry as "dig a hole and bury it."
- A single-walled tank in a tank chamber or sand-filled chamber, per clause 5.13 - commonly called a fire-rated room.
- A tank with integral secondary containment and an FRL of 240/240/240, complying with clause 5.9 - commonly called a fire-rated tank, and increasingly the simplest way to comply.
Option 1: Underground tanks (AS1940 clause 5.12)
Burying a tank underground can be an excellent way to save space on a tight site, but it comes with trade-offs worth weighing up: higher overall cost, a more complex installation process, and the risk of hidden services causing delays during construction. Once installed, the tank needs an ongoing monitoring program, and it's harder to inspect and repair. Leaks aren't easily visible, and it's a significant expense with no practical way to relocate or remove the tank at end of life.
Underground installation typically costs more than an above-ground equivalent, largely due to excavation work, which brings its own permits, land use consents, and specialised equipment. If a tank is being buried within a building, you'll also need to plan for access pits for servicing, proximity to property boundaries and building foundations, and corrosion protection.
Option 2: Fire-rated chamber (AS1940 clause 5.13)
A fire-rated chamber avoids excavation, but brings its own construction requirements. The walls, roof, and all penetrations into and out of the room need an FRL of 240/240/240, along with fire-rated ventilation and dampers, a removable roof for tank placement, and a fire-rated door designed to stay closed. Specific separation distances apply from other tanks, building services, foundations, and neighboring boundaries, and the whole room needs water-tight bunding sized to contain the volume of the largest tank inside it.
The concrete products used to build the chamber need FRL certification. FRL, or Fire Resistance Level, is the correct technical term for what's commonly called "fire rating", a building element's ability to withstand a standard fire test, for a given period, across three criteria:
- Structural adequacy: the element continues to support its load under fire conditions.
- Integrity: the element doesn't crack or disintegrate to the point where flames or gases can pass through.
- Insulation: the element doesn't transfer heat that raises the temperature on the unexposed side by more than 180°C above ambient.
An FRL of 240/240/240 means the element is expected to meet all three criteria for 240 minutes, or four hours, under test conditions. In practice, a fire-rated chamber carries many of the same complexities as an underground tank, and can end up costing more to install.
Option 3: Fire-rated tank (AS1940 clause 5.9.4)
Specifying a 4-hour fire-rated tank is becoming the most straightforward way to store fuel inside a building. It does take up more space than an underground tank, but the flexibility, cost, and time savings involved are often worth that trade-off.
AS1940 defines FRL by reference to AS1530.4, which applies specifically to building construction. Clause 1.2.24 requires structural adequacy, integrity, and insulation to be demonstrated on the complete tank. Where the tank is instead subject to a recognised US standard test, the NZ Hazardous Substances Regulations require SwRI 95-03 (see the regulation's interpretations, page 41), and only a 4-hour fire rating under that test is deemed equivalent to an FRL of 240/240/240. A 4-hour liquid hydrocarbon pool fire test through the Southwest Research Institute (SwRI) is an example of an appropriate test.
A 4-hour fire-rated tank compliant with SwRI 93-01 and 95-03 is permitted under AS1940 clause 5.9.2(a) and (b), and by clause 5.9.4(c), is treated as complying with the requirements for tanks in chambers (clauses 5.13.1 and 5.13.2). In practical terms, this means a 4-hour fire-rated tank can store flammable or combustible liquids inside a building without needing a separate fire-rated room.
In summary
Weighed against the other two options, a 4-hour fire-rated tank compliant with SwRI 93-01 and 95-03 is generally the simplest path to meeting the compliance requirements for storing fuel in a building. Regulation in this space has tightened as awareness of pollution and flood risk has grown, and the consequences of non-compliance can be significant.
Fuel storage tank design has continued to improve, and above-ground tanks with advanced leak detection and online contents monitoring now offer a level of reliability that wasn't available even a decade ago.
Specifying fuel storage for a building project? Get in touch with our team - we're happy to talk through what fits your site.
