SAQCC Gas LPG Commercial/Industrial cheat sheet

LPG vapour density is roughly 1.5-2.0 times that of air, so leaks pool at low points; ventilation openings and detectors belong at low level.

Propane and butane have different vapour pressures: commercial propane stays usable to about -40 °C, commercial butane only to about 0 °C, so winter blends are propane-enriched.

Liquid LPG expands about 0.3 % per °C; cylinders and vessels are never filled above roughly 80-85 % liquid volume to leave a vapour space for thermal expansion.

Approximate calorific values: propane 93 MJ/m3 (25,900 kJ/m3 gross), butane 122 MJ/m3 (gross); both burn with high primary aeration requirements (propane ~24:1 stoichiometric air).

Cylinder relief valves are set to protect against fire exposure, typically in the 15-17 bar range for propane cylinders, and discharge vapour not liquid.

LPG is odourised (ethyl mercaptan) so leaks are detectable at about one-fifth of the lower explosive limit; LPG LEL is roughly 2 % v/v and UEL roughly 10 % v/v.

A 48 kg LPG cylinder holds about 48 kg of liquid, which vapourises to roughly 24 m3 of propane gas at standard conditions (approx. 0.51 kg/L liquid density).

Regulators are two-stage on commercial installations: a first-stage regulator reduces cylinder pressure to about 1-2 bar, and a second-stage delivers 28-37 mbar for appliances.

Copper pipework is common for LPG but must be annealed and protected; steel pipe is used for larger commercial runs, and jointing compound must be LPG-resistant.

Natural gas is predominantly methane (typically 85-95 %), is lighter than air (relative density ~0.6), and rises and disperses on release, so detectors go high.

Typical South African natural gas gross calorific value is about 38-42 MJ/m3; stoichiometric air requirement for methane is about 9.5:1 (roughly 10 volumes air per volume gas).

Methane LEL is about 5 % v/v and UEL about 15 % v/v; combustion is only possible within this band, so gas detection alarms commonly trip at 10-20 % LEL.

Natural gas is odourised with mercaptan or THT to give a detectable smell at about 1 % v/v, well below the LEL.

Gas piping sizing uses pressure drop limits: typically no more than about 1 mbar drop for low-pressure (2-7 kPa) domestic/commercial runs, with velocity kept below roughly 20-25 m/s.

Installations require an isolating valve at the meter/entry, and appliance connections use approved unions; flueing must be checked for spillage with a CO analyser or smoke match test.

Combustion CO is produced by incomplete combustion: yellow lazy flame, sooting and CO above 20-30 ppm in flue gases indicate excess primary air deficiency or blocked flue.

For gas leak testing, use air or inert gas at 1.5 times working pressure (minimum 1 bar) for a defined hold period; never pressure-test with gas or oxygen.

Common refrigerants and their safety groups: R410A (A1), R32 (A2L, mildly flammable), R290 propane (A3, highly flammable), R717 ammonia (B2L, toxic), R744 CO2 (A1 but high pressure).

R410A is a near-azeotropic blend of R32/R125 (50/50) and must be charged as liquid; it operates at roughly 1.6 times the pressure of R22, so only R410A-rated gauges and hoses may be used.

Superheat and subcooling are the diagnostic measures: target superheat is typically 5-8 K at the evaporator and subcooling 5-10 K; low superheat suggests overcharge, high superheat suggests undercharge or restriction.

Refrigerant glide applies to zeotropic blends (e.g. R407C): bubble and dew points differ, so charging and leak checking must reference the correct point on the PT chart.

R32 and R290 are flammable; R290 systems are limited to small charges (typically under 150 g per circuit for domestic units) and require no ignition sources in the occupied space.

Ozone depletion potential: CFCs (R12) ODP 1.0, HCFCs (R22) ODP ~0.055, HFCs (R134a, R410A) ODP 0. GWP: R410A ~2088, R32 ~675, R290 ~3.

Recovery, not venting, is mandatory: recovered refrigerant must be stored in dedicated recovery cylinders, never in disposable or unmarked vessels, and cylinders must not be filled above 80 % liquid.

Moisture in a refrigeration circuit forms acid and ice at the metering device; a filter-drier is fitted on the liquid line and the system is evacuated to below 500 microns before charging.

Pressure testing with nitrogen is standard; oxygen-free nitrogen is used with a regulator, and the system is never pressurised with oxygen or air because of oil-combustion risk.

Cylinder colour codes (South African/ISO practice): oxygen black with white shoulder, acetylene maroon, nitrogen grey/black, argon grey, carbon dioxide grey, medical oxygen white body with black shoulder.

Cylinder identification must never rely on colour alone; the valve outlet thread and shoulder stamping (gas name, test date, working pressure) are the authoritative identifiers.

Oxygen is an oxidiser, not a fuel: it does not burn but accelerates combustion; oil or grease on oxygen fittings can ignite, so only oxygen-clean equipment is used.

Acetylene cylinders contain a porous mass and acetone; the maximum safe withdrawal rate is about one-seventh of the cylinder contents per hour, and pressure must never exceed 1.5 bar gauge.

Compressed gas cylinders are hydrostatically tested periodically (commonly every 5-10 years depending on gas and standard) and stamped with the next test date.

Cylinders are stored upright and secured, with full and empty separated, oxidisers separated from fuels by at least 3 m or a fire wall, and away from heat sources.

Medical oxygen purity is typically 99.5 % minimum; medical air is filtered and tested for dew point, CO, CO2 and oil content, and piped medical systems are identified by specific NIST/quick-connect fittings.

Burst disc and pressure-relief devices protect cylinders and manifolds; a cylinder heated by fire may rupture, so the area is evacuated and cooled from cover if safe.

A full 50 L oxygen cylinder at 200 bar holds roughly 10,000 litres of gas at atmospheric pressure (contents = water capacity x pressure).