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Welding hose colours.Know the gas before you connect.

Oxy-fuel hoses are coloured by the gas they carry, but the colours depend on where the hose was made. This page sets out the ISO 3821, North American, Australian, Japanese, Chinese and Indian schemes side by side, plus thread conventions, hose grades and the safety devices that belong on every set.

Four oxy-fuel hoses ending in brass nuts: a blue oxygen and red fuel gas pair to ISO 3821, and a green oxygen and red fuel gas pair to North American practice. The fuel gas nuts carry a groove.ISOUSAGrooved nut = fuel gas, left-hand thread

Colour schemes. Pick a standard.

Each scheme shows its hose colours drawn out, the standard behind it and the sources we checked. Fuel gas hose ends are drawn with the grooved nut used for left-hand threads. On-screen colours are approximate.

ISO 3821 International, UK and Europe

Gas welding equipment: rubber hoses for welding, cutting and allied processes

Corroborated
Issued by
ISO (TC 44/SC 8); adopted in Europe and the UK as EN ISO 3821 / BS EN ISO 3821
Edition
ISO 3821:2019 (fifth edition, replaces 2008)
Used in
UK, EU and EFTA countries, and many others that adopt ISO standards

Covers rubber single and twin hoses for gas welding, cutting, heating, brazing and arc welding shielding gas, from -20 to +60 °C. Normal duty hose is rated 20 bar; light duty hose is rated 10 bar and limited to 6.3 mm bore and below. High-pressure acetylene above 1.5 bar is excluded.

Oxygen: Blue hoseOXYGEN
OxygenBlue
Acetylene, hydrogen and other fuel gases: Red hoseACETYLENE
Acetylene, hydrogen and other fuel gasesRed

Not for LPG, MPS, natural gas or methane, which need a hose that resists them.

LPG, MPS, natural gas, methane: Orange hoseLPG
LPG, MPS, natural gas, methaneOrange
Universal fuel gas hose: Red / orange hoseALL FUEL GASES
Universal fuel gas hoseRed / orange

Usable for every fuel gas except fuel gas carrying flux.

Fuel gas carrying flux: Red, marked FLUX hoseFLUX
Fuel gas carrying fluxRed, marked FLUX
Air, nitrogen, argon, CO2 and other non-combustible gases: Black hoseARGON
Air, nitrogen, argon, CO2 and other non-combustible gasesBlack
  • The hose cover is coloured all the way through and printed with the standard, duty, size and gas or gas group.
  • ISO 3821 has an annex on alternative oxygen colour codes for countries whose national practice differs. The free preview does not show its contents, so check the hose marking if you meet an oxygen hose that is not blue.
  • UK guidance (BCGA CP7) repeats the same colour table. CP7 is now at Revision 10 (2026); the colour table was confirmed from Revision 7.
Sources (7) Corroborated
  1. ISO/FDIS 3821:2017 sample pages (iTeh Standards) (opens in a new tab)ISO text: scope, light and normal duty pressures, universal and flux fuel gas hose definitions, designation examples Blue (oxygen), Red/Orange (universal fuel gases), Red (fluxed fuel gases); Annex E on alternative oxygen colour codes exists
  2. ISO 3821 catalogue entry (iTeh Standards) (opens in a new tab)Fifth edition replaces ISO 3821:2008; ISO 3821:2019 is the published edition
  3. ISO 3821:2019 preview (ANSI Webstore) (opens in a new tab)Fifth edition changes: maximum working pressure defined, clauses 7 to 9 and marking revised; Clause 10 is hose colour and gas identification
  4. BCGA Code of Practice 7, The safe use of oxy-fuel gas equipment (Revision 7, 2014, copy hosted by a distributor) (opens in a new tab)Hose colour table to BS EN ISO 3821, hose assembly and connection standards, flashback arrestor and non-return valve requirements, leak testing, purging, inspection intervals, oil and grease rules
  5. BCGA publications list (opens in a new tab)CP7 is current at Revision 10, 2026
  6. Reichelt Chemietechnik: hoses for fuel gases and liquefied gases (opens in a new tab)Supplier summary of ISO 3821 colours: blue oxygen, red fuel gases, orange liquefied gases
  7. TWI Job Knowledge 13: Equipment for oxyacetylene welding (opens in a new tab)UK hoses blue for oxygen and red for acetylene; oxygen fittings right-hand, acetylene left-hand; flashback arresters in both lines with non-return valves

Checked 9 Nov 2026

Side by side. Same gas, different colour.

The hose colour each scheme gives to each gas. Select a scheme name to open its details. “Not specified” means we could not confirm a colour for that gas from the sources checked.

Welding hose colour by gas and scheme
Gas
OxygenBlueGreenGreenBlueBlue (older: black)Black (older) or blueBlue
AcetyleneRedRedRedRedRed or brownRedRed
LPG, propane, natural gasOrangeRed, Grade TRed, Grade TOrangeOrangeNot specifiedRed
Universal fuel gas hoseRed / orangeRed, Grade TRed, Grade TRed / orangeNot specifiedNot specifiedNot specified
Fuel gas with fluxRed, marked FLUXNot specifiedNot specifiedRed, marked FLUXNot specifiedNot specifiedNot specified
HydrogenRedRed, Grade TNot specifiedRedNot specifiedNot specifiedNot specified
Argon, CO2, nitrogenBlackBlackNot specifiedBlackNot specifiedNot specifiedBlue
Compressed airBlackNot specifiedNot specifiedBlackNot specifiedNot specifiedNot specified

Threads and nuts. Fuel gas turns the other way.

Colour is only one safeguard. Hose fittings are made so that oxygen and fuel gas connections will not fit each other.

Oxygen hose nut with plain hex and right-hand thread, tightened clockwise, beside a fuel gas hose nut with a groove cut around its corners and left-hand thread, tightened anticlockwiseOxygenRight-hand threadTighten clockwisePlain hexFuel gasLeft-hand threadTighten anticlockwiseGroove on corners
Nuts seen from the hose end. Not to scale.

ISO 3253 and EN 560

Hose connections for welding equipment up to 20 bar use parallel G threads (G 1/8 to G 1, to ISO 228-1). Fuel gas connections are left-hand; oxygen and non-combustible gas connections are right-hand, so a fuel hose cannot be screwed onto an oxygen outlet.

CGA E-1 (North America)

Hose nuts come in A-size (3/8-24 UNF, for small torches and light hose) and B-size (9/16-18 UNF, the usual size). Oxygen nuts are right-hand; fuel gas nuts are left-hand.

The groove tells you

Left-hand fuel gas nuts carry a notch or groove cut around the hex corners. Oxygen nuts are plain. Feel for the groove before you put a spanner on, and remember a left-hand nut tightens anticlockwise.

Never adapt across gases

Do not use adaptors to join a fuel gas hose to an oxygen fitting or the other way round. US rules ban adaptors that make oxygen and fuel connections interchangeable, and UK guidance bans copper fittings on acetylene hose.

Sources (9) Verified
  1. ISO 3253:1998 sample (iTeh) (opens in a new tab)Hose connection threads G 1/8 to G 1 to ISO 228-1; left-hand for fuel gases, right-hand for oxygen and non-fuel gases
  2. EN 560:2018 catalogue entry (iTeh) (opens in a new tab)European hose connections up to 20 bar: left-hand threads for combustible gases, right-hand for oxygen and non-combustible gases
  3. Dixon Valve: welding connectors catalogue 2022 (opens in a new tab)CGA 020 to 023 fittings: A-size 3/8-24 UNF and B-size 9/16-18 UNF; right-hand for oxygen, left-hand for acetylene; green oxygen and red acetylene hose
  4. Western Enterprises A-size fuel gas hose nut (CGA-021) (opens in a new tab)Fuel gas hose nut is 3/8-24 left-hand, CGA-021, 200 psig
  5. Introduction to Welding, 12.3 OFC equipment and setup (Washington SBCTC open textbook) (opens in a new tab)Green oxygen and red fuel hose; left-hand fuel connections marked by notches around the nut; flashback arrestors on hoses
  6. AIMS Industrial: oxy cutting and oxy-acetylene guide (opens in a new tab)Australian practice: blue oxygen, red or orange fuel gas; fuel fittings left-hand with a notched nut; AS 4603 flashback arrestors at both ends of each hose, 5-year service life typical
  7. TWI Job Knowledge 13: Equipment for oxyacetylene welding (opens in a new tab)UK hoses blue for oxygen and red for acetylene; oxygen fittings right-hand, acetylene left-hand; flashback arresters in both lines with non-return valves
  8. California Code of Regulations, Title 8, section 4839 (opens in a new tab)Fuel gas and oxygen hose must be easy to tell apart; note says red is generally accepted for fuel gas and green for oxygen; references the RMA hose specification and CGA E-1 connections
  9. BCGA Code of Practice 7, The safe use of oxy-fuel gas equipment (Revision 7, 2014, copy hosted by a distributor) (opens in a new tab)Hose colour table to BS EN ISO 3821, hose assembly and connection standards, flashback arrestor and non-return valve requirements, leak testing, purging, inspection intervals, oil and grease rules

Checked 9 Nov 2026

Hose grades. Match the hose to the fuel.

Not every fuel gas hose suits every fuel gas. LPG, propane and natural gas attack some rubbers, so the hose has to be rated for them.

ISO 3821 duty ratings
DutyBoreMax workingProofMin burst
Light dutyUp to 6.3 mm bore10 bar20 bar30 bar
Normal dutyAll sizes20 bar40 bar60 bar
North American grades (ARPM IP-7)
GradeFuel gasesTubeCover
Grade RAcetylene onlyNot flame or oil resistantNot flame or oil resistant
Grade RMAcetylene onlyNot flame or oil resistantFlame and oil resistant
Grade TAll fuel gasesFlame and oil resistantFlame and oil resistant

Under ISO 3821, red hose is for acetylene and similar gases, orange hose is for LPG, MPS and natural gas, and red/orange “universal” hose suits every fuel gas except one carrying flux. Under IP-7, only Grade T is suitable for fuels other than acetylene.

Sources (3) Verified
  1. ISO/FDIS 3821:2017 sample pages (iTeh Standards) (opens in a new tab)ISO text: scope, light and normal duty pressures, universal and flux fuel gas hose definitions, designation examples Blue (oxygen), Red/Orange (universal fuel gases), Red (fluxed fuel gases); Annex E on alternative oxygen colour codes exists
  2. Parker Hannifin TB4802: Welding hose grades (opens in a new tab)Grade R and RM are for acetylene only; Grade T for all fuel gases; types L, S, H and VD; RMA/CGA IP-7 scope
  3. Parker welding hose and assemblies catalogue (opens in a new tab)Red fuel gas, green oxygen, black inert gas hose (argon, CO2, helium, nitrogen); ARPM IP-7 and CGA E-1; 200 psi maximum working pressure on most hose

Checked 9 Nov 2026

Arrestors and valves. Stop the flame going back.

A flashback can travel up the hose to the regulator and cylinder. Non-return valves stop gases mixing in the hose; flashback arrestors stop the flame itself.

Oxy-fuel set layout: cylinder, regulator, flashback arrestor at the regulator outlet, hose, then non-return valve (or a second arrestor) at the blowpipe inletO2FANRVC2H2FANRVRegulatorsone per gasFlashback arrestorsat each regulator outletCylinderssecured uprightHosescolour-coded, no longer than neededNon-return valvesat the blowpipe inlet
Typical layout to UK guidance. Many sets also fit an arrestor at the torch end; follow the maker’s instructions.
Oxy-fuel set layout: cylinder, regulator, flashback arrestor at the regulator outlet, hose, then non-return valve (or a second arrestor) at the blowpipe inlet1Cylinder and regulatorone per gas, valves open slowly2Flashback arrestorat each regulator outlet3Hosecolour-coded by gas4Non-return valveat each blowpipe inlet5Blowpipepurge each hose, then light
Gas flows from step 1 to step 5. Many sets also fit an arrestor at the torch end.

Flashback arrestor

Made to EN ISO 5175-1. It contains a flame arrestor and usually a non-return valve, often with a temperature or pressure cut-off. UK guidance asks for one in both the oxygen and fuel gas lines, near the regulator; for acetylene within 1 m of it.

Non-return valve

Made to EN ISO 5175-2. A spring-loaded valve at the blowpipe inlet that stops gas flowing back into the other hose. It will not stop a flashback once one has started, so it does not replace an arrestor.

Long hoses and both ends

HSE advises arrestors at both the torch and the regulator where hoses are long. Australian practice (AS 4603) and Manitoba’s guidance both put devices at each end of each hose.

Replace on time

BCGA CP7 says to replace or refurbish regulators and flashback arrestors five years from manufacture unless the maker says otherwise, and to inspect them at least once a year. After any flashback, follow the maker’s instructions before reusing an arrestor.

Regulator colours

No hose standard sets a regulator colour, and BCGA CP7 does not either. Regulators are made for one gas and marked with it (ISO 2503 covers them up to 300 bar inlet). Many makers add a blue, green or red label or gauge ring, but read the gas name, not the colour. US oxygen gauges must say USE NO OIL.

Old hose protectors

Older floating-disc “hose protectors” do not meet the current standard. Several valves fitted in series also cut the flow to the torch.

Sources (9) Verified
  1. EN ISO 5175-1:2017 (Estonian Centre for Standardisation) (opens in a new tab)Safety devices incorporating a flame (flashback) arrestor, fitted downstream of regulators and upstream of blowpipes
  2. EN ISO 5175-2:2017 (Estonian Centre for Standardisation) (opens in a new tab)Safety devices not incorporating a flame arrestor, such as non-return valves
  3. BCGA Code of Practice 7, The safe use of oxy-fuel gas equipment (Revision 7, 2014, copy hosted by a distributor) (opens in a new tab)Hose colour table to BS EN ISO 3821, hose assembly and connection standards, flashback arrestor and non-return valve requirements, leak testing, purging, inspection intervals, oil and grease rules
  4. HSE INDG297: Safety in gas welding, cutting and similar processes (opens in a new tab)Flashback arresters near the regulators (and at the torch on long hoses), non-return valves at the blowpipe, leak testing, purging, no oil or grease with oxygen, no worm-drive clips, no repairs to leaking hose
  5. Manitoba government, A Safe Workplace G-15: Oxygen and acetylene set up (opens in a new tab)Green hose to the oxygen regulator, red hose to the acetylene regulator; non-return valves and flashback arresters at both ends; no oil or grease; refers to CSA W117.2
  6. AIMS Industrial: oxy cutting and oxy-acetylene guide (opens in a new tab)Australian practice: blue oxygen, red or orange fuel gas; fuel fittings left-hand with a notched nut; AS 4603 flashback arrestors at both ends of each hose, 5-year service life typical
  7. ISO 2503:2009 sample (iTeh) (opens in a new tab)Regulators for cylinders up to 300 bar, outlet pressures up to 20 bar; oxygen regulators cleaned and degreased
  8. OSHA 29 CFR 1910.253, Oxygen-fuel gas welding and cutting (opens in a new tab)Hose to the RMA/CGA rubber welding hose specification; connections to CGA standards; connection test at twice service pressure, minimum 300 psi; oxygen regulator gauges marked USE NO OIL
  9. OSHA 29 CFR 1926.350, Gas welding and cutting (construction) (opens in a new tab)Hoses distinguishable by colour or touch, not interchangeable; inspect each shift; test after flashback; couplings that cannot separate by a straight pull; keep oil and grease away

Checked 9 Nov 2026

Before you light up. Every time.

Hose colour tells you what should be inside. These checks make sure the set is safe to use.

Check the gas, then the colour

Read the gas name printed on the hose and regulator. Colours differ between countries and older stock, and an imported set may be green where you expect blue.

Inspect before every use

Look along each hose for cuts, burns, cracking, worn patches and loose tails. Replace damaged hose; do not tape or splice it. A leaking section can be cut out and the hose shortened with proper crimped fittings.

Leak test with the right fluid

Pressurise the set and test every joint with a leak detection spray or solution made for oxy-fuel systems (ammonia-free, and free of oils for oxygen). Never look for leaks with a flame.

Fit arrestors and NRVs

Make sure there is a flashback arrestor on each line at the regulator and a non-return valve on each blowpipe inlet, and that they are in date.

Purge before lighting

Purge each hose on its own before lighting, to clear any mixed gas, and purge again after any break. Remove or purge hoses left in confined spaces.

No oil or grease on oxygen

Oil and grease can ignite violently in oxygen. Keep regulators, fittings and hoses clean, do not handle them with oily gloves, and do not use jointing tape or paste on hose or regulator connections.

Use proper hose clips

Use crimped ferrules or clips made for gas hose. Worm-drive (jubilee) clips are not recommended, and never join an acetylene hose with copper.

After a flashback

Shut both torch valves and both cylinder valves. Let the torch cool and find the cause before relighting. Hose that has carried a flashback must be tested or replaced; US rules require a test at twice working pressure, at least 300 psi.

This is a summary, not a substitute for training, the equipment maker’s instructions or your site’s safe system of work. Follow your national rules and the gas supplier’s guidance.

Sources (4) Verified
  1. HSE INDG297: Safety in gas welding, cutting and similar processes (opens in a new tab)Flashback arresters near the regulators (and at the torch on long hoses), non-return valves at the blowpipe, leak testing, purging, no oil or grease with oxygen, no worm-drive clips, no repairs to leaking hose
  2. BCGA Code of Practice 7, The safe use of oxy-fuel gas equipment (Revision 7, 2014, copy hosted by a distributor) (opens in a new tab)Hose colour table to BS EN ISO 3821, hose assembly and connection standards, flashback arrestor and non-return valve requirements, leak testing, purging, inspection intervals, oil and grease rules
  3. OSHA 29 CFR 1926.350, Gas welding and cutting (construction) (opens in a new tab)Hoses distinguishable by colour or touch, not interchangeable; inspect each shift; test after flashback; couplings that cannot separate by a straight pull; keep oil and grease away
  4. OSHA 29 CFR 1910.253, Oxygen-fuel gas welding and cutting (opens in a new tab)Hose to the RMA/CGA rubber welding hose specification; connections to CGA standards; connection test at twice service pressure, minimum 300 psi; oxygen regulator gauges marked USE NO OIL

Checked 9 Nov 2026

Plan the job. Then cost it.

Work out shielding gas use and cylinder count, heat input and the cost per metre of weld with the Tradefox welding and fabrication calculators.

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