This invention relates to a method and apparatus for treating a raw product stream (raw synthesis gas/raw syngas) generated by underground coal gasification (UCG). In one aspect, the invention concerns a method and apparatus for cooling and initial cleaning of raw syngas gas, so that the treated UCG product stream is suitable for downstream applications such as for energy or chemical production. In another aspect, the invention concerns a method and apparatus for isolating, treating and handling a raw UCG product stream that is generated either when igniting or decommissioning an underground coal gasifier and, due to its consistency, is generally unsuitable for energy or chemical production.