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Gasfitting is a trade which is far larger and more complex than most people realise. Although many people encounter gasfitting on a domestic scale, or in a commercial situation such as a commercial kitchen, few come across it directly in the industrial area of manufacturing where much gasfitting is done.

From a householder perspective however, gasfitting is generally restricted to heating, cooking or water heating in the home. Few home owners consider undertaking gasfitting as part of a DIY project, however, a surprising number attempt it in mobile homes, caravans or boats, often with tragic results.

Gasfitting is essentially the act of installing gas pipes, appliances and flues. The legal definition of the scope of such work is found in the Plumbers, Gasfitters and Drainlayers Act 2006

This definition is comprehensive, and essentially makes it illegal for any person to undertake any of this work unless they are properly qualified, or at least properly supervised by a qualified person who also holds an appropriate licence.

Although the reasons for this may seem obvious, in fact fire or explosion as depicted in many popular films and TV programmes, is not the main danger from improper gasfitting. The greatest danger, and the cause of the vast majority of deaths and injuries, is from carbon monoxide poisoning due to incomplete combustion and improper flueing.


A Silent and Invisible Killer

Carbon monoxide (CO) is a flammable hydrocarbon gas.

But more important to this discussion is the fact that, carbon monoxide has a molecular shape which is similar to that of oxygen and carbon dioxide molecules. If inhaled, carbon monoxide displaces oxygen and combines readily with haemoglobin in the blood - in doing so, it starves the body of oxygen.

This is the key point in understanding why carbon monoxide is so dangerous - the fact that carbon monoxide molecules combine so easily with oxygen-carrying haemoglobin. Therefore, carbon monoxide is classified as a poison (toxic) because it kills by chemical action, rather than by suffocation, (a lack of air).

Effects of Carbon Monoxide Poisoning


Because carbon monoxide readily replaces oxygen in the blood, various body organs will rapidly become deprived of oxygen if carbon monoxide is inhaled. The first organ affected is the brain, and the first and most obvious effects are seen here. The exact symptoms will depend on the severity (quantity/concentration of carbon monoxide) and the length of exposure. Carbon monoxide has a half-life in the blood stream of five hours - that is - every five hours the amount of carbon monoxide in the body will halve. So if more than just a small amount of carbon monoxide has been absorbed, it will take some time for the body to deal with it.



Acute means 'sudden and serious'. In medical terms, the rapid absorption of carbon monoxide over a short time causing a sudden onset of symptoms is acute. If the air contains a large concentration of carbon monoxide, the effect will be serious and sudden - it is an issue of quantity.

Therefore, the amount of carbon monoxide in the atmosphere (measured in parts per million (PPM)) will indicate how serious the effect will be on humans and other animals. This is fully discussed with examples on the Carbon Monoxide (CO) Headquarters website.

Because of the time taken to clear carbon monoxide from the blood, if a fatal dose is absorbed, even if the patient is removed from the toxic environment and given oxygen, the result will be fatal anyway. Anything more than half a percent (500 PPM) may be fatal if exposure is longer than a couple of hours.

A serious (acute) case of carbon monoxide poisoning is likely to have a permanent effect, even if the victim does not die. A lack of oxygen to the brain can cause permanent brain damage of varying degrees; similarly internal organs such as the heart can also be permanently damaged.

Less serious cases of acute poisoning may cause nausea, dizziness, etc, but a full recovery will often be made provided the victim is removed from the scene and given time to recover. Short term acute symptoms include the following:

  • Dizziness
  • Nausea
  • Lack of concentration
  • Lethargy - unwillingness to move and inability to respond*
  • Headache
  • Blurred vision
  • Extremities (finger tips, nose) turn pink or bright red
  • Finally, unconsciousness and death.

*NOTE: A person suffering from carbon monoxide poisoning may experience such lethargy (and even contentment) that even if they know they are in serious danger, they are reluctant or unwilling to do anything about it. They may need to be physically carried/dragged from the room.


Chronic means 'slow and long term'. It refers to the situation in which a person suffers from the effects of a lower level of carbon monoxide inhalation over a prolonged period - often many years. Because the symptoms are usually not as serious as the acute symptoms, and often lessen or disappear when the victim is away from the source of the poisoning, it is often confused with other illnesses.

The long term affects of chronic (prolonged) carbon monoxide poisoning differ greatly from acute (one-off, sudden and serious) carbon monoxide poisoning. The patient tends to 'get better' when he/she is away from the carbon monoxide affected environment. Medical misdiagnosis can result in the victim being sent home to 'recover'.

Most often 'home' is where the problem is - the patient will be sent back into the toxic environment and be subjected to continued exposure.

Chronic cases are difficult to diagnose as the long-term effects of carbon monoxide poisoning differ greatly with individual circumstances. A victim will recover when away from the poisoned environment - often their own home - but experience symptoms again when returning. If your gas space heater is the cause of carbon monoxide spillage, symptoms will disappear when the heater is not in use, so you may become well during warmer months, only to show symptoms again when you start using the heater again as the weather cools. This cycle will continue (sometimes for years) so long as the faulty gas installation continues to spill carbon monoxide. Because the physical effects of oxygen deprivation on the organs have a serious long term detrimental effect, it is important that these differences be fully understood so they can be recognised as early as possible.

In pregnant women, carbon monoxide can be transported across the placenta, constituting a special risk to the foetus. Infants and young children are generally believed to be more susceptible to carbon monoxide than adults. The elderly are also thought to be more susceptible to carbon monoxide poisoning. A carboxyhemoglobin level of 0.4 to 0.7 percent is normally present in the blood of adults. In cigarette smokers, the range is 4 to 20 percent, which places smokers at an even greater risk if exposed to carbon monoxide.

In the short term, many of the symptoms are similar to acute poisoning, and include;

  • Dizziness
  • Nausea
  • Lack of concentration
  • Lethargy - unwillingness to move and inability to respond*
  • Headache
  • Blurred vision
  • Sore eyes, runny nose
  • Aching limbs and joints (which is why symptoms are often mistaken for a cold or flue)

In the medium to long term, other symptoms also begin to become noticeable. These include

Category Symptoms - a few in each category
Somatic/Physical Symptoms Headache, nausea, vomiting, muscle pain, joint pain, chronic fatigue, dizziness, vertigo, numbness, tingling of extremities.
Cognitive / Memory Impairments Executive functioning deficits, attention-concentration problems, multi-tasking problems, verbal and/or visual deficits, word-finding problems, word order problems, short-term memory problems, loss of intellectual capacity, slowed cognitive processing
Affective Disorders (Emotional / Personality effects) Mood changes, irritability, depression, anxiety, tearfulness, apathy, lack of motivation, loss of interest, anger, temper, social relationship problems, sleep disturbance personality change (eg. psychosis, schizophrenia)
Sensory & Motor Disorders (Visual, Auditory, etc.) Blurry vision, double vision (diplopia), accommodation problems, etc., etc., tinnitus (buzzing in ear), loss of hearing, hypersensitivity to chemicals, etc. (ie. MCS), slowed fine motor speed, coordination, decreased gross motor strength, speaking, eating, swallowing disorders
Gross Neurological Disorders Seizures, aphasia (can't speak), gait (walking) disturbances, balance problems, tremor


These symptoms can continue for many years, with some, in particular the physiological ones, often getting worse with time. Damage to the organs (eyes, lungs, circulatory system and other internal organs) can occur, or recur in a more serious version, many years after the event.

So while acute symptoms get better with time (provided the dosage is not fatal) chronic symptoms tend to get worse. That is why it is crucial to ensure that carbon monoxide does not discharge into a room, by ensuring in the first instance that combustion is as complete as possible, and secondly that proper flueing is installed.

What causes the Production of Carbon Monoxide in Gas Appliances?


The role of a flue in a gas appliance is exactly that of a chimney on a wood burning fire - to safely carry the products of combustion out of the building and into the atmosphere where they are diluted and dispersed. Some gas burners, gas hobs, for example, don't need flues (called unflued appliance) - but many do.

If an appliance does have a flue, it is very important for everyone's safety that the flue operates correctly.

Unflued appliances discharge all their products of combustion into the room, so precautions are taken to minimise the effect of this. In the first instance, these appliances use fully aerated burners, which are designed to produce a clean (blue) flame. Such appliances are also generally installed in rooms of a reasonable size (with a large volume of air) in addition to ventilation. Gas hobs in very small spaces like caravans and small boats can be hazardous - especially if there is minimal ventilation (closed windows, doors, hatches).

Production of some carbon monoxide is inevitable under any circumstances, and generally does not cause a problem. However, if carbon monoxide is to spill into a room from a flued appliance, this is of great concern.

Some burners are designed to produce yellow tipped flames - flame effect or decorative fires - for example - these burners must always be flued, and flued correctly!

The flueing system used must be designed and installed for the worst case scenario, and completely remove all products of combustion under all foreseeable circumstances. A flue which removes most combustion products most of the time is not satisfactory.

Spillage, or unplanned discharge of the products of combustion into the living space, is inevitably caused by inadequate or improper flueing. Even if a problem arises with the combustion process, to be safe, a proper flue system must be capable of removing these products under any atmospheric conditions.

Other Signs of Carbon Monoxide Spillage

Sick animals.
One of the first indicators of carbon monoxide spillage is often unexplained sickness, even death, of household animals, especially cats or dogs. Their smaller body size and the tendency for animals to sleep in front of a heater, means that any carbon monoxide discharged into the room has a disproportionate effect on family pets. A surprising number of victims of chronic carbon monoxide poisoning have reported sick or dead pets, many of whom have been seen by Vets unable to diagnose specific problems. Cats may have died after only a few months in the house - having displayed an inability to walk in straight lines, and constant illness, drowsiness and lack of appetite.

Animals showing symptoms like these is a strong indicator of the possibility of chronic carbon monoxide poisoning.

Any obvious signs of soot anywhere on an appliance or flue, is another indication of carbon monoxide spillage. If you see any sooting, it is important to stop using the appliance immediately and consult a competent registered gasfitter. Tell them that you suspect carbon monoxide spillage, and tell them why you suspect it. It is important that they particularly look in the vicinity of the down draft diverter.

If soot is found within the living space, this is evidence of both the production of serious quantities of carbon monoxide, and of the spillage of these products into the room.

The installation is intrinsically dangerous!!!

There are a number of possible reasons for incomplete combustion occurring, resulting in excessive carbon monoxide production. This needs to be diagnosed and rectified. There is however only one reason for spillage into the room - that is inadequate or improper flueing. The diagnosis and rectification of flueing problems is often more difficult than identifying and rectifying the cause of excessive carbon monoxide production. This may require the redesign and complete replacement of the flu.











What gasfitting can an unlicensed (unqualified) person do legally?

In addition to actual qualifications (National Certificate/s), plumbers, gasfitters and drainlayers must be licensed according to the Plumbers, Gasfitters and Drainlayers Act 2006.

There are several layers of licence designed to provide a balance between those in training (and/or who primarily work under close supervision), and those who supervise2 and certify the work of others.

Only certifying plumbers and gasfitters can uplift consents and supervise plumbing and gasfitting jobs

If your unsure if your Gasfitter is licensed to do the work you require, below is a link to the Plumbers Gasfitters and Drainlayers Boards Website. Click on link and follow commands to enter the details of the person you are enquiring about. This will show you exactly the qualifications this contractor has, and limitations of scope of work. Be careful to check this as any work undertaken by a un-licensed Gasfitter could void any future insurance claims if something was to go wrong and the installation was a part of the problem.

In short, about all that a non-registered person can do in relation to gasfitting is the replacement of empty gas bottles in a LPG gas supply. The definition of gasfitting includes pipes from the point of supply, and the point of supply for LPG installations is the outlet of the first pressure regulator. This allows consumers, or LPG suppliers, to disconnect empty gas bottles and connect full ones.

Changing LPG Bottles - Home, Boats and Caravans

Extreme care needs to be taken when connecting gas bottles to ensure they do not leak. LPG is heavier than air, and will fall to any low point where it will accumulate, waiting for any source of ignition. Every year fires and/or explosions (often causing serious injury or death) are caused by leaking LPG connections made to small (9 kg) LPG bottles in houses, boats and caravans. Any Gasfitting work that is to be done on either boat or caravan must be completed by a Certified or a Supervised Licensed Gas fitter.There is a specific code for the purpose of these type's of installations and require the attention of a Qualified Person.

There is a second important issue here - especially for boaties. Because LPG is heavier than air, any leak can result in gas accumulating in the bilge and cabin space. This of course poses a serious fire/explosion risk, but it also creates the potential for asphyxiation. LPG will displace air! If a child or pet, for example, is asleep below decks and LPG accumulates, it will displace the air and asphyxiate any living creature.

Therefore, when changing LPG bottles test all connections with a moderate solution of detergent and water.

  1. Prepare the solution (1 part detergent to 20 parts fresh water)
  2. Change the gas bottle
  3. Turn on the valve on the gas bottle fully, then back it off half a turn
  4. Brush the soapy solution on all joints
  5. Look for the formation of any bubbles
  6. If bubbles are detected, the gas cylinder should be turned off and the joint repaired, and the test repeated.

Certified Tradesperson?



Hiring a plumber, gasfitter
or drainlayer?

First check to see if they are
authorised to undertake the work
by asking to see their card.

All authorised tradespeople must carry
their authorisation card issued by the Board.

The card also details what a person's supervision requirements are, if any (on the reverse).

You can also check to see if a person is authorised on our online register or phone
us on 0800 743 262.