[1] Univ Bristol, Sch Civil Aerosp & Mech Engn, Dept Engn, Queens Bldg, Bristol BS8 1QU, Avon, England
[2] Jimma Univ, Dept Environm Hlth Sci & Technol, Jimma, Ethiopia
[3] Univ Leeds, Fac Engn & Phys Sci, Leeds, W Yorkshire, England
[4] Univ N Carolina, Gillings Sch Global Publ Hlth, Chapel Hill, NC 27515 USA