Hydrocarbons are compounds consisting only of carbon or hydrogen. Methane and propane belong to the hydrocarbons group. Hydrocarbons are included in fossile fuels. According to the definition of the World Health Organisation (WHO) hydrocarbons represent the main part of the volatile organic compounds (VOC). Furthermore methane fosters the greenhouse effect. The concentration of hydrocarbons can be measured by flue gas analysers as well using the catalytic the infrared (NDIR) measurement method.