Generally described as the country’s leading trouble - shooters, or investigators and experts for legal purposes in the field of heating and the chimney flue systems by which they are served, we are able to operate for the service or benefit of others.

Concerned with electrical and carbonaceous primary fuel fired systems our experience and expertise is primarily but not exclusively with the living environment in the domestic, residential and small commercial sector.

In cases of flue gas spillage from appliances, or inadequate flue and chimney flue performance, we have been credited with carrying out more investigations into such matters, than any other organisation in the UK.

The heating, legal and medical professions have in our experience accepted the great smoke screen of Carbon Monoxide (CO); as the dangerous product of combustion produced by carbonaceous fuels; including Natural Gas.

A belief that Natural Gas does not contain Carbon Monoxide (CO) whereas Coal Gas, Oven or Car Exhaust can provide a means of suicide has perhaps brought about an almost morbid fixation with Carbon Monoxide as a ‘deadly’ gas.

In our experience the subject to be addressed is that of Noxious Flue Gas; with or without Carbon Monoxide (CO) as a component part.

Carbon Monoxide.

Carbon Monoxide is indeed a poisonous gas. In sufficient volume it can and does kill people. It is however only one poison present in Noxious Flue Gas as produced by complete, or incomplete, combustion of carbonaceous primary fuel and a danger to humans and animals.

It is of course true that Natural Gas, as generally Methane Gas, only produces very minimal quantities of Carbon Monoxide (CO) in the course of complete combustion. The quantity of Carbon Monoxide (CO) produced after combustion and as discharged into the chimney flue is referred to as the CO/CO₂ (Carbon Monoxide/Carbon Dioxide) Ratio of Combustion. With complete combustion of Natural Gas for example this is a minimal quantity of Carbon Monoxide (CO) produced by the combustion and a CO/CO₂ ratio of 0.02 into the chimney flue, after the draught diverter, may be suggested as acceptable for appliance testing and test house purposes.

Carbon Monoxide (CO) may be produced at higher ratios in cases of defective appliance installation, operation, fluing, incorrect commissioning, fuel flow rates or burner pressures that produce incomplete combustion in the combustion chamber of the appliance.

We do not propose to concern ourselves with identification of higher levels of Carbon Monoxide (CO), such as those at present or attributable to immediate collapse or loss of life.

In the case of higher levels of Carbon Monoxide (CO) present in the indoor space or area, the identification of flue gas ‘spillage’ becomes easier; if not in fact very simple.

Oil and Solid Fuel Fired appliances generally create odour, or produce ‘smoke’, when combustion is not complete; or as established within the appliance manufacturer’s limits as expressed in the appliance installation instructions.

In this part of our dissertation we primarily, but not exclusively, concern ourselves with Gas Fired appliance burning Natural or Methane Gas as an ostensibly odourless gas; although treated with chemicals to provide a ‘safety’ odour.

The Flue Gas created by combustion and as discharged by an appliance may, or may not, contain Carbons and may, or may not, produce a distinctive brown stain on the surroundings to advertise their presence.

In our experience Noxious Flue Gas, spilling from a Gas Fired appliance, does not of necessity provide a readily identifiable odour to assist those involved or affected. Those regularly involved or exposed may of course be able themselves to identify, or describe, a distinctive odour but such generally appears to defy any well know acceptable description.

Identification of Noxious Flue Gas spillage from an appliance is often simplified thanks to obvious brown pattern staining around, or adjacent, to the appliance. The extent of staining of course indicates the presence of carbons in the Flue Gas. Such excess Carbons are not always present even in cases of high volume flue gas spillage into an indoor area.

Very high levels of Noxious Flue Gas products, spilling into an internal space, will generally be obvious to a perceptive occupants; except when a defect arises whilst the Occupant(s) is perhaps asleep.

We are increasingly involved in carrying out technical investigations into the reasons for loss of health and wellbeing by those humans and animals exposed to the long term discharge of low levels of Noxious Flue Gas into occupied and unoccupied spaces.

The cause of exposure is in our experience inevitably a defectively installed or maintained appliance or its chimney flue systems. Failure to identify a defect, possibly over many years of consecutive servicing, can be due to indifference, irresponsibility or the cost imposed in rectifying the defect.

Cases exist where an appliance appears to have performed satisfactorily in the past, despite known defects that have, over time, been allowed and considered acceptable.

Installation defects may exist because the importance of the defect is not realised and the person responsible for actually carrying out the servicing is not allocated the time or given the requested authority to carry out essential rectification: there are many such cases.

Some defects are of course not obvious to the Service Operative who is only expected to be skilled in performing an annual service in accordance with the appliance manufacturer’s instructions or carrying out fault finding in the event of an appliance break down. The Service Operative is not a Forensic Investigator or ‘Expert’.

A Service Operative required to undertake 20 calls per day comprising say 15 services and 5 breakdowns is not even likely to ‘take the case off the appliance’ during a Service; let alone carry out a responsible service. Often manufacturer’s appliance servicing instructions are inadequate.

Identification of Noxious Flue Gas, at low levels of concentration, demands very accurate monitoring equipment with low percentage reading error across its operating range. Such accuracy is often not generally available with electronic equipment which cannot perhaps even be zeroed in other than in external air where levels may be as high as that being discharged by the appliance operating in the internal space.

All monitoring equipment must be used with great care and skill. ‘Brownie Points’ are only awarded for identification of the component parts of Noxious Flue Gas! Failure to identify the presence of noxious fumes does not, of necessity, guarantee such fumes are not present and unrecognised. The identification of long term low level spillage of Carbon Monoxide (CO) and/or other Noxious Flue Gas is a complex subject.

Reliance upon identification of low level Carbon Monoxide (CO), within the spillage, becomes difficult. Levels identified must represent the spillage levels in the indoor space and not those levels present in the ambient air. Levels of 1 < 3 ppm. might be triggered by even short term Carbon Monoxide (CO) emission from another source or false alarm due to traffic, local industrial or other external levels at any particular time.

Passive Carbon Monoxide (CO) detectors designed to measure higher levels of say above 35 ppm are of course of value and benefit to householder and occupants of buildings; in the same manner as smoke alarms. Location of a passive Carbon Monoxide (CO) detector is however, in our experience, a far more challenging consideration than that for a smoke alarm.

In the year 2000 passive detectors manufactured to British Standard requirements do not, in general, operate to recognise and record low levels of Carbon Monoxide (CO) and as such may be of little value in detecting low levels and long term exposure to Carbon Monoxide (CO). Identification of low Carbon Monoxide (CO) levels, to the order of 0 < 10 ppm, can act as a simple tracer for the presence of other Noxious Flue Gas components in indoor spaces. It is not generally realised or accepted by those involved that a recording of Carbon Monoxide (CO) at 0 ppm does not imply there is no spillage of Noxious Flue Gas taking place into the dwelling.

Carbon Monoxide (CO) is not the only noxious product discharged from a defective appliance or chimney installation. There may be Cyanide or ‘Rocket Fuel’ in the indoor atmosphere as produced by combustion!

The total products of incomplete combustion are internationally unknown because the noxious products vary according to the quality of combustion taking place at any point in time.

When combustion of Natural Gas takes place it is generally, but not exclusively, accepted that the flue gas discharged at the appliance combustion chamber or flue outgo socket will include:

In practice the content of the flue gas can be loosely defined as ranging from Cyanide to Rocket Fuel; dependent upon the chemical reaction produced by the degree of combustion taking place in the appliance.

As a result of commercial propaganda and over time the Gas Industry and its consumers have been led to believe that Natural gas does not contain Carbon Monoxide (CO).

After combustion Natural Gas produces certain products of combustion. In theory complete combustion produces primarily Carbon Dioxide, Water Vapour and Nitrous products.

In practice it also produces small trace quantities of Carbon Monoxide (CO) in accordance with its appliance manufacturer’s established Carbon Monoxide/Carbon Dioxide ratio.

Certain appliances suffer incomplete combustion upon ‘start up’ when the combustion chamber and flue system is initially cold. Incomplete combustion is known to take place for at least 10 minutes and even up to 45 minutes after initial appliance ignition.

The production of Carbon Monoxide (CO) as a product of complete combustion is of course minimal almost to the point of insignificance to the health and wellbeing of humans and animals. The Carbon Monoxide produced is not of necessity pure CO.

The further combustion in the appliance moves away from complete combustion due to poor commissioning or incorrect appliance and flue installation, then noxious products of incomplete combustion, including increased levels of Carbon Monoxide (CO), will be produced.

The various Chemicals or Gases formed by combustion of the fuel represent the flue gas products discharged from the combustion chamber of the appliance. In our experience the identification of flue gas spillage, into an indoor space, can normally be easily identified by carrying out spillage tests using artificial smoke producing products; such as smoke matches or smoke pellets.

Such testing calls for a degree of skill and experience on the part of any operative carrying out such a test.

In general no other test can be said to be superior provided it is coupled with appliance commissioning tests and examination of the installation. Such is generally considered the most conclusive or positive and safest method of test and investigation.

Unfortunately for medical purposes there may be a requirement to identify the nature of chemical exposure suffered by humans or animals. The medical profession is in general far from informed on matters of exposure to Noxious Flue Gas be it Carbon Monoxide (CO), Nitrous Fumes (NOx) or Andrahydes, Aldehydes etc.

Current obsession with Carbon Monoxide (CO), which may or may not even be present in the flue gas spillage into an internal space, is unfortunate.

If Carbon Monoxide (CO) levels in the internal air of the space is higher than in the external ambient air then Noxious Flue Gas can be said to be entering the space. Thus Carbon Monoxide (CO) may become a useful tracer for the presence of other noxious gases rather than a major and significant poison itself to affect those humans and animals so exposed.

Systems should be investigated for installation or flue errors that may be causing loss of health and wellbeing in any given installation. Monitoring of flue gas is a separate issue: perhaps only necessary to assist the medical; but not the heating profession.

In our opinion the medical profession needs to know what other noxious chemicals are also present in the flue gas entering the space. Loss of health and wellbeing or specific symptoms in a patient should enable the medical profession to identify a patient’s exposure to some if not all Noxious Flue Gas components.

Currently it would seem that Carbon Monoxide (CO) is looked upon, by the medical profession, as the only tracer for flue gas exposure. Tests for CO in the Haemoglobin of blood are futile if not related to a circa 50% exposure decay rate every 4 hours.

At present the Heating Industry is being asked to identify the defect as if the annual service were an MOT; no defect no accident. In fact the role should be reversed whereby the medical profession identifies that a defect in the human, or animal, exists because of exposure to Noxious Flue Gas.

Monitoring is a complicated subject related to various factors that directly affect the noxious gas such as:

a. Its density

b. Its temperature & the temperature of the surrounding air.

c. Its purity

d. The overall volume being discharged

e. The volume and nature of the room or indoor space into which the noxious gas is escaping or being discharged.

f. The humidity in the room being monitored

As stated earlier ‘Brownie Points’ must only be awarded for identifying a noxious gas. A gas which may have drifted as it was carried across an indoor space or building by convective air currents and has, over a short time, increased in density due to cooling in the process.

There is no guarantee, or matter for acclaim, in not identifying the presence of Carbon Monoxide, Nitrous Fumes etc. that may well be present but have eluded detection.

The golden rule of flue gas monitoring is:

Any noxious gas as a product of combustion that is present in a room or indoor space in a greater volume, after the appliance is fired than before, serves to indicate the presence of Noxious Flue Gas off the appliance.

It becomes a matter of selection to identify the most useful known product of incomplete combustion that might be used to verify the type of ‘poison’ to which an individual has been exposed; for medical purposes.

P.T.J. Shannon.
Past president, IDHE.

12^th. December, 2000.