LPG and LNG installations and bulk storage
What this domain tests
This domain tests your understanding of LPG and LNG as stored fuels: properties, containment, pressure and temperature control, separation distances, fire protection and the differences between cylinder, bulk and cryogenic installations.
LPG fundamentals
LPG is stored as a liquid under pressure. The vapour is heavier than air, so leaks accumulate at low level and can travel to drains and basements. Cylinders must not be filled above the filling ratio, usually 80% of water capacity, to leave a vapour space for thermal expansion. Bulk vessels need relief valves, excess-flow protection, remote isolation and fire protection. Separation distances from buildings, boundaries and ignition sources are set by the Dangerous Goods Ordinance and the relevant code.
LNG fundamentals
LNG is methane-rich and stored cryogenically at about -162 degrees C. It is not stored under high pressure. Hazards include cryogenic burns, cold embrittlement, boil-off gas, rollover, rapid phase transition and vapour dispersion. Double containment, bunding, leak detection and flare or boil-off-gas recovery are central. Hong Kong's offshore LNG terminal supplies gas into the high-pressure network and power generation, so interface pressure control and metering matter.
Worked example
A 50 kg LPG cylinder has a water capacity of about 118 litres. At a filling ratio of 80%, the maximum liquid volume is 0.80 x 118 = 94.4 litres. With liquid LPG density around 0.54 kg/litre, the maximum fill mass is 94.4 x 0.54 = 51 kg, consistent with the nominal 50 kg rating. If a restaurant proposes two connected cylinders plus two spares, the aggregate is 200 kg. Check the Dangerous Goods Ordinance exempt quantity and licence threshold, the separation distances, and whether the manifold and changeover valve are protected from vehicle impact.
Traps that cost marks
- Filling cylinders by mass without checking water capacity and filling ratio.
- Treating LPG vapour as lighter than air and ignoring low-level accumulation.
- Forgetting that LNG is cryogenic, not simply a compressed gas.
- Omitting boil-off-gas handling or relief scenarios in an LNG design.
- Calculating cylinder quantities but ignoring spare cylinders, aggregate storage and licence thresholds.