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National Grid Task 70: Properties of Natural Gas and
Abnormal Operating Conditions exam, ACTUAL EXAM
COMPLETE QUESTIONS AND CORRECT ANSWERS LATEST
UPDATE THIS YEAR
National Grid Task-70: Properties of Natural Gas and Abnormal Operating Conditions exam,
SUMMARIZED EXAM TOPICS COVERED (POINT FORM)
• Physical & chemical properties of natural gas: methane (CH₄) as primary component
(70-90%), density (0.6-0.7 relative to air, lighter than air), heating value (approximately
1,000 BTU/scf), flammability range (4-14% gas in air by volume), ignition temperature
(1,000-1,200°F), specific gravity (0.6), vapor density (lighter than air, rises and
disperses), non-toxic but asphyxiant (displaces oxygen), odorized with mercaptan
(rotten egg smell) for leak detection.
• Abnormal operating conditions (AOCs): definition (events outside normal parameters
that may affect safety), examples (overpressurization, underpressurization, regulator
failure, relief valve lifting, gas detector alarm, odor complaint, abnormal flow, pipeline
damage, third-party damage, fire, explosion, freeze-ups, liquid carryover, gas migration,
unauthorized excavation).
• Leak detection and response: odor fade (loss of odorant due to adsorption or
oxidation), classification of leaks (Grade 1, Grade 2, Grade 3 per 49 CFR 192), leak survey
methods (flame ionization, combustible gas indicator (CGI), odor walk, leakage
classification, bar holing, sampling).
• Pressure regulation and overpressure protection: regulator types (spring-loaded,
pilot-operated, relief valves, monitor regulators), cause of overpressurization (regulator
failure, blockage, incorrect setpoint, freeze, mechanical damage), effects (appliance
damage, meter damage, fire, explosion, rupture), response (shut off gas, vent, notify
control center).
• Combustion characteristics: incomplete combustion produces carbon monoxide (CO),
complete combustion produces CO₂ and H₂O, blue flame indicates complete
combustion, yellow flame indicates incomplete combustion, air/fuel ratio (9.6:1 for
stoichiometric combustion), excess air, primary and secondary air.
• Meters and regulators: diaphragm meters, rotary meters, turbine meters, regulator
setpoint, lockup pressure, bleed rate, venting, relief valve setpoint, freezing (hydrate
formation), heater requirements, station layout (M&R stations).
• Pipeline integrity: corrosion (internal/external), third-party damage, excavation damage
(one-call, Miss Utility), stress, fatigue, pipe coating (tape, fusion bonded epoxy),
cathodic protection, test pressure, maximum operating pressure (MOP), design factor,
class location.
• Emergency response: gas control center notification, evacuation, ignition source
control, ventilation, protective actions, coordination with fire department, gas shutoff at
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curb valve or service line, securing the area, public safety, reporting requirements
(PHMSA, state).
• Carbon monoxide (CO): symptoms (headache, dizziness, nausea, death), sources
(incomplete combustion), detectors, alarm levels, response (ventilate, evacuate, shut off
gas appliances, call 911).
• Gas detection instruments: CGI (catalytic bead), flame ionization detector (FID), PID
(photoionization detector), sampling pumps, calibration, sensitivity, LEL (lower explosive
limit), UEL, ppm, %gas, oxygen deficiency meter.
1. A National Grid employee responds to a call with a strong odor of natural gas inside a
residence. Using a CGI, the reading is 40% LEL in the basement and 15% LEL on the first floor.
Outside the building, no gas is detected. This leak is classified as:
A) Grade 3
B) Grade 2
C) Grade 1
D) No leak
Answer: C
Rationale: Grade 1 leak when gas concentration is hazardous (≥ 20% LEL inside or near building)
or gas is migrating into building; immediate action required.
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2. Natural gas has a specific gravity of approximately 0.6. This means it is:
A) Heavier than air (1.0)
B) Lighter than air (1.0)
C) Same as air
D) Twice as heavy as air
Answer: B
Rationale: Specific gravity 0.6 = 60% density of air; natural gas rises and disperses.
3. The flammable (explosive) range of natural gas in air by volume is:
A) 1-3%
B) 4-14%
C) 15-25%
D) 50-75%
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Answer: B
Rationale: Natural gas (methane) ignites when air concentration is between 4% and 14% by
volume.
4. A regulator at a district station fails open, sending 60 psig to a residential service rated for 2
psig. What is the immediate abnormal operating condition?
A) Underpressurization
B) Overpressurization
C) Freeze-up
D) Liquid carryover
Answer: B
Rationale: Overpressurization occurs when downstream pressure exceeds design limits due to
regulator failure.
National Grid Task 70: Properties of Natural Gas and
Abnormal Operating Conditions exam, ACTUAL EXAM
COMPLETE QUESTIONS AND CORRECT ANSWERS LATEST
UPDATE THIS YEAR
National Grid Task-70: Properties of Natural Gas and Abnormal Operating Conditions exam,
SUMMARIZED EXAM TOPICS COVERED (POINT FORM)
• Physical & chemical properties of natural gas: methane (CH₄) as primary component
(70-90%), density (0.6-0.7 relative to air, lighter than air), heating value (approximately
1,000 BTU/scf), flammability range (4-14% gas in air by volume), ignition temperature
(1,000-1,200°F), specific gravity (0.6), vapor density (lighter than air, rises and
disperses), non-toxic but asphyxiant (displaces oxygen), odorized with mercaptan
(rotten egg smell) for leak detection.
• Abnormal operating conditions (AOCs): definition (events outside normal parameters
that may affect safety), examples (overpressurization, underpressurization, regulator
failure, relief valve lifting, gas detector alarm, odor complaint, abnormal flow, pipeline
damage, third-party damage, fire, explosion, freeze-ups, liquid carryover, gas migration,
unauthorized excavation).
• Leak detection and response: odor fade (loss of odorant due to adsorption or
oxidation), classification of leaks (Grade 1, Grade 2, Grade 3 per 49 CFR 192), leak survey
methods (flame ionization, combustible gas indicator (CGI), odor walk, leakage
classification, bar holing, sampling).
• Pressure regulation and overpressure protection: regulator types (spring-loaded,
pilot-operated, relief valves, monitor regulators), cause of overpressurization (regulator
failure, blockage, incorrect setpoint, freeze, mechanical damage), effects (appliance
damage, meter damage, fire, explosion, rupture), response (shut off gas, vent, notify
control center).
• Combustion characteristics: incomplete combustion produces carbon monoxide (CO),
complete combustion produces CO₂ and H₂O, blue flame indicates complete
combustion, yellow flame indicates incomplete combustion, air/fuel ratio (9.6:1 for
stoichiometric combustion), excess air, primary and secondary air.
• Meters and regulators: diaphragm meters, rotary meters, turbine meters, regulator
setpoint, lockup pressure, bleed rate, venting, relief valve setpoint, freezing (hydrate
formation), heater requirements, station layout (M&R stations).
• Pipeline integrity: corrosion (internal/external), third-party damage, excavation damage
(one-call, Miss Utility), stress, fatigue, pipe coating (tape, fusion bonded epoxy),
cathodic protection, test pressure, maximum operating pressure (MOP), design factor,
class location.
• Emergency response: gas control center notification, evacuation, ignition source
control, ventilation, protective actions, coordination with fire department, gas shutoff at
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curb valve or service line, securing the area, public safety, reporting requirements
(PHMSA, state).
• Carbon monoxide (CO): symptoms (headache, dizziness, nausea, death), sources
(incomplete combustion), detectors, alarm levels, response (ventilate, evacuate, shut off
gas appliances, call 911).
• Gas detection instruments: CGI (catalytic bead), flame ionization detector (FID), PID
(photoionization detector), sampling pumps, calibration, sensitivity, LEL (lower explosive
limit), UEL, ppm, %gas, oxygen deficiency meter.
1. A National Grid employee responds to a call with a strong odor of natural gas inside a
residence. Using a CGI, the reading is 40% LEL in the basement and 15% LEL on the first floor.
Outside the building, no gas is detected. This leak is classified as:
A) Grade 3
B) Grade 2
C) Grade 1
D) No leak
Answer: C
Rationale: Grade 1 leak when gas concentration is hazardous (≥ 20% LEL inside or near building)
or gas is migrating into building; immediate action required.
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2. Natural gas has a specific gravity of approximately 0.6. This means it is:
A) Heavier than air (1.0)
B) Lighter than air (1.0)
C) Same as air
D) Twice as heavy as air
Answer: B
Rationale: Specific gravity 0.6 = 60% density of air; natural gas rises and disperses.
3. The flammable (explosive) range of natural gas in air by volume is:
A) 1-3%
B) 4-14%
C) 15-25%
D) 50-75%
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Answer: B
Rationale: Natural gas (methane) ignites when air concentration is between 4% and 14% by
volume.
4. A regulator at a district station fails open, sending 60 psig to a residential service rated for 2
psig. What is the immediate abnormal operating condition?
A) Underpressurization
B) Overpressurization
C) Freeze-up
D) Liquid carryover
Answer: B
Rationale: Overpressurization occurs when downstream pressure exceeds design limits due to
regulator failure.
