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Longitudinal industrial hygiene study of N2O controls at a pediatric dental facility.

McGlothlin-J; Crouch-KG; Johnston-O
American Industrial Hygiene Conference and Exposition, May 19-23, 1997, Dallas, Texas. Fairfax, VA: American Industrial Hygiene Association, 1997 May; :40-41
Researchers from the National Institute for Occupational Safety and Health (NIOSH) conducted four in-depth field evaluations to evaluate nitrous oxide (N2O) exposure in children's pediatric dental facility over an 18-year period from December 1978 to February 1996. The purpose of this longitudinal industrial hygiene study was to evaluate the effectiveness of N2O controls to reduce waste anesthetic gases in pediatric dental operatories. The NIOSH recommended exposure limit for N2O is 25 ppm during administration. The first three field evaluations were conducted at the same facility, the fourth was conducted at a new facility in which the N2O ventilation design was based on NIOSH recommendations that are noted below. The first evaluation was conducted in December 1978 and showed N2O levels for dentists ranging from 110-3500 ppm, for dental assistants from 750-1300 ppm, and for the dental operatory, N2O concentrations ranged from 75-3000 ppm. NIOSH researchers recommended using a N2O scavenging exhaust system that had just been marketed to reduce exposures. The second evaluation was conducted in April 1988 and showed N2O levels for the dentists ranging from 133-1000 ppm, for dental assistants from 4-432 ppm, and for dental room concentrations from 8-144 ppm. NIOSH recommended improved work practices, better room ventilation, increasing the scavenging mask air exhaust rate to 45 liters per minute, and installing a scavenging system flow meter to monitor scavenging meter flow rates. The third evaluation was conducted in November 1992 in which dentist N2O levels ranged from 8-410 ppm, and dental assistants from 1-50 ppm. Improved scavenging mask fit, reduced mask leakage, improved room ventilation, and better work practices were recommended to reduce N2O exposures. The fourth field evaluation was conducted in February 1996. Dental NzO concentrations ranged from 3-172 ppm, dental assistants from 2-27 ppm, and room concentrations from 1-18 ppm. Improved work practices and calibrated scavenging gas flow meters were also recommended to control N2O. These control methods over time have had a major impact on reduction of N2O. This study has shown that N2O concentrations may be controlled to approximately 25 ppm or less by the following: (1) maintaining a leak-free N20 delivery system, (2) adjusting the scavenging system exhaust ventilation to approximately 45 liters per minute, (3) installing a flow meter to assure proper exhaust rate, (4) redesigning the scavenging mask for better patient fit, (5) using an auxiliary exhaust ventilation placed near the patient's mouth to capture excess N2O, and (6) installing a general ventilation system that does not recirculate N2O in the dental facility.
Nitrous-oxides; Exposure-levels; Exposure-limits; Humans; Children; Dentistry; Industrial-hygiene; Anesthesia; Anesthetics; Ventilation; Men; Women; Face-masks
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American Industrial Hygiene Conference and Exposition, May 19-23, 1997, Dallas, Texas