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SAQCC Gas LPG Commercial/Industrial study materials
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SAQCC Gas LPG Commercial/Industrial practice questions

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Question 1Liquefied Petroleum Gas (LPG)

At approximately what pressure does commercial propane exert a vapour pressure of about 1 MPa at 20 degrees Celsius?

  1. About 5.0 MPa
  2. About 2.5 MPa
  3. About 0.8 MPa Correct answer.
  4. About 0.1 MPa

Explanation

Commercial propane has a vapour pressure of roughly 0.8 MPa (about 8 bar gauge) at 20 degrees Celsius, which is why LPG storage vessels and pipework are rated well above that pressure. The value rises steeply with temperature, so design pressure must account for the maximum expected ambient temperature.

Question 2Liquefied Petroleum Gas (LPG)

Why is the vapour pressure of a commercial LPG mixture higher than that of pure propane at the same temperature?

  1. Because the mixture contains lighter components such as propane and ethane Correct answer.
  2. Because the mixture contains lighter components such as butane
  3. Because the mixture contains heavier components such as pentane
  4. Because the mixture has a higher molecular weight

Explanation

Commercial LPG is a mixture, and lighter hydrocarbons such as ethane and propane contribute higher partial pressures than heavier ones. The overall vapour pressure is the sum of the components' contributions, so lighter blends give higher pressure.

Question 3Liquefied Petroleum Gas (LPG)

What is the main hazard created when LPG liquid vaporises rapidly on release to atmosphere?

  1. Formation of a hot buoyant gas cloud
  2. Formation of a solid hydrate plug
  3. Formation of a cold, dense flammable vapour cloud Correct answer.
  4. Formation of a stable non-flammable mixture

Explanation

Rapid vaporisation absorbs heat from the surroundings, cooling the liquid and producing a cold, dense vapour that is heavier than air. This dense cloud can travel at low level toward ignition sources.

Question 4Liquefied Petroleum Gas (LPG)

Which of these is the correct lower explosive limit for LPG in air?

  1. Around 9 percent by volume
  2. Around 15 percent by volume
  3. Around 2 percent by volume Correct answer.
  4. Around 0.5 percent by volume

Explanation

The lower explosive limit for LPG in air is roughly 2 percent by volume, meaning concentrations below this are too lean to ignite. The upper limit is around 10 to 11 percent.

Question 5Liquefied Petroleum Gas (LPG)

Why must LPG cylinders always be stored and used in the upright position?

  1. To allow the cylinder to be weighed accurately
  2. To prevent the pressure relief valve from opening
  3. To avoid condensation forming in the cylinder
  4. To keep the liquid phase away from the vapour outlet Correct answer.

Explanation

In an upright cylinder the vapour space is at the top, so the outlet draws vapour. If the cylinder lies on its side, liquid can reach the outlet and be drawn into the regulator or appliance, causing liquid carry-over and an uncontrolled flame.

Question 6Liquefied Petroleum Gas (LPG)

A 48 kg LPG cylinder is being stored in a cage outdoors in direct sun. What is the main reason for providing shade?

  1. To stop the cylinder from rusting
  2. To keep the regulator from freezing
  3. To limit the rise in internal pressure Correct answer.
  4. To prevent the gas from condensing

Explanation

Solar heating raises the cylinder temperature and therefore the vapour pressure inside it. Shade limits the temperature rise and keeps internal pressure within the cylinder's design limits.

Question 7Liquefied Petroleum Gas (LPG)

Which property of LPG makes it suitable for use in a vapour-withdrawal cylinder rather than requiring a pump?

  1. Its high boiling point relative to ambient
  2. Its ability to vaporise at ambient temperature under its own vapour pressure Correct answer.
  3. Its low calorific value
  4. Its high density relative to water

Explanation

LPG has a boiling point below ambient temperature at atmospheric pressure, so it vaporises naturally inside the cylinder and supplies vapour under its own pressure. This allows vapour-withdrawal appliances to operate without a pump.

Question 8Liquefied Petroleum Gas (LPG)

What is the purpose of a regulator in an LPG installation?

  1. To measure the volume of gas used
  2. To increase gas pressure for the burner
  3. To reduce cylinder pressure to a safe, stable delivery pressure Correct answer.
  4. To remove moisture from the gas

Explanation

A regulator reduces the high cylinder or vessel pressure to a stable lower pressure suitable for the appliance and maintains that pressure as demand varies. It does not measure gas or treat the gas.

Question 9Liquefied Petroleum Gas (LPG)

A first-stage regulator on a commercial installation is set to about 0.1 MPa. What is its role when a second-stage regulator is fitted downstream?

  1. To vaporise liquid LPG in the line
  2. To reduce vessel pressure to an intermediate pressure for the second stage Correct answer.
  3. To act as a safety shut-off valve
  4. To provide final appliance pressure directly

Explanation

Two-stage systems use a first-stage regulator to bring vessel pressure down to a stable intermediate pressure, which the second-stage regulator then reduces to appliance pressure. This gives more stable delivery and reduces freeze-up risk.

Question 10Liquefied Petroleum Gas (LPG)

Why can a regulator freeze up during periods of high vapour demand?

  1. Because the regulator is exposed to direct sunlight
  2. Because the cylinder is nearly empty
  3. Because the gas contains water that freezes
  4. Because rapid vaporisation and pressure reduction absorb heat and cool the regulator Correct answer.

Explanation

Reducing pressure and vaporising liquid absorb heat, which can chill the regulator body below the freezing point of any moisture present. This can cause ice formation and reduced flow.

Question 11Liquefied Petroleum Gas (LPG)

What is the main reason an LPG bulk vessel is filled to no more than about 80 percent of its water capacity?

  1. To leave a vapour space for thermal expansion of the liquid Correct answer.
  2. To allow the vessel to be purged with air
  3. To keep the vessel weight below transport limits
  4. To prevent the regulator from flooding

Explanation

The liquid expands significantly as temperature rises, so a vapour space is left to accommodate that expansion without the vessel becoming liquid-full. A liquid-full vessel can develop hydraulic pressure that exceeds its design limits.

Question 12Liquefied Petroleum Gas (LPG)

A bulk LPG vessel is being filled on a hot day. Which factor most directly determines the maximum safe filling quantity?

  1. The age of the vessel
  2. The ambient wind speed
  3. The current vapour pressure reading
  4. The liquid density at the fill temperature Correct answer.

Explanation

The fill limit is based on the mass or volume of liquid that will still leave adequate vapour space at the maximum expected temperature, and that depends on liquid density at the fill temperature. Filling by volume must be corrected for density.

Question 13Liquefied Petroleum Gas (LPG)

Why is LPG considered heavier than air for ventilation design purposes?

  1. Its vapour density is about half that of air
  2. Its vapour density equals that of air
  3. Its vapour density is about 10 times that of air
  4. Its vapour density is about 1.5 to 2 times that of air Correct answer.

Explanation

LPG vapour has a density roughly 1.5 to 2 times that of air, so leaks tend to accumulate at low points and in pits. Ventilation must therefore be provided at low level as well as high level.

Question 14Liquefied Petroleum Gas (LPG)

In a commercial kitchen with LPG appliances, where should low-level ventilation openings be located?

  1. Near the floor and at high level Correct answer.
  2. Inside the appliance enclosure
  3. At ceiling level only
  4. Only on the wall opposite the appliances

Explanation

Because LPG vapour is heavier than air, low-level openings allow accumulated gas to escape, while high-level openings remove hot combustion products and any lighter products of combustion. Both are needed for effective ventilation.

Question 15Liquefied Petroleum Gas (LPG)

What does the term 'ullage' refer to in an LPG vessel?

  1. The liquid level gauge reading
  2. The sediment at the vessel bottom
  3. The vapour space above the liquid Correct answer.
  4. The pipework connecting the vessel to the regulator

Explanation

Ullage is the vapour space left above the liquid surface in a vessel or cylinder. Maintaining adequate ullage allows for liquid expansion as temperature rises.

Question 16Liquefied Petroleum Gas (LPG)

Which of these is the most appropriate method for detecting an LPG leak during a routine inspection?

  1. Listening for a whistling sound
  2. Applying a soap solution to joints and observing for bubbles Correct answer.
  3. Smelling the gas at close range
  4. Holding a flame near the joint

Explanation

A soap solution applied to joints will form bubbles where gas escapes, giving a safe and reliable indication of a leak. Flame testing is dangerous and prohibited.

Question 17Liquefied Petroleum Gas (LPG)

An LPG installation uses a flexible hose to connect a cylinder to fixed pipework. What is the main inspection requirement for that hose?

  1. It should be painted to protect it from sunlight
  2. It should be coiled tightly to save space
  3. It should be replaced every month regardless of condition
  4. It should be checked for cracking, perishing and expiry date Correct answer.

Explanation

Flexible hoses have a limited service life and can deteriorate through UV exposure, ozone and mechanical damage. Inspection should look for cracking, perishing, kinks and the marked expiry date.

Question 18Liquefied Petroleum Gas (LPG)

What is the purpose of the excess-flow valve fitted to an LPG cylinder or vessel outlet?

  1. To limit the escape of gas if the downstream pipework fails Correct answer.
  2. To prevent the cylinder from being overfilled
  3. To regulate the delivery pressure to the appliance
  4. To measure the quantity of gas withdrawn

Explanation

An excess-flow valve closes or restricts flow when the flow rate exceeds a set value, such as when a downstream pipe or hose ruptures. This limits the size of a release.

Question 19Liquefied Petroleum Gas (LPG)

A pressure relief valve on an LPG vessel is found to be weeping. What is the correct action?

  1. Tag the vessel out of service and arrange for qualified repair Correct answer.
  2. Paint over the valve to seal it
  3. Ignore it because relief valves often weep
  4. Plug the outlet to stop the leak

Explanation

A weeping relief valve indicates a fault and is a safety concern because it can fail to reseat and may not protect the vessel. The vessel should be isolated and repaired by a competent person.

Question 20Liquefied Petroleum Gas (LPG)

What is the main function of a vaporiser on a commercial LPG installation?

  1. To store LPG at low pressure
  2. To increase the calorific value of the gas
  3. To filter particles from the liquid
  4. To convert liquid LPG into vapour at a controlled rate Correct answer.

Explanation

A vaporiser adds heat to liquid LPG so it changes to vapour at a controlled rate, which is needed when natural vaporisation from the vessel cannot meet peak demand. It does not change the fuel's calorific value.

Question 21Liquefied Petroleum Gas (LPG)

Why must the outlet of a pressure relief valve on an LPG vessel be piped to a safe discharge point?

  1. To reduce the noise of discharge
  2. To direct any release away from occupied areas and ignition sources Correct answer.
  3. To allow the gas to be recovered for reuse
  4. To prevent the valve from freezing

Explanation

Relief valve discharge can be large and flammable, so it is routed to a safe location away from occupied areas, air intakes and ignition sources. Discharge must not be restricted by the piping.

Question 22Liquefied Petroleum Gas (LPG)

A technician needs to purge air from new LPG pipework before commissioning. Which method is appropriate?

  1. Fill the pipe with water and drain it
  2. Purge with compressed air until gas is detected
  3. Leave the pipe open to atmosphere for a week
  4. Purge with an inert gas followed by LPG vapour to the appliance Correct answer.

Explanation

Air in LPG pipework creates an explosive mixture, so the line is purged with an inert gas and then with LPG vapour until the gas is proven at the appliance. Purging to a safe discharge point is essential.

Question 23Liquefied Petroleum Gas (LPG)

What is the primary reason LPG installations require bonding and earthing?

  1. To improve the calorific value of the fuel
  2. To reduce the pressure in the vessel
  3. To stop the regulator from icing
  4. To prevent static electricity from igniting gas during transfer or leakage Correct answer.

Explanation

Movement of LPG during transfer and the flow of gas can generate static charge, and a discharge could ignite a flammable mixture. Bonding and earthing provide a path to dissipate that charge safely.

Question 24Liquefied Petroleum Gas (LPG)

A commercial LPG installation has a leak and the gas has entered a basement. What is the first priority action?

  1. Evacuate and eliminate ignition sources, then isolate the supply from a safe point Correct answer.
  2. Enter the basement to close the nearest valve
  3. Start the ventilation fan to clear the gas
  4. Open all basement windows to ventilate

Explanation

Life safety comes first: evacuate the area, remove ignition sources and isolate the gas supply from a safe location, then call for emergency assistance. Entering a gas-filled space risks asphyxiation and ignition.

Question 25Liquefied Petroleum Gas (LPG)

Which of these is the correct reason for fitting a flame failure device to a commercial LPG burner?

  1. To increase the burner output
  2. To reduce the gas pressure at the burner
  3. To filter the gas before combustion
  4. To shut off the gas if the flame is extinguished Correct answer.

Explanation

A flame failure device senses whether the flame is present and shuts off the gas supply if it is lost. This prevents unburned gas from being released into the combustion chamber or the room.

Question 26Liquefied Petroleum Gas (LPG)

Which property of LPG is most important when selecting a leak detection method?

  1. It has a distinctive odour Correct answer.
  2. It is non-flammable
  3. It is colourless and odourless
  4. It is lighter than air

Explanation

LPG is odorized with ethyl mercaptan to give it a distinctive smell, which allows leaks to be detected by smell. This is a key safety feature. Colour and flammability are not relevant to detection, and LPG is heavier than air.

Question 27Liquefied Petroleum Gas (LPG)

What is the primary hazard if LPG accumulates in a low-lying area such as a pit or drain?

  1. It can form a flammable mixture with air Correct answer.
  2. It can freeze any moisture present
  3. It can react with water to produce a toxic gas
  4. It can cause asphyxiation by displacing air

Explanation

LPG is flammable and, being heavier than air, can accumulate in low areas and form a flammable mixture with air. Asphyxiation is a secondary risk, and LPG does not react with water to produce toxic gas or freeze moisture under normal conditions.

Question 28Liquefied Petroleum Gas (LPG)

Which of the following is a common commercial LPG cylinder size in South Africa?

  1. 48 kg Correct answer.
  2. 5 kg
  3. 19 kg
  4. 9 kg

Explanation

In South Africa, LPG cylinders are commonly available in sizes such as 5 kg, 9 kg, 19 kg, and 48 kg. The 48 kg cylinder is widely used in commercial and industrial applications. The other sizes are also standard but are more typical for domestic use.

Question 29Liquefied Petroleum Gas (LPG)

What is the purpose of the collar or shroud on an LPG cylinder?

  1. To increase the cylinder's capacity
  2. To improve stability when stacked
  3. To protect the valve from damage Correct answer.
  4. To provide a lifting point

Explanation

The collar or shroud surrounds the valve and protects it from impact damage during handling and transport. It is not designed for lifting or stacking, and it does not affect capacity.

Question 30Liquefied Petroleum Gas (LPG)

Which type of valve is commonly fitted to the outlet of a commercial LPG cylinder to allow connection to a regulator?

  1. Polar valve Correct answer.
  2. Ball valve
  3. Butterfly valve
  4. Gate valve

Explanation

Small LPG cylinders typically use a polar valve (also known as a cylinder valve) that incorporates a pressure relief device and a connection for the regulator. Gate, ball, and butterfly valves are not used as cylinder outlet valves.

Question 31Liquefied Petroleum Gas (LPG)

What is the main reason for using copper pipe in LPG installations?

  1. It is resistant to corrosion by LPG Correct answer.
  2. It is cheaper than steel
  3. It has a higher pressure rating than steel
  4. It is easier to bend than steel

Explanation

Copper is resistant to corrosion by LPG and is commonly used for small-bore LPG lines. While it is malleable, the primary reason is corrosion resistance. Steel has a higher pressure rating and may be cheaper depending on size.

Question 32Liquefied Petroleum Gas (LPG)

What is the purpose of a hydrostatic test on an LPG vessel?

  1. To check for leaks under normal operating pressure
  2. To clean the interior of the vessel
  3. To verify the vessel's strength and integrity Correct answer.
  4. To measure the vessel's capacity

Explanation

A hydrostatic test involves filling the vessel with water and pressurizing it to verify its structural integrity and strength. Leak testing is done at lower pressures, capacity is determined by measurement, and cleaning is a separate process.

Question 33Liquefied Petroleum Gas (LPG)

Which of the following is a correct procedure for checking for gas leaks on an LPG installation?

  1. Smell the area around the joints
  2. Listen for a hissing sound
  3. Apply soapy water to joints and look for bubbles Correct answer.
  4. Use a match to see if the gas ignites

Explanation

Applying soapy water to joints and observing bubbles is a safe and effective method for detecting leaks. Using a flame is dangerous, and relying on smell or sound is unreliable and unsafe.

Question 34Liquefied Petroleum Gas (LPG)

What is the function of a gas regulator in an LPG installation?

  1. To filter impurities from the gas
  2. To shut off the gas supply in an emergency
  3. To measure the gas consumption
  4. To reduce and control the gas pressure Correct answer.

Explanation

A regulator reduces the high pressure from the cylinder or vessel to a lower, stable pressure suitable for appliances. It does not measure consumption, filter impurities, or act as an emergency shut-off valve.

Question 35Liquefied Petroleum Gas (LPG)

In a commercial LPG installation, what is the purpose of a second-stage regulator?

  1. To automatically switch between cylinders
  2. To reduce cylinder pressure to a lower intermediate pressure
  3. To reduce intermediate pressure to the appliance operating pressure Correct answer.
  4. To provide overpressure protection

Explanation

A two-stage regulator system uses a first-stage regulator to reduce cylinder pressure to an intermediate pressure, and a second-stage regulator to reduce that intermediate pressure to the appliance operating pressure. Overpressure protection and automatic changeover are functions of other devices.

Question 36Liquefied Petroleum Gas (LPG)

What is the maximum filling limit for an LPG cylinder, expressed as a percentage of its water capacity?

  1. 80% Correct answer.
  2. 95%
  3. 85%
  4. 90%

Explanation

LPG cylinders are filled to a maximum of 80% of their water capacity to allow for liquid expansion due to temperature changes. Filling beyond this limit can lead to hydraulic pressure and rupture.

Question 37Liquefied Petroleum Gas (LPG)

Which of the following is a requirement for the location of an LPG cylinder installation?

  1. It must be at least 10 metres from openings
  2. It must be at least 3 metres from openings Correct answer.
  3. It must be at least 1 metre from openings
  4. It must be at least 5 metres from openings

Explanation

South African standards typically require LPG cylinders to be located at least 3 metres from openings such as doors, windows, and airbricks. This distance helps prevent gas from entering buildings.

Question 38Liquefied Petroleum Gas (LPG)

What is the purpose of a flashback arrestor in an LPG system?

  1. To reduce the gas pressure
  2. To filter out impurities
  3. To prevent a flame from travelling back into the gas supply Correct answer.
  4. To measure gas flow

Explanation

A flashback arrestor is a safety device that prevents a flame from travelling back through the gas line into the source, which could cause an explosion. It does not regulate pressure, filter gas, or measure flow.

Question 39Liquefied Petroleum Gas (LPG)

Which of the following is a correct method for leak testing a new LPG pipe installation?

  1. Introduce a small flame at joints
  2. Pressurize with LPG and check for pressure drop
  3. Pressurize with air and check for pressure drop Correct answer.
  4. Pressurize with water and check for leaks

Explanation

New LPG pipework is typically pressure-tested with air or nitrogen, and a pressure drop indicates a leak. Using LPG for testing is dangerous, water testing is not suitable for gas lines, and using a flame is extremely hazardous.

Question 40Liquefied Petroleum Gas (LPG)

What is the main hazard associated with the use of a gas hose on an LPG installation?

  1. It can react with LPG
  2. It can be damaged by heat or abrasion Correct answer.
  3. It can filter out the odorant
  4. It can increase gas pressure

Explanation

Gas hoses are susceptible to physical damage from heat, abrasion, or kinking, which can lead to leaks. LPG is compatible with the hose material, and hoses do not increase pressure or filter odorant.

Question 41Liquefied Petroleum Gas (LPG)

When must an LPG cylinder be hydrostatically tested?

  1. Every 5 years
  2. Every 10 years Correct answer.
  3. Every 15 years
  4. Only when damage is suspected

Explanation

In South Africa, LPG cylinders are typically required to be hydrostatically tested every 10 years. This periodic testing ensures the cylinder's integrity.

Question 42Liquefied Petroleum Gas (LPG)

What is the purpose of a pressure relief valve on an LPG vessel?

  1. To release excess pressure to prevent rupture Correct answer.
  2. To allow filling of the vessel
  3. To measure the liquid level
  4. To drain water from the vessel

Explanation

A pressure relief valve automatically releases excess pressure to prevent the vessel from rupturing. It is not used for filling, level measurement, or draining.

Question 43Liquefied Petroleum Gas (LPG)

Which of the following is a correct action if an LPG leak is detected in a commercial installation?

  1. Immediately shut off the gas supply and ventilate the area Correct answer.
  2. Try to locate the leak with a flame
  3. Continue operating the appliances
  4. Cover the leak with a cloth

Explanation

The correct action is to shut off the gas supply at the source and ventilate the area to disperse the gas. Using a flame is dangerous, continuing operation is unsafe, and covering the leak is ineffective.

Question 44Liquefied Petroleum Gas (LPG)

What is the primary reason for installing LPG appliances with a clearance from combustible materials?

  1. To allow for maintenance access
  2. To improve combustion efficiency
  3. To prevent ignition of the materials by heat Correct answer.
  4. To reduce noise

Explanation

Clearances from combustible materials are specified to prevent the heat from the appliance from igniting nearby materials. Maintenance access, combustion efficiency, and noise reduction are not the primary reasons.

Question 45Liquefied Petroleum Gas (LPG)

Which of the following is a requirement for the ventilation of a commercial kitchen using LPG appliances?

  1. Ventilation openings must be at high level only
  2. Ventilation must be provided at both high and low level Correct answer.
  3. No ventilation is required if appliances are flued
  4. Ventilation openings must be at low level only

Explanation

Ventilation must be provided at both high and low level to allow air for combustion and to safely disperse any LPG, which is heavier than air. High-level openings alone may not clear LPG, and low-level alone may not provide sufficient combustion air.

Question 46Liquefied Petroleum Gas (LPG)

What is the purpose of a gas manifold in a cylinder installation?

  1. To provide emergency shut-off
  2. To reduce the gas pressure
  3. To measure the gas consumption
  4. To connect multiple cylinders to a common supply line Correct answer.

Explanation

A manifold connects multiple cylinders together to provide a larger gas supply and allow automatic changeover. It does not regulate pressure, measure consumption, or provide emergency shut-off.

Question 47Liquefied Petroleum Gas (LPG)

What is the correct procedure for changing an empty LPG cylinder on a manifold?

  1. Close the cylinder valve, disconnect the empty cylinder, connect a full cylinder, and leak test Correct answer.
  2. Use a flame to check for leaks after reconnection
  3. Open the valve on the empty cylinder to relieve pressure before disconnecting
  4. Disconnect the empty cylinder while the system is under pressure

Explanation

The correct procedure is to close the cylinder valve, disconnect the empty cylinder, connect a full cylinder, and then leak test the connection. Disconnecting under pressure is dangerous, opening the valve on an empty cylinder is unnecessary, and using a flame is unsafe.

Question 48Liquefied Petroleum Gas (LPG)

A commercial LPG installation has a regulator that is frosting up. What is the most likely cause?

  1. The gas is contaminated with air
  2. The regulator is undersized for the demand Correct answer.
  3. The cylinder is overfilled
  4. The pipework is too large

Explanation

Frosting on a regulator indicates that the gas is being drawn off at a rate higher than the regulator can handle, causing excessive cooling due to the latent heat of vaporization. An undersized regulator or excessive demand can cause this. Overfilling, oversized pipework, or air contamination do not typically cause frosting.

Question 49Liquefied Petroleum Gas (LPG)

What is the minimum distance required between an LPG cylinder installation and a source of ignition?

  1. 2 metres
  2. 3 metres Correct answer.
  3. 5 metres
  4. 1 metre

Explanation

South African standards typically require a minimum distance of 3 metres between LPG cylinders and sources of ignition such as electrical switches or flames. This reduces the risk of ignition of any leaked gas.

Question 50Liquefied Petroleum Gas (LPG)

In a large commercial LPG installation, why is a vaporizer sometimes necessary?

  1. To increase the pressure of the gas
  2. To filter impurities from the gas
  3. To convert liquid LPG to vapour at a controlled rate Correct answer.
  4. To reduce the gas pressure

Explanation

A vaporizer is used to convert liquid LPG into vapour at a controlled rate when the natural vaporization from the cylinder or vessel is insufficient for the demand. It does not increase pressure, filter gas, or reduce pressure.