Which two-letter code indicates a simple asphyxiant?

• A. OX
• B. SA
• C. W with a line
• D. P

Answer: (B)

Two-letter code SA identifies simple asphyxiants—gases that crowd out or dilute the breathable oxygen in the air rather than poisoning you with a toxin. The danger is not chemical toxicity but oxygen deprivation, which can cause dizziness, unconsciousness, or death, especially in enclosed spaces. Responders rely on this code to know that the primary hazard is reduced oxygen, so ventilation and appropriate respiratory protection (like SCBA) are essential when entering affected areas. Examples include nitrogen and argon, which displace oxygen; carbon dioxide can also act as a simple asphyxiant at high concentrations. Other codes point to different hazards—oxidizers indicating fire risk, or symbols signaling water reactivity or environmental concerns—so they don’t describe the oxygen-displacement danger conveyed by SA.