One problem which sometimes occurs both in reciprocating and in oil-flooded units is the occurrence of internal fires and explosions. This phenomenon is not fully understood, but appears to be associated either with the use of an incorrect oil, running with a low oil level or not keeping strictly to the correct maintenance procedure. The presence of rust, aluminium or magnesium in the system can contribute to the danger. Combustion can start in the reclaimer vessel of a flooded unit where the oil is present in a finely divided form. The build-up of carbon deposits appears to serve as a starting point for fires. Regular cleaning and strict attention to manufacturer’ s recommendations will usually prevent this problem. BS 6244 should be studied for guidance on safety and includes information on avoiding the potential for fires.