A sprinkler head cover including an end wall and a side wall extending from and around the end wall to form a cavity therebetween. The spill inhibitor body defines an opening therethrough and has a plurality of compliant finger projections extending from the spill inhibitor body. A gas distribution system is in fluid connection with the gas inlet for providing a first gas and a second gas, wherein the gas distribution system can substantially replace one of the first gas and the second gas in the plasma zone with the other of the first gas and the second gas within a period of less than 5 seconds.