The OR was polluted with formaldehyde by placing 6 open dishes of formalin in the center of the room on top of the chest of a mannikin lying on an OR bed. When a sufficiently high level of formaldehyde was detected, the dishes were covered and removed from the room. The room ventilation system was not in operation during the experiments in order to reduce the rate of natural gas exchange. The airrecirculating device was left on while formaldehyde levels were rising. Neither the catalytic material nor activated carbon were in the device while the room was exposed to formalin. Formaldehyde levels were monitored under the following conditions: 1) without activated carbon and without catalyst; 2) with activated carbon; 3) with both activated carbon and catalyst.