Microbiological Evaluation of a Large-Volume Air Incinerator

Abstract

Two semiportable metal air incinerators, each with a capacity of 1,000 to 2,200 standard ft3 of air per min, were constructed to sterilize infectious aerosols created for investigative work in a microbiological laboratory. Each unit has about the same air-handling capacity as a conventional air incinerator with a brick stack but costs only about one-third as much. The units are unique in that the burner housing and combustion chamber are airtight and utilize a portion of the contaminated air stream to support combustion of fuel oil. Operation is continuous. Aerosols of liquid and dry suspensions of Bacillus subtilis var. niger spores and dry vegetative cells of Serratia marcescens were disseminated into the two incinerators to determine the conditions required for sterilization of contaminated air. With the latter organisms (concentration 2.03 X 107 cells/ft3 of air), a temperature of 525 F (274 C), measured at the firebox in front of the heat exchanger, was sufficient for sterilization. To sterilize 1.74 x 107 and 1.74 X 109 wet spores of B. subtilis per ft3, the required temperature ranged from 525 to 675 F (274 to 357 C) and 625 to 700 F (329 to 371 C), respectively. Air-sterilization temperature varied with each incinerator. This was because of innate differences of fabrication, different spore concentrations, and use of one or two burners With dry B. subtilis spores (1.86 X 108/ft3), a temperature of 700 F was required for sterilization. With dry spores, no difference was noted in the sterilization temperature for the two incinerators.

New studies on the heat resistance of hamster-adapted scrapie agent: Threshold survival after ashing at 600°C suggests an inorganic template of replication

“…(19,20). The best-studied examples of microbial heat resistance are found among bacterial spores, which typically are used to test the efficiency of autoclaves and incinerators: wet spores of Bacillus subtilis and Serratia marcescens have been shown to resist brief exposures to temperatures between 270°C and 340°C, and some viability of dry spores persists after exposure to 370°C (21). None of these organic molecules or microorganisms has been shown to retain biological or replicating activity after exposures to temperatures above 400°C, and certainly none would be expected to survive 600°C.…”

Microbiological Safety Evaluation of a Solid and Liquid Pathological Incinerator

“…Until eachfabricated incinerator is challenged with bacterial test spores, the most resistantmicroorganisms known to man, to establish operating temperatures sufficient to achieve sterilization; the unit may be operatedunder a false sense of security. The need for testing each incinerator even of the same design and fabricated by the same manufacturer was noted on tests run on air incinerators for incineration of contaminated air from Class III cabinets used with infectious material [2,3].…”

“…All of them have to meet the following requirements: (I) Prevent exposure of laboratory personnel. (2) Protect refuse handlers and possible scavengers.…”