Gases · CAS Database
Acetylene
Acetylene (CAS 74-86-2) — Fuel gas for welding and cutting. Get the SDS and OSHA HazCom guidance you need to store, label, and handle it safely on the job site.
Verified vs OSHA sources · October 5, 2026
CAS Registry Number CAS 74-86-2 · also known as Ethyne, C2H2
Overview
Fuel gas for welding and cutting
Acetylene on the job site
Acetylene is the fuel gas for oxy-acetylene cutting, welding, and heating. It's a simple asphyxiant, but its defining hazard is instability: acetylene is chemically unstable under pressure and can decompose explosively, which is why it must never be used above 15 psi at the torch and why cylinders are packed with a porous filler and acetone to hold the gas safely. Handle a cylinder roughly, use it on its side, or draw it too fast and you undermine that safety system.
The rules are specific and non-negotiable: keep cylinders upright and secured (a cylinder used on its side can pull liquid acetone into the line), never exceed 15 psi delivery, use flashback arrestors and check valves, leak-test with soapy water, and store fuel cylinders separated from oxygen. In enclosed spaces, ventilate against oxygen displacement. A flashback that reaches the cylinder is the failure mode these controls exist to prevent.
Key takeaways
- Acetylene decomposes explosively under pressure — never exceed 15 psi at the torch.
- Keep cylinders upright and secured (on their side pulls acetone into the line); use flashback arrestors and check valves.
- Leak-test with soapy water, separate fuel from oxygen storage, and ventilate enclosed spaces against asphyxiation.
Field guidance for planning and training — not a substitute for the manufacturer Safety Data Sheet, which controls the exposure limit, PPE, and handling for your specific product.
OSHA Exposure Limits
OSHA permissible exposure limit (PEL) and secondary limit for Acetylene on a US construction site. Where a substance-specific 1926 standard applies, its codified limit is shown; otherwise the figure comes from Table 1 to 29 CFR 1926.55, the construction air-contaminants table. Where 1926.55 does not list the substance, the Safety Data Sheet (Section 8) controls.
| Limit | Value | Basis / citation |
|---|---|---|
| OSHA PEL | See SDS §8 | 29 CFR 1926.55 Table 1OSHA entry: Acetylene |
| Action level | See SDS / standard | Not all substances define an action level |
| Averaging period | See SDS §8 | Compare with ACGIH TLV / NIOSH REL — often more protective than the OSHA PEL |
Listed as a simple asphyxiant: the table sets no concentration limit, and the controlling factor is available oxygen, which must be at least 19.5%.
Many OSHA PELs date to 1971 and may be less protective than current ACGIH/NIOSH values; always check the manufacturer SDS (Section 8) for the controlling limit and engineering-control guidance. Not legal advice.
GHS Classification
Physical Properties
Where Acetylene shows up on the job
Trades that commonly handle Acetylene, each with an OSHA HazCom guide built for the chemicals and tasks on that kind of site:
OSHA & HazCom Compliance Requirements
For construction work, Hazard Communication is governed by 29 CFR 1926.59 (adopts 29 CFR 1910.1200). Employers who use Acetylene must:
- •Maintain an accessible SDS for Acetylene (readily accessible during each work shift, 29 CFR 1910.1200(g)(8))
- •Label all containers with GHS-compliant labels (29 CFR 1910.1200(f)(1) shipped / 29 CFR 1910.1200(f)(6) workplace)
- •Include it in the workplace chemical inventory
- •Train employees on hazards before initial assignment
- •Retain employee exposure and medical records per 29 CFR 1910.1020 — 30-year retention applies to exposure/medical records, not to SDSs generically
HazCom (1910.1200 / construction 1926.59) covers labels, SDSs, and training only — it does not impose chemical storage segregation. Flammable & combustible liquid storage for construction is 29 CFR 1926.152; segregation of incompatibles is planned from SDS Sections 7 and 10. Not legal advice; state-plan states may have stricter rules.
Handling & Secondary-Container Labeling
When you transfer Acetylene into a workplace (secondary) container, OSHA gives two compliant options under 29 CFR 1910.1200(f)(6):
- •(f)(6)(i): full GHS label elements (as on the shipped container)
- •(f)(6)(ii): product identifier + words/pictures/symbols (or combination) that provide AT LEAST general information on the hazards
There is no volume/size cutoff for secondary containers — the ≤100 ml / ≤3 ml accommodations (29 CFR 1910.1200(f)(12) (added by the HCS 2024 final rule)) apply only to the manufacturer's shipped container. A portable container filled for the immediate use of the worker who fills it needs no label (29 CFR 1910.1200(f)(8)).
GHS Hazard Classification under OSHA HCS
OSHA's Hazard Communication Standard adopts the GHS (primarily GHS Revision 7 (HCS 2024)). It requires 8 hazard pictograms (Appendix C, Figure C.1). The Environment pictogram (GHS09) is not required by OSHA — Not in App C; outside OSHA jurisdiction; voluntary.
The 8 OSHA-required pictograms:
For flammable liquids, OSHA classifies by flash point and boiling point (App B.6.1 / 1910.106(a)):
- •Category 1: FP < 73.4°F AND BP <= 95°F
- •Category 2: FP < 73.4°F AND BP > 95°F
- •Category 3: FP >= 73.4°F AND <= 140°F
- •Category 4: FP > 140°F AND <= 199.4°F
The specific GHS classification of Acetylene comes from its Safety Data Sheet (Section 2). Use the live classification panel above and the manufacturer SDS to confirm pictograms and categories.
HCS 2024 Update Deadlines
Under the Hazard Communication Standard 2024 update (aligned primarily GHS Revision 7):
- •May 19, 2026 — manufacturers, importers, and distributors update substance labels & SDSs (1910.1200(j)(2)(i))
- •November 20, 2026 — employers update workplace labeling, the written program & training (1910.1200(j)(2)(ii))
During the interim, parts may comply with the 2012 HCS, the 2024 HCS, or both.
Quick Actions
Put Acetylene on your written inventory, print the workplace label your containers need, and keep your supplier’s sheet reachable on the jobsite.
The safety data sheet for your product comes from the supplier who sold it to you — no public registry can provide it. For the underlying chemistry, the public record is on PubChem.
Where this fits in your HazCom program
- SDS management — collecting the sheet, keeping it current, and making it readable during each work shift.
- GHS labels & workplace labeling — what has to appear on the shipped container, and what a secondary container needs instead.
Free Compliance Tools for Acetylene
Also on a welding & metalwork job
Frequently Asked Questions
What is Acetylene (CAS 74-86-2)?
Fuel gas for welding and cutting
What are the OSHA HazCom requirements for Acetylene on a construction site?
For construction work, Hazard Communication is governed by 29 CFR 1926.59 (adopts 29 CFR 1910.1200). Employers who use Acetylene must maintain an accessible Safety Data Sheet (SDS), label containers with GHS-compliant labels, include the chemical in the workplace chemical inventory, and train workers on its hazards before initial assignment.
What is the OSHA permissible exposure limit (PEL) for Acetylene?
The applicable exposure limit (OSHA PEL, and where stricter, the ACGIH TLV or NIOSH REL) for Acetylene is listed in Section 8 of its Safety Data Sheet. OSHA construction air-contaminant limits are in Table 1 to 29 CFR 1926.55; many OSHA PELs predate current science, so an SDS may cite a more protective ACGIH/NIOSH value.
When does the updated HCS 2024 labeling apply to Acetylene?
Under the Hazard Communication Standard 2024 update (aligned primarily GHS Revision 7), chemical manufacturers, importers, and distributors must update substance labels and SDSs by May 19, 2026, and employers must update workplace labeling, the written program, and training for substances by November 20, 2026. During the interim, parties may comply with the 2012 HCS, the 2024 HCS, or both.
How do I label a secondary (workplace) container of Acetylene?
Under 29 CFR 1910.1200(f)(6) you have two options: (i) the full GHS label elements as on the shipped container, or (ii) the product identifier plus words, pictures, symbols, or a combination that provide at least general hazard information. There is no volume/size cutoff for secondary containers. A portable container filled for the immediate use of the worker who fills it does not require a label (29 CFR 1910.1200(f)(8)).
How long must SDS and exposure records for Acetylene be kept?
Under 29 CFR 1910.1020, 30-year retention applies to employee exposure and medical records (medical records: duration of employment plus 30 years) — not to SDSs generically. Where an SDS is not retained, a record of the chemical's identity, where it was used, and when must be kept for at least 30 years.
Where can I find the SDS for Acetylene?
Under 29 CFR 1910.1200(g)(6) and (g)(7), the manufacturer, importer or distributor that sold you Acetylene must send its Safety Data Sheet with the first shipment, and again with the first shipment after the sheet is updated. HazComFast keeps the sheets you collect in one inventory per jobsite, searchable by product, manufacturer or CAS number, and your jobsite's SDS load onto the phone on their own.
Sources & Primary References
Regulatory data on this page is sourced from HazComFast's verified regulatory module (29 CFR 1926.59 / 1910.1200 and substance-specific 1926 standards), last verified October 5, 2026 against eCFR, OSHA.gov, and the Federal Register. Physical-property data comes from PubChem. Confirm it against the manufacturer Safety Data Sheet. This page is informational and is not legal advice.
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