Resources › Tank Maintenance
Diesel Tank Cleaning and Maintenance:
Schedules, Inspections and What AS 1940 Requires
A compliant tank and a clean tank are two different things — and most sites are only running one of the two schedules.
- AS 1940 Scope
- Inspection Intervals
- Cleaning & Entry
- Records
A diesel storage tank needs two separate maintenance schedules: a safety and compliance schedule driven by AS 1940 and your state's dangerous goods rules, and a fuel-quality schedule driven by water, sludge and microbial growth. Most sites run one and assume it covers the other. Inspections are weekly to quarterly, cleaning is triggered by what the bottom samples show rather than by the calendar, and tank entry is confined space work that is never improvised.
Fuel-quality maintenance and compliance maintenance get confused constantly, and the confusion runs in both directions. Sites with an immaculate compliance folder still put water through injectors, because nothing in AS 1940 asks about the condition of the fuel. Sites with clean, dry, well-filtered fuel still fail an inspection, because nothing in a fuel-polishing routine looks at bund integrity or separation distances.
You need both. This guide sets out what the standard actually governs, what an inspection routine looks like at each interval, when a tank has crossed from “maintain” into “clean”, how cleaning is done without hurting anyone, and what records to keep so that twelve months from now the tank can tell you what has been happening to it.
Two Separate schedules every tank needs — compliance and fuel quality
Zero Requirements in AS 1940 about the condition of the fuel inside the tank
Permit Tank entry is confined space work under AS 2865 — never an improvised job
What AS 1940 Covers — and What It Does Not
AS 1940, The storage and handling of flammable and combustible liquids, is the Australian Standard that governs how fuel is stored on a site. Diesel sits in it as a combustible liquid rather than a flammable one, because its flash point is well above ambient — which is why a diesel installation is treated differently from a petrol one, not why it is treated casually.
The standard itself is not law. It becomes enforceable where your state's dangerous goods or work health and safety regulations call it up, which most do, and where an insurer, a principal contractor or a local council requires it by contract. The practical effect is the same: on most commercial and industrial sites, AS 1940 is the benchmark you will be measured against.
Broadly, it deals with:
- Tank design, construction and installation — including how tanks are supported, secured and positioned
- Bunding and spill containment — the compound around a tank, its capacity, and how rainwater is dealt with
- Separation distances — from boundaries, buildings, ignition sources and protected places
- Venting — normal and emergency relief
- Ignition control — electrical equipment, earthing and bonding, hot work
- Fire protection and spill response — extinguishers, spill kits and what is kept where
- Signage and placarding
- Inspection, testing and maintenance of the installation, and the records that prove it happened
The gap the standard leaves
Nothing in AS 1940 covers the condition of the fuel inside the tank — not water content, not microbial growth, not particulate cleanliness, not shelf life. A tank can be fully compliant and full of fuel that will destroy an injector set. That is the gap the second schedule fills, and it is covered in our guides to diesel shelf life, diesel bug and water in diesel.
Two other standards come up alongside it and are worth knowing by name: AS 1692, which covers steel tanks for flammable and combustible liquids, and AS 4897, which covers underground petroleum storage systems. If your tank is underground, the underground standard and your state's UPSS regulations drive the leak-detection and integrity-testing obligations, and they are considerably heavier than anything that applies above ground.
The Two Schedules, Side by Side
|
Compliance schedule |
Fuel-quality schedule |
| Driven by |
AS 1940, state DG/WHS regulations, insurer |
Water, sludge, microbes, particulate |
| Asks |
Is the installation safe and contained? |
Is the fuel fit to burn? |
| Looks at |
Bund, shell, fittings, vents, signage, spill kit |
Bottom samples, water layer, filters, sediment |
| Triggered by |
The calendar and the regulation |
What the samples show |
| Evidence |
Inspection register, test certificates |
Dip records, sample results, filter change log |
| Failure looks like |
A notice, a claim declined, a fine |
Blocked filters, injector failure, downtime |
Run them together on the same walk-around and they cost very little extra time. Run only one and the other will find you eventually.
The Inspection Routine
The intervals below are a practical baseline for an above-ground bulk diesel installation. Check them against your own risk assessment, your state's requirements and any manufacturer schedule for the tank and equipment — a large fixed installation near a boundary and a farm tank in an open paddock do not warrant the same routine.
| Interval |
Compliance checks |
Fuel-quality checks |
| Weekly |
Walk the tank: obvious leaks, damage, spills; spill kit present and stocked; fill point locked |
Visual check of filter housings and separator bowls |
| Every delivery |
Fill point seal condition; delivery supervised; spill tray in place |
Bottom sample before and after; check the paperwork against the dip |
| Monthly |
Bund clear of water, debris and stored items; bund drain valve closed and locked; extinguisher in date and accessible; signage legible |
Water-finding paste dip and record the depth; drain the sump; drain the separator bowl |
| Quarterly |
Vents and rain caps clear and undamaged; lids, hatches and gaskets sound; valves, hoses, nozzles and swivels inspected; gauges reading correctly; electrical equipment and earthing intact |
Filter differential or flow check; replace filter elements as indicated; desiccant breather element |
| Annually |
Full documented inspection of shell, coating, supports and bund; test and tag electrical equipment; review the register; confirm separation distances still hold after any site changes |
Fuel sample to a laboratory; review twelve months of dip records; internal inspection where access allows |
| Long interval |
Integrity or tightness testing to the manufacturer's and the standard's schedule — considerably more frequent and more prescriptive for underground tanks |
Tank clean or fuel polish, triggered by sample results rather than by date |
The single most useful line in that table is the monthly dip. One reading tells you whether you have water today. Twelve tell you where it is coming from.
The checks people skip
- The bund drain valve. It exists so that clean rainwater can be released. It is supposed to be closed and locked between uses, and it is the thing most often found sitting open. An open bund is not a bund.
- Water standing in the bund. It reduces the capacity you are relying on and it corrodes the tank supports and the shell from the outside.
- Items stored inside the bund. Drums, pallets and equipment displace containment volume.
- The vent. A blocked vent is a genuine hazard on a tank being filled, and a vent without a rain cap is a direct route for water into the fuel.
- Hoses and nozzles. They age in sunlight, and they are the part of the installation most likely to fail with someone holding it.
- The gauge. A level gauge nobody trusts is a gauge nobody reads, and a leak is invisible until someone is reconciling deliveries against usage. Automatic tank gauging and tank level monitoring remove the guesswork, and gauges with water detection report the layer without anyone dipping.
When Does a Tank Actually Need Cleaning?
Cleaning is not an annual ritual. It is a response to evidence, and the evidence is in the bottom of the tank. Clean when:
- Bottom samples show sludge, dark sediment or a stringy biomass layer at the fuel-water interface
- A water layer keeps returning after the sump has been drained, and the ingress path has been fixed
- Filters are blocking rapidly and the elements come out loaded with dark, soft material rather than dry particulate
- The tank has held fuel long past its useful life, or has held fuel of unknown history
- Rust or scale is coming through into the filters
- You are changing what the tank holds, taking it out of service, or bringing a second-hand tank into service
- An internal inspection shows coating failure or corrosion product on the floor
If the fuel itself is still good and the problem is water and fine particulate rather than heavy sludge, fuel polishing is the lighter option: the tank contents are circulated through water separation and fine filtration until the fuel meets a target cleanliness, without taking the tank out of service. Polishing does not remove a sludge bed from the floor. Where there is a sludge bed, the tank needs cleaning.
How Diesel Tanks Are Cleaned
Isolate and empty
The tank is taken out of service, isolated, and the usable fuel is pumped out — usually through filtration into a clean holding tank so it can go back in afterwards. The last few hundred millimetres, the water layer and the sludge come out separately as waste.
Remove the residue
The floor of a tank that has not been cleaned in years holds a mixture of water, rust, sand, degraded fuel, additive residue and microbial biomass. It is pumped, scraped or vacuumed out.
Clean the internal surfaces
Walls, floor, baffles and the underside of the roof are washed down — typically with a fuel-compatible cleaning solution or high-pressure wash — and the rinse is recovered as waste.
Inspect
Once the surfaces are clean you can actually see the tank: weld seams, pitting, coating condition, corrosion around the water line, the state of the sump and the internal fittings. This inspection is half the value of the job, and it is the point at which “clean the tank” occasionally becomes “replace the tank”.
Return to service
Dry, refit and reseal fittings, then refill — ideally through filtration — and take a fresh bottom sample so you have a clean baseline to measure future readings against.
Entry versus no-entry cleaning
Not every clean requires someone inside the tank. No-entry methods — vacuum extraction, remote nozzles, rotating jet heads and camera inspection through an existing opening — handle a great many tanks and remove the single largest risk from the job. Entry cleaning gives the most thorough result and the best inspection, and it is also the point at which the job becomes serious.
Tank Entry Is Confined Space Work
This is the part of tank maintenance that gets people killed, and it is the part most often underestimated.
The inside of a fuel tank is a confined space. The atmosphere can be oxygen-deficient, it can hold flammable vapour, and it can hold vapour from the cleaning process itself. Entry is governed by AS 2865, Confined spaces, and by your state's WHS regulations, and in practice it requires:
- A risk assessment and a confined space entry permit for the specific job
- Atmospheric testing before entry and monitoring throughout — oxygen, flammable gas and contaminants
- Purging and ventilation to make the atmosphere safe, and continuous ventilation while work continues
- Isolation of the tank from all fuel lines, and lock-out/tag-out of anything that could start
- A standby person outside, in continuous contact with whoever is inside
- A rescue plan and the equipment to execute it, with retrieval gear rigged before entry — not fetched afterwards
- Trained personnel, appropriate PPE, and non-sparking tools and intrinsically safe equipment
- A hot work permit where any cutting or welding is involved, which is a separate and higher level of control again
This one is not negotiable
None of that is optional and none of it is a formality. If your site does not hold confined space permits and rescue capability as routine, this is a job for a specialist contractor. That is not a cost — it is the correct decision.
Waste, Records and the Evidence Trail
The waste is regulated. Sludge, water and contaminated fuel drawn from a diesel tank are contaminated waste, not stormwater and not general refuse. They carry hydrocarbons, microbial matter and heavy sediment. Collect them, store them appropriately and dispose of them through a licensed waste contractor in line with your state EPA's requirements. Keep the disposal documentation — it is part of the evidence trail.
Keep a tank register. For each tank: capacity, contents, construction, installation date, bund details, and every inspection, test, cleaning, repair and modification with dates and names. It is the first thing an inspector asks for, the first thing an insurer asks for after an incident, and the only way anyone will ever know when the tank was last opened.
Record the readings, not just the actions
“Dipped for water — OK” tells you nothing next year. “Water 4 mm” tells you the layer grew 3 mm since last month, and that is a finding.
Design the Maintenance Out of the Tank
Most of the work above exists because of decisions made when the tank was installed. The ones that matter:
- A sump and a drain valve at the low point. This turns water removal into a two-minute monthly job instead of a project. A flat-floored tank with no drain point is a tank you will eventually pay to have cleaned.
- A pickup positioned above the floor, so that any water or sediment that does settle never reaches the dispensing line.
- Sealed, lockable fill points and a rain-capped vent, so the two fastest routes for water are closed.
- An inspection hatch you can actually use, sized and positioned for no-entry cleaning and camera inspection.
- Integral bunding. A self-bunded tank brings its containment with it, sealed against weather ingress by design, which removes an entire column from the inspection table above. At bulk scale the FUELTAINER range applies the same principle, and the full diesel systems range covers the configurations in between.
- Filtration and water separation on the dispensing line, with a bowl that can be seen and drained — part of the diesel accessories range, along with the fittings that keep the openings sealed.
- Monitoring you do not have to remember. Fuel management systems with reconciliation turn a slow loss into an alert rather than an annual surprise.
An older single-skin tank on a poured bund with a perished lid seal and no drain point can be maintained. It simply costs more attention every month, for the whole of its life, than a tank designed to be maintained.
Frequently Asked Questions
How often should a diesel tank be cleaned?
There is no fixed interval — cleaning is triggered by condition, not by the calendar. Dip and sample the tank monthly, and clean it when bottom samples show sludge, heavy sediment or microbial growth, when a water layer keeps returning after the ingress path has been fixed, when filters block rapidly with soft dark material, or when the tank is being taken out of service or brought back into it. A well-sealed tank with a working sump drain and a disciplined monthly routine may go many years without needing a full clean.
What does AS 1940 require for diesel tank maintenance?
AS 1940 governs the safe storage and handling of flammable and combustible liquids, and diesel sits in it as a combustible liquid. It sets requirements around tank design and installation, bunding and spill containment, separation distances, venting, ignition control, fire protection, signage, and the inspection, testing and maintenance of the installation — together with records that show it was done. It does not set any requirement about the condition of the fuel itself, so a compliance schedule needs a fuel-quality schedule alongside it. The standard is called up by state dangerous goods and WHS regulations, so check what applies in your state.
Can I clean a diesel tank myself?
Parts of it, yes — draining the sump, drawing off water, changing filters and inspecting through an open hatch are routine site tasks. Entering the tank is not. The interior of a fuel tank is a confined space under AS 2865, and entry requires a permit, atmospheric testing and monitoring, purging and ventilation, isolation and lock-out, a standby person, a rescue plan with retrieval equipment rigged in advance, and trained personnel. If your site does not hold that capability as routine, engage a specialist contractor.
What is the difference between fuel polishing and tank cleaning?
Fuel polishing treats the fuel: the tank contents are circulated through water separation and fine filtration until the fuel meets a target cleanliness, usually without taking the tank out of service. Tank cleaning treats the tank: it is emptied, the sludge and residue are removed, the internal surfaces are washed and the shell is inspected. Polishing is the right answer when the fuel is still good and the problem is water and fine particulate. It will not remove a sludge bed from the tank floor — that needs a clean.
How often should you inspect a diesel storage tank?
A practical baseline for an above-ground bulk tank is a weekly walk-around for leaks, damage and spill kit condition; a monthly check of the bund, signage and fire equipment together with a water dip and sump drain; a quarterly inspection of vents, seals, hoses, valves, gauges and electrical equipment; and a full documented annual inspection of the shell, coating, supports and bund. Underground tanks carry heavier leak-detection and integrity-testing obligations under the underground storage rules.
What do you do with the sludge and water from a diesel tank?
Treat it as contaminated waste. It contains hydrocarbons, water, rust and often microbial matter, and it must not go to ground, to stormwater or into general waste. Collect it, store it appropriately, and dispose of it through a licensed waste contractor in line with your state EPA's requirements — and keep the disposal documentation as part of the tank's record.
What causes sludge to build up in a diesel tank?
Sludge is an accumulation of several things: water that has settled at the bottom, rust and scale from the tank shell, dust and sand carried in with deliveries, gums and sediment formed as the fuel oxidises with age, and the biomass produced by microbial growth living at the fuel-water interface. Water is the common thread — it drives the corrosion, it enables the microbial growth and it accelerates the fuel degradation. Keeping water out is the single most effective way to stop sludge forming.
Do I need to keep records of diesel tank maintenance?
Yes. Keep a register for each tank recording its capacity, contents, construction, installation date and bund details, plus every inspection, test, clean, repair and modification with dates and names — and record the actual readings, not just that a check was done. It is what an inspector asks for, what an insurer asks for after an incident, and the only way to tell whether a water layer is growing month on month or was a one-off.