a method and apparatus for cleaning workpieces , particularly printed circuit boards upon which electrical components have been soldered , is capable of using a potentially flammable or explosive liquid cleaning solvent . in one embodiment , there are two immersion wash stages between which is a spray wash stage . the spray wash stage is formed as a closed chamber which is sealed when the immersion wash stages by liquid seals . to reduce the danger of fire or explosion in the spray wash stage an inert gas such as nitrogen is introduced into the closed chamber . in another embodiment the spray nozzles are immersed in liquid solvent in a combined immersion / spray wash stage . this reduces atomization of the flammable solvent further reducing the danger of fire or explosion .