 The recommendation also says that where this is not possible, 300 Bq/m3 should be selected as the highest level.A national reference level should not be a limit, but should represent the maximum acceptable annual average radon concentration in a dwelling.The actionable concentration of radon in a home varies depending on the organization doing the recommendation, for example, the EPA encourages that action be taken at concentrations as low as 74 Bq/m3 (2 pCi/L), and the European Union recommends action be taken when concentrations reach 400 Bq/m3 (11 pCi/L) for old houses and 200 Bq/m3 (5 pCi/L) for new ones.