Carbon monoxide incidents

A CO alarm going off, a report of fumes, or someone taken ill: these are among the most serious calls an engineer will deal with. The first job is to protect people. The second is to find the cause without destroying the evidence if there has been a gas incident.

What counts as a gas incident

IGEM/G/11 defines a gas incident as a fire, an explosion or exposure to carbon monoxide that has led to a death, unconsciousness or someone being taken to hospital, or to property damage that makes part or all of the property uninhabitable.

If you're first on site at an incident

• Don't disturb the scene. It must be preserved as evidence for any investigation. But if it's safe to do so, make the situation safe.
• Call straight away: the emergency services, where needed, and the gas emergency service (for LPG, the gas supplier), telling them about the incident.
• Record everything you do. It will help whoever investigates.

If you arrive at a property where an incident may have happened, find out by asking the gas user or responsible person, and by looking for warning labels, notices or paperwork and finding out why they're there.

Reports of fumes or a CO alarm

Not on site? Report it to the gas emergency service (for LPG, the supplier) straight away. They will attend and make the situation safe. Ask for a reference number.

When the emergency service attends, its engineer visually inspects the gas appliances. If there's nothing obviously unsafe, they label every appliance "DANGER DO NOT USE" and, with the user's permission, turn them all off. Their warning notice says the appliances have been inspected but can't be confirmed as safe, and mustn't be used until a Gas Safe registered business has checked them. That's usually where you come in.

Following up after the emergency service

IGEM/G/11 Supplement 1 covers this visit in domestic premises. Before you go in, carry out a site-specific risk assessment. To take the job on, you need to be competent to work on every gas appliance in the property. Then:

1. Tightness test the installation to rule out a gas escape.
2. Test each appliance as you find it, before changing anything.
3. Check every gas appliance: that the flue works, that there's enough combustion air, the operating pressure or heat input (or both), the combustion performance, and that it operates safely.
4. Confirm safe combustion with a calibrated electronic portable combustion gas analyser that meets BS EN 50379-3.
5. Classify anything unsafe under IGEM/G/11, and report anything that meets RIDDOR (see 14.5).
6. Give the responsible person a work record of every check and test, with the results.

You should also understand combustion, the likely sources of CO from every fuel, how CO moves through a property, its effects, and the right standard (the BS EN 50291 series) and positions for CO alarms and what their alerts mean.

Recognising CO poisoning

Early symptoms of CO poisoning can look like everyday illnesses, and are easily mistaken for food poisoning, a virus, flu or just tiredness. HSE lists these signs to look out for:

• headaches or dizziness
• breathlessness
• nausea
• tiredness
• pains in the chest or stomach
• erratic behaviour
• problems with vision
• loss of consciousness.

If anyone in the property seems unwell with symptoms like these, IGEM/G/11 says to advise them to get medical attention straight away and to make the gas installation safe.

Classifying what you find

Under Table 1 of IGEM/G/11, these are Immediately Dangerous:

• a flued appliance showing signs of spillage or leakage of combustion products, with no evidence it has been put right
• an alarm going off, or someone with symptoms, where the flue terminal is in a position that could let combustion products back into the property
• confirmed re-entry of combustion products giving CO levels in the building of 10 ppm or more
• a flueless appliance showing signs of poor combustion.

If anyone seems unwell with symptoms that might be caused by CO, advise them to get medical attention straight away, and make the gas installation safe. Even if nobody is ill, or the CO reading is under 10 ppm, investigate further to confirm the appliance is safe.

When to escalate

Some cases need an engineer with specialist investigation competence, such as the CMDDA1 qualification:

• You can't find the cause. Leave the gas disconnected, classify the installation as ID, and escalate.
• The gas appliances are satisfactory, but nothing explains the alarm or the symptoms. Escalate to rule out CO in the surrounding air.
• The user reports another alarm, fumes or a smell in the last 3 months with no obvious cause. If you're on site, disconnect the gas and escalate. If you aren't, report it to the emergency service or LPG supplier.

Other sources of CO

CO doesn't only come from gas appliances. Also consider solid fuel and oil-fired appliances, engines, gas appliances in neighbouring properties, damaged appliance seals and condensate drains. Where you suspect CO from next door, contact the gas emergency service or LPG supplier. For other fuels, the procedure points to the relevant advisory body: OFTEC for oil, the Solid Fuel Association for solid fuel, the local authority's environmental health department for sources such as a landfill site, and the local water company where drains are suspected. Where other fuel-burning appliances may be the source, a specialist qualified for them must decide whether they are safe.

Sources: IGEM/G/11 Ed. 2 Section 7gas incidents IGEM/G/11 Ed. 2 6.2.3ESP attendance IGEM/G/11 Ed. 2 Table 1situation 1.4 IGEM/G/11 Supp. 1 (2022) 2.3, 4.1–4.4, 5.1follow-up visit RIDDOR 2013 reg. 11(1)gas incidents HSE: Carbon monoxide (web)symptoms CCN1 Issue 16 §8assessed

▸Tutor notes

• Walk through a call from a customer whose CO alarm is sounding: what you say on the phone, who you call, and what you do when you attend after the emergency service.
• Ask why the appliances must be tested as found, before anything is adjusted.
• Discuss the three escalation cases, and why an engineer who has found nothing wrong still can't close the job.
• Ask learners why CO poisoning is so often missed, using HSE's point that the early symptoms look like flu, food poisoning or tiredness.