SA (simple asphyxiant gas)
On an NFPA 704 fire diamond, SA in the white section at the bottom marks a simple asphyxiant gas: a gas such as nitrogen, argon or helium that is dangerous because it displaces the oxygen in the air.
How to read it
It is one of the three special hazard symbols of the NFPA 704 fire diamond. NFPA's FAQ lists the gases as nitrogen, helium, neon, argon, krypton and xenon. Riverside County and Fire Engineering both add carbon dioxide, and Fire Engineering also lists methane and propane. Fire Engineering describes simple asphyxiants as gases that displace oxygen and leave an atmosphere with less than 19.5% oxygen. The details are on the product's safety data sheet.
Also searched as: nfpa sa, simple asphyxiant.
These explain what a rating on the diamond means. For handling, storage and first aid, refer to the product’s label and safety data sheet.
Where you'll see it
Fire Engineering shows SA on a sign over a carbon dioxide tank outside a convenience store, and Riverside County's guidance for restaurants notes that the door to the carbon dioxide storage area has historically needed a larger sign.
Look-alikes
There is no GHS pictogram for a simple asphyxiant. OSHA's label elements give it the signal word “Warning” and the statement “May displace oxygen and cause rapid suffocation”, with no pictogram. The GHS gas cylinder is a different mark: it is for gases under pressure, whatever the gas.
More NFPA 704 fire diamond
Browse symbols drawn with letters and numbers.
Sources
- Frequently Asked Questions on NFPA 704, National Fire Protection Association, published by the Cambridge Fire Department (Massachusetts), Question 5
- NFPA 704 Guidance Document: Frequently Asked Questions (FAQ), EPO-372 (Rev 04/21), Riverside County Department of Environmental Health, Hazardous Materials Management Branch, Pages 1–2
- Understanding NFPA 704 Placarding Is Critical to Life Safety of First Responders, Brian Daboul, 29 January 2024, Fire Engineering
- Allocation of Label Elements (29 CFR 1910.1200, Appendix C), 29 CFR 1910.1200 Appendix C, U.S. Occupational Safety and Health Administration, C.4.31
- WHMIS - Pictograms (OSH Answers), Canadian Centre for Occupational Health and Safety
- Comparison of NFPA 704 and HazCom 2012 Labels (Quick Card), National Fire Protection Association and U.S. Occupational Safety and Health Administration
Last reviewed September 30, 2026 by Rory Hansen. How we research