BOC BOC Plumbing and Water Systems 2 — Questions and Answers
Question 1: What is the primary cause of water hammer in a plumbing system?
- Undersized water heater
- Sudden stoppage or change in water flow velocity (Correct answer)
- Excessive pipe insulation
- Low water pressure at the meter
Correct answer: Sudden stoppage or change in water flow velocity
Water hammer is a pressure surge caused by the momentum of water being suddenly stopped or redirected, such as when a solenoid valve closes quickly.
Question 2: Which bacteria is of greatest concern in a building's hot water and cooling tower systems due to risk of Legionnaires' disease?
- E. coli
- Legionella pneumophila (Correct answer)
- Staphylococcus aureus
- Pseudomonas aeruginosa
Correct answer: Legionella pneumophila
Legionella pneumophila thrives in warm water (77–113°F) in building systems and causes Legionnaires' disease when aerosolized water is inhaled.
Question 3: What minimum hot water storage temperature does ASHRAE 188 recommend to control Legionella growth?
- 100°F (38°C)
- 120°F (49°C)
- 140°F (60°C) (Correct answer)
- 160°F (71°C)
Correct answer: 140°F (60°C)
ASHRAE 188 and the CDC recommend storing domestic hot water at or above 140°F (60°C) to prevent Legionella proliferation in storage tanks.
Question 4: Which type of pipe is most susceptible to pinhole leaks from aggressive water chemistry or dezincification?
- PEX (cross-linked polyethylene)
- Cast iron
- Copper (Correct answer)
- PVC schedule 40
Correct answer: Copper
Copper piping is vulnerable to pinhole leaks when water has low pH, high chloramines, or high dissolved oxygen, all of which accelerate pitting corrosion.
Question 5: What is the function of a thermostatic mixing valve (TMV) at a building's hot water system?
- To blend cold and recirculated water to prevent freezing
- To blend hot and cold water to deliver a safe, scalding-free temperature at fixtures (Correct answer)
- To regulate incoming water pressure
- To divert hot water to priority zones first
Correct answer: To blend hot and cold water to deliver a safe, scalding-free temperature at fixtures
A TMV mixes hot storage water (maintained at high temperature for Legionella control) with cold water to deliver tempered water at a safe use temperature, typically 110°F.
Question 6: In a cooling tower water treatment program, why is biocide treatment essential?
- To prevent scale on condenser tubes
- To control microbial growth including Legionella and algae (Correct answer)
- To lower the pH of the recirculating water
- To reduce blowdown frequency
Correct answer: To control microbial growth including Legionella and algae
Cooling towers are warm, aerated water environments ideal for microbial growth; biocide treatment kills bacteria, algae, and biofilm to protect health and system performance.
BOC BOC Plumbing and Water Systems 2
What is the primary cause of water hammer in a plumbing system?