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 1 Nitrous oxide control in the dental operatory: auxiliary exhaust and mask leakage, design, and scavenging flow rate as factors
Authors Crouch-KG; Johnston-OE 
Source Am Ind Hyg Assoc J 1996 Mar; 57(3):272-278 
Link http://dx.doi.org/10.1080/15428119691015007 
NIOSHTIC No. 00230482 
AbstractLocal exhaust systems were tested for use in reducing exposures to nitrous-oxide (10024972) (N2O) in the dental operatory, and an improved mask was developed to reduce mask leakage. The local exhaust systems tested included one that rested on the chest and another that was installed in a type of mouth prop. Field studies were conducted in the dental operatory of the pediatric ward of a teaching hospital. Eight operations were conducted using the chest mounted and mouth prop exhaust systems. N2O concentrations were measured in the breathing zones of the dentist and dental assistant. Neither the chest mounted system nor the new mouth prop exhaust system had a significant effect on N2O levels when the high speed drill was in use. With the drill off, the chest mounted exhaust had a significant effect on exposure. In laboratory tests with a breathing machine and head form, both exhaust systems appeared to control leakage from the mouth. The primary source of leakage was found to be the mask. Increasing scavenging flow decreased mask leakage, but decreased the N2O concentration within the mask. Improved mask fit lowered leakage. A slotted skirt was added to the outer shell of a mask to control leakage. The authors conclude that a commonly used mask does not reliably control N2O emissions, even with scavenging. Increasing the pressure of the mask against the face provided a better fit, and reduced leakage. Use of a redesigned mask with a flexible slitted skirt on the outer shell effectively captured gas leaking from the inner shell. 
KeywordsNIOSH-Author; Dentistry; Exhaust-ventilation; Nitrogen-oxides; Face-masks; Control-technology; Anesthetics 
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