Mixed Deck — All ACS Topics Flashcards

What does 'approved' mean when referring to gas appliances and fittings under GSIUR 1998?

Answer: Certified as meeting the relevant essential requirements under the Gas Appliances Regulation (EU) 2016/426 or equivalent UK legislation

Gas appliances must carry CE or UKCA marking (post-Brexit) demonstrating conformity with the Gas Appliances Regulation — using unapproved appliances is a breach of GSIUR 1998.

What does the term 'dead leg' mean in gas pipework?

Answer: A section of gas pipework that terminates in an unused capped-off fitting, with no appliance connected, which retains dead gas in the line

A dead leg is a capped pipe run left in the installation from a previous appliance — it retains gas in the unused section and represents an unnecessary length of pressurised pipe that should ideally be removed.

What is the minimum separation distance between a gas meter box and an electricity meter box when installed externally on a building?

Answer: 150mm horizontally or as specified in GS(IU)R 1998 and network operator standards (typically 150–300mm)

Gas and electricity meters must be separated by sufficient distance to prevent gas accumulation near electrical equipment that could cause ignition — network operator standards specify the precise separation required.

What is the correct procedure for locating a gas leak using a leak detection fluid?

Answer: Pressurise the installation and apply the fluid to each joint and connection, observing for bubble formation that indicates a leak

Leak detection fluid (or electronic detector) is applied to pressurised joints while gas is flowing; bubbles indicate a leak at that point — a systematic approach from meter to appliance is used.

What is the purpose of a 'draught diverter' on an open-flued appliance?

Answer: To protect the burner from downdraught, preventing wind-driven reversals of flue flow from extinguishing the flame or causing combustion products to spill into the room

A draught diverter introduces dilution air between the heat exchanger and flue, neutralising the effect of negative or positive pressure fluctuations in the flue and preventing them from disrupting combustion.

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?

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.

During a landlord's gas safety inspection, an engineer finds that the Emergency Control Valve (ECV) has been completely boxed in behind a newly installed kitchen unit, with no access panel. According to the Gas Industry Unsafe Situations Procedure (GIUSP), how should this situation be classified?

Answer: At Risk (AR)

An inaccessible ECV is classified as 'At Risk' (AR) under the GIUSP. This is because, while there may not be an immediate gas leak, the inability to access the valve in an emergency presents a potential danger to life or property. The engineer must explain the risk, turn off the gas with permission, and issue a Warning Notice.

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?

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).

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'?

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.

An engineer is installing a new, room-sealed, fanned-draught boiler. According to BS 5440-1, what is the minimum horizontal distance required between the centre of the flue terminal and an opening window on the same wall?

Answer: 300 mm

BS 5440-1 specifies the minimum clearances for flue terminals to prevent products of combustion from re-entering the property. For a fanned-draught, room-sealed appliance, the minimum horizontal distance from the centre of the terminal to an opening (such as a window or door) is 300 mm.

What action should be taken if a new installation fails a tightness test before purging?

Answer: Locate and repair the fault before any further testing or purging

Any fault must be located and repaired before proceeding, as introducing gas into a leaking system would create an immediately dangerous situation.

What prior documentation should an engineer bring to an ACS reassessment?

Answer: Their current ACS certificates, Gas Safe registration card, identification, and evidence of relevant work experience and any CPD undertaken

Bringing current ACS certificates, Gas Safe card, photo ID, and evidence of experience demonstrates eligibility for reassessment and allows the assessor to confirm the units requiring renewal.

Under the Building Regulations 2010 (Part J), what notification must be given when a new gas appliance is installed?

Answer: The installation must be notified to the local building control authority, typically through the Gas Safe Register's competent person scheme

Instalation of certain gas appliances is notifiable building work under Part J; Gas Safe registered engineers can self-certify through the competent person scheme, notifying building control on behalf of the customer.

Which condition in a flue system can cause 'backdraught' and allow combustion gases to enter a room?

Answer: Negative pressure in the building from extract fans, trickle vents, or sealed rooms that reverses the natural draught in the flue of an open-flued appliance

Modern buildings are often very airtight; powerful extract fans or extractor hoods can create negative internal pressure that reverses the draught in an open flue, causing combustion gases including CO to spill into the room.

If a gas supply has been interrupted and then restored, in what order should appliances be purged and re-lit?

Answer: One appliance at a time, starting with the one nearest the meter

Appliances should be purged and re-lit one at a time, starting with the appliance nearest the meter, to ensure a controlled and safe purging process.

According to the Gas Safety (Installation and Use) Regulations 1998, a landlord must keep records of gas safety checks. For how long must they retain the record of each annual check?

Answer: Until two further safety checks have been carried out.

Regulation 36(3)(b) of the GSIUR 1998 requires landlords to keep a record of each gas safety check until two further checks of the relevant appliance or flue have been made. This ensures a history of at least the last three checks is available for inspection.

A customer refuses you permission to disconnect an appliance that you have classified as 'Immediately Dangerous' (ID). What is the correct procedure to follow for a Natural Gas installation?

Answer: Inform the customer of the danger, apply a 'Danger Do Not Use' label, and immediately report the situation to the National Gas Emergency Service.

If a customer refuses permission to disconnect an 'Immediately Dangerous' appliance, the engineer cannot force the disconnection. The correct procedure is to clearly explain the danger, apply warning labels, and immediately contact the National Gas Emergency Service Provider (ESP). The ESP has the legal powers to enter the premises and make the situation safe, which may include disconnecting the supply.

According to BS 7967, when using a portable flue gas analyser, what is the primary ratio used to assess the combustion safety of a gas appliance?

Answer: CO / CO2 ratio

British Standard BS 7967 provides guidance on the use of electronic portable combustion gas analysers. It specifies action levels based on the ratio of Carbon Monoxide (CO) to Carbon Dioxide (CO2) in the flue gases. This ratio is a key indicator of how completely the fuel is being burned and is used to determine if an appliance is safe or requires remedial action.

What is the legal requirement regarding gas pipework installed in a void or duct?

Answer: Gas pipework in voids or ducts must be sleeved and ventilated so that any gas escape does not accumulate and can disperse safely

GSIUR 1998 requires that gas pipework passing through voids and enclosed spaces is installed in a ventilated sleeve so that any leaking gas can escape to a safe location and not accumulate.

Before an engineer begins to physically remove an existing gas meter for replacement, what is the most critical safety check that must be performed immediately after closing the Emergency Control Valve (ECV)?

Answer: A check to ensure the ECV is not passing gas (let-by test).

Before breaking any gas seal downstream of a valve, it is a fundamental safety requirement to verify that the valve is holding tight and not allowing gas to pass. This is often called a 'let-by' test. If the ECV is passing gas, attempting to remove the meter would cause a significant and dangerous gas escape. This check must be completed before any union is loosened.