Gas unsafe situations procedure: ID, AR and NCS explained

Where the rules come from: GSIUR and GIUSP

Two things are easy to mix up. The Gas Safety (Installation and Use) Regulations 1998 — GSIUR — are the law. They set the duties: only competent, Gas Safe registered people work on gas, and anyone who knows of a gas fitting that is or may be dangerous has to act on it rather than leave it. GSIUR says you must deal with an unsafe situation; it does not spell out the step-by-step method.

The method is the Gas Industry Unsafe Situations Procedure — GIUSP — published by IGEM as IGEM/G/11, Edition 2, most recently amended in July 2025. It replaced Gas Safe Register’s Technical Bulletin 001, which carried the older Edition 7.1 and is now withdrawn. GIUSP is what turns "this is unsafe" into a defined classification and action. So in revision terms: GSIUR is the legal duty, GIUSP is how you carry it out. If a question asks what you must do about a defect, it is testing GIUSP; if it asks who may work on gas or what the law requires, it is testing GSIUR.

This page is revision support, not authority to carry out gas work. Live testing, disconnection and making safe are for competent Gas Safe registered engineers following the current procedure and manufacturer instructions.

The unsafe categories and the separate NCS description

GIUSP uses two unsafe classifications: ID and AR. NCS was removed from the procedure because it describes a safe standards shortfall. Businesses may still record and advise on that shortfall separately.

• Immediately Dangerous (ID): a danger to life or property is present now, or would be the moment the appliance or installation is used. This is the most urgent outcome.
• At Risk (AR): one or more recognised faults exist that are not a danger right now but could become one in use. Serious, but not an immediate emergency.
• Not to Current Standards (NCS): a safe standards shortfall, outside the current GIUSP unsafe classifications. Record and advise separately.

The two questions that sort any defect

You do not memorise a list of which faults are ID and which are AR — installations differ, and the assessment rewards the reasoning, not rote recall. Instead you ask two questions in order.

• Question one: is this a danger to life or property now, or would it be as soon as the appliance is used? If yes, it is Immediately Dangerous and you stop there.
• Question two (only if the first is no): could this defect become a danger to life or property in use? If yes, it is At Risk.
• Where assessment establishes a safe standards shortfall, record and explain it separately. NCS is not a third GIUSP unsafe category.

Immediately Dangerous (ID): the action

For an ID situation the priority is to remove the danger. With the customer’s permission, turn off and disconnect the appliance or installation and make it safe, attach a “Danger Do Not Use” label, and issue a warning notice recording what you found and did, asking the responsible person to sign it. The point examiners look for is that you leave the situation safe, not merely documented.

Permission is the twist. You cannot force your way onto a customer’s appliance — turning off and disconnecting needs their agreement. If permission to disconnect is refused, try to turn the appliance off and warn the responsible person clearly of the danger. For natural gas, contact the gas emergency service straight away (0800 111 999) and record the job reference and the time; the emergency service has legal powers to make a natural gas installation safe. For LPG, contact the gas supplier instead, because those powers do not extend to LPG unless the supply contract gives a right of entry. A "safe" answer never involves leaving a known immediate danger connected and simply walking away.

At Risk (AR): the action

For At Risk, again with the customer’s permission, turn off the appliance or installation, attach a “Danger Do Not Use” label, issue a warning notice, and advise that it must not be used until the fault is put right. In a few At Risk cases turning off would not reduce the risk, for example a building put up over a plastic gas service pipe or an LPG bulk tank sited in the wrong place. Those are referred to the responsible person or organisation to resolve: no label is attached, and the warning notice says who to contact. The difference from ID is urgency and framing: there is no present emergency, so the emphasis is on preventing use until repair rather than on emergency escalation. If the customer refuses to let you turn it off, you advise and record — you cannot compel them, but you make the risk and the advice unmistakable.

Turning off has a set order: the appliance isolation valve; if that is not possible, remove the electrical fuse; if that is not possible either, turn off the appliance control and fix the label to it. Turning down a room thermostat or setting the timer to off is not acceptable.

NCS: a separate record of a safe standards shortfall

NCS was removed from the procedure in Edition 7 (2015), because a shortfall against current standards is not unsafe; Gas Safe Register inspected against that edition from July 2016. You can still tell the customer that the installation is below current standards and why, and recommend it is brought up to standard. Put that advice on your job report, not on a warning notice or other safety paperwork. The appliance may stay in use because it is safe now. A classic exam trap is over-classifying a purely cosmetic or historic non-conformity as At Risk. If it is safe today and would not become dangerous in use, it is NCS.

Labels, warning notices and the paperwork

• A warning notice records the defect, the classification and the action taken, and the responsible person is asked to sign it to show they have received and understood it. A copy is left with them, or on site if no one is there, and you keep a copy. Being able to say what a warning notice is and who gets it is common in questions.
• The “Danger Do Not Use” label is attached to the appliance or installation, whether it is Immediately Dangerous or At Risk, so the danger is visible to anyone who approaches it, not just the person who took the paperwork. The warning notice records which category it is.
• Turning off or disconnecting always needs the customer’s permission first — this single rule underpins the "what if they refuse" branch of most scenarios.
• RIDDOR is a separate legal duty. Report to HSE within 14 days any gas fitting, including flues and ventilation, that is dangerous enough to cause or be likely to cause death, unconsciousness or hospital treatment because of its design, installation, modification or servicing, even if you repaired it on the spot. A fitting that is dangerous only through lack of maintenance is not RIDDOR-reportable, so not every ID or AR finding is reportable. Make it safe first, then report.
• If the gas user is not the owner, for example a tenant, give the owner or managing agent the details in writing.
• Record any refusal to disconnect, turn off or sign: a refusal does not remove the danger. Keeping your records for at least six years is advisable.

Worked scenarios: classify then act

• An open-flued heater is spilling combustion products into the room while it runs. Danger now → Immediately Dangerous: with permission turn off and disconnect, label ID, issue a warning notice, and if permission is refused warn and call the gas emergency service.
• An open-flued appliance works normally, but its existing flue terminal is in a prohibited zone. Nothing is spilling now, but it could become dangerous in use → At Risk: with permission turn off, attach a “Danger Do Not Use” label, issue a warning notice and advise no use until it is corrected. If a CO alarm has sounded or someone has had symptoms, and the terminal could let products into the property, treat it as Immediately Dangerous.
• An older but sound installation uses a fitting that today’s standard would site differently, with no danger now or in use → Not to Current Standards: record, inform and advise, appliance stays in use.
• You find a genuinely immediately dangerous appliance and the customer refuses to let you disconnect it. You do not simply leave: you try to turn it off, warn them plainly of the danger, make the classification clear on the notice, and contact the gas emergency service for natural gas or the gas supplier for LPG. Refusal changes your options, not the danger.

Worked classifications: flue terminals and flame supervision

IGEM/G/11 includes a table of common situations with the category the industry applied to each. The table is not exhaustive, and the final decision is the engineer’s, based on the installation in front of them and the appliance manufacturer’s instructions. Its entries show the two questions in use: is it a danger now, and if not, could it become dangerous in use?

• An existing open flue whose terminal is in a prohibited zone: At Risk. If products are spilling into the room, it is Immediately Dangerous instead.
• A natural-draught open flue ending beside or facing a wall: At Risk. The procedure says this termination is not acceptable for any natural-draught open-flued appliance.
• An existing open flue with defects such as a non-compliant terminal position, too little vertical rise before the first bend or an unsuitable terminal: the engineer decides whether the defects are serious enough to make the installation At Risk.
• A missing flue terminal or a damaged flue, with no combustion products entering the building: At Risk.
• A flue that now discharges into an internal space, such as a conservatory built around a room-sealed terminal: Immediately Dangerous.
• A terminal that could let products of combustion into the property, where a CO alarm has gone off or someone has had symptoms: Immediately Dangerous. Confirmed re-entry of products that raises the CO level in the building is also Immediately Dangerous.
• A flame supervision device that does not work, fails to danger or has been disabled: Immediately Dangerous. The same entry covers other safety devices, including regulators, spillage monitoring devices, air pressure switches and high-limit thermostats.
• A catering appliance with an enclosed burner that was never fitted with a flame supervision device: At Risk. If a device was fitted and no longer works, the Immediately Dangerous entry applies.
• Two or more appliances on one flue where one of them has no flame supervision device: At Risk.

Exam angle and common mistakes

• Getting ID and AR the wrong way round. Ask the "danger now?" question first and answer it honestly — present danger is ID, potential-in-use is AR.
• Treating NCS as "ignore it". NCS still means record, inform and advise; the appliance staying in use is a conclusion, not a licence to say nothing.
• Forgetting permission. Any answer that turns off or disconnects a customer’s appliance without noting that permission is needed is incomplete, and the "permission refused" branch is a favourite.
• Confusing GSIUR with GIUSP. The regulations are the legal duty; the procedure sets the ID and AR safety actions — name the right one for what the question asks.
• Leaving a known immediate danger connected. The safe answer always removes or contains the danger and escalates when permission is refused.