I am attempting to specify materials for particular applications in electrical equipment in an oil sands refining plant. Our specification requires the interior of the substation be G3 environment (as defined by ISA) with respect to H2S and SOx contamination. These are <50 ppb for H2S and <300 ppb for SO2/SO3. Electrical equipment external to the sub could be subject to higher concentrations but the overall concentration expected is extremely low (perhaps averaging the G# levels). Our electrical substation design demands tin-plated copper wherever possible but this product is not always available to us. We have asked for brass or SS valves for liquid filled transformer's radiators/sample connections and tin-plated copper, brass or SS for electrical terminals that are open to the environment. We have be unable to obtain anything other than silver contacts for breakers and relays so must live with the consequences of those selections - perhaps this will mean increased maintenance for these areas. Where conformal coating is available for printed circuit boards we have requested this feature. My question: are these the correct choices for materials? Please advise if other "commonly" available materials (e.g. bronze, aluminum, etc.) may be better choices. I am an electrical engineer with no background material sciences so beg your indulgence in these matters.