Gas Safe ACS - Accredited Certification Scheme Pipework and Fittings Questions and Answers — Questions and Answers
Question 1: An engineer is installing 22mm copper pipework to supply a domestic gas boiler. According to BS 6891, what is the correct method for protecting this pipework where it passes through a solid wall?
- Wrap the pipe in denso tape and seal the ends.
- Ensure the pipe is sleeved for its full length within the wall, and seal the annular space at one end. (Correct answer)
- Paint the pipe with a corrosion-resistant paint before embedding it directly in the mortar.
- Encase the pipe in a larger plastic pipe and fill the void with expanding foam.
Correct answer: Ensure the pipe is sleeved for its full length within the wall, and seal the annular space at one end.
BS 6891 and Regulation 19 of GSIUR 1998 require that when gas pipework passes through a solid wall or floor, it must be protected. The correct method is to place the pipe inside a suitable sleeve that runs the full width of the structure. The space between the gas pipe and the sleeve (the annular space) must be sealed at one end to prevent gas from an escape tracking into the building's structure, while allowing for ventilation or minor movement at the other.
Question 2: When carrying out a tightness test on a new domestic gas installation with a total volume of 0.015 m³, what is the standard duration for the stabilisation period after pressurising the system to 20 mbar?
- 5 minutes
- 10 minutes
- 2 minutes
- 1 minute (Correct answer)
Correct answer: 1 minute
According to IGE/UP/1B (Tightness testing and direct purging of small Natural Gas installations), for a new installation, after the system is pressurised to 20 mbar (+/- 0.5 mbar), a stabilisation period of 1 minute is required to allow the air temperature within the pipework to stabilise before commencing the let-by and tightness test.
Question 3: Which of the following jointing methods is NOT permissible for connecting steel pipework on a domestic Natural Gas installation operating at low pressure (21 mbar)?
- Capillary soft solder fittings. (Correct answer)
- Longscrew connectors with appropriate sealant.
- Welded joints.
- Tapered thread screw joints.
Correct answer: Capillary soft solder fittings.
Capillary soft solder fittings are only suitable for use with copper pipework. For steel pipework on low-pressure domestic gas installations, permissible jointing methods include tapered thread screw joints (using appropriate sealant), longscrew connectors, or welded joints. BS 6891 provides detailed specifications for acceptable jointing materials and methods.
Question 4: A gas engineer needs to install pipework through a timber floor joist. According to BS 6891 and building regulations, what is the maximum diameter of a hole that can be drilled through the centre of a 200mm deep joist without requiring structural calculations?
- 65mm
- 75mm
- 50mm (Correct answer)
- 100mm
Correct answer: 50mm
BS 6891 and building regulations guidance (such as Approved Document A in England) state that holes drilled through the centre (neutral axis) of a timber joist should not exceed 0.25 (or 1/4) of the joist's depth. For a 200mm deep joist, this equates to a maximum hole diameter of 50mm (200mm x 0.25 = 50mm).
Question 5: According to the Gas Safety (Installation and Use) Regulations 1998, what is a key requirement for installation pipework run in an unventilated void, such as a floor duct or ceiling space?
- The pipework must be painted yellow for easy identification.
- The pipework must be constructed of continuously welded steel.
- The void must be filled with a non-combustible insulation material.
- The pipework must be contained within a ventilated duct. (Correct answer)
Correct answer: The pipework must be contained within a ventilated duct.
Regulation 19(6) of the Gas Safety (Installation and Use) Regulations 1998 states that where installation pipework is not itself contained in a ventilated duct, it must not be installed in any shaft, duct or void which is not adequately ventilated. Therefore, if the void itself is unventilated, the pipe must be enclosed within its own ventilated duct to safely disperse any potential gas escape.
Question 6: An engineer is replacing a section of 28mm gas pipework. Before cutting into the existing pipe, the section must be safely purged. What is the primary purpose of purging the pipework 'out of service'?
- To increase the pressure in the pipe to check for weaknesses.
- To clean the inside of the pipe from debris and corrosion.
- To introduce a pleasant smell to the gas for easier leak detection.
- To displace the flammable gas with air or an inert gas to prevent an explosive mixture. (Correct answer)
Correct answer: To displace the flammable gas with air or an inert gas to prevent an explosive mixture.
Purging gas pipework 'out of service' is a critical safety procedure to remove flammable gas before any work that could create an ignition source (like cutting) is performed. The process involves using air or an inert gas, such as nitrogen, to push the flammable gas out of the pipe section in a controlled manner, thus eliminating the risk of forming an explosive gas/air mixture.
Gas Safe ACS - Accredited Certification Scheme Pipework and Fittings Questions and Answers
An engineer is installing 22mm copper pipework to supply a domestic gas boiler.
According to BS 6891, what is the correct method for protecting this pipework where it passes through a solid wall?