Selectivity of ChemDAQ Ethylene Oxide Monitors

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ChemDAQ has developed a proprietary chemical filter that is placed in the sensor’s gas path. The filter reacts chemically with both alcohols, carbon monoxide and most other interference gases but the filter still lets the EtO pass through. Thus since only the EtO reaches the sensor, the monitor is highly specific and false alarms rarely occur.

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1. ChemDAQ Inc. • 135 Industry Drive • Pittsburgh, PA • 15275 phone 412.787.0202 • fax 412.788.2526 ©ChemDAQ Inc, 2008. Doc. No. CL-100-A-0.00 Selectivity of ChemDAQ Ethylene Oxide Monitors Introduction Ethylene oxide (ETO) is a commonly used sterilant gas, used to sterilize medical supplies and equipment that cannot be heat or steam sterilized. Ethylene oxide has very high efficiency, but is also toxic and has been classified by the International Agency for Research on Cancer as a class I known human carcinogen. In light of EtO’s potential health hazards, the Occupation Safety and Health Administration (OSHA) has promulgated regulations under 29 CFR 1910.1047 that set the permissible exposure limit (PEL) for EtO to 1 ppm, calculated as an eight hour time weighted average, and to 5 ppm excursion limit, calculated as a 15 minute time weighted average. OSHA also requires prompt alert in the event a major leak (1047(h)(2) and that exposure records be kept for 30 years. The ChemDAQ sterilant gas detection system has been designed to meet all of the OSHA requirements for EtO providing both 15 minute and 8 hours time weighted average readings as well as continuous real time gas readings. Interference Problems The ChemDAQ monitor, (and gas monitors from other manufacturers) uses electrochemical sensors that respond well to EtO with adequate sensitivity to EtO, however these sensors also respond to other easily compounds that are found in the healthcare workplace. Examples of such compounds are ethanol and isopropanol vapors and low levels of carbon monoxide (<< OSHA PEL of 50 ppm). Since the monitor is unable to distinguish between a sensor response to an alcohol and EtO and the resulting false alarms have plagued electrochemical based monitors for EtO from all suppliers. This interference problem has given electrochemical sensors for EtO a poor reputation in the healthcare industry, because of the widespread use of alcohol based cleaning and disinfection products. ChemDAQ Solution – The Spot-On® Filter ChemDAQ has developed a proprietary chemical filter that is placed in the sensor’s gas path. This filter is currently patently pending. The filter reacts chemically with both alcohols, carbon monoxide and most other interference gases but the filter still lets the EtO pass through. Thus since only the EtO reaches the sensor, the monitor is highly specific and false alarms rarely occur. The filter is consumed upon reaction with the interferent gas and must be replaced periodically. ChemDAQ replaces the filter each time the sensor is calibrated. ChemDAQ sensors are periodically swapped out with fresh calibrated sensors to ensure peak performance. Factory calibration avoids many of the problems associated with field calibration with reactive gases. Residual Cross Sensitivity While the Spot-On filter does remove most interference gases, EtO is not the only gas that will pass through filter. Testing has shown that alkenes such as ethylene (CH 2 =CH 2 ) will also pass through the filter. Other alkenes such as propylene behave similarly and will pass through the ChemDAQ filter. In some situations this can cause a problem. In once case, a customer, a medical equipment manufacturer, was using liquid propane forklifts (LPG) near their EtO monitors and was seeing some interference problems even with sensors with fresh filters. It turns out that LPG can contain up to 20 % propylene and trace levels of this gas ending up in the air and resulted in a reading on the nearby ChemDAQ EtO monitor. Once the problem was identified, it could be solved. However LPG and other sources of alkenes are rarely used in healthcare settings and so the cross sensitivity to alkenes is generally not an issue in this application.

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