Control of Nitrous Oxide in Dental Operatories
DHHS (NIOSH) Publication Number 96-107
Dental workers are exposed to Nitrous Oxide (N2O) during administration of this anesthetic gas to patients. Exposures should be minimized to prevent short-term behavioral and long-term reproductive health effects that can be produced by N2O.
NIOSH research has shown controls including System Maintenance, Ventilation and Work Practices can effectively reduce N2O concentrations in dental operations to approximately 25 ppm during analgesia administration, the exposure limit recommended by NIOSH. Uncontrolled exposures to N2O have exceeded 1000 ppm. Three methods of control are recommended:
- Inspect and maintain the anesthetic delivery system to prevent N2O leaks in all hoses, connections, fittings. Repair all leaks immediately. (See ILLUSTRATION)
- Scavenging System– Use Scavenging. Exhaust ventilation of N2O from the patient’s mask should be maintained at an air flow rate of 45 LPM, measured by a calibrated flow device, and vented outdoors — not into the room ventilation system.
- Room Ventilation– Where possible, use 100% clean outdoor air for dental operatory ventilation. Supply, and exhaust vents should be well separated to allow good mixing and prevent “short-circuiting.”
- Auxiliary Exhaust Ventilation– Local exhaust hood should be placed near the patient’s mouth to capture excess N2O from breathing.
- Select scavenging masks of proper sizes to fit patients.
- Prudent use of N2O to appropriately sedate patients is encouraged.
- Monitor the air concentration of N2O to insure Controls are effective in achieving low levels during dental operations.
- NIOSH Technical Report: Control of Nitrous Oxide in Dental Operatories
- NIOSH Alert: Controlling Exposures to Nitrous Oxide During Anesthetic Administration
- NIOSH Manual of Analytical Methods, Method 6600, Nitrous Oxide, Issue 2, 1994
- Information about local sources for technical assistance, monitoring equipment for N2O, flow meters, and auxiliary devices.
The principal contributors to this HAZARD CONTROLS are James D. McGlothin, Division of Physical Sciences and Engineering, and Barbara L. Dames and Jerome P. Flesch, Education and Information Division, NIOSH. This document is in the public domain and may be freely copied or reprinted. NIOSH encourages all readers of this HAZARD CONTROLS to make it available to all interested employers and workers.
|Step by Step Approach for Controlling N2O
|Visually inspect all N2O equipment (reservoir bag, hoses, mask,connectors) for worn parts, cracks, holes, or tears.
|Replace defective equipment and/or parts.
|Turn on the N2O tank and check all high to low pressure connections for leaks. Use a non-oil-based soap worn solution to check for bubbles at high pressure connectors, or use a portable infrared gas analyzer.
|Determine leak source and fix. If tank valve leaks, replace tank; if O-rings, gaskets, valves, hoses, or fittings, replace. Contact the manufacturer for parts tact the manufacturer for parts replacement. For threaded pipe fittings, use Teflon tape. Do not use this tape on compression fittings.
|Select scavenging system and mask. Mask should come in various sizes to patients. Scavenging systems should operate at air flow rate of 45 lpm.
|Provide a range of mask sizes for patients. Check to see that noise levels at the mask are acceptable when the scavenging system exhaust rate is operated at 45 lpm.
|Connect mask to hose and turn on vacuum pump before turning on N2O. Scavenging system vacuum pump must have capacity to scavenge 45 lpm per dental operation.
|Determine proper vacuum pump size for maintaining 45 lpm flowrates, especially when interconnected with other dental scavenging systems. If undersized, replace pump.
|Place mask on patient and assure a good, comfortable fit. Make sure reservoir bag is not over or under inflated while the patient is breathing.
|Secure mask with “slip” ring Secure mask with “slip” ring for “good activity” from patient breathing.
|Check general ventilation for good room air mixing. Exhaust vents should not be close to air supply vents (use smoke tubes to observe air movement in room.)
|If smoke from smoke tubes indicate room air mixing is poor, then increase the airflow or redesign. If exhaust vents are close to air supply vents, relocate (check with ventilation engineers to make adjustments).
|Conduct personal sampling of dentist and dental assistant for N2O exposure. Use diffusive sampler or infrared gas analyzer (see sampling methods).
|If personal exposures exceed 150 ppm during administration, improve mask fit and make sure it is secure over the patient’s nose. Minimize patient talking while N2O is administered.
|Repeat procedure in step 7.
|If personal exposures are less than 150 ppm but greater than 25 ppm, implement auxiliary exhaust ventilation near the patient’s mouth. Capture distance should no greater than 10 inches from the patient’s nose and mouth area and exhaust no less than 250 cfm at the hood opening. Avoid getting between the auxiliary exhaust hood and patient’s mouth and nose area.
Sampling Methods for N2O
NIOSH recommends air sampling for N2O be conducted periodically to: (1) measure worker exposures to N2O during anesthetic administration Personal Sampling, and (2) control N2O leaks in the delivery, scavenging and ventilation systems Area Sampling. Sampling can be used to measure personal breathing zone exposures of dental workers, and to detect leaks in the anesthetic delivery system, ineffective capture by the scavenging system, reentry in the room ventilation system, and circulation to other areas of the dental offices. Sampling methods available are summarized below.
- Real-Time Sampling Sampling that provides direct, immediate and continuous readout of N2O concentration in air utilizes a portable Infrared Gas Analyzer (IGA) as recommended by the NIOSH analytical Method 6600. Since this method provides continuous sampling and instantaneous feedback, sources of N2O leakage and effectiveness of control measures can be immediately determined.
- Time-Integrated Sampling
- Bag Sampling Sample for a selected time period, such as NIOSH recommended method for sampling, during the time of anesthetic administration to a patient. This is accomplished by collecting an integrated air sample in a plastic bag, impervious to N2O leakage, using a portable battery-powered pump. Analysis of the bag sample is accomplished using the Infrared Gas Analyzer. The N2O concentration obtained is an “average value” for the entire sampling period.
- Diffusive Sampler or real-time or bag sampling-lGA analysis is not available, time-integrated samples using a Diffusive Sampler (sometimes called a Passive Dosimeter) for N2O can be collected and then sent to a commercial laboratory for analysis. These samplers are easy to use and inexpensive. Sampling time is controlled by removing the cap to start sampling and replacing it to stop sampling. An accurate accounting of the sampling time (cap off/cap on) is required for the laboratory analysis. The Diffusive Sampler can be used to measure a dental worker’s exposure by attaching it to the lapel (breathing zone) and uncapping/recapping during the actual administration of N2O.