Because of the toxicity of Hg, it is important to know the amount of Hg emissions released by point sources. Several methods are available to measure Hg emissions. These methods differ in level of complexity, application conditions, and their ability to speciate Hg. The scope of this document is description of the procedure for the determination of vapor phase Hg mass concentration in stack gas using carbon traps based on US EPA Method 30B. The procedure can be applied in countries around the world.