Emission of viable bacteria in the exhaust flue gases from a hospital incinerator.

The exhaust gases from an oil-fired hospital waste incinerator were examined during normal incinerator operation. The design-specified operating temperature was 800 degrees C in the primary combustion chamber and 1000 degrees C in the secondary chamber. Flue gas temperatures, measured from the sampling point at the base of the exhaust stack, varied over the range 186-305 degrees C, and bacteria were recovered from this position in numbers up to 400 cfu m-3 (mean 56 cfu m-3). No sampling was performed at the top of the stack where flue gases were discharged to the atmosphere. Isolates were predominantly gram positive, i.e. Bacillus spp., coagulase negative staphylococci and Staphylococcus aureus, although low numbers of gram negative species (Pseudomonas fluorescens and other pseudomonads) were also recovered. Our results suggest that incineration may not constitute an absolute method of sterilization for clinical waste.