Years ago, when OSHA was just getting started, an industrial hygienist friend of mine, told me “that if you are going to see a dentist, go early in the morning – if you wait, he might be groggy from inhaling nitrous oxide”. Well, I would not expect to have the wrong tooth pulled if I waited until 3PM., but it is conceivable that his (and these days, or her) finer judgment or muscular control could be affected. It may sound silly, but to this day I opt for earlier appointments if there is some possibility my doctor might be exposed to some anesthetic gas. Fast forward: I just read that a clinic has been fined $10,000 (later reduced to $1,800) for high employee exposure to nitrous oxide. It is easy to understand why nitrous oxide can be such a persistent problem. Consider:
- Nitrous oxide is customarily used in large volumes at a high concentration.. Usually, the mix is about 70% oxygen to 30% nitrous oxide. This has the potential to release large quantizes of nitrous oxide into the clinical environment
- Although highly concentrated nitrous oxide has a slightly sweetish odor, at low concentrations it has no perceptible odor. Without an instrument, you cannot tell that an unacceptable concentration is present. There are, fortunately good tools to monitor the exposure to nitrous oxide. For finding leaks, a portable device such as an infra-red meter may be used. To measure personal exposure, diffusive samplers are commonly employed.
- Despite best efforts, ventilation systems can fail. Especially if the wind is blowing in such a direction that the exhaust air is drawn back into the clinic. Years ago I used the technique of releasing a bolus of nitrous oxide into the room of a clinic and following its subsequent removal via ventilation. I was often surprised by how persistent the nitrous oxide remained in the room air. To paraphrase an old saying, if you work in a dental clinic, “Breather Beware”.
- · There is excellent information on the control of nitrous oxide in the dental clinic, involving both engineering design and proper use of equipment, OSHA expects that the clinical use of nitrous oxide is consistent with such guidelines.[i],[ii]
- There is no OSHA standard for nitrous oxide. OSHA has a horrid problem in setting new standards – one estimate is that if the full process for setting a standard is followed, given the time required for hearings, appeals, publishing in the Federal Register, etc. it takes about eighteen years for new standard to take effect. Instead OSHA relies on the “General duty clause”, which often means that the standard, if not already established by OSHA, relies on other respected standards, such as the TLV, which is an exposure level established by the American Conference of Governmental Hygienists. Their TLV for nitrous oxide is 50 ppm (90 mg/m(3)) as a TWA for a normal 8-hour workday and a 40-hour workweek
Point of disclosure: Twisuk Punpeng, before he became my doctoral student, made fundamental findings about the adsorption of nitrous oxide on the type of molecular sieve now used by Sensors Safety and other companies to sample nitrous oxide.[iii] I’m continually surprised by the interconnections in this small, small world..