What are the dangerous gases in the home?
September 15th to 21st is gas safety week, which is an annual event to raise awareness of gas safety and the importance of taking care of domestic gas appliances. So, what are the gases associated with domestic appliances and why are they so dangerous?
Natural gas is actually a mixture of naturally occurring gases which can be used as a fuel. The main constituent is methane, which is the smallest hydrocarbon molecule. A hydrocarbon is a material made from atoms of hydrogen and carbon and it can be burnt to create heat, to fire a boiler and heat your water, or cook a beautiful steak and kidney pudding, with lots of rich gravy in a soft suet casing.
At low concentrations, below approximately 5% by volume, methane will burn nicely and “safely”, but at a concentration above that it becomes explosive. This concentration is known as the lower explosive limit. An explosion is a very rapid, and uncontrolled burning, and the first objective of domestic gas safety is to make sure that the level of gas never reaches this critical level. Once it is at that level something simple like switching on a light, can create a spark and ignite the gas, creating an explosion. Gas explosions are very destructive.
When a hydrocarbon gas burns in an abundance of fresh air the carbon atoms combine with the oxygen in the air and form carbon dioxide. The hydrogen atoms combine with the oxygen and form water (H2O). This process is called complete combustion and it is what ideally happens in your boiler, your cooker and inside the engine of your motor car.
Carbon dioxide is colourless. At low concentrations the gas is odourless. However, at sufficiently high concentrations, it has a sharp, acidic odour. It is often thought of as primarily an asphyxiant, depleting the levels of oxygen and making the atmosphere unbreathable. However, CO2 is toxic in its own right and can have a damaging effect on health long before it would have displaced enough oxygen to asphyxiate someone. Carbon dioxide has a long-term workplace exposure limit of 5000 parts per million (0.5%) and is fatal at around 10% by volume. This is not usually a problem in domestic environments as the carbon dioxide will disperse into the wider atmosphere, keeping it well below this dangerous level.
The situation gets worse when there is less oxygen available, a situation created by poor boiler maintenance or ventilation. Then the hydrogen still combines to make water, but there is less oxygen available for the carbon to combine with. This is called incomplete combustion and results in soot (pure carbon) and the formation of carbon monoxide.
Carbon monoxide is an odourless and colourless toxic gas. Having a similar density to air, it is readily inhaled. It is much more toxic than carbon dioxide with a long-term workplace exposure limit of 100 parts per million, and is deadly within two hours at 1600 parts per million.
The red part of your blood is red because of a material called haemoglobin. Haemoglobin acts like a little person with a wheelbarrow. First, they visit your lungs and fill their barrow with the oxygen you breath in, and they take it and deliver it to the parts of the body which need it. From there they pick up the carbon dioxide the body makes using the oxygen and take it back to the lungs for you to exhale it. Breathing in carbon monoxide fills the wheelbarrow with quick drying concrete, so there is no room for the oxygen or the carbon dioxide, and so the haemoglobin can no longer make its deliveries. If this happens enough the body becomes starved of oxygen and dies. This is how carbon monoxide poisoning occurs.
The symptoms of exposure to low levels of carbon monoxide can be similar to those of food poisoning and flu.
The longer the gas is inhaled, the worse the symptoms will be. People may lose balance, vision and memory and, eventually, consciousness. Long-term exposure to low levels of carbon monoxide can also lead to neurological symptoms, such as difficulty thinking or concentrating and frequent emotional changes – for example, becoming easily irritated, depressed or making impulsive or irrational decisions. This can occur because people do not realise there is a lower level of the gas present, because it cannot be seen or smelled, and this is why carbon monoxide detectors are recommended.
So, in this gas safety week, as you sit and tuck in to your scrumptious steak and kidney pudding, just have a quick think about when you last had your boiler serviced and whether it might be a good idea to get a carbon monoxide detector. Stay safe!