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STANDARDS · ISO

ISO 7840 fuel hose: A1 against A2, the fire test and what surveyors check

UPDATED 9 NOVEMBER 2026 · 1 FINDINGS · 5 SOURCES

What ISO 7840 covers, the difference between A1 and A2 fuel hose, how it lines up with the US Coast Guard's Type A1 and A2 hose, which hose goes where, and how to cite ISO 7840 in a finding.

AT A GLANCE
ISO 7840
OFFICIAL TITLE
Small craft, Fire-resistant fuel hoses (ISO 7840)
COVERS
Fire-resistant hose for petrol, diesel and their ethanol and FAME blends in permanently installed fuel systems on small craft. Non-fire-resistant hose is ISO 8469
SURVEYORS CHECK
The marking printed on every fuel hose, A1 or A2 where fire resistance is needed, the hose's age and condition, and its clamps
GET THE TEXT
Sold by ISO and national standards bodies, as ISO or EN ISO

Fuel hose is one of the few parts of a boat where the marking on the part tells the surveyor almost everything. ISO 7840 is the international standard for fire-resistant fuel hose on small craft. The letter says whether it's fire resistant. The number says how much fuel vapour gets through the wall.

What it covers

From the published scope: general requirements and physical tests for fire-resistant hoses carrying petrol, petrol with ethanol, diesel and diesel with FAME, at working pressures up to 0.34 MPa for hoses up to 10 mm bore and 0.25 MPa up to 63 mm. It applies to permanently installed fuel systems. Hose entirely within an outboard's splash well is excluded. Non-fire-resistant hose is ISO 8469, and the fuel system as a whole is ISO 10088.

A1 and A2. In the earlier edition published as a free preview:

Marking Fire resistant Permeation
ISO 7840 - A1 Yes, withstands 2.5 minutes in the fire test 4 g/(m²·h) or less
ISO 7840 - A2 Yes Over 4 up to 12 g/(m²·h)

The B classes are the non-fire-resistant equivalents under ISO 8469. The latest revision of ISO 7840 also adds requirements for low permeation hose; buy it for the current figures.

The US side. US boats use the same letters through the Coast Guard's own hose types in 33 CFR 183.558. BoatUS explains that type A is more fire resistant, required where more than five ounces could spill if the hose were cut, and type 1 loses less by permeation than type 2.

What surveyors check against it

The marking. Read every fuel hose: ISO 7840 A1 or A2, or USCG Type A1 or A2. Unmarked hose, or hose meant for water or coolant, is a finding.

The right hose in the right place. On US-built boats, A1 between pump and carburettor and from tank to engine, under 183.558. On CE boats, check against ISO 10088.

Age and condition. BoatUS's test: wipe the hose with a dry rag and smell it. A fuel smell means the hose has deteriorated. Check the joints for fuel stains and the clamps for corrosion.

See fuel hose type and age.

Citing it in a finding

"Fuel feed hose from tank to engine unmarked and cracked at the tank end. Replace with fire-resistant fuel hose marked ISO 7840 A1, or USCG Type A1, with stainless clamps." Quote the printing you found, or say none was visible.

Findings judged against ISO 7840

Each page shows how the defect is found, what decides the grade and example findings written up at A, B and C.

ENGINE AND FUEL

Fuel hose type and age

What USCG Type A1, A2, B1 and B2 fuel hose means, which hose goes where under ABYC H-24 and H-33, what a surveyor looks for, what replacement costs and three example findings graded A, B and C.

How to find and write it up

Frequently asked

What is the difference between A1 and A2 fuel hose?

Both are fire resistant. The number is permeation, how much fuel passes through the hose wall. In the earlier edition of ISO 7840 available as a free preview, class 1 hose loses 4 g per square metre per hour or less, and class 2 more than 4 up to 12. So A1 lets less fuel vapour through than A2.

Where must A1 hose be used?

In US boats under 33 CFR 183.558, hose between the fuel pump and the carburettor must be USCG Type A1, and hose from the tank to the engine must be A1 unless a B1 hose would release no more than five ounces of fuel in 2.5 minutes if cut. Vent and fill lines may be A1 or A2, or B1 or B2 under the same five ounce test.

What is the ISO 7840 fire test?

In the earlier edition's preview, the hose, filled with fuel, has to withstand a fire for 2.5 minutes without leaking after the fuel in the tray is lit.

How is ISO 7840 hose marked?

The earlier edition's preview requires the marking "ISO 7840 - A1" or "ISO 7840 - A2" in letters at least 3 mm high. Read the printing along the hose; unmarked fuel hose can't be shown to meet either standard.

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