CNG Properties and Safety 5

Question 1

A CNG vehicle technician notices frost forming on a fuel line fitting during fueling. What does this indicate?

Accepted Answer

Normal operation due to gas expansion and cooling

Answer

A dangerous overpressure condition requiring immediate shutdown

Answer

The cylinder is nearly empty

Answer

Water contamination in the fuel system

Question 2

What is the main environmental advantage of CNG over diesel fuel?

Accepted Answer

CNG combustion produces significantly lower NOx, particulate matter, and CO2 than diesel

Answer

CNG produces zero greenhouse gas emissions

Answer

CNG is biodegradable if spilled into soil

Answer

CNG vehicles produce no exhaust at all

Question 3

What type of regulator reduces CNG pressure from cylinder pressure to engine operating pressure?

Accepted Answer

A multi-stage pressure regulator

Answer

A back-pressure regulator

Answer

A check valve assembly

Answer

A solenoid bypass valve

Question 4

Under DOT regulations, what information must be permanently marked on a CNG cylinder?

Accepted Answer

DOT specification, service pressure, serial number, and requalification date

Answer

Vehicle VIN, owner name, and state of registration

Answer

Manufacturer's warranty number and fuel type only

Answer

Purchase date, installer name, and fueling station address

Question 5

Why are Type 4 CNG cylinders (full composite with plastic liner) potentially problematic for fire situations compared to Type 1 metal cylinders?

Accepted Answer

Composite materials can delaminate or fail without visible warning when exposed to heat

Answer

They rupture at lower pressures than metal cylinders

Answer

They cannot be equipped with pressure relief devices (PRDs)

Answer

They are too light to remain secured in the vehicle chassis

Question 6

What is methane's specific gravity relative to air, and why does it matter for safety planning?

Accepted Answer

Less than 1.0 (approximately 0.55) — it rises and accumulates at ceiling level

Answer

Greater than 1.0 — it sinks to floor level, requiring floor drains

Answer

Equal to 1.0 — it distributes evenly throughout a space

Answer

Greater than 2.0 — it requires special heavy-gas containment

Question 7

Which scenario would most likely cause a CNG cylinder to fail the visual inspection portion of a requalification test?

Accepted Answer

Deep corrosion pits, bulging, or impact damage exceeding manufacturer limits

Answer

Surface condensation from temperature changes

Answer

Faded label text from UV exposure

Answer

Slight discoloration of the cylinder exterior paint