It is imperative to protect the DL1 from excessive amount of glycol fog, mineral oil and smoke. That is why DL1 incorporates two stage air filtering to reduce these risks to minimum: however , the user MUST regularly check the internal and external filters. When used in closed or fixed environment where fog or haze is used, we recommend at least a weekly check. Internal filters can be rinsed with mild soap and water. External filter must be replaced.