DC THIRD CLASS STATIONARY BOILER
ACTUAL EXAM 2026 QUESTIONS WITH
VERIFIED SOLUTIONS AND DETAILED
EXPLANATIONS | UPDATED LICENSE PREP
STUDY GUIDE GRADED A+
• This study guide contains 200 verified exam-style questions covering all topics
tested on the DC Third Class Stationary Boiler License Exam, each with five answer
options, the correct answer clearly highlighted, and a detailed EXPERT RATIONALE
to reinforce understanding.
• Work through each question carefully, review every EXPERT RATIONALE even for
questions you get right, and revisit any topic where you miss more than two
questions in a row — this method builds both knowledge and exam confidence.
DC THIRD CLASS STATIONARY BOILER ACTUAL EXAM 2026 200 QUESTIONS
WITH VERIFIED SOLUTIONS AND DETAILED EXPLANATIONS
1. What is the primary purpose of a safety valve on a steam boiler?
A) To regulate steam pressure for process use
B) To allow manual pressure release by the operator
C) To control feedwater flow into the boiler
D) To measure steam temperature at the outlet
E) To automatically release excess pressure and prevent explosion
Correct Answer: E) To automatically release excess pressure and prevent
explosion
EXPERT RATIONALE: The safety valve is the most critical safety device on a boiler. It
opens automatically when steam pressure exceeds the maximum allowable working
pressure (MAWP), releasing steam to atmosphere and preventing catastrophic boiler
failure or explosion.
,2. What does MAWP stand for in boiler terminology?
A) Minimum Allowable Working Pressure
B) Maximum Allowable Water Pressure
C) Mechanical Allowance for Working Parts
D) Monitored Allowable Water Parameters
E) Maximum Allowable Working Pressure
Correct Answer: E) Maximum Allowable Working Pressure
EXPERT RATIONALE: MAWP is the maximum pressure at which a boiler is permitted
to operate as determined and stamped by the manufacturer in accordance with the
ASME Boiler and Pressure Vessel Code.
3. A boiler is considered to have low water condition when:
A) The feedwater temperature drops below 100°F
B) The steam pressure exceeds MAWP
C) The blowdown valve is opened
D) The safety valve lifts unexpectedly
E) The water level falls below the minimum safe operating level
Correct Answer: E) The water level falls below the minimum safe operating
level
EXPERT RATIONALE: Low water condition is one of the most dangerous boiler
emergencies. When water drops below the minimum safe level, boiler heating surfaces
become exposed to steam and direct flame, causing overheating, metal weakening, and
potential explosion.
4. Which code governs the construction and inspection of boilers in the United
States?
,A) NFPA 85 Boiler and Combustion Systems Hazards Code
B) API 510 Pressure Vessel Inspection Code
C) OSHA 1910.217 Mechanical Power Press Standard
D) NEC Article 430 Motor Circuits Standard
E) ASME Boiler and Pressure Vessel Code
Correct Answer: E) ASME Boiler and Pressure Vessel Code
EXPERT RATIONALE: The ASME (American Society of Mechanical Engineers) Boiler
and Pressure Vessel Code is the nationally recognized standard governing the design,
fabrication, inspection, and repair of boilers and pressure vessels in the United States.
5. What type of boiler uses tubes filled with water surrounded by hot
combustion gases?
A) Fire-tube boiler
B) Cast iron sectional boiler
C) Electric boiler
D) Coil-type boiler
E) Water-tube boiler
Correct Answer: E) Water-tube boiler
EXPERT RATIONALE: In a water-tube boiler, water flows inside the tubes while hot
combustion gases pass around the outside of the tubes. This design allows higher
pressures and faster steam generation compared to fire-tube boilers.
6. In a fire-tube boiler, combustion gases travel:
A) Inside the water drums
B) Through the steam dome
, C) Around the outside of the boiler shell
D) Through the feedwater heater
E) Through tubes surrounded by water
Correct Answer: E) Through tubes surrounded by water
EXPERT RATIONALE: In a fire-tube boiler, hot combustion gases pass through tubes
that are submerged in water inside the boiler shell. The heat transfers through the tube
walls into the surrounding water, generating steam.
7. What is the function of the steam gauge on a boiler?
A) To measure the temperature of feedwater
B) To indicate the water level in the boiler drum
C) To control fuel flow to the burner
D) To regulate the blowdown cycle
E) To indicate the steam pressure inside the boiler
Correct Answer: E) To indicate the steam pressure inside the boiler
EXPERT RATIONALE: The steam gauge (pressure gauge) is connected to the steam
space of the boiler and provides a continuous reading of the internal steam pressure.
Operators must monitor this gauge to ensure pressure stays within safe operating limits.
8. How often should a boiler operator perform a bottom blowdown?
A) Once per month only
B) Only during annual inspection
C) Every 72 hours regardless of conditions
D) Only when the safety valve lifts
ACTUAL EXAM 2026 QUESTIONS WITH
VERIFIED SOLUTIONS AND DETAILED
EXPLANATIONS | UPDATED LICENSE PREP
STUDY GUIDE GRADED A+
• This study guide contains 200 verified exam-style questions covering all topics
tested on the DC Third Class Stationary Boiler License Exam, each with five answer
options, the correct answer clearly highlighted, and a detailed EXPERT RATIONALE
to reinforce understanding.
• Work through each question carefully, review every EXPERT RATIONALE even for
questions you get right, and revisit any topic where you miss more than two
questions in a row — this method builds both knowledge and exam confidence.
DC THIRD CLASS STATIONARY BOILER ACTUAL EXAM 2026 200 QUESTIONS
WITH VERIFIED SOLUTIONS AND DETAILED EXPLANATIONS
1. What is the primary purpose of a safety valve on a steam boiler?
A) To regulate steam pressure for process use
B) To allow manual pressure release by the operator
C) To control feedwater flow into the boiler
D) To measure steam temperature at the outlet
E) To automatically release excess pressure and prevent explosion
Correct Answer: E) To automatically release excess pressure and prevent
explosion
EXPERT RATIONALE: The safety valve is the most critical safety device on a boiler. It
opens automatically when steam pressure exceeds the maximum allowable working
pressure (MAWP), releasing steam to atmosphere and preventing catastrophic boiler
failure or explosion.
,2. What does MAWP stand for in boiler terminology?
A) Minimum Allowable Working Pressure
B) Maximum Allowable Water Pressure
C) Mechanical Allowance for Working Parts
D) Monitored Allowable Water Parameters
E) Maximum Allowable Working Pressure
Correct Answer: E) Maximum Allowable Working Pressure
EXPERT RATIONALE: MAWP is the maximum pressure at which a boiler is permitted
to operate as determined and stamped by the manufacturer in accordance with the
ASME Boiler and Pressure Vessel Code.
3. A boiler is considered to have low water condition when:
A) The feedwater temperature drops below 100°F
B) The steam pressure exceeds MAWP
C) The blowdown valve is opened
D) The safety valve lifts unexpectedly
E) The water level falls below the minimum safe operating level
Correct Answer: E) The water level falls below the minimum safe operating
level
EXPERT RATIONALE: Low water condition is one of the most dangerous boiler
emergencies. When water drops below the minimum safe level, boiler heating surfaces
become exposed to steam and direct flame, causing overheating, metal weakening, and
potential explosion.
4. Which code governs the construction and inspection of boilers in the United
States?
,A) NFPA 85 Boiler and Combustion Systems Hazards Code
B) API 510 Pressure Vessel Inspection Code
C) OSHA 1910.217 Mechanical Power Press Standard
D) NEC Article 430 Motor Circuits Standard
E) ASME Boiler and Pressure Vessel Code
Correct Answer: E) ASME Boiler and Pressure Vessel Code
EXPERT RATIONALE: The ASME (American Society of Mechanical Engineers) Boiler
and Pressure Vessel Code is the nationally recognized standard governing the design,
fabrication, inspection, and repair of boilers and pressure vessels in the United States.
5. What type of boiler uses tubes filled with water surrounded by hot
combustion gases?
A) Fire-tube boiler
B) Cast iron sectional boiler
C) Electric boiler
D) Coil-type boiler
E) Water-tube boiler
Correct Answer: E) Water-tube boiler
EXPERT RATIONALE: In a water-tube boiler, water flows inside the tubes while hot
combustion gases pass around the outside of the tubes. This design allows higher
pressures and faster steam generation compared to fire-tube boilers.
6. In a fire-tube boiler, combustion gases travel:
A) Inside the water drums
B) Through the steam dome
, C) Around the outside of the boiler shell
D) Through the feedwater heater
E) Through tubes surrounded by water
Correct Answer: E) Through tubes surrounded by water
EXPERT RATIONALE: In a fire-tube boiler, hot combustion gases pass through tubes
that are submerged in water inside the boiler shell. The heat transfers through the tube
walls into the surrounding water, generating steam.
7. What is the function of the steam gauge on a boiler?
A) To measure the temperature of feedwater
B) To indicate the water level in the boiler drum
C) To control fuel flow to the burner
D) To regulate the blowdown cycle
E) To indicate the steam pressure inside the boiler
Correct Answer: E) To indicate the steam pressure inside the boiler
EXPERT RATIONALE: The steam gauge (pressure gauge) is connected to the steam
space of the boiler and provides a continuous reading of the internal steam pressure.
Operators must monitor this gauge to ensure pressure stays within safe operating limits.
8. How often should a boiler operator perform a bottom blowdown?
A) Once per month only
B) Only during annual inspection
C) Every 72 hours regardless of conditions
D) Only when the safety valve lifts
