An arrangement and process of mitigating contaminants has a flow element intermediate a first space with contaminated matter (including contaminated gas) and a second space. Contaminated matter is drawn from the first space into the flow element and then urged into segregated contaminated gas and residual contaminated matter collected in the second space. Segregated contaminated gas is merged with gas from the second space to form mixed gas and treated to form primary treated gas which is directed to generate at least some of the drawing of contaminated matter from the first space into the flow element. Mixed gas can be treated by passing it through passages in the flow element coated with decontaminating agent and/or through a decontamination unit. The flow element allows for air flow to effectively act as a one-way barrier obstructing migration of contaminated matter from the second space back to the first space.