Written in response to a particular inquiry, this article is posted since it is of general interest.
Calibration is a very important issue. One of Interscan’s competitors recommends calibrating its EtO monitor with CO (Carbon Monoxide). There is nothing wrong with using CO to calibrate an analyzer, assuming it is a CO analyzer that you are calibrating. While no detector is 100% specific, the point behind employing the use of an EtO detector, is that one wants to measure long term low level exposures to EtO. You want to be assured your EtO monitor is sensitive to, and is responding accurately to EtO. The best way to determine this is by calibrating and testing the monitor against a know standard of EtO.
Whereas on the one hand you expressed understandable concern that IPA produces a 1:1 interfering response on our EtO monitor, you also stated you thought it may be a viable alternative as a calibration standard. Again, you want to know your EtO monitor is responding to EtO. If you have an EtO alarm, you want to know EtO is truly the cause. On the other hand, if you knowingly expect (due to particular circumstances) to have an EtO alarm, and the monitor does not respond (alarm) to EtO, you would want to check calibration and verify response to a known concentration of EtO.
The main issues are calibration and accuracy. Everything else pales in comparison, because everything else is based on those two. As it is, we still wonder how a unit that has sufficient interference from CO, and is calibrated with CO will be able to accurately discern 0.5 ppm of EtO, anyway. This, by far, should be the main concern, as I guarantee you that there is more than 0.5 ppm CO in your SPD all the time. In short, CO or any other so-called surrogate gas does not take the place of a reliable EtO standard.
Would you really want to defend a legal case, basing your instrument calibration on a gas other than the one you should be monitoring?
EtO Calibration gas is available from SpecAir, Auburn, ME. (800) 292‑6218 Generally, the concentration is approximately 2–5 ppm. (Each cylinder is specifically marked). Although you expressed concern over using EtO as a calibration gas, please keep the following OSHA regulation in mind:
The employer shall ensure that no employee is exposed to an airborne concentration of ethylene oxide in excess of 1 ppm as an 8-hr TWA. The employer shall ensure that no employee is exposed to an airborne concentration of ethylene oxide in excess of 5 ppm as averaged over a sampling period of 15 min.
[29 CFR 1910.1047(c) (7/1/98)]**QC REVIEWED**
As an alternative to field calibration and actually using EtO calibration gas in the field, Interscan offers our ECS Program (Electronic Calibration Service). This would involve the purchase of EtO sensors (corresponding to the number of sampling points) to start you off in the exchange aspect of the program. Our instruments are already provided with sensors. When it comes time to calibrate, you remove the sensors which were originally installed in the monitoring system, follow the 7 simple steps on the ECS Certificate,and install the “new” sensors. The sensors removed from the system are sent back to Interscan, where we challenge them with actual EtO and send them back with a certificate. The charge to certify the sensors is $215.00 per sensor.