ANSI/ASHRAE 34 defines the IDLH for anhydrous ammonia as how many ppm?

• A. 300 ppm
• B. 350 ppm
• C. 400 ppm
• D. 320 ppm

Answer: (D)

IDLH means the concentration that could cause life-threatening health effects or incapacitation if someone is exposed for a short period. For anhydrous ammonia, ANSI/ASHRAE 34 sets this threshold at 320 ppm. This value helps determine how systems are labeled, what PPE is required, and how ventilation and alarm setpoints are planned in ammonia refrigeration. It reflects toxicology data showing that around this concentration, exposure can produce serious respiratory irritation and rapid health deterioration in enclosed or poorly ventilated spaces, making rescue difficult. The other numbers don’t align with the official IDLH value established in the standard for this substance.