Liquid insulation is a type of mineral oil made by refining a fraction of the hydrocarbons collected during the distillation of a petroleum crude stock. The basic requirement of this mineral oil has to be in agreements with standard specifications developed by groups of experts such as ASTM Standard Specification D3487 and International Electrotechnical Commission (IEC) Specification 296. These are guidelines for the acceptable mineral insulating oil characteristics for new transformer oil. Mineral insulating oils are complex mixtures of many individual hydrocarbon compounds, and the relative amounts of these hydrocarbons can be different in crude oil that comes from different sources. Generally, these hydrocarbon compounds are members of three classes such as alkanes, naphthenes, and aromatic hydrocarbons. As a result of malfunction, gases such as hydrogen (H2 ), methane (CH4 ), acetylene (C2H2 ), ethylene (C2H4 ), ethane (C2H6 ), propane (C3H8 ) and butane (C4H10 ) are generated as a result of the decomposion of insulating oil.

The main constituents of Kraft paper are cellulose (90%), lignin (6% - 7%), hemicelluloses or pentosans (3% - 4%), traces of metallic cations and also absorbed water (typically 2% - 4% water/paper weight ratio). Degradation of paper is strongly influenced by scission and shortening of cellulose chain. The cellulose is depolymerized by a succession of chemical reactions that cause chain scissions and the release of gases and water into the surrounding oil, and some larger molecules such as furfurals.