Auxiliary Ventilation for the Control of Nitrous Oxide in a Dental Clinic

Abstract

The purpose of this research was to evaluate the feasibility of using auxiliary (local) ventilation, in conjunction with a scavenging system, as a means of controlling nitrous oxide (N₂O) in a dental clinic. Four systems, one system using only scavenging and three different local exhaust systems in conjunction with scavenging, were evaluated in a dental clinic. Personal samples were collected on the dental hygienist and the dental assistant and area samples were collected 15 inches from the patient to determine the feasibility of reducing exposures below the National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL) for N₂O. System zero employed no auxiliary ventilation; only a scavenging system was used to control the N₂O. System 1 employed a scavenging system and a commercially available hood consisting of a 2.5-inch-diameter nonflanged circular hood and 4 feet of 2.5-inch-diameter duct equipped with three adjustable pivot points. The pivoting duct was connected to a 3-inch-diameter flexible duct and to a fan. System 2 consisted of a scavenging system and a 3-inch-diameter flexible duct connected to a fan. System 3 consisted of a scavenging system and a 6-inch-diameter flexible duct connected to a fan. Hood flanges were not employed due to space constraints. Systems 1 through 3 used the nonflanged ends of the ducts as the hood openings. The air-flow rates for systems 1, 2, and 3 were 160, 250, and 630 cubic feet per minute, respectively. The system 1 hood was placed 6 to 8 inches from each patient's mouth. The system 2 hood was placed 6 to 10 inches from each patient's mouth, and system 3 was placed 12 inches from each patient's mouth. The position of the hood openings was variable for systems 1 and 2 because the exhaust hoods were moved between and during observations as needed to allow the dental staff to perform a dental procedure. System 1 was not effective in lowering the N₂O exposure. Systems 2 and 3 were effective in lowering the dental assistants' breathing zone samples to below the NIOSH REL of 25 parts N₂O per million parts (ppm) of air. Systems 2 and 3 also were effective in lowering the area N₂O concentrations, which were 12 to 17 inches from each patient's mouth, to levels below the NIOSH REL of 25 ppm. The dental hygienist's breathing zone samples were greater than the NIOSH REL for all the systems tested. Increasing the capture velocities and thus improving the control could be achieved by either increasing the air-flow rates or moving the hood closer to each patient's mouth. Because of unacceptable noise levels created by increased air-flow rates, locating the hood closer to the patient may be the most effective means to improve the exhaust systems.