Fuel Gas, LPG and Combustion Systems
This domain tests gas piping and combustion safety under Mabhas 17 (natural gas) and the relevant LPG rules: pipe sizing, materials, appliance pressures, ventilation, flues and testing.
Pressures and sizing
Iranian natural gas is distributed to appliances at roughly 17 mbar (about 1/4 psi), with some commercial equipment at 25 mbar; LPG is supplied at about 28–30 mbar through a regulator. Size pipe by the longest-length method with the code allowable pressure drop (typically around 0.5 in wc ≈ 1.25 mbar for low-pressure systems), applying the tables to the total connected load with the code's diversity allowance. Use steel pipe of the specified schedule, or approved polyethylene outside and below ground; joints in concealed shafts must be welded or otherwise minimised and the shaft ventilated. Provide a main shut-off at entry and a valve ahead of every appliance, sleeve every wall and floor penetration, and keep gas pipe out of bedrooms, lift shafts, air ducts and unventilated voids. LPG is heavier than air: no cylinders in basements, and stored quantities and ventilation are limited.
Worked example
A 120 kW boiler on natural gas at 9.7 kWh/m³ lower heating value takes 120 / 9.7 = 12.4 m³/h. Add a six-burner range at roughly 3.5 m³/h and the connected load is about 15.9 m³/h. Gas pipe is sized on connected load with the code's diversity, then checked for the allowable drop from meter to the farthest appliance - not from the boiler alone.
Traps
Using LPG calorific values for natural gas; sizing on the boiler only and forgetting cooking loads; ignoring the pressure drop to the far appliance; venting a regulator into a room; providing no combustion-air opening; and testing with air at the wrong pressure or for too short a period without a witnessed record.