ESDU 92012 discusses the effects of methods of combustion on the potential for deposition and the consequences for efficiency. Mechanisms by which surfaces become contaminated with particles and deposits as a result of chemical reactions and corrosion are outlined. The principles of combustion are considered in detail in relation to the use of coal, oil, natural gas or waste products as fuel with particular reference to heat transfer surface contamination. The chemical reactions responsible for deposit formation are outlined for the different fuels. Techniques, largely empirical, for assessing fouling and slagging propensity are provided and discussed. Based on an appreciation of the mechanisms of fouling and slagging, techniques are presented for limiting the problems in combustion systems; they include blending, combustion conditions, and the use of additives. Cleaning techniques for use during operation or after shut-down are summarised. Some consideration is given to the implications of fouling and slagging for the design of combustion equipment and tentative recommendations are made on good design practice.