LIMITED WATER-TO-AIR BACTERIAL TRANSFER FROM A RESIDENTIAL EVAPORATIVE AIR COOLER

The sump of an evaporative air cooler (EAC) artificially was contamina ted with greater than or equal to 10(6) colony-forming units (CFU) mL( -1) of Micrococcus luteus, a pigmented, gram-positive, coccoid bacteri um. Air in the room served by the EAC was sampled during EAC operation to detect water-to-air transfer of the test bacterium. Median indoor air concentrations of the tracer bacterium were 2.4 and 1.2 CFU m(-3) at the low and high EAC fan speeds (respective air flow rates and air velocities through the EAC pads, 23 and 44 m(3) min(-1) and 0.47 and 0 .89 m s(-1)), for an estimated source strength, or transfer rate, of a pproximately 55 CFU min(-1). The rate at which tracer bacteria circula ted through the EAC pads during these tests was greater than or equal to 9 x 10(9) CFU min(-1). Tracer bacteria were detected indoors during operation of a highly contaminated EAC, but the relative tracer trans fer rate and resultant air concentration were low. Proper EAC operatio n and maintenance likely would ensure minimal human exposure to potent ially harmful microorganisms and other materials that could multiply o r collect in EAC sump waters and be transferred to indoor air as a res ult of sump water dripping or splashing.