Abstract Description: Last April, US EPA has announced the final National Emission Standards for Hazardous Air Pollutants (NESHAP ) rules regarding ethylene oxide (EtO) for commercial sterilization facilities. The updated standards require significant reductions in the emission of EtO. The extremely carcinogenic nature of EtO poses substantive risks for exposure. Due to the new requirements, many facilities are looking for more sensitive solutions for continuous emissions monitoring (much less than 1 ppm EtO). To address the new requirements, we developed an ambient air analyzer for ethylene oxide based on Cavity Ringdown Spectroscopy (CRDS).
CRDS is an ultra-sensitive method of spectroscopy that takes advantage of an optical cavity that retro-reflects light back and forth between a pair of mirrors. This creates kilometers of optical path length which greatly increases the depth of absorption by the Beer-Lambert law. Remarkably, the measurement is insensitive to intensity fluctuations that limit traditional direct absorption methods. This is because it records the decay of light leaking out of the cavity. The decay rate is inversely proportional to the absorption coefficient. CRDS is among the most sensitive analytical approaches for real-time continuous emissions monitoring, and the nature of our instrument makes it ideal for monitoring sterilizing facilities, in workspaces, and fenceline applications. Due to the design simplicity, it can handle a wide range of ambient humidity conditions and is robust in the field. The noteworthy components are the laser, reference cell, high reflectivity mirrors, detector, and steel sample cell. The flow path is optimized for both ambient sampling and the strongly oxidative environment caused by ethylene oxide. The laser is a solid-state laser, ubiquitous in the telecom industry. It has a demonstrated service life of more than a decade. The refence cell is coupled to the laser via optical fibers making misalignment improbable, and the detector has no moving parts. We have partnered with other organizations to conduct field worthiness testing, and the ongoing results show excellent performance and reliability. It has been successfully shipped to several locations and extensively used with no degradation in performance. We achieved a lower detection limit of 1 ppb in ambient air. Ultimately, our analyzer is insensitive to interferers and represents a unique modern tool to measure EtO. These proof-of-concept studies prove it is a useful tool for reliable monitoring of EtO in and around sanitization facilities, ensuring that the facilities are compliant, and safe for employees and the wider community.
