Gas Safe Registration (ACS) Liquefied Petroleum Gas (LPG) - Domestic and Park Homes Syllabus

Liquefied Petroleum Gas (LPG) - Domestic and Park Homes syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Liquefied Petroleum Gas (LPG) - Domestic and Park Homes in Gas Safe Registration (ACS), not a summary of it.

1. 1

   LPG Properties and Supply

   3 topics

   • Properties of propane and butane
     • Relative density (heavier than air) and pooling hazard
     • Calorific value and vapour pressure differences
     • Boiling points and cold-weather performance
   • LPG storage and supply systems
     • Cylinder vs bulk tank supply
     • Separation distances and cylinder location
     • Two-stage regulation and automatic changeover
   • LPG-specific legislation
     • UKLPG codes of practice
     • Operating pressure of 37 mbar for propane
2. 2

   LPG Pipework and Tightness Testing

   3 topics

   • Pipe sizing differences for LPG
   • Tightness testing at LPG working pressures
   • Purging and pressure testing LPG installations
3. 3

   LPG in Park Homes, Boats and Leisure (PD/LEI)

   4 topics

   • Residential park homes (CPA1)
     • Skirting ventilation and underfloor void hazards
     • Appliance and flue requirements in park homes
   • Boats and inland waterway craft (BMP)
   • Touring caravans and leisure accommodation vehicles
   • Permanent dwellings and self-build LPG (PDLP)

Liquefied Petroleum Gas (LPG) - Domestic and Park Homes flashcards for Gas Safe Registration (ACS)

20 of 50 cards from the Liquefied Petroleum Gas (LPG) - Domestic and Park Homes deck — real questions with worked answers.

1. What are the chemical formulas of propane and butane?

   Propane is $\ce{C3H8}$ and butane is $\ce{C4H10}$. Both are saturated hydrocarbons (alkanes) and are the two main constituents of LPG.

2. What are the approximate boiling points of propane and butane, and why does this matter for cold-weather use?

   Propane boils at about $-42\,^{\circ}\text{C}$ and butane at about $-2\,^{\circ}\text{C}$. Butane will not vaporise once its temperature falls below roughly $0\,^{\circ}\text{C}$, so it is unsuitable for outdoor/cold conditions; propane vaporises down to $-42\,^{\circ}\text{C}$ and is used outdoors and in winter.

3. What are the relative densities of propane and butane compared with air, and the key safety consequence?

   Propane has a relative density of about $1.5$ and butane about $2.0$ (air $= 1$). Both are heavier than air, so leaking LPG sinks and collects at low level — drainage points, cellars and bilges — which is why low-level ventilation is essential and LPG is not stored below ground level.

4. State the approximate gross calorific values of propane and butane by volume.

   Propane is approximately $93\text{–}95\ \text{MJ/m}^{3}$ and butane approximately $121\text{–}122\ \text{MJ/m}^{3}$. Butane carries more energy per cubic metre because its molecule contains more carbon and hydrogen atoms.

5. Write the balanced complete-combustion equation for propane.

   $$\ce{C3H8 + 5O2 -> 3CO2 + 4H2O}$$ One volume of propane requires five volumes of oxygen, or roughly 24 volumes of air, for complete combustion.

6. Write the balanced complete-combustion equation for butane.

   $$\ce{2C4H10 + 13O2 -> 8CO2 + 10H2O}$$ One volume of butane requires $6.5$ volumes of oxygen, or roughly 30 volumes of air, for complete combustion.

7. What are the approximate flammability (explosive) limits of propane and butane in air?

   Propane: about $2.1\%$ to $9.5\%$ by volume in air. Butane: about $1.8\%$ to $9.0\%$. These ranges are much narrower and lower than natural gas ($\approx 5\%\text{–}15\%$), so relatively small leaks can form an explosive mixture.

8. What is the liquid-to-gas expansion ratio for propane and for butane?

   One volume of liquid propane expands to about $274$ volumes of gas; one volume of liquid butane to about $233$ volumes of gas. A small liquid leak therefore produces a very large volume of flammable vapour.

9. What are the standard appliance working (operating) pressures for propane and butane in a domestic permanent dwelling?

   Propane appliances operate at a nominal $37\ \text{mbar}$ and butane appliances at a nominal $28\ \text{mbar}$ at the appliance inlet (compared with $20\ \text{mbar}$ for natural gas).

10. Why is an odorant added to LPG, and which compound is typically used?

    LPG is naturally odourless, so a stenching agent — typically ethyl mercaptan (ethanethiol) — is added to give a strong distinctive smell so that leaks can be detected by smell.

11. What are the approximate ignition (auto-ignition) temperatures of propane and butane?

    Propane auto-ignites at about $470\,^{\circ}\text{C}$ and butane at about $410\,^{\circ}\text{C}$.

12. What is the approximate stoichiometric (chemically correct) air concentration for propane and butane?

    For complete combustion the ideal mixtures are about $4\%$ propane in air and about $3.1\%$ butane in air. Operating near stoichiometric gives the hottest, most efficient flame.

13. What are the standard UK (Calor) cylinder colours for propane and butane?

    Propane cylinders are red and butane cylinders are blue. Propane cylinders also use a left-hand-thread POL/clip-on valve outlet, distinguishing them from butane fittings.

14. What are the approximate vapour pressures of propane and butane in a cylinder at $15\,^{\circ}\text{C}$?

    Propane is at roughly $7\ \text{bar}$ and butane at roughly $2\ \text{bar}$ at $15\,^{\circ}\text{C}$. Vapour pressure rises with temperature, which is why propane cylinders are built to a higher pressure rating.

15. What is the difference between vapour offtake and liquid offtake from an LPG vessel?

    Vapour offtake draws gaseous LPG from the top of the vessel for normal appliance supply via a regulator. Liquid offtake draws liquid from the bottom (for forklifts, vaporisers or autogas) and must be re-vaporised before use; the two require different valves and connections.

16. Describe the function of a two-stage regulation system on a bulk LPG tank.

    The first-stage regulator reduces tank vapour pressure (which can be several bar) to an intermediate pressure of about $0.75\ \text{bar}$ ($75\ \text{kPa}$); the second-stage regulator at or near the building reduces this to the appliance working pressure of $37\ \text{mbar}$. Two-stage regulation gives more stable outlet pressure across varying tank pressure and demand.

17. What is the purpose of an automatic changeover valve on a twin-cylinder propane installation?

    It automatically switches the supply from the empty (service) cylinder to the full (reserve) cylinder without interrupting gas flow, and an indicator shows when the first cylinder is empty so it can be replaced while supply continues.

18. What do the regulator safety features OPSO and UPSO do?

    OPSO (Over-Pressure Shut-Off) closes the gas supply if downstream pressure rises too high (e.g. regulator failure); UPSO (Under-Pressure Shut-Off) closes the supply if pressure falls too low (e.g. a major downstream leak or empty vessel). Both must be manually reset after operating.

19. What minimum separation distance is typically required between a small bulk LPG storage tank (up to ~1.1 tonnes) and a building, boundary or fixed ignition source?

    Normally $3\ \text{m}$. This may be reduced (e.g. to $1.5\ \text{m}$) where a suitable fire wall/radiation barrier is installed between the tank and the hazard, per the UKLPG Codes of Practice.

20. Which single regulation is the principal legal framework for LPG installation, maintenance and use work in Great Britain?

    The Gas Safety (Installation and Use) Regulations 1998 (GSIUR). LPG is a relevant 'gas' under these regulations, so the duties on competence, Gas Safe registration and safe working apply equally to LPG work.

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