Is acetylene heavier or lighter than air?

Slightly lighter — relative vapour density is about 0.91. It does not reliably rise and disperse, though, so it can still accumulate in poorly ventilated spaces. Ventilation must be at high level and adequate; do not assume a leak will clear itself.

Can acetylene explode without oxygen?

Yes. This is what makes acetylene different from other fuel gases. Under pressure, heat or shock it can decompose exothermically into carbon and hydrogen with no oxidant present. That is why it is dissolved in a solvent inside a porous mass, and why a hot cylinder is an emergency.

Why does acetylene smell of garlic?

Pure acetylene is nearly odourless. The characteristic garlic smell comes from impurities, principally phosphine. The odour is a useful leak indicator but must never be relied on as the primary means of detection.

What extinguisher should be kept near acetylene work?

Dry powder is recommended. The priority in an acetylene fire is to stop the gas flow by closing the valve if it is safe to reach; extinguishing the flame while gas continues to escape can create an explosive accumulation.

How long must a cylinder stand upright before use if it has been horizontal?

At least one hour, and longer is better. This lets the acetone settle back into the porous mass. Using a cylinder immediately after it has been lying down draws solvent into the system.

Where do I get the signed PDF version?

This page is the current SDS and is kept up to date. A signed PDF is available on request for audit and regulatory files — contact us and we will issue it against your order reference.

Acetylene Safety Data Sheet (SDS/MSDS) | UN 1001

Product: Acetylene, dissolved
CAS number: 74-86-2
UN number: UN 1001
Transport class: 2.1 — Flammable gas
Specification: IS 308
Revision: 1 · 6 August 2026

Also known as: Dissolved acetylene · DA · Ethyne · C₂H₂

Section 1 — Identification

Product name: Acetylene, dissolved Synonyms: Dissolved acetylene, DA, ethyne Chemical formula: C₂H₂ CAS number: 74-86-2 · EC number: 200-816-9 · UN number: UN 1001 Specification: IS 308

Identified uses: Oxy-fuel cutting, welding, brazing and flame heating; flame hardening; atomic absorption spectroscopy (ultra-high-purity grade). Uses advised against: Any use in equipment not rated for acetylene. Never in contact with copper or high-copper alloys.

Supplier: The Kamrup Industrial Gases Limited.

Section 2 — Hazards identification

GHS classification: Flammable gases, Category 1 · Gases under pressure, Dissolved gas · Chemically unstable gas, Category A.

Signal word: DANGER

Hazard statements

H220 — Extremely flammable gas.
H230 — May react explosively even in the absence of air.
H280 — Contains gas under pressure; may explode if heated.

Precautionary statements

P210 — Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking.
P377 — Leaking gas fire: do not extinguish unless the leak can be stopped safely.
P381 — Eliminate all ignition sources if safe to do so.
P403 — Store in a well-ventilated place.

The principal hazard is that acetylene can decompose explosively under pressure, heat or shock without any oxidant present. It is not simply a flammable gas.

Asphyxiation is a secondary hazard: in an enclosed space acetylene displaces oxygen.

Section 3 — Composition

Component	CAS	Concentration
Acetylene	74-86-2	≥98 % (industrial, IS 308) / 99.99 % (UHP)
Acetone (solvent, industrial grade)	67-64-1	Balance, retained in porous mass
DMF (solvent, UHP grade)	68-12-2	Balance, retained in porous mass

The cylinder contains a porous mass charged with solvent. The acetylene is dissolved in that solvent, not present as free compressed gas.

Section 4 — First aid

Inhalation. Move the casualty to fresh air, keeping yourself safe — do not enter an oxygen-deficient atmosphere without breathing apparatus. If breathing has stopped, give artificial respiration. Seek medical attention.

Skin contact. Unlikely to cause injury as a gas. Rapidly escaping gas can cause cold burns — flush with tepid water, do not rub, and seek medical attention.

Eye contact. Flush with water. Seek medical attention if irritation persists.

Note for medical personnel. Acetylene is a simple asphyxiant with mild anaesthetic properties at high concentration. Treat according to symptoms.

Section 5 — Firefighting

Suitable media: Dry powder is recommended. Water spray may be used to cool cylinders from a protected position.

Specific hazards. Cylinders exposed to fire may undergo internal decomposition and can rupture, potentially some time after the external flame is out. Acetylene cylinders may require prolonged cooling even once the fire is extinguished.

Do not extinguish a burning gas leak unless the flow can be stopped safely — a flame is preferable to an unignited accumulation.

Advice for firefighters. Evacuate the area. Cool cylinders from a distance and behind protection. Self-contained breathing apparatus is required. A cylinder that is hot, discoloured or sooting at the valve should be treated as a potential rupture hazard.

Section 6 — Accidental release

Evacuate the area and eliminate ignition sources if it is safe to do so. Ventilate — but note that fans must be of the appropriate protection class for a flammable atmosphere. Close the cylinder valve if it can be reached safely. If a leak cannot be stopped, move the cylinder into open air away from heat, ignition sources and the public only if safe, then call the fire service and your supplier.

Do not attempt repairs on a cylinder or valve.

Section 7 — Handling and storage

Handling. Only trained persons. Move cylinders on a trolley, valve closed and cap fitted. Keep the system free of oil and grease. Open the valve slowly; never crack it to blow out dust. Purge air before lighting and leak-test every connection with an approved detection fluid. Fit flashback arrestors and non-return valves at the regulator and the torch. Do not exceed the safe withdrawal rate.

Storage. Upright, secured, in a lockable and well-ventilated store. Never in basements, occupied rooms, unventilated spaces or public areas. Segregate from oxidising gases — particularly oxygen — and from heat and ignition sources. Prevent water pooling around cylinder bases. Operate first-in, first-out. No smoking.

Never allow the cylinder to exceed 70 °C, and never apply heat to thaw a valve or increase flow.

Section 8 — Exposure controls

Acetylene is a simple asphyxiant rather than a toxic gas; controls target flammability and oxygen displacement. Provide ventilation at high level sufficient to prevent accumulation, use electrical equipment of the correct protection class, and monitor oxygen levels in confined spaces.

Personal protection: flame-resistant clothing, leather gauntlets, safety footwear, and eye protection to the correct shade for the work.

Section 9 — Physical and chemical properties

Property	Value	Source
Physical state	Gas — supplied as a dissolved gas	—
Appearance	Colourless	—
Odour	Garlic-like, from impurities (principally phosphine)	—
Molecular weight	26.037 g/mol	NIST
Triple point	−80.8 °C at 1.28 bar	NIST
Normal boiling point	−83.6 °C	NIST
Critical temperature	35.2 °C	NIST
Critical pressure	61.4 bar	NIST
Flammability limit — lower	≈2.3 % (V) in air	Literature
Flammability limit — upper	See the note below	—
Autoignition temperature	≈305 °C	Literature
Vapour density (air = 1)	≈0.91	Literature
Solubility in solvent	Highly soluble in acetone and DMF	—

The upper flammability limit is not the meaningful number for acetylene. Most fuel gases are hazardous only between a lower and an upper concentration in air. Acetylene is different: it can decompose exothermically with no oxidant present at all, which is why its GHS classification includes H230 — may react explosively even in the absence of air, and why it must be dissolved in a solvent within a porous mass rather than simply compressed. Treat any concentration as hazardous. Figures quoting an upper limit around 80 % describe only the acetylene-in-air combustion range and understate the hazard.

Acetylene does not exist as a stable liquid under normal commercial conditions.

Thermophysical constants from the NIST Chemistry WebBook (public domain). Flammability and ignition figures are standard literature values. All values in this section are to be confirmed against KIGL’s own analytical data before sign-off — this sheet describes KIGL product and should carry KIGL numbers.

Section 10 — Stability and reactivity

Unstable. May decompose explosively under pressure, heat or mechanical shock without an oxidant.

Incompatible materials: copper and alloys above roughly 65 % copper, silver, mercury and their compounds — acetylene forms shock-sensitive explosive acetylides with these. Also incompatible with oxidising agents including oxygen, chlorine and other halogens.

Conditions to avoid: heat above 70 °C, pressure above the rated filling pressure, shock and vibration, and back-flow of oxygen into the acetylene system.

Section 11 — Toxicological information

Simple asphyxiant. High concentrations displace oxygen and produce headache, dizziness, incoordination and ultimately unconsciousness. Mild anaesthetic effects at very high concentration. No significant chronic toxicity is attributed to acetylene itself; impurities such as phosphine are separately hazardous and are controlled by the product specification.

Section 12 — Ecological information

Not classified as environmentally hazardous. Does not persist or bioaccumulate. Released gas disperses in air. Spent carbide lime slurry from acetylene generation is alkaline and must be handled under local effluent rules.

Section 13 — Disposal

Do not discharge into any place where accumulation could be hazardous. Return cylinders — including apparently empty ones, which always retain dissolved gas — to the supplier. Do not attempt to dispose of a cylinder as scrap.

Section 14 — Transport


UN number	UN 1001
Proper shipping name	ACETYLENE, DISSOLVED
Class	2.1 — Flammable gas
Label	Flammable gas

Transport upright and secured, valves closed, regulators removed, caps fitted, in an open or very well-ventilated vehicle. Never carry cylinders in an unventilated compartment, including apparently empty ones. Separate from the driver’s compartment. Unload on arrival — do not use a vehicle as a store.

Section 15 — Regulatory information

Gas Cylinders Rules, 2016 (PESO) — design approval, filling, inspection and transport.
Calcium Carbide Rules, 1987 — storage and handling of the feedstock.
IS 308 — dissolved acetylene specification.
IS 7312 — cylinders for dissolved acetylene.
IS 14814 — acetylene safety code.
IS 13497 — fusible plugs for acetylene cylinders.
EN ISO 3807 — acetylene cylinders, porous mass and type testing.
ADR 2025 — UN 1001 transport of dangerous goods.

Further detail on our acetylene standards page.

Section 16 — Other information

Revision 1, issued 6 August 2026.

Compiled from Indian and international standards and established literature. The information relates to acetylene as supplied and does not release the user from assessing their own installation and application.

A signed PDF copy is available on request for audit files. This HTML page is the current version.

Acetylene (C₂H₂) Safety Data Sheet