Open-path FTIR air monitoring of phosphine around large fumigated structures

Storage structures (silos, warehouses, and similar structures) are routinely fumigated for disinfestation of pests. This process includes sealing the structure, adding a fumigant (phosphine, methyl bromide, and other fumigants), maintaining a certain concentration of the fumigant, and aerating the structure after all fumigant has been removed or has dissipated. Phosphine concentrations in the air surrounding large fumigated structures at a tobacco storage facility were measured using an open-path Fourier transform infrared (FTIR) spectrometer system. These measurements provided more comprehensive data than could be obtained with multiple single-point detection devices. Specifically, this novel application of open-path FTIR was investigated to more completely characterize phosphine concentrations over long path lengths using a single FTIR. Phosphine levels were below the detection limit [<0.07 parts per million (ppm)] approximately 20 meters (m) east of a warehouse. Phosphine was detected at approximately 4 ppm inside a warehouse at the end of fumigation and just prior to aeration. Levels of phosphine directly in front of the doors of another fumigated warehouse, immediately after aeration, ranged from <0.07 to 8.3 ppm. Six different sampling paths were also used to investigate the levels of phosphine in various areas of the facility. Average phosphine levels in air around sealed warehouses under active fumigation were found to be the below detection limit. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 116–120, 2001