Section R. 325.52011 - Recirculation of air from exhaust systemsRule 11.
(1) The recirculation of air containing a contaminant whose permissible exposure limit is equal to or exceeds 1000 ppm, 15 mg/m3, or 50 mppcf, shall be permitted if the exhaust ventilation system is equipped with an air-cleaning device capable of reducing the contaminant concentrations to 10% or less of their permissible exposure limits in the returned air.(2) The director may allow the recirculation of air containing a contaminant whose permissible exposure limit is less than 1000 ppm, 15 mg/m3, or 50 mppcf, if the toxicity of the contaminant and the degree of air cleaning to be achieved create an environment that will not impair the health of the workers, and if the contaminant concentrations in the return air does not exceed 10% of its permissible exposure limits.(3) A recirculation system shall include an alternate air duct connection to discharge the return air outside of the building if necessary to protect the workers' health.(4) Spray-finishing operations using flammable and combustible materials shall be as prescribed in General Industry Safety Standard Part 76 "Spray Finishing Using Flammable and Combustible Materials," as referenced in R 325.52002.Mich. Admin. Code R. 325.52011
2005 AACS; 2016 MR 6, Eff. 3/31/2016