Destruction of toxic and environmental harmful gases

Abstract

Environmental and Occupational Health and Safety or OH&S issues have influenced the focus to capture / destroy toxic and environmental harmful gases expelled from fumigated storage. These storages are aerated to Threshold Limit Value (TLV) levels at the completion of fumigation to ensure it is safe for human reentry. Most fumigants by design are toxic and some have additional environmental hazards. The once universal fumigant, methyl bromide (CH₃Br), while restricted by the Montreal Protocol because it is an ozone depletor, is still used commercially in tonnage quantities. The use of CH₃Br is now mostly restricted to Quarantine Pre-Shipment (QPS) fumigations. The CH₃Br dose level is approximately 10.000 ppm and the recommended maximum respiratory level is 5 ppm. The universal fumigant gas, phosphine (PH₃), a very toxic gas, has a recommended TLV of 0.3 ppm. The sterilant, ethylene oxide (EtO), a known carcinogen, could have niche fumigation-sterilisation applications if the aerated gas could be destroyed. The use of heat to decompose toxic gases can involve the extracted contaminated air being fed into a burner where the hot zone destroys and decomposes the vulnerable fumigant gas. While flame burning at high temperature pyrolysis is 100% effective with EtO, most fumigants will form acidic by-product. Other issues include the need to re-locate capture and destruction equipment to service multiple locations and the large dilution required to reach TLV levels. A current alternative consists of adsorbing fumigants on activated charcoal. The spent activated charcoal requires chemical processing and or burial. There are cost issues with the initial purchase of the activated charcoal and post-treatment chemical processing of the adsorbed fumigant. Another disposal option is the burial of the spent charcoal in landfill sites. The ongoing safe use of fumigants is critical to important export industries especially the large volume bulk grain and export timber market.

Keywords: Fumigants, Capture, Destruction, Incineration, Acidic reactants.