100+ Free ACS LAU1/CONGLP1 LPG and LPG Changeover Practice Questions

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2026 Statistics

Key Facts: ACS LAU1/CONGLP1 LPG and LPG Changeover Exam

100%

Safety Pass Mark

Gas Safe ACS Scheme

37 mbar

Propane Operating Pressure

BS 5482-1 / UKLPG

1:250

Liquid-to-Vapor Expansion (Propane)

UKLPG CoP

Prepare for the Gas Safe ACS CONGLP1/LAU1 LPG changeover assessment with 100 realistic practice questions covering BS 5482, UKLPG Codes of Practice, GSIUR 1998, and IGEM/UP/1B.

Sample ACS LAU1/CONGLP1 LPG and LPG Changeover Practice Questions

Try these sample questions to test your ACS LAU1/CONGLP1 LPG and LPG Changeover exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1What is the relative density of Commercial Propane vapor compared to air (where air = 1.0)?

A.0.55

B.1.00

C.1.50

D.2.00

Explanation: Commercial Propane vapor has a relative density of approximately 1.50 relative to air (1.0). Because it is 1.5 times heavier than air, unburnt Propane vapor will sink to the floor and accumulate in low-level areas, cellars, and drains.

2What is the relative density of Commercial Butane vapor compared to air?

A.0.60

B.1.20

C.1.50

D.2.00

Explanation: Commercial Butane vapor has a relative density of approximately 2.0 relative to air. This makes Butane twice as heavy as air, causing leaked gas to settle rapidly at ground level.

3At atmospheric pressure, what is the approximate boiling point of Commercial Propane?

A.0°C

B.-12°C

C.-42°C

D.-161°C

Explanation: Commercial Propane has a boiling point of approximately -42°C at atmospheric pressure. This low boiling point allows Propane to continue off-gassing and vaporizing effectively even in sub-zero winter outdoor temperatures in the UK.

4When liquid Commercial Propane expands into gas vapor at atmospheric pressure, what expansion ratio is produced?

A.1:50

B.1:100

C.1:250

D.1:600

Explanation: 1 unit volume of liquid Commercial Propane expands to approximately 250 unit volumes of gas vapor at atmospheric pressure (1:250). This high expansion ratio means that even a small liquid leak creates a massive volume of flammable vapor.

5What are the approximate lower and upper flammability limits of Commercial Propane in air by volume?

A.1.8% to 8.5%

B.2.2% to 9.5%

C.5.0% to 15.0%

D.12.0% to 25.0%

Explanation: Commercial Propane has a flammable range of approximately 2.2% (Lower Explosive Limit - LEL) to 9.5% (Upper Explosive Limit - UEL) by volume in air. Below 2.2% the mixture is too lean to ignite, and above 9.5% it is too rich.

6What is the approximate lower explosive limit (LEL) of Commercial Butane in air?

A.1.8%

B.2.2%

C.5.0%

D.9.5%

Explanation: Commercial Butane has a Lower Explosive Limit (LEL) of approximately 1.8% by volume in air. Its upper limit is around 8.5%.

7What is the gross calorific value of Commercial Propane per cubic metre of vapor?

A.38.7 MJ/m³

B.50.0 MJ/m³

C.95.0 MJ/m³

D.121.0 MJ/m³

Explanation: Commercial Propane vapor has a gross calorific value of approximately 95 MJ/m³ (approx 25 kWh/m³), which is roughly 2.5 times higher per m³ than Natural Gas (~38.7 MJ/m³).

8Why does unburnt LPG present a greater hazard in low-level areas compared to Natural Gas?

A.LPG has a higher ignition temperature than Natural Gas.

B.LPG is lighter than air and traps oxygen near the floor.

C.LPG is heavier than air and will not readily disperse without low-level ventilation.

D.LPG reacts chemically with concrete floors to produce hydrogen gas.

Explanation: LPG vapors (Propane SG 1.5, Butane SG 2.0) are heavier than air. Unlike Natural Gas (SG 0.6) which rises and dissipates through high vents, LPG pools in hollows, cellars, and floor areas, requiring dedicated low-level openings for safe discharge.

9What phenomenon occurs when LPG vapor is drawn off from a cylinder faster than latent heat can be absorbed from surrounding air?

A.Thermal runaway and over-pressurization

B.Cylinder auto-ignition

C.Cylinder auto-refrigeration and frosting of the cylinder body

D.Instantaneous liquid lock in the burner

Explanation: Liquid LPG requires latent heat of vaporization to turn into gas. If the off-take rate exceeds the cylinder's heat absorption capacity, the liquid temperature and pressure drop rapidly, causing moisture from the air to freeze on the cylinder wall (frosting) and restricting gas flow.

10Which chemical odorant is added to Commercial LPG to enable leak detection by smell?

A.Ethyl mercaptan (ethanethiol)

B.Carbon monoxide

C.Methylene chloride

D.Sulfur dioxide

Explanation: LPG is naturally odorless. An odorizing agent, typically Ethyl Mercaptan (Ethanethiol) or dimethyl sulfide, is added during refining so that leaks can be readily detected by scent at concentrations well below the lower explosive limit.

About the ACS LAU1/CONGLP1 LPG and LPG Changeover Exam

Comprehensive practice question bank for the ACS LAU1 / CONGLP1 LPG Changeover certification exam, covering domestic and commercial LPG storage, regulation, conversion, testing, and appliance commissioning under UK regulations.

Questions

100 scored questions

Time Limit

2.5 hours

Passing Score

100%

Exam Fee

GBP 350 (Gas Safe Register / ACS (Energy & Utility Skills))

ACS LAU1/CONGLP1 LPG and LPG Changeover Exam Content Outline

15%

LPG Properties & Characteristics

Physical properties, vapor pressure, relative density, flammable limits, and expansion ratios of Commercial Propane and Commercial Butane.

15%

Changeover Procedure (NG to LPG)

Systematic changeover protocols from Natural Gas to LPG, including appliance rating adjustments and pipe sizing differences.

15%

LPG Cylinder & Vessel Supplies

Cylinder siting, manifold automatic changeover valves, bulk vessel separation distances (BS 5482 / UKLPG CoP 1), and emergency shut-off valves.

15%

Pressure Regulation & Pipework

First-stage and second-stage regulators, Over-Pressure Cut-Off (OPCO), Under-Pressure Cut-Off (UPCO), operating pressures (37mbar / 28mbar), and pipe sizing.

10%

Burner Conversions & Injectors

Injector orifice downsizing, primary air shutter adjustments, aeration requirements, flame characteristics, and burner pressure checks.

10%

Flueing & Ventilation for LPG

Ventilation sizing for low-level LPG installations, high/low air supply vents, compartment ventilation, and flue termination clearances.

10%

Tightness Testing & Purging

Tightness testing procedures for LPG vapor installations (IGEM/UP/1B / BS 5482), permissible pressure drops, let-by testing, and inert/direct purging.

10%

Safety Controls & Valves

Flame supervision devices (thermocouples, flame ionization, FSDs), excess flow valves (EFV), emergency control valves (ECV), and thermal cut-offs.

How to Pass the ACS LAU1/CONGLP1 LPG and LPG Changeover Exam

What You Need to Know

Passing score: 100%
Exam length: 100 questions
Time limit: 2.5 hours
Exam fee: GBP 350

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

ACS LAU1/CONGLP1 LPG and LPG Changeover Study Tips from Top Performers

1Memorize the relative densities and expansion ratios for Propane (1.5, 1:250) and Butane (2.0, 1:233).

2Understand the multi-stage pressure regulation system: bulk supply 1st stage (0.75-2 bar) down to 2nd stage appliance inlet pressure (37 mbar Propane).

3Focus on low-level ventilation rules: LPG requires ventilation openings at floor level to allow heavier-than-air gas to disperse harmlessly outdoors.

4Review tightness test procedures carefully, including let-by duration (1 min) and test pressure (20 mbar or operating pressure) under IGEM/UP/1B.

Frequently Asked Questions

Who needs the ACS CONGLP1 / LAU1 LPG Changeover assessment?

Registered Gas Safe engineers holding Core Natural Gas qualifications (such as CCN1 or COCN1) who wish to extend their scope of registration to install, service, and convert gas appliances for Liquid Petroleum Gas (LPG).

What is the key difference between Natural Gas and LPG safety requirements?

LPG vapor (Propane SG 1.5, Butane SG 2.0) is heavier than air, meaning unburnt gas collects in low areas, drains, and cellars, requiring low-level ventilation and strict separation distances from gullies and openings.

What standards govern LPG installation in the UK?

Key standards include BS 5482-1, UKLPG (Liquid Gas UK) Codes of Practice 1 and 24, IGEM/UP/1B for tightness testing, and the Gas Safety (Installation and Use) Regulations 1998 (GSIUR).