Gas Smell in Property: Emergency Procedure, Tightness Test Sequence and Unsafe Situation Classification

Summary

Gas leaks are among the most serious hazards a Gas Safe engineer will encounter. Unlike most domestic faults that cause inconvenience or expense, an undetected gas leak can cause an explosion, fire, or asphyxiation. The speed and precision of the initial response can determine whether an incident becomes a near-miss or a fatality.

Gas engineers arrive at properties that smell of gas in three circumstances: as the emergency responder after the householder has called the emergency line; as a follow-up visit after the emergency service has isolated the supply and left; or on a routine visit where they detect a smell while doing other work. The correct procedure differs slightly in each case, but the underlying principle is the same: do not allow the supply to be restored until you have located, repaired, and re-tested every suspect joint.

The classification of unsafe situations is a formal requirement under Gas Safe responsibilities and the IGEM/UP/10 procedure. Every Gas Safe engineer must be able to correctly classify an unsafe situation, communicate this to the customer, and take appropriate action. Incorrect classification — either under-classifying (leaving a dangerous situation) or over-classifying (condemning a serviceable appliance) — both carry serious professional and legal consequences.

Key Facts

• Gas Emergency Number — 0800 111 999 (24/7); National Gas Emergency Service managed by Cadent on behalf of all UK gas transporters
• ECV — Emergency Control Valve; the first isolation point after the meter; customer-operable; quarter-turn valve
• IGEM/UP/10 — Handling and Investigation of Gas Emergencies; published by IGEM; the reference standard for unsafe situation classification
• ID1 — Immediately Dangerous — Situation must be made safe immediately; gas isolated; label affixed; no reconnection until repaired
• AR — At Risk — Not immediately dangerous but could become so; customer informed and advised; label affixed
• NCS — Not to Current Standards — Does not meet current requirements but no immediate risk; advisory label only
• Tightness test — IGEM/UP/1B procedure; U-gauge manometer at working pressure; confirm no leakage before reconnecting
• Natural gas odorant — Methyl mercaptan (and other odorants) added at approx. 8ppm; detectable by humans at well below explosive limits (4% LEL)
• LEL (Lower Explosive Limit) — Natural gas: 4% by volume in air; above this, an ignition source can cause explosion
• Gas detector — Catalytic bead or infrared detector; should be used in all suspect areas before re-entering
• Documentation — All gas emergencies must be documented: customer name, address, date, findings, action taken, serial number of label affixed; retain copies
• Duty to warn — Gas Safe engineers have a legal and professional duty to warn customers of unsafe situations, even if outside their original scope of work

Quick Reference Table: Unsafe Situation Classification

Detailed Guidance

Immediate Response Decision Tree

Gas smell reported in property
              |
     Open windows and doors
              |
     Do NOT operate electrical switches
     Do NOT use mobile phones near smell
     Do NOT smoke
              |
     Turn off ECV at meter
     (quarter-turn perpendicular to pipe)
              |
     Evacuate all persons from building
              |
     Call 0800 111 999 from outside
              |
     Await National Gas Emergency Service
              |
    Service attends and checks with gas detector
              |
          /         \
   LEAK FOUND      NO LEAK FOUND
         |                |
  Isolate supply   Reinstate supply
  Affix warning    Advise monitoring
       |
  Arrange Gas Safe
  engineer for repair
  and re-commission

Tightness Testing Sequence After a Gas Emergency

When attending after an emergency isolation, the engineer must conduct a full tightness test before reconnecting the supply. This is more comprehensive than a post-installation test because the source of the leak is unknown.

Step 1: Visual survey Before applying pressure, walk through the property and visually inspect all visible pipework, joints, meters, and appliances. Look for:

• Corrosion on pipework (particularly where embedded in walls or under floors)
• Physical damage (pipework struck by drill, nail, screw)
• Disconnected flexible hose (hob, cooker, fire)
• Old or damaged flexible hoses
• Signs of previous plumbing work near gas pipes

Step 2: Apply tightness test Per IGEM/UP/1B:

1. Ensure all appliance cocks are closed
2. Connect U-gauge to test point
3. Apply 20–25mbar pressure to installation
4. Wait 1 minute; note any pressure drop
5. A drop indicates a leak; no drop means the main installation is sound

Step 3: Isolate sections to locate leak If tightness test fails, systematically isolate sections:

1. Isolate one branch at a time using service valves
2. Repeat tightness test on reduced installation
3. If test passes with one branch isolated → leak is in that branch
4. Repeat until specific section located

Step 4: Leak detection on suspect section

• Apply leak detection fluid (Snoop or equivalent) to all joints in suspect section
• Use electronic gas detector to confirm leak presence and location
• Never use naked flame for leak detection

Step 5: Repair and re-test

• Repair the identified leak (replace joint, fitting, or section of pipe)
• Repeat full tightness test on complete installation
• Record: findings, action taken, post-repair test result

Classification Decisions in Common Scenarios

Scenario 1: Smell of gas with no obvious source, tightness test passes

• Smell may have been transient (appliance re-lit, someone cooking)
• Conduct thorough checks of all flexible connections and appliance connections
• If no defect found and test passes: advise customer on good practice; NCS if any minor issues; not emergency
• Recommend if smell recurs: call emergency line immediately

Scenario 2: Corroded section of exposed pipework, no active leak

• Classify AR if corrosion is significant and deterioration likely to progress
• Advise customer in writing; recommend replacement
• If corrosion is severe and pipework appears structurally compromised: ID1; isolate

Scenario 3: Disconnected flue on open-flued appliance, gas supply on

• Combustion products including CO entering room
• Immediate ID1 classification
• Isolate appliance supply; ventilate room; affix label
• Advise customer not to use until flue repaired and appliance recommissioned

Scenario 4: Flexible hose kinked or cracked

• If leak confirmed or hose is severely damaged: isolate appliance
• Replace hose; re-test
• AR classification until repair if no immediate leak but hose clearly end-of-life

Scenario 5: Gas fire with non-functioning FFD

• AR classification in most cases
• Advise customer in writing; gas fire should not be used until repaired
• A gas fire without FFD will not automatically shut off if flame extinguished by draught

Documenting Unsafe Situations

Documentation is a professional obligation and a legal protection for the engineer.

Required records:

• Customer name and full address
• Date and time of visit
• Description of the unsafe situation found
• Classification assigned (ID1 / AR / NCS)
• Action taken (isolated, label affixed, verbal advice, written advice)
• Serial number of label affixed
• Whether the customer was present and understood the situation
• Whether the situation was referred to the gas emergency service

Where to keep records:

• Engineer's copy: minimum 2 years
• Gas Safe register: unsafe situations must be reported to Gas Safe
• If not registered with Gas Safe: report to HSE

Reporting to Gas Safe: Gas Safe Registered engineers must notify Gas Safe of all ID1 situations and AR situations where the customer refuses to act. Gas Safe may arrange a follow-up check or pass to HSE.

Working Safely During a Gas Emergency Investigation

Personal safety:

• Conduct gas smell investigations only in adequately ventilated conditions
• Never enter a poorly ventilated space where gas may have accumulated without gas detector and confirmed ventilation
• If gas concentration approaches LEL: evacuate immediately; do not use detector in high-concentration area (explosion risk)
• Have a clear exit route identified before entering any enclosed or below-ground area

Ignition source control:

• All electrical equipment switched off at source if possible (not at switches — which can arc)
• Battery-powered equipment only in suspected gas-contaminated areas
• No mobile phones in suspect areas (though modern smartphones have very low ignition risk, it is good practice)
• No flame-producing equipment (soldering irons, blow torches) until area confirmed clear

Frequently Asked Questions

What should a homeowner do if they smell gas when the Gas Safe engineer is not present?

The standard emergency procedure applies regardless of whether an engineer is present:

1. Do not switch any electrical devices on or off
2. Open all windows and doors immediately
3. Turn off the ECV at the gas meter
4. Leave the building
5. Call 0800 111 999 from outside the building
6. Do not re-enter until the emergency service has attended and declared it safe

Can a Gas Safe engineer re-light appliances after an emergency isolation without further work?

Only if a full tightness test has been conducted and passed, the source of the original smell has been identified and repaired, and all appliances have been checked. Never re-establish a supply following an emergency isolation without completing the full tightness test sequence. Simply re-lighting is not an acceptable reinstatement.

What is the difference between the National Gas Emergency Service and a Gas Safe engineer?

The National Gas Emergency Service (0800 111 999) operates 24/7 and will attend any property with a suspected gas emergency. They can isolate the supply at the ECV or emergency control, ventilate the property, and make the immediate situation safe. They do not carry out repairs or recommission appliances — that requires a Gas Safe registered engineer. After the emergency service has attended and isolated the supply, the householder must arrange a Gas Safe engineer to locate and repair the fault.

Is a Gas Safe engineer obligated to report all gas leaks?

Yes. Under the Gas Safety (Installation and Use) Regulations 1998 and IGEM/UP/10, a Gas Safe registered engineer must report all ID1 situations to Gas Safe, and all situations where a customer refuses to allow a dangerous situation to be made safe. There is also a general duty under the Health and Safety at Work Act to inform the appropriate authority of serious risks. Failing to report a known dangerous situation is a disciplinary and potentially criminal matter.

Regulations & Standards

• Gas Safety (Installation and Use) Regulations 1998 — primary gas safety legislation; defines duty to warn and report unsafe situations

• IGEM/UP/10 — Handling and Investigation of Gas Emergencies: unsafe situation classification and procedure

• IGEM/UP/1B — Tightness testing and purging of natural gas installations

• Health and Safety at Work etc. Act 1974 — overarching duty of care

• Gas Industry Unsafe Situations Procedure (GIUSP) — industry-wide procedure derived from IGEM/UP/10

• Gas Safe Register: Unsafe Situations — Gas Safe guidance on classification and reporting

• HSE: Gas Safety Emergencies — HSE overview of gas emergency responsibilities

• IGEM Publications — IGEM/UP/10 and IGEM/UP/1B purchase/download

• gas meter upgrade — Meter responsibilities and emergency isolation procedures

• cooker installation — Tightness testing after cooker installation