Monitoring and removing excess carbon dioxide and carbon monoxide is an essential aspect of refuge chambers. Both gases have potentially harmful effects on occupants is the gases are not sufficiently removed.
In sealed environments, the natural by-products affecting inhabitants include carbon monoxide (chemical formula CO) and carbon dioxide (chemical formula CO2) which can build up and poison the air.
In high enough concentrations, both CO and CO2 can cause serious injury, leading to a loss of consciousness and eventually, death. Removal of these harmful gases is, therefore, a vital necessity for any refuge chamber, especially if mains (mine) air fails or becomes compromised.
Carbon dioxide (CO2) is a colourless and odourless gas, existing in Earth’s atmosphere as a trace gas at a concentration of about 400ppm (0.04%) by volume. Natural sources of CO2 include volcanoes and hot springs and being soluble in water it occurs naturally in groundwater, rivers, lakes, ice caps, glaciers, and seawater. It is also present in deposits of petroleum and natural gas.
Carbon dioxide is produced by all aerobic organisms when they metabolise carbohydrate and lipids to produce energy by respiration. It is returned to the air via the lungs of air-breathing land animals, including humans. Carbon dioxide is also produced during the processes of decay of organic materials and by the combustion of wood, carbohydrates and fossil fuels such as coal, peat, petroleum and natural gas.
Carbon dioxide is not classified as toxic or harmful in its own right, but it is an asphyxiant gas which can reduce or displace the normal oxygen concentration in breathing air. Breathing of oxygen-depleted air can lead to death by asphyxiation (suffocation).
In concentrations above 1%, it can cause drowsiness and a slight shortness of breath in some people. Levels between 7 and 10% can cause suffocation, even in the presence of sufficient oxygen, exhibited as dizziness, headache, visual and hearing dysfunction and unconsciousness within a few minutes to an hour. The physiological effects of acute carbon dioxide exposure are grouped together under the term hypercapnia, a subset of asphyxiation. Occupational exposure levels are set at 0.5% for a duration of eight hours.
Humans exhale CO2 at a rate of approximately 30 Litres per hour. A group of people in a confined, sealed space like a refuge chamber will quickly contaminate the breathable air with CO2 in far less time than it would take to deplete the oxygen.
Carbon monoxide (CO) is a colourless, odourless, and tasteless gas that is slightly less dense than air. It is highly toxic to haemoglobic animals (including humans) when encountered in concentrations above 35ppm.
In the atmosphere, CO is produced from incomplete combustion and is present in exhaust gasses of vehicles and other engines, as well as from the combustion of most fuels. It is also produced in low quantities in normal animal/human metabolic processes and in human blood at levels of between 0 and 3% for healthy adults. This level is higher in heavy smokers.
CO has been referred to as the “Silent Killer” and CO poisoning is the most common type of fatal air poisoning. Once CO is inhaled, CO combines with haemoglobin to produce carboxyhaemoglobin, which becomes ineffective at delivering oxygen around the body. Oxygen levels are displaced in the blood causing vital organs to starve. Therefore, causing people to suffocate and lose consciousness.
CO molecules will not detach from haemoglobin, leaving them bound to the protein for long periods of time, often making CO poisoning irreversible. Concentrations as low as 667ppm (0.667%) may cause up to 50% of the body’s haemoglobin to convert to carboxyhaemoglobin. A level of 50% carboxyhaemoglobin may result in seizure, coma, and even fatality.
The most common symptoms of CO poisoning may resemble other types of poisonings and infections, including symptoms such as a headache, nausea, vomiting, dizziness, fatigue, and a feeling of weakness. Neurological signs include confusion, disorientation, visual disturbance, syncope (fainting), and seizures.
Occupational exposure levels are limited to 50ppm of CO over the long term. The effects of CO are compounded in the enclosed environment of a refuge chamber and therefore must be removed.
Removal of Gases in a Refuge Chamber
During entrapment, occupants consume oxygen and expire CO2 and CO as part of normal respiration. CO can also enter the chamber during occupant entry and if the compressed air intake is compromised. It is essential to have a reliable and measurable method of monitoring and removing CO and CO2 from the air. This is achieved using digital gas monitoring systems and chemical scrubbing.
Closely monitoring gas levels in the refuge chamber allows occupants to take corrective actions to maintain a safe and inhabitable environment during an emergency.
Click here for more information on Scrubbing Systems.
CO and CO2 are often mistaken for one another. Both gases are odourless and colourless, target the cardiovascular system and can enter the body through inhalation, skin and/or eyes. They also cause similar symptoms such as headaches, dizziness, seizures, and hallucination.
To the right is a summary list of the differences between the two gases.