Acetylene is a highly flammable gas and forms explosive mixtures with air over an unusually wide range of concentrations (2 to 80%). Acetylene can polymerize exothermically, leading to deflagration. Acetylene is relatively nontoxic and has been used as an anesthetic. Inhalation of acetylene can be hazardous because of its action as a simple asphyxiant. Acetylene is also well known for its inhibitory properties and its interactions with microbial processes such as nitrogen fixation, nitrous oxide reduction, ammonium oxidation, methanogenesis and alkane oxidation. Rhodococcus spp. can aerobically metabolize acetylene through reactions catalyzed by the enzyme acetylene hydratase ([http://www.ncbi.nlm.nih.gov/pubmed/6121789|Kanner & Bartha, 1982]), and Klebsiella penumonia can do the same using nitrogenase ([http://www.ncbi.nlm.nih.gov/pubmed/2268290|Lowe et al., 1990]). The strict anaerobe Pelobacter acetylenicus can also carry out the acetylene hydratase reaction ([http://www.ncbi.nlm.nih.gov/pubmed/7592321|Rosner & Schink, 1982]).