Properties and Safety Flashcards
7 cards from real CNG practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Properties and Safety flashcards as text
A CNG vehicle technician notices frost forming on a fuel line fitting during fueling. What does this indicate?
Answer: Normal operation due to gas expansion and cooling
Frost forming on CNG fittings during fueling is normal and results from the Joule-Thomson effect — rapid gas expansion causes significant cooling of the fittings.
What is the main environmental advantage of CNG over diesel fuel?
Answer: CNG combustion produces significantly lower NOx, particulate matter, and CO2 than diesel
CNG combustion results in significantly lower NOx, particulate matter (PM), and CO2 emissions compared to diesel, making it cleaner for air quality.
What type of regulator reduces CNG pressure from cylinder pressure to engine operating pressure?
Answer: A multi-stage pressure regulator
CNG fuel systems use a multi-stage pressure regulator to step down cylinder pressure (3,600 psi) progressively to the low pressure required by the engine (typically under 10 psi).
Under DOT regulations, what information must be permanently marked on a CNG cylinder?
Answer: DOT specification, service pressure, serial number, and requalification date
DOT regulations require CNG cylinders to be permanently marked with the DOT specification number, service pressure, serial number, manufacturer, and requalification/expiration date.
Why are Type 4 CNG cylinders (full composite with plastic liner) potentially problematic for fire situations compared to Type 1 metal cylinders?
Answer: Composite materials can delaminate or fail without visible warning when exposed to heat
Composite cylinders can suffer internal delamination or degradation from heat exposure that is not visible externally, making post-fire inspection critical before returning to service.
What is methane's specific gravity relative to air, and why does it matter for safety planning?
Answer: Less than 1.0 (approximately 0.55) — it rises and accumulates at ceiling level
Methane has a specific gravity of approximately 0.55 (lighter than air), so it rises and can accumulate near ceilings, which dictates where gas detectors and ventilation must be placed.
Which scenario would most likely cause a CNG cylinder to fail the visual inspection portion of a requalification test?
Answer: Deep corrosion pits, bulging, or impact damage exceeding manufacturer limits
Deep corrosion pits, bulging, dents, or impact damage exceeding the manufacturer's specified tolerances are grounds for cylinder rejection during visual requalification inspection.