MASTER GAS FITTER PRACTICE EXAM QUESTIONS
AND ANSWERS WITH RATIONALES | LATEST EXAM
UPDATE
SECTION 1: GAS THEORY & PROPERTIES (Questions 1-15)
Question 1
Which physical property of natural gas directly influences the sizing of gas piping systems
and the pressure drop calculations?
A. Specific gravity of 1.52
B. Specific gravity of 0.60
C. Vapor density of 2.0
D. Molecular weight of 44
Correct Answer: B
Explanation: Natural gas has a specific gravity of approximately 0.60 relative to air (1.0),
making it lighter than air. This property affects flow characteristics, pressure drop
calculations, and pipe sizing formulas. Lighter gases flow more easily through piping
systems and rise in the event of a leak, influencing system design and safety
considerations.
Question 2
,A gas fitter observes that the gas pressure in a closed system increases from 10 psi to 12
psi when the ambient temperature rises from 60°F to 80°F. Assuming constant volume,
which gas law explains this phenomenon?
A. Boyle's Law
B. Charles's Law
C. Gay-Lussac's Law
D. Dalton's Law
Correct Answer: C
Explanation: Gay-Lussac's Law states that the pressure of a gas is directly proportional to
its absolute temperature when volume is held constant (P₁/T₁ = P₂/T₂). The scenario
describes a pressure increase with temperature increase at constant volume, which is
exactly this law. This principle is critical for understanding pressure-temperature
relationships in gas distribution systems.
Question 3
When calculating the flow capacity of a gas pipeline, which combination of factors must be
considered according to the fundamental gas flow equations?
A. Pipe diameter only
B. Pipe diameter, length, pressure drop, and gas specific gravity
C. Pipe material and fitting count only
D. Operating temperature and atmospheric pressure only
Correct Answer: B
Explanation: Gas flow capacity depends on multiple interrelated factors including pipe
inside diameter, total equivalent length (including fittings), allowable pressure drop, gas
specific gravity, and initial pressure. The fundamental flow equations (such as Spitzglass,
Weymouth, or Panhandle) incorporate these variables. Proper pipe sizing requires
considering all these factors for safe and efficient system operation.
Question 4
,A gas fitter is installing a propane system. Propane has a vapor density of 1.52 relative to
air. What is the most significant safety implication of this property?
A. Propane will dissipate quickly through roof vents
B. Propane will accumulate in low-lying areas and confined spaces
C. Propane will rise to the ceiling in enclosed spaces
D. Propane will mix uniformly throughout the space
Correct Answer: B
Explanation: With a vapor density of 1.52 (heavier than air), propane will settle in low areas
such as basements, floor drains, and pits. This creates a significant explosion hazard as
the gas can accumulate in confined spaces where ignition sources may exist. Gas fitters
must design systems with adequate ventilation and install gas detectors in these
vulnerable locations.
Question 5
During a routine inspection, you measure the heating value of a natural gas sample at
1,050 BTU per cubic foot. The customer's appliance is rated for 100,000 BTU/hr input. What
is the minimum gas flow rate required for this appliance?
A. 95.2 cubic feet per hour
B. 100.0 cubic feet per hour
C. 105.0 cubic feet per hour
D. 110.5 cubic feet per hour
Correct Answer: A
Explanation: The required gas flow rate is calculated by dividing the appliance input rating
by the heating value of the gas: 100,000 BTU/hr ÷ 1,050 BTU/ft³ = 95.2 ft³/hr. This
calculation ensures the appliance receives adequate fuel to achieve its rated output. Gas
fitters must verify that supply piping can deliver this volume plus additional capacity for
other appliances on the system.
Question 6
, Which characteristic of liquefied petroleum gases (LPG) presents the greatest challenge
during system design compared to natural gas systems?
A. Lower heating value per cubic foot
B. Higher operating pressures requiring specialized regulators
C. Gas-to-liquid volume ratio of approximately 270:1
D. Requirement for stainless steel piping only
Correct Answer: C
Explanation: LPG expands from liquid to vapor at a ratio of approximately 270:1. This high
expansion ratio means that even small liquid leaks can create significant vapor volumes,
increasing explosion risks. This characteristic requires special design considerations
including liquid traps, proper vaporization equipment, and careful system layout to prevent
liquid slugging in vapor lines.
Question 7
A gas fitter is calculating the maximum capacity of a 2-inch nominal pipe carrying natural
gas over a 200-foot equivalent length with a 0.5 psi pressure drop. Which additional gas
property must be included in the flow calculation?
A. Gas specific gravity only
B. Gas specific gravity and viscosity
C. Gas specific gravity, viscosity, and compressibility factor
D. Gas specific gravity, viscosity, and critical temperature
Correct Answer: B
Explanation: Accurate gas flow calculations must consider both specific gravity (which
affects density and flow characteristics) and viscosity (which affects friction losses). While
compressibility becomes significant at very high pressures (above 100 psig), for typical low-
pressure gas systems (under 1 psi), specific gravity and viscosity are the primary gas
properties needed for accurate flow capacity calculations.
Question 8
AND ANSWERS WITH RATIONALES | LATEST EXAM
UPDATE
SECTION 1: GAS THEORY & PROPERTIES (Questions 1-15)
Question 1
Which physical property of natural gas directly influences the sizing of gas piping systems
and the pressure drop calculations?
A. Specific gravity of 1.52
B. Specific gravity of 0.60
C. Vapor density of 2.0
D. Molecular weight of 44
Correct Answer: B
Explanation: Natural gas has a specific gravity of approximately 0.60 relative to air (1.0),
making it lighter than air. This property affects flow characteristics, pressure drop
calculations, and pipe sizing formulas. Lighter gases flow more easily through piping
systems and rise in the event of a leak, influencing system design and safety
considerations.
Question 2
,A gas fitter observes that the gas pressure in a closed system increases from 10 psi to 12
psi when the ambient temperature rises from 60°F to 80°F. Assuming constant volume,
which gas law explains this phenomenon?
A. Boyle's Law
B. Charles's Law
C. Gay-Lussac's Law
D. Dalton's Law
Correct Answer: C
Explanation: Gay-Lussac's Law states that the pressure of a gas is directly proportional to
its absolute temperature when volume is held constant (P₁/T₁ = P₂/T₂). The scenario
describes a pressure increase with temperature increase at constant volume, which is
exactly this law. This principle is critical for understanding pressure-temperature
relationships in gas distribution systems.
Question 3
When calculating the flow capacity of a gas pipeline, which combination of factors must be
considered according to the fundamental gas flow equations?
A. Pipe diameter only
B. Pipe diameter, length, pressure drop, and gas specific gravity
C. Pipe material and fitting count only
D. Operating temperature and atmospheric pressure only
Correct Answer: B
Explanation: Gas flow capacity depends on multiple interrelated factors including pipe
inside diameter, total equivalent length (including fittings), allowable pressure drop, gas
specific gravity, and initial pressure. The fundamental flow equations (such as Spitzglass,
Weymouth, or Panhandle) incorporate these variables. Proper pipe sizing requires
considering all these factors for safe and efficient system operation.
Question 4
,A gas fitter is installing a propane system. Propane has a vapor density of 1.52 relative to
air. What is the most significant safety implication of this property?
A. Propane will dissipate quickly through roof vents
B. Propane will accumulate in low-lying areas and confined spaces
C. Propane will rise to the ceiling in enclosed spaces
D. Propane will mix uniformly throughout the space
Correct Answer: B
Explanation: With a vapor density of 1.52 (heavier than air), propane will settle in low areas
such as basements, floor drains, and pits. This creates a significant explosion hazard as
the gas can accumulate in confined spaces where ignition sources may exist. Gas fitters
must design systems with adequate ventilation and install gas detectors in these
vulnerable locations.
Question 5
During a routine inspection, you measure the heating value of a natural gas sample at
1,050 BTU per cubic foot. The customer's appliance is rated for 100,000 BTU/hr input. What
is the minimum gas flow rate required for this appliance?
A. 95.2 cubic feet per hour
B. 100.0 cubic feet per hour
C. 105.0 cubic feet per hour
D. 110.5 cubic feet per hour
Correct Answer: A
Explanation: The required gas flow rate is calculated by dividing the appliance input rating
by the heating value of the gas: 100,000 BTU/hr ÷ 1,050 BTU/ft³ = 95.2 ft³/hr. This
calculation ensures the appliance receives adequate fuel to achieve its rated output. Gas
fitters must verify that supply piping can deliver this volume plus additional capacity for
other appliances on the system.
Question 6
, Which characteristic of liquefied petroleum gases (LPG) presents the greatest challenge
during system design compared to natural gas systems?
A. Lower heating value per cubic foot
B. Higher operating pressures requiring specialized regulators
C. Gas-to-liquid volume ratio of approximately 270:1
D. Requirement for stainless steel piping only
Correct Answer: C
Explanation: LPG expands from liquid to vapor at a ratio of approximately 270:1. This high
expansion ratio means that even small liquid leaks can create significant vapor volumes,
increasing explosion risks. This characteristic requires special design considerations
including liquid traps, proper vaporization equipment, and careful system layout to prevent
liquid slugging in vapor lines.
Question 7
A gas fitter is calculating the maximum capacity of a 2-inch nominal pipe carrying natural
gas over a 200-foot equivalent length with a 0.5 psi pressure drop. Which additional gas
property must be included in the flow calculation?
A. Gas specific gravity only
B. Gas specific gravity and viscosity
C. Gas specific gravity, viscosity, and compressibility factor
D. Gas specific gravity, viscosity, and critical temperature
Correct Answer: B
Explanation: Accurate gas flow calculations must consider both specific gravity (which
affects density and flow characteristics) and viscosity (which affects friction losses). While
compressibility becomes significant at very high pressures (above 100 psig), for typical low-
pressure gas systems (under 1 psi), specific gravity and viscosity are the primary gas
properties needed for accurate flow capacity calculations.
Question 8
