CARO Refrigerant Properties and Safety 2 — Questions and Answers
Question 1: Under ASHRAE Standard 34, what safety classification is assigned to ammonia (R-717)?
- A1
- B2L (Correct answer)
- A2L
- B1
Correct answer: B2L
Ammonia has higher toxicity (B) and lower flammability with a slow burning velocity (2L), so it is classified B2L.
Question 2: Compared to air, ammonia vapor at room temperature is:
- About 60% as dense, so it tends to rise (Correct answer)
- About twice as dense, so it settles to the floor
- The same density, so it mixes evenly
- Heavier than air only when it is dry
Correct 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.
Question 3: What is the NIOSH Immediately Dangerous to Life or Health (IDLH) concentration for ammonia?
- 25 ppm
- 50 ppm
- 300 ppm (Correct answer)
- 5,000 ppm
Correct answer: 300 ppm
NIOSH sets the ammonia IDLH at 300 ppm.
Question 4: At atmospheric pressure, anhydrous ammonia boils at approximately:
- -28°F (Correct answer)
- -41°F
- 32°F
- -109°F
Correct answer: -28°F
Ammonia's normal boiling point is about -28°F (-33°C), which is why spilled liquid flashes rapidly.
Question 5: Which metal must NOT be used in contact with ammonia in a refrigeration system?
- Carbon steel
- Stainless steel
- Copper and brass (Correct answer)
- Cast iron
Correct answer: Copper and brass
Ammonia, especially with any moisture present, attacks copper and copper alloys such as brass.
Question 6: What is the approximate flammable range of ammonia in air by volume?
- 1% to 7%
- 4% to 75%
- 15% to 28% (Correct answer)
- 30% to 50%
Correct answer: 15% to 28%
Ammonia is flammable only at fairly high concentrations, roughly 15% to 28% by volume in air.
Question 7: Why should a liquid line never be isolated by closing valves at both ends while full of cold liquid refrigerant?
- The refrigerant will freeze solid
- Warming liquid expands and can produce extreme hydrostatic pressure (Correct answer)
- Oil will separate and plug the line
- The refrigerant will decompose into toxic gases
Correct 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.
CARO Refrigerant Properties and Safety 2
Under ASHRAE Standard 34, what safety classification is assigned to ammonia (R-717)?