Ammonia Safety: Properties, Exposure, and Emergency Response
Why ammonia demands respect
Ammonia (R-717) is an efficient refrigerant but a toxic, flammable-in-a-limited-range, and corrosive gas. A candidate must know the key numbers and the reasoning behind them. Ammonia is lighter than air, so it rises and tends to collect at ceilings and high points; it is also readily absorbed by water, which is why water spray or fog is used to knock down a release. The flammable range is roughly 15 to 28 percent by volume in air, and ignition requires a hot source; the practical defense is ventilation and eliminating ignition sources during a release. Its sharp, pungent odor is detectable well below harmful concentrations, which is a genuine safety advantage.
Exposure and first aid
Know the exposure limits and the first-aid sequence. The permissible exposure limit is 50 ppm (8-hour TWA), and the IDLH is 300 ppm. Above that, escape-only respirators are inadequate; only supplied-air or self-contained breathing apparatus belongs in the hot zone. First aid: move the victim to fresh air, remove contaminated clothing, and flush skin and eyes with copious water for at least 15 minutes. Never attempt to neutralize ammonia on skin with acid; dilution with water is the rule.
Traps and worked example
A common trap is confusing the odor threshold with a safe level, or assuming a cartridge respirator is acceptable for a large leak. Another is forgetting that liquid ammonia on skin causes freeze burns as well as chemical burns. Worked example: a gauge reads 150 psig on a vessel; if a question asks for the approximate saturation temperature, first convert to about 165 psia, then read the ammonia table (roughly 80 F) rather than reading 150 directly.
Emergency response
Sound the alarm, evacuate upwind and to higher ground only if ventilation is safe, account for personnel, and let trained responders with SCBA and water fog handle the release. Never enter a vapor cloud to close a valve without PPE and a buddy.