Ventilation repairs are typically scheduled in advance to perform preventative maintenance, all work in chemical fume hoods affected must cease prior to the repair work and all chemicals should be removed from the hoods. During ventilation repairs, the air exchange rate in the laboratory will be affected, since chemical fume hoods often provide or supplement exhaust from the laboratory, when they are offline the air exchange rate will be significantly reduced and air pressure in the laboratory may become positive; all operations involving hazardous chemicals within that laboratory or building must be discontinued. Laboratory operations may resume in the laboratory or building once ventilation has been restored and if it is confirmed that all ventilation systems are operating correctly.
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