Carbon monoxide (CO) which is the by-product of the incomplete combustion of coal has accompanied humanity since they learned to use fire. It may be assumed that in the first homes where fireplaces were situated in the central point and smoke used to vent out through an opening in the roof there was a possibility of generating high concentrations of carbon monoxide which could negatively affect the health and life of the inhabitants (1). The first historical mention of the harmful effect of carbon monoxide is attributed to Aristotle who noticed that coal fumes lead to “a heavy head and death” (2).

Carbon monoxide is produced as a result of processes of incomplete combustion of coal, wood and many organic substances with the insufficient supply of oxygen. During proper combustion coal generates combustion gases containing ca. 1% of carbon monoxide while even 30% of CO may be produced in improper combustion conditions (3). Carbon monoxide is an odorless and colorless gas which does not cause the irritation of respiratory tracts, its molecular weight is 28.01 and its density in reference to that of air is 0.967 (4). In the regulation of the Minister of Health dated 28.09.2005 (Journal of Laws No. 201, item 1674) on hazardous substances it has been classified as an extremely flammable gas and a toxic substance which poses a serious threat to human health. In regulations specifying the acceptable limits of CO concentration the occupational exposure limit has been defined as 23 mg/m³ and the short-term exposure limit (STEL) has been defined as 117 mg/m³. Healthcare room standards define the maximum volume in indoor air as 30 mg/m³ within 24 hours and 100 mg/m³ within 30 minutes (4, 5).

A natural source of carbon monoxide in nature is mainly the oxidation of methane in the atmosphere and the releasing of CO from oceans. Other natural sources are fires of forests and of grasses, volcanoes and storms. A contemporary source of human exposure to the harmful effect of carbon monoxide is primarily industrial activity. The most frequent sources of carbon monoxide in industrial conditions are mines and steelworks. Significant concentrations of CO may occur in boiler rooms, especially those with furnaces fired with culm, in car workshops and garages as well as during using various types of burners. Another source of exposure are heating systems. It is estimated that in Poland over a half of the 6 million households using the gas network possesses gas heaters of flow water. Improper use of heating installations, too tight windows and blocking vent grilles results in the lack of airflow into the rooms and thus incomplete combustion of gas and the production of toxic carbon monoxide concentrations (6). The reason for the occurrence of high carbon monoxide concentrations may also be the meteorological situation when during the formation of the so-called inversions the air movement may favor the injecting of combustion gases into flats. The combustion gases which enter the rooms this way contain not only carbon monoxide but also carbon dioxide and other combustion products possessing a specific smell (7).

Carbon monoxide poses a threat in every concentration and due to the difficulty of identifying it, it is often referred to as a “silent murderer”. According to the statistics of the National Fire Service in the years 2010-2015 in Poland there were over 24 000 carbon monoxide incidents as a result of which over 12 000 people were injured and 477 died (fig. 1).

Due to the physical properties of carbon monoxide detecting its presence in atmosphere without applying professional devices isn’t possible. The aim of preventive actions based mainly on conducting informative campaigns is applying home CO detectors. They allow for the early detection of the increased concentration of carbon monoxide. Despite of the widespread availability of home detectors their application still isn’t common, that is why in the heating season there are many cases of exposure to the toxicity of CO which generate the need for the interventions of emergency services. Currently detectors allowing for detecting carbon monoxide in atmosphere constitute standard equipment of units of State Fire Service and of Voluntary Fire Departments. They allow for measuring the concentration level of the gas in the inspected room.

Detectors allowing for confirming the presence of CO are based on three main technologies. These include the chemo-optical technology applying i.a. Gell cells, devices applying metal semiconductors as well as electrochemical detectors (8). Regardless of the technology detecting the presence of carbon monoxide is highly significant due to the toxic effect generated in the human organism even by small concentrations of carbon monoxide. The concentration of the gas in atmospheric air causes the occurrence of symptoms which depend on the time which the intoxicated person spent in the toxic environment. A light headache occurs as a result of a 2-3 hour exposure to the concentration ranging from 100 to 200 ppm (0.01-0.02%). With the concentration 400 ppm (0.04%), a strong headache occurs after 60 minutes of inhalation. The gas concentration at the level of 800 ppm (0.08%) causes dizziness, vomiting and convulsions after 45 minutes, and after two hours it leads to a lasting coma. The concentration which is twice as high – 1600 ppm (0.16%) causes a strong headache, vomiting and convulsions within 20 minutes and within 2 hours it leads to death. Higher concentrations cause the occurrence of worrying symptoms already after a few minutes and death occurs within 3-30 minutes of remaining in an atmosphere containing from 3200 ppm (0.32%) to 12 800 ppm (1.28%) of the toxic gas (tab. 1) (9, 10).