OPERATORY VENTILATION AND SCAVENGER EVACUATION RATE INFLUENCE ON AMBIENT NITROUS-OXIDE LEVELS

Investigations have shown that greater than Federally-recommended leve ls of ambient nitrous oxide often exist in the dental workplace. The p urposes of this investigation were to examine the influences of (1) op eratory ventilation rate and (2) scavenger evacuation rate on ambient nitrous oxide concentrations within a closed dental operatory. This la boratory investigation utilized a scavenging nasal mask assembly (Port er/Brown) to deliver 40% nitrous oxide in oxygen, at a total flow rate of 5 L/min, to a mannequin positioned supinely in a dental chair. Eig ht experimental groups were assigned based on combinations of operator y air exchange rates (0, 5, 10, or 15 room air changes per hour) and s cavenger evacuation rates (18.8 L/min and 21.4 L/min). Ambient nitrous oxide levels were monitored at four locations (0, 15.3, 30.7, and 61. 4 cm) from the nasal mask by means of an infrared spectrophotometer (M iran 1B). The operatory air exchange rate was measured with a flow hoo d (Short Ridge) and manipulated to one of the desired ventilation rate s. Time-weighted average (TWA) concentrations of ambient nitrous oxide (ppm) were continuously recorded at 15-second intervals with a microp rocessor (DL332F Datalogger) connected directly to a microcomputer. Th e results demonstrated that significantly reduced (p < 0. 05) ambient nitrous oxide levels were achieved with increasing room air exchange r ates and the high scavenger evacuation rate. It was concluded that ope ratory ventilation and scavenger evacuation rates were significant con trol measures available for reduction of ambient nitrous oxide to Fede rally recommended levels.