Refrigerant Properties and Safety Flashcards

Under ASHRAE Standard 34, what safety classification is assigned to ammonia (R-717)?

Answer: B2L

Ammonia has higher toxicity (B) and lower flammability with a slow burning velocity (2L), so it is classified B2L.

Compared to air, ammonia vapor at room temperature is:

Answer: About 60% as dense, so it tends to rise

Ammonia's molecular weight of about 17 versus air's roughly 29 makes dry ammonia vapor lighter than air.

What is the NIOSH Immediately Dangerous to Life or Health (IDLH) concentration for ammonia?

Answer: 300 ppm

NIOSH sets the ammonia IDLH at 300 ppm.

At atmospheric pressure, anhydrous ammonia boils at approximately:

Answer: -28°F

Ammonia's normal boiling point is about -28°F (-33°C), which is why spilled liquid flashes rapidly.

Which metal must NOT be used in contact with ammonia in a refrigeration system?

Answer: Copper and brass

Ammonia, especially with any moisture present, attacks copper and copper alloys such as brass.

What is the approximate flammable range of ammonia in air by volume?

Answer: 15% to 28%

Ammonia is flammable only at fairly high concentrations, roughly 15% to 28% by volume in air.

Why should a liquid line never be isolated by closing valves at both ends while full of cold liquid refrigerant?

Answer: Warming liquid expands and can produce extreme hydrostatic pressure

Trapped liquid expands as it warms and can burst piping or valves unless a relief path is provided.