AS 4343 Hazard Level Calculator Australia

Author

Byron Raal, CAS Founder-Editor About the author

Checked against

AS/NZS 1200AS 4343

Date last checked

18 August 2026

Not sure whether your air receiver has to be registered with your state regulator? Put its design pressure and volume in below. This tool works out the AS 4343 hazard level and what that level usually means for design and item registration under the model WHS framework. Whether your specific vessel must be registered also depends on jurisdiction-specific rules and express exclusions: NSW, for example, excludes hazard level A to C pressure vessels that do not require periodic internal inspection, and several jurisdictions exclude serially produced vessels. Confirm the duty with your regulator or a competent person before you rely on any result.

The AS 4343 hazard level calculator works out the hazard level of your pressure vessel under AS 4343:2014 using the full formula H = P x V x Fc x Ff x Fs, then explains what that level usually means for design and item registration under the model WHS framework, with jurisdiction-specific exceptions flagged. Enter your receiver’s design pressure, volume, contents type and service factor, and the tool runs the same arithmetic already published on our pressure vessel registration guide, showing the working so the result is auditable rather than a black box.

1How do I calculate the AS 4343 hazard level of my air receiver?

Use H = P x V x Fc x Ff x Fs, where P is design pressure in MPa, V is volume in litres, Fc is 10 for a gas such as clean compressed air, Ff is 1.0 for a non-harmful gas, and Fs is 1 for standard service. For a typical compressed-air receiver this simplifies to H = 10 x P (MPa) x V (litres). A 1,000 L receiver at 800 kPa (0.8 MPa) gives H = 10 x 0.8 x 1,000 = 8,000, which falls in Hazard Level C (above 1,000 up to 10,000 MPa.L), which commonly triggers item (plant) registration as well as design registration, though registration is state and territory specific and subject to jurisdictional exceptions (Victoria has not required item registration since 1 July 2014). Confirm your duty with your state or territory WHS regulator. A widespread industry error treats the PV product (pressure times volume, without the Fc, Ff and Fs factors) as directly comparable to these thresholds. It is not the same number, and using it produces the wrong hazard level. Use the calculator below to run your own vessel’s numbers correctly.

The AS 4343 hazard level ladder

Hazard level is set by H, the pressure hazard value in megapascal litres (MPa.L). Higher H means higher level.

A · Highest hazard

H above 316,227,766 (10^8.5) MPa.L

B · High hazard

H above 10,000 up to 316,227,766 (10^8.5) MPa.L

C · Medium hazard

H above 1,000 up to 10,000 MPa.L

D · Low hazard

H above 316.2 (10^2.5) up to 1,000 MPa.L

E · Lowest hazard

H up to 316.2 (10^2.5) MPa.L

Typical air receiver

1,000 L at 800 kPa

H = 8,000 → Level C

Source: AS 4343 pressure equipment hazard levels.

2AS 4343 Hazard Level Calculator

Enter your vessel’s design pressure and volume below. You get its AS 4343 hazard level and what that usually means for registration, with the working shown so you can check it. The service-factor list covers the Clause 2.2.5 factors in both directions, including the reductions, but it cannot tell you which of them applies to your vessel. Settle that with a competent person.

3How this calculator works

How the hazard value H is worked out

The full formula carries five factors. For compressed air, three of them are fixed, so it collapses to a clean rule.

Full AS 4343 formula

H = P × V × Fc × Ff × Fs

P = pressure (MPa)
V = volume (litres)
Fc = contents factor
Ff = fluid state factor
Fs = special factor

for compressed air, Fc = 10, Ff = 1.0, Fs = 1

Compressed air rule

H = 10 × P (MPa) × V (litres)

Registration is state and territory specific. Design registration and item registration commonly apply, subject to state and territory exceptions.

Source: AS 4343 pressure equipment hazard levels.

AS 4343:2014 Clause 2.2.1 specifies the hazard level computation method as H = P x V x Fc x Ff x Fs, where P is design pressure in MPa, V is volume in litres, Fc is the compressibility and mass factor (Table 3.1: 0.1 for vacuum, 1 for liquid, 10 for gas), Ff is the fluid contents factor (Table 3.1 and Clause 2.2.2: 1/3 for non-harmful liquid, 1.0 for non-harmful gas, 3 for harmful, 10 for very harmful, 1000 for lethal), and Fs is the location or service factor (Clause 2.2.5, which runs in both directions: 1 for standard service, 3 for one of the special conditions in Clause 2.2.5(a), 10 for two or more of them, 30 for a design pressure above 50 MPa under Clause 2.2.5(b), and 1/3 or 1/10 where one or more of the mitigating conditions in Clause 2.2.5(c) apply, which do not apply to fired boilers). Clean compressed air is treated as non-harmful gas from -30C to 120C. Clause 3.2.6(a) changes a non-harmful gas to a harmful gas above 90C or below -30C, and air is the explicit exception that lifts the 90C ceiling to 120C because of Joule-Thomson cooling. The exception lifts the ceiling only. The -30C floor still applies to air, so a vessel with a design temperature below -30C takes Ff = 3, not 1.

The computed H value is classified against the AS 4343 Table 2.1 thresholds: Hazard Level A (H above 316,227,766, that is 10^8.5), Level B (above 10,000 up to 316,227,766), Level C (above 1,000 up to 10,000, that is 10^3 to 10^4), Level D (above 316.2 up to 1,000, that is 10^2.5 to 10^3) and Level E (316.2 or below, that is 10^2.5), all in MPa.L. A result that lands exactly on a boundary takes the lower hazard level here, because CAS follows Clause 2.2.8. The standard is not consistent on this point: Clause 2.2.8 is written about the product P x V or P x D rather than the computed H value, and Table 2.1 as printed uses greater-than-or-equal at the floor of bands B, C and D, which would send an exact boundary up instead. Settle a result that lands exactly on a boundary with a competent person before you act on it. Every constant, threshold and worked example in this calculator is drawn directly from the CAS Pressure Vessel Registration Australia guide, which documents the full Table 2.1 hazard-level boundaries and the AS/NZS 1200:2015 and AS 4343:2014 relationship in detail. This calculator automates the arithmetic that page already shows step by step. It makes one interpretive call, and it is the boundary rule set out above: where Clause 2.2.8 and Table 2.1 as printed disagree at an exact boundary, CAS follows Clause 2.2.8 and takes the lower level. For the full band story, including how Clause 2.2.8 settles a value that lands exactly on a boundary, see AS 4343 hazard levels explained.

4Before you rely on a result

Use your vessel’s design pressure and its full design-temperature range, minimum and maximum, not its operating values. Operating values can under-classify the hazard level. The standard service factor Fs is assumed to be 1, and Clause 2.2.5 moves it in both directions. Conditions that raise it are fired equipment, quick-actuating closures except on vacuum vessels, siting at a major hazard facility, road tankers and transportable vessels over 200 litres when they transport their contents under pressure, and pressure vessels intended for human occupancy with a design pressure above 0.01 MPa holding non-harmful gas: one of those gives Fs = 3 and two or more give Fs = 10. Two of those conditions do not stack the way that sounds. For road tankers and transportable vessels, and for human-occupancy vessels, Clause 2.2.5(a) says the fired-equipment, quick-actuating-closure and major-hazard-facility conditions are not intended to apply additionally, so a human-occupancy vessel that also has a quick-actuating closure is not automatically an Fs = 10 case. Major-hazard-facility siting carries its own override as well: Clause 2.2.5(a)(iii) lets a risk assessment establish that a higher hazard level should be adopted for the equipment, and that is a judgment no service factor can express. A design pressure above 50 MPa gives Fs = 30 under Clause 2.2.5(b). Clause 2.2.5(c) lowers it instead, to 1/3 where one of its three mitigating conditions applies and to 1/10 where two or more apply, and those reductions do not apply to fired boilers. The 120 degrees C air allowance applies to clean air only, and it lifts the upper limit only. Above 120 degrees C the air is treated as harmful gas, and so is air with a design temperature below -30 degrees C, because Clause 3.2.6(a) keeps the low-temperature limb for air. Either way Ff = 3, not 1. Contamination, including oil carryover, may change the contents classification, depending on what’s in the air and how much, so classify the actual contents and establish the right Ff with a competent person. This method is for pressure vessels. Pressure piping uses a different method. One more limit worth knowing: this tool runs Equation 2.1 and nothing else. AS 4343 Clause 2.1.2(d) tells you to review the result against Clauses 2.2.6 to 2.2.9 and 2.2.11 to 2.2.13 before you settle on a hazard level, and those clauses carry overrides the formula cannot reach. Two of them matter most. Clause 2.2.6 puts non-harmful liquid between 0 and 65 degrees C at Level E where PV is below 100,000 MPa.L. Clause 2.2.11 puts a lethal-gas vessel at Level D where PV is 0.1 MPa.L or less, which is a higher level than the formula alone returns. Clause 2.2.4 also sets special volume rules for multi-chamber, multi-phase, jacketed, coil and boiler vessels. None of that is built into this calculator. If your vessel holds anything other than clean compressed air, treat the number here as the arithmetic step only and have a competent person apply the rest of the standard.

5Registration guidance

Registration is state and territory specific. In model WHS jurisdictions, pressure equipment other than pressure piping at Hazard Levels A to D generally requires design registration. Item (plant) registration generally applies to boilers at Hazard Levels A to C and pressure vessels at Hazard Levels A to C, subject to jurisdictional exceptions such as gas cylinders, automotive LP Gas fuel vessels, serially produced pressure vessels, AS/NZS 1200 exclusions, and in NSW an additional exception for pressure vessels that do not require periodic internal inspection. Victoria has not required item registration since 1 July 2014, but design registration and inspection and maintenance duties still apply. Confirm your vessel’s registration duty with your state or territory WHS regulator before you rely on any result.

6The error this calculator is built to prevent

A widespread industry miscitation treats the PV product (pressure multiplied by volume, in kPa.L or MPa.L) as directly comparable to the AS 4343 hazard level H thresholds. It is not the same number: H incorporates the Fc, Ff and Fs factors. For gas contents at standard service, Fc is 10 and Fs is 1, so dropping the factors understates H by a full order of magnitude. The multiplier is Fc times Ff times Fs, not a flat ten, so where Clause 2.2.5(c) brings Fs down to 1/10 the PV product and H are equal and no correction is owed. The CAS pressure vessel registration guide documents a specific, verified instance of this error: some industry guidance has cited “Class B for receivers above 100 L at 800 kPa”, when the correct threshold, applying the full formula, is closer to 1,250 L at 800 kPa. At the cited 100 L the error is two full hazard levels, since the true level there is D; above 125 L and up to 1,250 L the true level is C, one level out. A facility relying on the incorrect threshold may have registered vessels that only required design registration (Level D) or no registration at all (Level E), or may be running an unregistered Level C vessel that should have been notified. This calculator runs the correct formula every time, removing the arithmetic step where the error is most often introduced.

7Frequently asked questions

What is the AS 4343 hazard level formula?

H = P x V x Fc x Ff x Fs, where P is design pressure in MPa, V is volume in litres, Fc is the compressibility and mass factor (10 for gas), Ff is the fluid contents factor (1.0 for non-harmful gas such as clean compressed air), and Fs is the location or service factor (1 for standard service). For a typical clean-compressed-air receiver at standard service, this simplifies to H = 10 x P (MPa) x V (litres).

Why can’t I just multiply pressure by volume to get my hazard level?

Because the PV product on its own omits the Fc, Ff and Fs factors that AS 4343 requires. For gas contents at standard service, Fc is 10 and Fs is 1, so the raw PV product understates the true H value by an order of magnitude. That gap depends on Fs. Where Clause 2.2.5(c) allows a reduction to 1/10, H and the PV product are the same number, so do not apply a blanket factor of ten. A widespread industry error does exactly this, and has led to receivers being registered at the wrong hazard level, sometimes registering vessels that never needed it and sometimes leaving vessels that did need registration unregistered.

What happens if my result lands exactly on a hazard-level boundary?

This tool follows AS 4343 Clause 2.2.8, which says that a value equalling the boundary between two categories takes the lower category. So an H value of exactly 10,000 (the B/C boundary) comes out as Level C, not Level B. You should know the standard is not consistent here. Clause 2.2.8 is written about the product P x V or P x D rather than the computed H value, and Table 2.1 as printed uses greater-than-or-equal at the floor of bands B, C and D, which would send an exact boundary up instead. CAS treats Clause 2.2.8 as the governing rule, but a result landing exactly on a boundary is one to settle with a competent person rather than to rely on from a calculator.

Does my hazard level determine whether I need to register my receiver in every state?

Registration is state and territory specific. In model WHS jurisdictions, pressure equipment other than pressure piping at Hazard Levels A to D generally requires design registration, and item (plant) registration generally applies to boilers at Hazard Levels A to C and pressure vessels at Hazard Levels A to C. These duties are subject to jurisdictional exceptions such as gas cylinders, automotive LP Gas fuel vessels, serially produced pressure vessels, AS/NZS 1200 exclusions, and in NSW an additional exception for pressure vessels that do not require periodic internal inspection. Victoria has not required item registration since 1 July 2014, but design registration and inspection and maintenance duties still apply. Confirm your vessel’s registration duty with your state or territory WHS regulator before you rely on any result. For the lodgement pathway in your jurisdiction, see the state guides for NSW, Victoria, Queensland, WA, SA, Tasmania, NT and the ACT.

Is this calculator a substitute for a professional hazard-level assessment?

No. This tool runs the published AS 4343:2014 formula on the numbers you enter, and its accuracy depends entirely on those inputs being correct for your actual vessel. An independent pressure-equipment specialist should verify your vessel’s design pressure, volume and contents classification against its actual design documentation before you rely on any hazard-level result for compliance purposes, particularly if your result is close to a boundary.