Guide
Oxy-acetylene hoses: colour codes left-hand fuel threads, clamps, and when a hose must be scrapped
Oxy-acetylene hose is red for acetylene and blue for oxygen under ISO 3821, which replaced the withdrawn IS 447 in India. Fuel connections have left-hand threads with notched nuts. Hoses are fixed with proper clamps, never wire, checked daily, kept off the floor, and scrapped after any flashback or cut.
- Hose standard
- IS 447:1988
- Fuel threads
- Valves and fittings for flammable gases have left-hand threads; left-hand hexagon nuts carry notches on the corners
- Fixing
- Attach hoses firmly with clamping collars; do not attach them with iron wire
- Burst margin
- Minimum bursting pressure four times working pressure
- Electrical continuity
- Resistance between the end couplings of an acetylene pipeline hose not to exceed 10⁶ ohm
The hose is the weakest part of an oxy-acetylene set. It is the only component made of rubber, the only one dragged across a floor, the one closest to the sparks and the one most often repaired with whatever is to hand. Most of the rules about hoses exist to stop two things: the wrong gas reaching the wrong place, and a hose failing near a flame. This page sets out the colour and thread conventions, the fixing rules, the specification behind a good hose, and when one must be scrapped.
Colour and thread: two safeguards against the wrong gas
| Feature | Acetylene and fuel gases | Oxygen | Source |
|---|---|---|---|
| Hose colour | Red | Blue | ISO 3821 |
| Older British colour | Red | Black | BS practice recorded in the 1965 literature |
| Thread direction | Left-hand | Right-hand | Gas Cylinders Rules 2016, Rule 4(3) |
| Identification of thread | Notches on the corners of the hexagon or nut | Plain hexagon | IS 3224:2021 cl 9.1.2 |
| Arrestor colour band, if used | Red | Blue | IS 11006:2011, Annex B |
Colour tells the operator which hose is which. Thread direction makes the mistake physically awkward. Rule 4(3) of the Gas Cylinders Rules 2016 requires left-hand outlet threads on valves for flammable gases not listed in IS 3224 and right-hand for all others; IS 3224 clause 9.1.2 requires any left-hand hexagon on a valve outlet, and any left-hand nut, to carry notches on its corners so the thread can be recognised at a glance. The 1965 literature records the same rule for regulators: right-hand for gases that include oxygen, left-hand for combustible gases including acetylene. An adaptor that converts one to the other removes the only mechanical protection the set has, and does not belong in a workshop.
India has no current hose standard of its own. IS 447:1988, rubber hose for welding, is withdrawn with no superseding standard, and the live reference is ISO 3821. A buyer should ask for hose marked to ISO 3821, with the gas service shown on the hose. IS 1323:1982, the Indian code for oxy-acetylene structural welding, still names IS 447 and IS 6016 for hose and hose connections; those references are now historical.
Clamps, never wire
The C.P.I. 1968 safety code's instruction was blunt: attach the tubes firmly to the joints with clamping collars; do not attach them with iron wire. The British literature of 1965 said the same, that it is not good practice to wire hose to the connector and that clips should be used. Wire bites into the cover and the lining at a point, and as the rubber creeps under that point load the seal relaxes. A wired joint that held on Monday weeps on Friday, and it weeps at the hose tail, under the operator's hand, next to the flame. Use the crimped ferrule supplied with the hose assembly, or a band clip of the right size, and check the tightness whenever the hose is moved.
Rules that matter
The 1953 British welding-hose standard, BS 700, as compiled in the 1965 literature, gives the logic of hose specification even though its figures are now history:
What a good hose is made to
- a lining, a fabric reinforcement and an abrasion-resistant cover, the plies well bonded;
- a minimum bursting pressure four times the working pressure, the working pressure then normally 80 to 220 psi;
- a lining that does not ignite in oxygen at 360 °C;
- a limit on acetone-soluble matter in the rubber, because acetone carried over from a cylinder attacks some rubbers;
- in some specifications, no more than 10 % swelling in diameter at twice working pressure.
Indian pipeline practice uses the same margins in a different setting. IS 15190 (Part 1):2002 requires Class 1 acetylene hoses to withstand 1.5 times their maximum working pressure, Class 2 hoses a burst of not less than 11 times the maximum absolute working pressure, Class 3 hoses 35 times, and an electrical resistance between the end couplings of not more than 10⁶ ohm so the hose cannot hold a static charge. Filling plants are stricter still: the Form E licence conditions require high-pressure acetylene hoses to ISO 14113 with a burst pressure of not less than 1,000 bar.
The oxygen-side requirement is the one that matters most for a welder. The 1965 literature records that after a backfire it is the oxygen hose that may ignite, possibly through hot carbon particles passing down the line. Rubber that would smoulder in air burns fiercely in oxygen. A clean, oil-free, correctly specified oxygen hose, with an arrestor at the regulator outlet, is the defence. The events themselves are explained on backfire, sustained backfire and flashback.
Matching the hose to the job
Bore matters as much as specification. The 1965 literature grouped blowpipes by acetylene throughput: small sheet-metal blowpipes up to about 35 cubic feet an hour, medium blowpipes up to about 100, and heavy heating blowpipes up to 400 cubic feet an hour, about 11 cubic metres. It noted that such large blowpipes need a matching oxygen and acetylene supply and wide-bore hoses of adequate size. A heavy heating or gouging nozzle on a light, long hose starves at the tip, and a starved nozzle runs hot and backfires, and a backfire is the event that can set the oxygen hose alight, as the previous section explains. Choose the hose bore from the blowpipe maker's table for the largest nozzle that will be used, keep runs no longer than the job needs, and remember that every extra metre of hose is extra volume of gas to purge before lighting.
Rules that matter
The C.P.I. 1968 code's workplace list reads as a toolbox talk:
Laying out the hoses
- fit work stations and cylinder trolleys with holders on which hoses can be wound as far as necessary;
- bring the hoses to the place of work, as far as possible, from the rear on the right;
- protect the hoses from jets of sparks, from bending and from crushing, and replace damaged hoses at once;
- pay off enough length and, where several hoses run in parallel, fix them so they do not tangle;
- lay long runs at a suitable height;
- check the tightness of valves, hoses, joints and unions and remedy any leak at once.
The 1965 cutting procedure adds one practical point: make sure there is enough slack in the hose for the whole line of the cut before starting, so the operator never pulls a hose tight across hot metal. Hoses do not belong across gangways, through doors that close on them, or under the wheels of trolleys and fork-lifts.
Rules that matter
When to scrap a hose
- Any cut, burn, crack, blister or soft spot in the cover.
- Any hose that has carried a flashback or a hose fire, whatever it looks like afterwards.
- Any hose that has had oil or grease on the oxygen side.
- Any hose whose colour or marking cannot be read.
- Any hose that fails a leak test with a bubble-forming leak-detection fluid along its length (on oxygen hose, a fluid made for oxy-fuel service rather than soapy water, per IMCA Safety Flash 02/14); the method is on the leak detection page.
A damaged end may be cut off and a new ferrule fitted if the rest of the hose is sound. Tape is never a repair.
Rules to apply
- Red for acetylene, blue for oxygen, ISO 3821 marking on both.
- Left-hand notched nuts on the fuel side; no adaptors.
- Crimped ferrules or proper clips; never wire.
- Arrestors to IS 11006 at both regulator outlets; non-return valves at the torch.
- Inspect before every shift; scrap after any flashback.
The full pre-start routine is on the daily safety checklist. IS 11006 requires each flashback arrestor to be marked with its gas, and a colour band where used is red for fuel and blue for oxygen.
Oxy-acetylene hoses — frequently asked questions
What colour is acetylene hose?
Red, for acetylene and other fuel gases. Oxygen hose is blue under the international hose standard ISO 3821, which is the live reference in India now that IS 447 has been withdrawn. Older British practice, recorded in the 1965 literature, used black for oxygen, so older sets and some imported equipment still carry black oxygen hose. Whatever the colour, the left-hand thread on the fuel side is the real safeguard.
Why does the acetylene hose have a left-hand thread?
So that a fuel hose cannot be screwed on to an oxygen fitting by mistake. IS 3224:2021 Table 1 gives acetylene a left-hand outlet and oxygen a right-hand one; Rule 4(3) of the Gas Cylinders Rules 2016 extends left-hand threads to flammable gases not listed in IS 3224; and IS 3224:2021 clause 9.1.2 requires left-hand hexagons and nuts to have notched corners so the thread direction is visible. Never use an adaptor that defeats the convention.
Can I use wire to fix a hose to its connector?
No. The C.P.I. 1968 code says to attach the tubes firmly to the joints with clamping collars and not to attach them with iron wire, and the 1965 British literature says the same: clips, not wire. Wire cuts into the hose cover and lining and gives a point seal that relaxes as the rubber creeps, which becomes a leak at the most vulnerable joint in the set. Use crimped ferrules or the proper hose clips.
How often should welding hoses be checked?
Look along every hose before each shift for cuts, burns, cracks, swelling and soft spots, and check the end fittings and clamps for tightness. Leak-test the connections whenever a hose is fitted; on the oxygen side IMCA advises a fluid made for oxy-fuel systems rather than soapy water. The C.P.I. 1968 code requires damaged tubes to be replaced at once; there is no such thing as a safe taped repair on an oxygen or acetylene hose.
Can a hose be repaired by cutting out the damaged part?
A hose can be shortened by cutting off a damaged end and refitting a proper ferrule or clamp, if the remaining length is sound throughout. Joining two pieces of hose with a splice adds two more joints to the system and should be done only with a purpose-made hose connector. Tape is never a repair. A hose that has carried a flashback is scrapped, not cut back.
Why is oxygen hose made to a stricter specification?
Because rubber burns fiercely in oxygen. The 1965 literature records the British requirement that the hose lining must not ignite in oxygen at 360 °C, and notes that after a backfire the oxygen hose is the one that may ignite, possibly from hot carbon particles. Keep oxygen hose clean and free of oil, and never use oxygen hose for fuel or fuel hose for oxygen.
How should hoses be laid at the workplace?
The C.P.I. 1968 code gives a practical list: wind hoses on holders as needed, bring them to the work from the rear on the right, keep them clear of sparks, bending and crushing, lay long runs at a suitable height and fix parallel hoses so they do not tangle. Do not run hoses through doorways that close on them or under vehicle routes, and leave enough slack for the whole line of a cut.
References
- Bureau of Indian Standards. (2002). Acetylene Pipelines — Code of Practice (IS 15190 (Part 1):2002).
- Bureau of Indian Standards. (2021). Valve for Compressed Gas Cylinders excluding LPG (IS 3224:2021, Fourth Revision).
- C.P.I. (1968). Safety in the production and use of acetylene. Paris.
- Government of India. (2016). Gas Cylinders Rules, 2016 (G.S.R. 1081(E)). Petroleum and Explosives Safety Organisation.
- IMCA Safety Flash 02/14, Hose fire caused by flashback in oxygen and acetylene hoses https://imca-int.com/resources/safety/safety-flashes/0214-hose-fire-caused-by-flashback-in-oxygen-and-acetylene-hoses
- International Organization for Standardization. (n.d.). Gas welding equipment — Rubber hoses for welding, cutting and allied processes (ISO 3821).
Enquiries
Request a quotation
State the gas or equipment, the quantity or capacity, and your location. KIGL will confirm the grade, the cylinder or plant size, and whether the location can be served from Noonmati, or through the agent network.