Electrical apparatus in industry for use in the presence of explosive gases must be specially designed to prevent the apparatus from igniting the gas. In the case of flameproof enclosures, any holes and gaps in the enclosure wall must be sufficiently long and narrow to prevent transmission of a possible gas explosion inside the enclosure to an external explosive cloud. Furthermore, there are tight requirements to the maximum permissible gap surface roughness. This article describes an experimental study of the influence of mechanical and corrosive damage of flame gap surfaces on gap performance for IIA gases in air, using propane as test gas. It was found that, contrary to common presumptions, gap surfaces can suffer considerable damage without this causing any reduction of gap performance. In some cases, significant mechanical surface damage in fact improves gap performance. (c) 2012 American Institute of Chemical Engineers Process Saf Prog 32: 4956, 2013